Products & Equipment : Combiners

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More than 600 solar equipment and service providers will display their products at the Solar Power International conference and expo in Las Vegas September 13–15. In this preview article, I highlight 17 companies that provide a wide range of solutions for system integrators. Some of the equipment detailed here recently launched or is set to launch at the event. Some is time-tested in fielded systems across the US. And some represents new or out-of-the-box ideas that may or may not take hold, but that nonetheless represent the dynamic innovation that keeps the solar industry moving forward.

Modeling, Measurement and Testing

Aurora Solar - Booth WSUA12

Aurora Solar develops cloud-based software that enables sophisticated solar project engineering design, provides workflow management functionality, and facilitates sales and customer acquisition for solar installers and financers. The company launched in 2013 with the backing of the US Department of Energy’s SunShot Initiative. The Aurora design platform includes features such as 2-D and 3-D modeling, 3-D visualizations, irradiance maps and annual shade values, automatic roof setbacks, electric bill and financial analysis, sales proposals and remote shading analysis, as well as engineering features such as performance simulations. Monthly and annual per seat pricing is available, as are enterprise-scale packages. The basic subscription is $159 per month, per seat, and includes the features listed. The premium-level product costs $259 per month, per seat, and offers additional features including monthly shade values, site modeling with LIDAR, NEC validation, single-line diagrams, BOS components and detailed bills of materials.
Aurora Solar /

Curb - Booth W902

Launched in 2012, Curb is a new entrant to the solar and energy efficiency market. Its home energy monitoring system offers integrators a compelling option for circuit-by-circuit energy use monitoring and visualization at a low price point ($399). Curb designed its data acquisition system for mounting in a home’s load center. The system includes 18 CT sensors for individual circuit monitoring. This level of monitoring granularity facilitates specialized tasks—for example, determining how much energy electric vehicle charging is consuming. The Curb system can measure on-site energy generation from PV systems and integrate production values with home consumption data. Curb includes a variety of notifications for events, such as when a user has accidentally left on a given appliance. Additional features include a power budget manager that allows users to track progress against a monthly energy budget. The software identifies changes in consumption and provides suggestions for conserving energy and money. With the upcoming launch of its home energy intelligence product, Curb plans to take its platform a step further with functionality that aims to predict appliance failure and identify required maintenance for components such as HVAC or refrigerator compressors.
Curb / 844.629.2872 /

Folsom Labs - Booth 3053

At the core of San Francisco–based Folsom Labs’ design efforts is the principle that every PV system design decision can and should be quantified in terms of its yield and financial implications. To further this goal, Folsom Labs develops HelioScope, a PV system design tool that integrates system layout and performance modeling to simplify the process of engineering and selling solar projects. The platform integrates easy-to-use design tools and bankable energy yield calculations. A core differentiator for HelioScope is that it is designed on a component-based model, which separately models each piece of the system (individual module, conductor or inverter, for example). Folsom Labs offers both monthly and yearly subscription rates. The cost of a single-seat monthly subscription is $79 and includes automatic CAD export, energy simulation, shade optimization, one-click sharing, a component library of 45,000 items, global weather data and PAN file support. Solar professionals can use HelioScope to design and model PV plants with capacities of up to 5 MW.
Folsom Labs /

Seaward Solar - Booth W824

Seaward Solar is a division of the UK-based Seaward Group. Its line of PV test equipment is one of the more recent development efforts in the company’s 75-year history in electrical safety test measurement instruments. Seaward Solar’s offerings include products used in PV system commissioning and operation verification, such as conductor insulation testers, irradiance meters and I-V curve tracers. The company recently announced the launch of its new PV210 multipurpose PV tester, which combines installation and commissioning tests with the ability to perform I-V curve analysis. Simple push-button operation allows users to conduct all the electrical commissioning tests required by IEC 62446, including open-circuit voltage, short-circuit current, maximum power point voltage, current and power, and insulation resistance. In addition, the PV210 performs I-V curve measurements in accordance with IEC 61829 to determine whether the measured curve deviates from the expected profile. For full, detailed analysis, users can transfer measured data from the test instrument to an accompanying PVMobile Android app to create high-definition color displays of the I-V and power curves for individual PV modules or strings.
Seaward Solar / 813.886.2775 /


LG Solar - Booth 1447

LG’s activity in solar module development dates back to 1985, when it (under the brand GoldStar Electronics) conducted its initial multicrystalline PV cell R&D. Since then the South Korean company, part of the global LG Group, has rebranded and become a household name in appliances and personal electronics. Another LG Group subsidiary, LG Chem, is on the front lines of designing and manufacturing lithium-ion batteries for use in stationary solar-plus-storage systems. LG Solar initiated mass production of its PV technology in 2010. It recently announced the US availability of its NeON 2 72-cell module models, developed for commercial and utility-scale installations. The three models—LG365N2W-G4, LG370N2W-G4 and LG375N2W-G4—have rated power outputs ranging from 365 W to 375 W. The new models expand LG’s high-efficiency PV lineup, which includes the 60-cell NeON 2, with rated power outputs of 305 W–320 W and module efficiencies of 18.6%–19.5%.
LG Solar /

SolarWorld - Booth 911

SolarWorld has more than 40 years of history in solar module design and manufacturing, dating back to Bill Yerkes’ founding of Solar Technology International and ARCO Solar’s development efforts in the 1970s, the assets of which SolarWorld acquired. Today, SolarWorld offers a full line of Sunmodule products, including two glass-on-glass bifacial Bisun models, as well as system packages that incorporate Quick Mount PV’s railless Quick Rack system and power electronics from vendors such as ABB, Enphase and SMA America. In July, SolarWorld announced the launch of its 1,500 Vdc–rated 72-cell SW 340–350 XL MONO module line, which is available with 340 W, 345 W and 350 W maximum power. The introduction of the high-voltage XL product positions SolarWorld to take advantage of the expanding deployment of 1,500-Vdc PV power plants in the US.
SolarWorld / 503.844.3400 /

Sunpreme - Booth 2125

Headquartered in Sunnyvale, California, and launched in 2009, Sunpreme is differentiating itself from commodity module vendors with the development of thin-film, high-efficiency, bifacial, double-glass frameless modules. The company bases its unique cell architecture on its patented Hybrid Cell Technology (HCT) platform, which utilizes four amorphous silicon thin-film depositions on surface-engineered silicon substrate. The frameless double-glass module design does not require electrical grounding. Sunpreme’s Maxima GxB module line includes five modules, two of which integrate Tigo Energy’s TS4-L (long-string) dc optimizers. The highest-power module, the GxB 370W, has a power output of 370 W STC and a module efficiency of 19.1%. Sunpreme specifies a bifacial output for the GxB 370W of 444 W, with a 20% boost in power from the module backside and a resulting module efficiency of 22.9%.
Sunpreme / 866.245.1110 /

Ten K Solar - Booth 759

Ten K Solar, founded in 2008, leverages a unique nonserial architecture with its module and integrated system design.  Its Apex module line includes the Apex 500W Mono (500 W monocrystalline) and the Apex 440W Poly (440 W polycrystalline). Both modules utilize 200 half-cells connected in a matrix (serial and parallel connections). This structure allows current to flow through multiple pathways within a module, improving partial shade performance, reducing the impact of soiling and hot spots, and eliminating a single point of potential failure within the module. Module-level power electronics convert the internal module voltage (<18 Vdc) to an operating voltage of 35 Vdc–59 Vdc. Ten K expands on this shade- and fault-tolerant low-voltage parallel architecture with its ballasted DUO PV system for low-slope roofs and ground-mounted arrays. The DUO system configuration, which integrates groups of parallel-connected microinverters on a shared dc bus, places rows of modules in tandem, back-to-back, to maximize power density and energy yield per square foot.
Ten K Solar / 952.303.7600 /

Power Electronics

Delta - Booth 2259

Delta Group is the world’s largest provider of switching power supplies and dc brushless fans, as well as power management equipment, networking products and renewable energy solutions, including solar inverters. Historically, Delta has positioned itself somewhat behind the scenes in the US solar market, as other vendors have rebranded the OEM’s inverter products. However, Delta is developing its presence in the US, introducing new solutions to the market. Two recent examples are its 7 kW RPI H7U single-phase inverter and its 80 kW M80U 3-phase string inverter. The UL-certified RPI H7U features a secure power supply for limited daytime power production when the grid is not present, and 4 MPP trackers with a full-power MPPT range of 185 V–470 V at 240 Vac and a wide operating voltage range of 30 V–500 V. Integrators continue to deploy high-power 3-phase string inverters in increasingly large multimegawatt PV plants. Delta’s 80 kW M80U inverter will support this upward capacity trend. The inverter has a maximum input voltage rating of 1,100 V, a full-power MPPT range of 600 V–800 V and an operating voltage range of 200 V–1,000 V. Options for connection on the dc side include 16 source-circuit fuseholders, two 3/0 AWG terminal blocks and 18 pairs of MC4 connectors for wire harness compatibility. With a unit weight of 180.6 pounds or less, depending on configuration, the M80U is light enough to permit a two-person installation.
Delta /

OutBack Power - Booth 2825

OutBack Power designs and manufactures inverter/chargers, charge controllers, integration equipment and monitoring solutions for stand-alone and utility-interactive battery-based renewable energy systems. Currently a member of the Alpha Group, OutBack was founded in 2001. Battery-based PV systems are inherently more complicated than grid-direct ones. The accumulated experience of established power electronics companies such as OutBack is a valuable asset for integrators when applications require advanced system configurations. In 2011, OutBack released its Radian series of hybrid, utility-interactive split-phase 120/240 Vac inverter/chargers. Available in 4,000 W and 8,000 W power classes, the Radian features two ac inputs for grid and ac generator connectivity and a high degree of component integration. With the recent introduction of four VRLA storage batteries optimized for specific applications such as float service or regular deep cycling, OutBack now offers a comprehensive product family for energy storage applications listed to the relevant UL standards.
OutBack Power / 360.435.6030 /

SMA America - Booth 959

SMA Solar Technology was founded in 1981. Its US subsidiary, SMA America, was the first inverter manufacturer to offer high-voltage string inverter models in the US market. In addition to developing single- and 3-phase string inverters, SMA has also devoted significant resources to the development of high-power central inverters for multi-megawatt medium-voltage utility-scale PV plants. As the US and global inverter markets have evolved, more manufacturers are focusing on either string inverters or central inverters. SMA is one of a shrinking group of inverter vendors that continue to create solutions in both product classes for utility-interactive applications. One example is its second-generation Medium Voltage Block for utility-scale applications deploying its Sunny Central 1850-US, 2200-US and 2500-EV central inverters. SMA’s 3-phase inverter lineup, the Sunny Tripower series, currently includes six models with rated power capacities of 12 kW–60 kW and 480 Vac output. The company has also been redesigning its single-phase inverter family. It recently launched updated Sunny Boy 3.0-US, 3.8-US, 7.0-US and 7.7-US models, which join the 5.0-US and 6.0-US models it introduced earlier this year, to provide integrators with greater design and installation flexibility. SMA plans to release a high-voltage Tesla-compatible battery inverter for the US market in early 2017. It has also made a significant investment in incorporating MLPE technology from Tigo Energy into its systems, in anticipation of module-level rapid-shutdown requirements in NEC 2017.
SMA America / 916.625.0870 /

Trackers, Racking and Mounting

Array Technologies - Booth 2805

Array Technologies (ATI) began manufacturing solar trackers in Albuquerque, New Mexico, in 1992 and has continually evolved, redesigned and scaled its solar tracking equipment, systems and services in step with the solar industry, especially in the utility-scale PV plant market. ATI launched its third-generation centralized DuraTrack HZ v3 horizontal single-axis tracker in 2015 and continues to be a strong proponent of centralized tracking systems. The DuraTrack HZ v3 has an algorithm with a GPS input tracking method and a ±52° tracking range of motion with backtracking functionality. The system’s drivetrain has sealed gearboxes designed to be maintenance-free for the life of the plant. The DuraTrack HZ v3 has a 135 mph 3-second-gust exposure-C allowable wind-load rating. A passive mechanical wind protection system that does not require power to operate safeguards the tracker during high-wind events and eliminates the maintenance requirements associated with active stow components. Configurations for c-Si modules include one-up in portrait orientation and two-up in landscape orientation, as well as four-up in landscape for thin-film modules. To speed module installation, ATI has developed an innovative single-fastener module clamp with integrated grounding.
Array Technologies / 855.872.2578 /

Beamreach Solar - Booth 2941

Beamreach Solar (formerly Solexel, founded in 2007) showed the demo installation of its Sprint PV system to big crowds of curious onlookers at July’s Intersolar North America event in San Francisco. Developed specifically for weight-constrained, low-slope commercial rooftops with TPO membranes, the system integrates a 60-cell monocrystalline 290 W, 295 W or 300 W module with a composite frame and an integrated racking system. The weight per module, including its racking components, is 38 pounds. The system is not ballasted or penetrating, but rather adheres directly to the TPO roofing membrane. Each row of modules simply snaps into the back feet of the previous row. The lack of metal components eliminates the need for equipment grounding. For shipping, Beamreach packs 26 modules with integrated racking components on a single pallet. Time will tell whether the Beamreach Sprint system will gain traction in the field; however, its design clearly exemplifies the innovation that is happening across the PV industry.
Beamreach Solar / 408.240.3800 /

SunLink - Booth 2037

SunLink launched its first racking systems for commercial rooftops in 2004 and helped pioneer the design and deployment of ballasted PV array mounting systems. More recently, the company has been expanding its product portfolio and expertise to include project development and O&M, SCADA and data monitoring services, and PV tracker systems. SunLink will launch its TechTrack Distributed single-axis tracker in Q3 2016. The self-powered tracker uses a slew drive, a 24 Vdc motor, a lithium-iron phosphate battery and an integrated PV module to drive the tracker. Its tracking range of motion is ±60°. Installers can mount modules one-high in portrait orientation, and array configurations are optimized for 90 modules per 30 kWdc row. A secure modified Zigbee mesh network provides on-site communication between the tracker controllers. The TechTrack Distributed system reacts intelligently to real-time conditions to increase generation and reduce the risk of damage to the power plant. Dynamic stabilization provides damping during critical events such as high winds. The tracker is designed for 105 mph and 5 psf standard loads and is configurable for wind loads of up to 150 mph and snow loads of up to 60 psf.
SunLink / 415.925.9650 /

Conductor Aggregation and Management

CAB Solar Booth 311

Under its CAB Solar brand, the Cambria County Association for the Blind and Handicapped manufactures a range of products that include cable rings and saddles for PV cable management, while providing rehabilitation and employment services to persons with disabilities living in Cambria County, Pennsylvania. Elevated cable systems are gaining popularity in utility-scale PV plants, and CAB was an early supplier to these projects. CAB Solar’s PVC-coated rings and saddles feature a high–dielectric grade, flame-retardant and UV-stabilized coating, applied to 100% of the product’s surface. The resulting rings and hangers are electrically insulated and durable in corrosive environments. CAB offers an extensive range of PV wire management solutions, including multicarrier hangers that provide physical separation between dc source-circuit conductors, ac cables and data transmission circuits. The company also manufactures high-visibility safety vests, bags, pouches and holders for the safe organization and transport of hand tools, cordless tool batteries, meters and communication devices in rooftop and other environments.
CAB Solar / 814.472.5077 /

HellermannTyton - Booth 625

HellermannTyton is a global manufacturer of cable management, identification and network connectivity products. Its North American headquarters are located in Milwaukee, Wisconsin. Its products for PV applications include Solar Ties and Solar E-Clips that enable flexible and secure routing of conductor and cable bundles. HellermannTyton also offers Solar Identification printers, labels and software systems that provide professional and durable PV system labeling. Its Ratchet P Clamp is an innovative solution for cable management. The adjustable ratchet clamp mechanism is available in four sizes for cable bundles or conduit ranging from 0.24 inch to 2 inches. In addition, the product is available with three lengths of mounting plates and 15°, 30°, 90° and 180° angle orientations. The Ratchet P Clamp is designed for easy opening using a small flathead screwdriver. Installers can stack the clamps for parallel cable runs and offset applications.
HellermannTyton / 800.537.1512 /

SolarBOS - Booth 935

Founded in 2004, SolarBOS focused from the start on configurability, with its first product a configurable 600 Vdc source-circuit combiner box that allowed customers to specify the number of circuits and the NEMA rating of the enclosure. This approach remains a core feature of the extensive range of combiner boxes, recombiners, disconnects, battery connection panels and cable assemblies SolarBOS offers today, including many product versions listed for 1,000 Vdc and 1,500 Vdc applications. In 2015, SolarBOS rolled out its Wire Solutions products for deployment in the growing number of commercial and utility-scale systems that use pre-engineered wire harness and cable assemblies. The company’s product family for these applications includes overmolded Y harnesses with or without inline fuses, homerun cable assemblies and combiner box whips. All wire harness assemblies are custom manufactured to client specifications. Customers can choose from various wire gauges and conductor jacket colors, industry-standard connectors and custom labels at each connection point.
SolarBOS / 925.456.7744 /

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At Solar Power International last year, a sales representative for one of our distribution partners inquired: “Why do so many of my customers order 30 A fuses in their source-circuit combiner boxes?” This is a good question. After all, most crystalline silicon (c-Si) PV modules have a short-circuit current (Isc) rating in the 8–9 A range and carry a 15 A–series fuse rating. This is so common that source-circuit combiners typically come standard with 15 A series fuses. Occasionally, an engineer might specify 20 A fuses to account for thermal derating. However, 30 A fusing assumes an Isc of roughly 18 A, which is an unprecedented series fuse rating for today’s PV modules.

So why do integrators request combiners with 30 A fuses? The answer is not a function of module ratings per se, but rather of how system integrators deploy these modules. Specifically, more and more installation companies use special Y-connector assemblies to parallel PV source circuits in the array field as a way to optimize electrical balance of system (eBOS) costs.

About Y-Connectors

Most industry veterans have seen parallel branch connectors or Y-connector assemblies at conferences or pictured in trade publications or product catalogues. For example, both Amphenol and Multi-Contact offer male and female branch connectors rated for 30 A, as well as overmolded Y-connector assemblies with optional inline fuses. Many eBOS companies also offer customizable Y-connector assemblies. What these connectors and assemblies all have in common is that they have two inputs and one output, allowing installers to make plug-and-play parallel connections within the array.

Until recently, paralleling source circuits within an array was most common in thin-film applications. Compared to c-Si PV modules, thin-film technologies tend to have a higher Voc and a lower Isc. As a result, it behooves integrators to use wire harnesses with inline fuses to parallel thin-film PV source circuits prior to landing them in a combiner box. This practice is cost-effective because it improves conductor utilization within the array and limits the number of combiner box inputs.

Designers can apply these same principles to c-Si PV arrays. After all, touch-safe fuseholders in combiner or inverter wiring boxes are generally 30 A rated, whereas most PV modules have a 15 A series fuse–rating. Therefore, integrators may be able to improve project economics by using Y-connectors to parallel a pair of source circuits ahead of these fuseholders. Before evaluating the potential cost savings associated with this approach, let us review some practical considerations.

Code implications. NEC Section 690.9 requires overcurrent protection for PV modules or source circuits, except when there are no external sources of fault current, or when the short-circuit currents from these sources do not exceed the ampacity of the conductors and the maximum series fuse rating. To make a parallel connection ahead of a combiner box, designers need to account for potential sources of fault currents as well as the module manufacturer’s series fuse ratings. Generally speaking, parallel connections within the array require Y-connector assemblies with inline fuses. In effect, designers need to relocate 15 A series fuses from the combiner box out into the array wiring.

Since parallel connections increase current, designers also need to evaluate conductor ampacity between the Y-connector and the dc combiner or inverter-input wiring box. To achieve the desired cost savings, integrators need to be able to parallel source circuits within the array without unnecessarily incurring the expense of larger-diameter conductors. To avoid having to step from 10 AWG to 8 AWG copper conductors, for example, designers should avoid or minimize situations that require conductor ampacity adjustments according to Article 310. The two most common ampacity adjustment scenarios relate to the number of current-carrying conductors (see Table 310.15[B][3][a]) and distance above the roof (see Table 310.15[B][3][c]). When paralleling source circuits within the array, therefore, it generally makes sense to limit the number of conductors bundled or grouped together to no more than three and to maintain a distance above the roof of at least 12 inches.

Manufacturer limitations. While most of the finger-safe fuseholders for 10 mm by 38 mm fuses found in combiner boxes are manufacturer rated for 30 A, the busbars connected to the fuseholders are not always capable of carrying 30 A of current. Integrators should check with the combiner or inverter manufacturer to ensure that the product is compatible with the use of 30 A fuses.

In some cases, equipment manufacturers require an allowance for heat dissipation where fuseholders are fused at 30 A. The concern is that a lack of space between fuseholders can cause a fuseholder to overheat, potentially melting the plastic and causing a fault. This is not an issue when inputs are fused at 15 or 20 A, as is typical of most string inverter or combiner box applications. However, it may become an issue under continuous loading at full power with 30 A fuses. Landing input conductors on alternating fuseholders, as shown in Figure 1, and removing the unused fuses is one way to improve heat dissipation.

Commissioning and maintenance. From a commissioning and maintenance perspective, incorporating Y-connectors into the PV array wiring does compromise convenience somewhat. After all, landing individual source circuits in combiner boxes provides commissioning agents and service technicians with a convenient means of isolating individual circuits, both to validate proper installation and to establish baseline performance parameters. Using Y-connectors pushes some of the parallel connection points into the array, which can complicate some routine maintenance and troubleshooting procedures, such as taking Voc measurements on a single source circuit.

Arrays fielded with Y-connectors may also require specialized diagnostic tools. After array commissioning, source-circuit voltage measurements are less important than I-V curve traces, as the latter provide more insight into array health. To capture I-V curve traces on source circuits paralleled using a Y-connector, service technicians must have access to an I-V curve tracer rated to process the combined short-circuit current of both strings. At present, the Solmetric PVA-1000S is the only handheld I-V curve tracer offered with an optional 30 A measurement capability. With this 30 A–rated PV Analyzer, technicians can perform an I-V curve trace in a combiner box on two paralleled c-Si PV source circuits. If technicians have access to a 15 A–rated I-V curve tracer only, they will need to isolate the source circuits entering a Y-connector and trace each I-V curve individually.

Cost Reductions

The reason system integrators are willing to make a small sacrifice in convenience is that the proper use of Y-connectors reduces installed system costs. The savings are twofold: material savings associated with a reduction in the total length of PV Wire within the array field, and labor savings, since installers do not have to make as many terminations in source-circuit combiners.

To realize the maximum PV Wire savings, installers need to locate both poles of each PV source circuit at roughly the same spot within the array table. Using the leapfrog wiring method illustrated in Figure 2 is a good way to accomplish this. Where module wire whips are long enough to accommodate leapfrog wiring, this method eliminates about 30–60 feet of PV Wire per source circuit compared to daisy-chain wiring, with the reduction depending on string length (which is largely a function of nominal system voltage). Leapfrog wiring alone can reduce material costs by as much as $20,000 on a 5 MW PV system. (See “Cost-Saving PV Source Circuit Wiring Method,” SolarPro, April/May 2014.) Integrators can reduce material costs even further by combining leapfrog wiring with Y-connectors.

Case study. To illustrate, let us consider a hypothetical example where the basic building block for a large-scale PV array is a 50 kW string inverter that is processing power from a 240-module array table. Each array table is mechanically configured two modules high by 120 modules wide and wired electrically with 12 parallel-connected 20-module source circuits. The wire whips are long enough to accommodate leapfrog wiring. A main service road runs north and south along the east edge of the array.

As shown in Figure 3, the total length of PV Wire per array table is a function of both inverter placement and array wiring. Locating the inverter at the east end of an array table, as assumed in Option 1, provides service technicians with optimal inverter access for O&M purposes but requires the most PV Wire per inverter. Mounting the inverter in the middle of an array table, as shown in Option 2, dramatically reduces PV Wire requirements, but complicates array serviceability. Service technicians will have a harder time reaching each inverter. It may also be impractical or undesirable to run ac conductors within the array field. Option 3, which combines leapfrog wiring with Y-connectors, provides the best of both worlds as it allows for optimal inverter placement and reduces the use of PV Wire significantly.

As compared to Option 1, the combination of leapfrog wiring and Y-connectors in Option 3 effectively reduces the homerun conductor length within the array by half. This setup does not offer a free lunch, however, as the cost to purchase Y-connectors and inline fuses offsets some of the PV Wire savings. While it is possible to purchase inline fuseholders and unfused Y-connectors separately and plug them together in the field, it is generally more cost-effective to purchase an integrated assembly. Companies such as Amphenol, Eaton, Shoals Technologies Group and SolarBOS all offer Y-connector assemblies with integral inline fuses. When purchasing an all-in-one solution, integrators should order extra assemblies for O&M purposes; in the rare event that one fuse blows, they will need to replace the entire assembly.

Table 1 estimates the total material and labor savings associated with deploying array-table configuration Option 3 rather than Option 1. Assuming that 10-gauge PV Wire costs $0.20/foot, you can save more than $400 per array table by adding Y-connectors at the end of each adjacent pair of source circuits (2,070 ft. × $0.20/ft.). While it will cost $240 to add six pairs of fused Y-connector assemblies (12 Y-connectors x $20/each), the net material savings per array table are roughly $174 ($414 less $240). Labor savings are estimated at 1 hour per array table and reflect the fact that installers will spend less time managing homerun conductors within the array (saving roughly 45 minutes) and will have to make only half as many dc terminations at the inverter (saving roughly 15 minutes). Assuming a labor rate of $80 per hour, the total material and labor savings are $254 per array table, which extrapolates to $5,080 per MWac ($0.005/W).

Of course, every array is different, and material and labor costs vary from region to region, so results may vary. However, this case study is a good example of the type of analysis that can help reduce costs, improve profits and win more projects. According to GTM Research, the utility-scale solar market in the US will approach 12 GW in 2016. If each one of these large-scale projects could reduce eBOS costs by a half cent per watt, the industry as a whole would save $60 million.

Eric Every / Yaskawa–Solectria Solar / Lawrence, MA /

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As safety requirements for PV systems change, balance of system manufacturers are playing an increasingly important role in the solar industry ecosystem.

As recently as 8 years ago, it was not uncommon for system integrators to build combiner boxes in the field. This practice went away under NEC 2008, as the Code-making panel revised 690.4(D) to require that source-circuit combiners intended for use in PV power systems be “identified and listed for the application.” To comply, system integrators had to use source-circuit combiners listed to UL 1741. Today, these listing requirements apply to all dc combiners.

More recent Code changes have further influenced the design and construction of listed dc combiners. For example, the Code-making panel added general requirements for fuse-servicing disconnecting means in 690.16(B) of NEC 2011 and more specific requirements for roof-mounted dc combiner disconnecting means in 690.15(C) of NEC 2014. It also added dc arc-fault circuit protection requirements in 690.11 of NEC 2011 and rapid-shutdown requirements in 690.12 of NEC 2014. The revised ground-fault detection and interruption requirements in 690.5(A) of NEC 2014 also have implications for dc combiners used in PV systems deployed with central inverters.

To get a feel for how dc combiners and PV system design practices are evolving in light of these new Code requirements, I reached out to equipment vendors and system engineers. The following responses address changes in the dc combiner market, popular product features, challenging Code requirements, cost concerns and new products or features on the horizon.

On Balance

> We published our last combiner box article in 2011. How has the market for dc combiners changed in the last 3 years? What dynamics are driving those changes?

“We have seen a significant change in design and certification requirements for dc combiners. Balance of system (BOS) products are no longer left to the installer’s discretion on-site. Engineers, developers and contractors are looking at BOS products as an integral part of the overall system and are requiring products that carry third-party certification. Further, as PV projects have increased in capacity, the throughput of dc combiners has increased accordingly. Code requirements are also driving demand for circuit-breaker PV output-circuit combiners. Circuit breakers are a reliable and cost-effective means of providing overcurrent protection for high-value equipment, as well as a disconnecting means at the inverter input.”

—Patrick Kane, product manager, Eaton

“Large system integrators used to be hesitant to use combiners with disconnects. Now, the largest integrators all use disconnect combiners. The dynamic driving that decision is system operation and maintenance (O&M). While O&M was rarely discussed 3 years ago, there are entire conferences dedicated to the topic today. The market for PV output-circuit combiners is also greatly changed. Prior to NEC 2011, it was rare to come across PV output-circuit combiners with disconnects or circuit breakers. Now most combiner manufacturers offer both fused-disconnect and circuit breaker options for these products.”

—Bill Brooks, PE, principal, Brooks Engineering

“One of the biggest changes we have implemented is the use of dc circuit breakers in lieu of fuses in our recombiner [PV output-circuit combiner] boxes and cabinets. Circuit breakers allow end users to reset tripped circuits without replacing expensive fuses, which reduces spare parts inventory costs. Some inverter manufacturers are also moving away from using fuses at the inverter input bus. The market has also transitioned to using 1,000 V–rated PV source-circuit combiners with an integral 250 A or 400 A load-break–rated disconnect switch. This change was Code driven and makes it safer for technicians installing or servicing the system.”

—Tom Willis, director of sales, AMtec Solar

“There have been many significant changes over the last 3 years. UL 1741 was revised, allowing us to list 1,000 Vdc–rated products to the standard. We now have access to 100% load-break–rated, enclosed and dead-front switches listed to UL 98B that enhance system reliability and safety. UL also created a new product safety standard specifically for distributed-generation wiring harnesses. UL 9703 allows us to develop multistring wiring harnesses with inline fuseholders that can reduce electrical BOS costs. For example, we noticed that many of the fuses we previously sold with our combiner boxes were rated at 15 A, even though the fuseholders in those same boxes were rated at 30 A. This led to our developing the inline fuse assembly. By combining source circuits in the field, we are able to reduce the number of homerun conductors going back to the combiner box, and we can use 30 A fuses in the fuseholders. This design approach reduces both the physical size of the combiner box and the amount of wire used in the field. The industry has also completely shifted from copper to aluminum dc feeders.”

—Jason Whitaker, chief technology officer, Shoals Technologies Group

“We have seen most commercial and practically all utility-scale PV systems transition from 600 to 1,000 Vdc. Developers and integrators looking to reduce costs are primarily driving the move to 1,000 V–rated systems and components. More recently, we have started to see the impact of new Code requirements, such as arc-fault protection and rapid shutdown. These requirements come into play where jurisdictions have adopted the 2011 or 2014 edition of the NEC.

—Claude Colp, applications engineer, Solectria Renewables

“The increased deployment of ungrounded and 1,000 Vdc PV arrays has led vendors to design and list more dc combiners for these applications. But these applications also play to the strengths of 3-phase 480 Vac string inverters. System integrators are regularly using transformerless string inverters for commercial systems up to 500 kW in capacity. I have even seen string inverters used for systems in the 2 MW range.”

—Marvin R Hamon, PE, principal, Hamon Engineering

“We are seeing the biggest changes in the commercial market. Commercial project designers are moving away from central inverters in favor of using multiple 1,000 V–rated 3-phase string inverters that output direct to 480 Vac. This transition is driven in part by the availability of high–power-density transformerless string inverters and in part by AHJs starting to enforce new Code requirements. When AHJs first started to adopt NEC 2011, they did not enforce the dc arc-fault circuit-protection requirements in 690.11 because listed products were not available. That is no longer the case. Also, some jurisdictions are already enforcing the rapid-shutdown requirements in NEC 2014.

—Daniel Sherwood, director of product management, SolarBOS

“The biggest drivers of change in the combiner market are the requirements for dc arc-fault circuit protection and rapid shutdown. At first, the lack of commercially available and highly reliable dc arc-fault circuit interrupter (AFCI) products stalled the enforcement of 690.11 and the implementation of this technology. As soon as listed products were available, AHJs became less lenient and started requiring dc AFCI per Code. On the one hand, central inverters generally cannot provide dc arc-fault protection and need AFCI combiners—which can cost twice as much as standard dc combiners—to meet 690.11. On the other, most string inverters can perform the dc AFCI function. Since string inverters were already positioned as a cost-effective alternative to central inverters, dc arc-fault protection requirements have tilted the scales in favor of string inverters.”

—Randy Batchelor, systems technology engineer, Borrego Solar

“We look at the commercial and utility market sectors independently, as each has a unique set of needs. Changes in the commercial market sector are largely driven by new Code requirements such as arc-fault protection and rapid shutdown. To meet these needs, we have introduced 16- and 24-string dc combiners with arc-fault protection and rapid-shutdown capabilities for PV systems that use central inverters. We have also developed an easy-to-install low-slope roof mounting rack for 3-phase inverters in conjunction with some of the largest inverter manufacturers in the world. System integrators can use our PowerRack to install 3-phase string inverters within 10 feet of a commercial roof-mounted PV array as a cost-effective means of providing rapid shutdown per NEC 2014; these inverters also provide dc arc-fault protection.

“Changes in the utility market sector are primarily driven by the need to reduce installation costs on larger and larger projects. To meet the needs of this market, we have introduced products designed to reduce field installation time. For example, we sell cable harnesses and dc combiners with integrated cable whips that can save hours of installation time per combiner box.”

—John Buckley, executive sales and marketing, Bentek

> What are the most popular dc combiner products and product features today? To what extent does that vary based on the adopted NEC edition?

“Based on how many non-disconnecting combiners we sell, price is extremely important. System integrators primarily use non-disconnecting combiners in jurisdictions that have not yet adopted NEC 2011. While combiners used to be simple—an enclosure, source-circuit overcurrent protection devices (OCPDs) and some power distribution lugs or busbars—that is changing as jurisdictions start to enforce new Code requirements. Many states have already adopted NEC 2014, which effectively requires more complex and sophisticated dc combiners.”

—Robin Gudgel, president, MidNite Solar

“Tilt-out, touch-safe fuseholders are standard for source-circuit combiners, as they have been for years. Disconnecting means for these combiners are either manual or remote-actuated contactors. The 2014 Code cycle is the first edition to require load-break–rated disconnects on source-circuit combiners for roof-mounted PV systems [690.15(C)]. However, the use of disconnect combiners, both on and off the roof, has been a best practice in the industry for many years. PV output-circuit combiners are commonly fused-disconnect or circuit breaker units, unless contactor combiners are employed at the source-circuit combiner level. These changes are due to the fuse-servicing requirements introduced in NEC 2011 690.16(B).”

—Bill Brooks, Brooks Engineering

“Integrated disconnecting means are a popular dc combiner product feature due to the convenience a disconnect provides during commissioning and servicing activities. There are also important safety benefits associated with having disconnects in the array field. NEC 2014 requires that combiner boxes have many smart features—such as arc-fault protection and rapid-shutdown functionality—beyond simply providing a location for OCPDs.”

—Tobin Booth, chief executive officer, Blue Oak Energy

“The products we use vary substantially based on the Code cycle a particular jurisdiction enforces and whether the application is roof or ground mounted. If an AHJ enforces NEC 2008, we use standard dc combiners in all applications. Where NEC 2011 applies, we deploy roof-mounted systems that provide dc arc-fault protection, but use standard dc combiners in ground-mounted applications. In jurisdictions that have adopted NEC 2014, we provide dc arc-fault protection in all applications and rapid shutdown for roof-mounted systems. While BOS vendors offer many optional product features—such as blown-fuse indicators, integrated wire whips and surge protection—we feel these optional features generally increase up-front costs without adding much value in terms of lowering the levelized cost of energy. So we tend to go with the most stripped-down product version and use compression lugs for PV output-circuit conductors. For PV output-circuit combiners, however, we like the 100%-rated circuit breaker option, because the additional cost of breakers compared to fused disconnects is generally more than offset by associated wire size reductions. Since string-level monitoring has proven cost prohibitive, we always use zone-level monitoring.”

—Randy Batchelor, Borrego Solar

“Landed and modified boxes are very popular with our customers. We specialize in taking work out of the field and putting it into a controlled manufacturing environment. We can simplify field installation for our customers by prelanding pigtails or wiring harnesses, or preinstalling cable glands or mounting struts. Our most popular off-the-shelf product is a 400 A, NEMA 4 combiner box that takes advantage of our inline fuse assemblies and has room to land up to two 750 MCM conductors in parallel.”

—Jason Whitaker, Shoals Technologies Group 

“While requirements vary somewhat based on jurisdiction and Code cycle, our customers are typically interested in 1,000 V–rated disconnecting combiners with fiberglass enclosures. Fiberglass enclosures are popular because they are lightweight and nonconductive, and can be mounted in virtually any position due to their environmental rating. Integral disconnects provide an easy and cost-effective way to meet Code requirements. Customers are also looking for ways to improve on-site productivity. This means that our combiner boxes often include factory-drilled holes or factory-installed connectors or wire whips.”

—Patrick Kane, Eaton

“Arc-fault combiners and 3-phase inverter racks are popular in the commercial sector where AHJs enforce the 2011 or 2014 Code cycle. The rapid-shutdown requirements in NEC 2014 have also created residential market demand for contactor-based BOS components. Typically, system integrators do not need to use third-party dc combiners in residential string inverter systems. However, system designers may need to incorporate a remote-actuated roof-mounted switch into these systems to comply with 690.12. As a result, we have released a Rapid Shutdown Module [a pass through wiring box] with source-circuit contactors specifically for string-inverter systems where circuits are combined at the inverter input. We have also introduced source-circuit combiners with PV output-circuit contactors.”

—John Buckley, Bentek

“It is a hodgepodge market. Most AHJs require dc arc-fault protection now for roof-mounted projects. While commercial projects with central inverters need arc-fault combiners, commercial or residential projects with string inverters do not. We still sell a lot of standard disconnect combiners for residential, commercial and utility applications.”

—Daniel Sherwood, SolarBOS

“The most popular features we see in combiner boxes today are 1,000 Vdc ratings, dc arc-fault protection and rapid-shutdown capabilities. Some of our proprietary BOS solutions, such as the recently released ARCCOM combiner, are optimized to work exclusively with Solectria inverters. Typically projects that fall under the 2011 or 2014 NEC editions make use of these new products. We also work with leading BOS vendors—such as Bentek, Shoals and SolarBOS—to increase the options available to our customers.”

—Claude Colp, Solectria Renewables

“Where jurisdictions have adopted the 2014 Code cycle, even ground-mounted systems need to have dc arc-fault protection. This is driving up not only the initial cost of combiner boxes, but also the cost of installation and maintenance. To help reduce product lead times and costs, we are working with our supply chain, researching new components and standardizing on one enclosure size.”

—Tom Willis, AMtec Solar


> Which of the new Code requirements has proven the most difficult to meet or implement using dc combiners?

“The biggest challenge is meeting dc arc-fault protection requirements without nuisance tripping. It is very complex to design a product that differentiates between a dc arc-fault signature and inverter switching noise.”

—Patrick Kane, Eaton

“It is challenging to implement dc arc-fault protection. A device may work under a specific set of circumstances in the laboratory, but that laboratory-designed device may not actually work in the real world due to minor circumstantial changes.”

—Tobin Booth, Blue Oak Energy

“We have found that dc arc-fault detection products available today are either too sensitive or not sensitive enough, which results in nuisance tripping, failure to trip or both. It is also costly to integrate these products into dc combiners and attain UL certification.”

—Tom Willis, AMtec Solar

“Everyone working on dc arc-fault detection has run into the issue of interference and external noise resembling that of a series arc. Early dc arc-fault detection systems would trip if someone walked in front of a module and changed the current of the string. We have come a long way since those early systems by creating specific algorithms designed to differentiate between normal inverter noise and a series arc-fault signature. While there is still more refinement taking place throughout the industry, everyone involved is motivated to create a robust solution.”

—Claude Colp, Solectria Renewables

“Providing dc arc-fault protection is by far the most challenging Code requirement to meet. Most arc-fault detection circuits rely on frequency domain analysis to detect the high-frequency noise generated by an arcing fault. The problem is that PV arrays are generally connected to inverters that are a potential source of high-frequency noise. Every inverter has a different noise signature, and some are noisier than others. It took us a long time and a lot of engineering hours to come up with a dc arc-fault detection scheme that we are comfortable deploying with almost every inverter model without worrying about nuisance tripping. But the minute you think you have the nuisance trip problem solved, someone comes out with a new inverter. The 2014 Code specifically calls for arc-fault protection even on utility ground-mount projects, which seems like regulatory overreach to me. Who is going to suffer if there is an arc fault on some large PV power plant in the middle of the Mojave Desert or on top of a concrete-capped landfill?”

—Daniel Sherwood, SolarBOS

“DC arc-fault protection is challenging due to both the noisy electrical environment and the fact that dc combiners are located between the current source and the load. Listed arc-fault combiners generally detect arcing faults only in the PV source circuit and not in the PV output circuit. This leaves the PV system only partially compliant with the NEC.

—Marvin R Hamon, Hamon Engineering

“Rapid shutdown is the most challenging new Code requirement. Fortunately, we saw the writing on the wall back in 2009 and began working on remotely actuated disconnecting combiner designs. We started over many times and put a lot of thought into the operation of our rapid-shutdown system, which we had to develop in the absence of a dedicated UL product safety standard. For example, we integrated hardwired feedback that tells first responders when PV system circuits are actually controlled per 690.12. While this was a major design challenge, we consider positive feedback an essential safety feature for rapid-shutdown systems that use disconnecting combiners.”

—Robin Gudgel, MidNite Solar

“To provide dc arc-fault detection and rapid shutdown, we are primarily using 3-phase string inverters in commercial roof-mounted applications subject to NEC 2014. One of the most challenging design problems is how to meet rapid-shutdown requirements where we cannot place string inverters within 10 feet of the array. For example, SMA Sunny Tripower series inverters have a dual MPPT input and normally come with an ungrounded, split-bus six-string combiner—the Connection Unit 1000-US. Since SMA does not offer a contactor combiner, we worked closely with our BOS supplier to develop a unique product with four contactors in it that we could place near the array to meet rapid-shutdown requirements. Then we worked with SMA to verify that the dc arc-fault protection function in its Tripower inverters would still operate properly in this configuration.”

—Randy Batchelor, Borrego Solar

“New Code requirements have introduced a fresh set of design challenges. But improving system safety ultimately benefits the PV industry as a whole. Technically, it is not difficult to meet the new requirements per se. The real challenge is improving safety while minimizing the associated costs and maintaining production efficiency.”

—Jason Whitaker, Shoals Technologies Group

> Do you think that adding cost and complexity to dc combiners will cause the market to move away from these products?

“No, the Code is requiring additional cost and complexity. Often the combiner box is the only practical place to locate an arc-fault detection circuit or is the only piece of equipment you can locate close enough to an array to meet rapid-shutdown requirements. I am more concerned that the 2017 Code cycle could require module-level rapid shutdown, as this would significantly drive up costs while providing only an incremental improvement in the level of safety. Worst of all, those extra costs would hit the solar industry the same year that the federal tax credits are scheduled to drop from 30% to 10%.”

—Daniel Sherwood, SolarBOS

“No, market demand is driving increasing cost and complexity. Changes in Code requirements will open up new opportunities for dc combiner manufacturers and stimulate demand for new products.”

—Marvin R Hamon, Hamon Engineering

“As customers require increasingly sophisticated dc combiners, we will focus on developing solutions that enhance safety and value—even as design complexity increases.”

—Patrick Kane, Eaton

“Yes, we are already seeing the market move away from dc combiners. We have customers today who are using 3-phase string inverters with built-in arc-fault protection on systems as large as 5 MW. Just 3 years ago, the North American market used string inverters only in residential and small commercial applications.”

—Tom Willis, AMtec Solar

“To some degree, yes. While systems of less than 5 MW in capacity [could move away from these products], I believe dc combiner boxes will continue to serve as the major component for dc source-circuit aggregation in utility-scale solar farms.”

—Tobin Booth, Blue Oak Energy

“Yes, the additional cost of dc combiners means they will make up a larger percentage of the overall electrical BOS costs. Further, the complexity of new combiner boxes requires more maintenance and care, which means that the cost of O&M labor will also increase. Ultimately, the industry will look for ways to cut out this cumbersome means of delivering dc power to the inverter station. In the next year, we will see a lot of innovation in how power is harnessed and connected to the inverter.”

—Jason Whitaker, Shoals Technologies Group

“The commercial rooftop market is moving away from using multiple roof-mounted source-circuit combiners and large ground-mounted PV output-circuit combiners in favor of using one dc combiner per string-inverter input. While source- and output-circuit combiners are still used in ground-mounted systems, many companies are using inline fusing instead of source-circuit combiners. Another design option is to use a combination of inline fusing with source-circuit combiners run at higher current levels. A source circuit can have multiple strings in parallel. In fact, this practice was common 20 years ago, and the industry is gravitating back in this direction because it may make financial sense. The jury is still out as to whether this trend will last. The market is closely scrutinizing the reliability and cost implications of designs that use inline fusing, and the final decision will likely come down to O&M considerations.”

—Bill Brooks, Brooks Engineering

“I see numerous things happening in the industry that are forcing the market in the direction of microinverters. But if microinverters do not last through their warranty period, [relying on them] could ultimately give the industry a black eye. The complexity of combiners has gone crazy in the past few years. Commercial installations will need arc-fault combiners for central inverter systems. This [requirement] will likely force designers to use string inverters that provide arc-fault protection. We have spent 4 years working on arc-fault combiner designs and still do not have a product on the market. This R&D is a major expense for a combiner manufacturer. If companies cannot quickly fix product designs that meet UL but do not work properly in the field, then nuisance tripping could drive them out of business.”

—Robin Gudgel, MidNite Solar

“Absolutely. We are already shifting designs toward string inverters. This is driven in part by the fact that 3-phase string inverters provide dc arc-fault protection and in part by concerns about using more-complex combiners, which are more expensive and potentially less reliable. We are also looking at ways to otherwise reduce the need for dc combiners, such as using wiring harnesses or shifting to 1,500 V systems.”

—Randy Batchelor, Borrego Solar

“As NEC requirements evolve, BOS components evolve to meet them. For example, when it comes to the new rapid-shutdown requirements in 690.12 of NEC 2014, ac modules and microinverter systems have an inherent advantage over conventional string or central inverter systems. A traditional dc combiner cannot meet the rapid-shutdown requirement, and more-complex dc combiners are not usually cost competitive. So we designed our Rapid Shutdown System, which consists of a Rapid Shutdown Controller located at the service entrance and a Rapid Shutdown Module located within 5 or 10 feet of the array. This is a viable rapid-shutdown solution for residential systems or commercial systems where you cannot install string inverters on the roof.

“While BOS components will continue to evolve, there is a dichotomy in the market. On the one hand, the NEC continues to tighten system safety requirements. On the other, the market demands lower-cost PV systems. So the challenge for system integrators is figuring out how to design systems that can cost-effectively meet more stringent Code requirements. This dichotomy is the reason why system integrators are installing 3-phase string inverters on commercial rooftops. Based on the total cost of ownership, this design strategy is generally the best way to provide dc arc-fault protection. Further, if you mount these string inverters within 10 feet of an array, which you can accomplish using our RapidRack, then the installed system also meets 690.12.”

—John Buckley, Bentek

Balancing Act

> How will dc combiners and related BOS evolve over the next 3 to 5 years? What new products and product features do you expect or want to see going forward?

“The pending reduction in the federal Investment Tax Credit will be a catalyst for integrators to identify new cost-cutting opportunities. As a result, it is likely that we will see a trend toward 1,500 V PV systems. We may also see commercially viable energy storage solutions come to market over the next 3 to 5 years. This will transform the entire industry, in part by removing obstacles associated with higher levels of PV penetration. Hybrid solar plus storage systems will also enable new business models, such as peak demand shaving for businesses. Module-level shutdown is also a real possibility, given the 2017 Code proposals and conversations. This would represent a fundamental change in inverter and PV system architecture.”

—Claude Colp, Solectria Renewables

“Large combiners will all have contactors for rapid shutdown and dc arc-fault protection. However, the market for these products may shrink as transformerless string inverters take over the commercial market.”

—Robin Gudgel, MidNite Solar

“In light of the new NEC 2014 rapid-shutdown requirements—and the more stringent requirements projected for NEC 2017—we may see increased demand for remotely actuated disconnecting combiners with contactors. However, if 690.12 is revised to require module-level rapid shutdown as part of the 2017 cycle of revisions, that would significantly reduce the need for remotely actuated disconnecting combiners.”

—Marvin R Hamon, Hamon Engineering

“For commercial-scale and roof-mounted projects, we see a future where dc optimizers may greatly reduce our dc BOS costs or where string inverters and microinverters shift the BOS costs from the dc side of the system to the ac side. This change is already happening, with string inverters taking a major market share and platforms such as SolarEdge and tenK Solar gaining traction in the commercial market. NEC 2017 will have more-restrictive requirements for rapid shutdown, which could result in a shift to module-level power electronics even for large commercial systems on rooftops. In addition to meeting the more restrictive rapid-shutdown requirements, dc optimizers can reduce the need for combiner boxes by increasing the number of modules per string; dc optimizers also place arc-fault protection at the module, which eliminates the need for dc arc-fault protection at the combiner.

We also expect that NEC 2017 will allow for engineering supervision on large-scale PV systems that are not installed on buildings. If so, we do not expect to see dc arc-fault protection deployed in ground-mounted PV systems of more than 5 MW in capacity. We expect that wiring harnesses will become increasingly prevalent in these types of PV systems, possibly eliminating the need for traditional combiners.”

—Randy Batchelor, Borrego Solar

“We think that dc combiners will ultimately become obsolete. Shoals has developed and listed a patent-pending combinerless dc solution where the dc feeder serves as the ‘combiner’ component. The deployment of this large-format cable assembly at sites that use central inverters—coupled with the increasing use of string inverters—spells the beginning of the end for dc combiners in commercial- and utility-scale PV arrays.”

—Jason Whitaker, Shoals Technologies Group

“We are starting to get into products on the ac side of the inverter. As string inverters and microinverters become more popular, there is an increased demand for products such as ac switches and ac panels to combine the output of multiple inverters. There is also room for improvement with rapid-shutdown equipment. We have some ideas in the works for ways to make it work better and cost less.”

—Daniel Sherwood, SolarBOS

“We expect that ac BOS products will displace some traditional dc combiner products. System integrators are increasingly installing 3-phase string inverters on commercial rooftops. This creates market demand not only for inverter-mounting racks, but also for new ac combiner products that can aggregate the outputs of multiple 3-phase inverters prior to a connection at a low-voltage transformer or a service panel. For example, our AC PowerBUSS product can combine the outputs of up to 12 commercial 3-phase string inverters. It has a NEMA 4 enclosure, which means that integrators can use our RapidRack mount to install the AC PowerBUSS on low-slope roofs alongside roof-mounted string inverters. As we have all seen, system safety requirements can change a lot in just a few years. But BOS vendors do not have the organizational inertia of a PV module or inverter OEM, which allows our company to design and release products in months that would take an OEM years to bring to market. This speed to market is essential as it allows us to satisfy the current and future needs of system integrators, engineers and installers in ways that module and inverter OEMs cannot.”

—John Buckley, Bentek

“I expect the residential market to transition to ac modules with built-in arc-fault detection and module-level rapid shutdown. Meanwhile, we are going to see even larger utility projects of 1 GW or more operating at 1,500 Vdc. These computer-controlled PV power plants will be able to open or close subarray blocks, store PV energy when grid operators do not need it, deliver stored energy to the grid on demand or divert energy from the grid to the storage system. Sensors will detect arc faults, ground faults, reverse voltages, under voltages and unintended voltages. There will be sensors built into each module that will talk to an automatic cleaning system, which will clean the panels as needed. Since our core expertise is in engineering, we are well positioned for these changes and the systems of the future. We have revamped our manufacturing operation and are evaluating new components with our supply chain partners.”

—Tom Willis, AMtec Solar

“I expect to see more control and reporting features for combiner boxes. We are just beginning to see sophisticated control and system operation capabilities for PV systems.”

—Tobin Booth, Blue Oak Energy

“Inverters seem to be getting larger and larger in ground-mounted applications. There is a practical limit on the maximum inverter capacity in large-scale systems, though that limit varies based on operating voltage. Massive pressure to reduce construction and O&M costs will largely drive innovation in these systems. While cost is king in large projects, it is interesting to note how the definition of cost has evolved over the last few years. For example, 3 years ago the lowest cost of construction was king. Today, the lowest lifecycle cost is king. In other words, designers and owners have realized that system costs are more accurately represented when operational costs are evaluated along with up-front costs. Inverters in roof-mounted applications, however, seem to be getting smaller and smaller. While there may be a practical limit on the minimum inverter capacity that is optimal for roof-mounted systems, other factors impact this market. Most notably, these systems must comply with rapid-shutdown requirements for PV systems on buildings. Refinements or changes to 690.12 will drive BOS innovation and component selection in rooftop systems for the next 3 to 5 years.”

—Bill Brooks, Brooks Engineering

“To support PV project economics, it is critical that we continue to drive productivity improvements during installation and maintenance, while providing compact configurations for higher-capacity projects. The solutions that are helping support these efficiencies include integral mounting, preterminated ‘plug-and-play’ cable harnesses and whips, fast turnaround on custom designs and more-robust connections inside combiner boxes to reduce maintenance.”

—Patrick Kane, Eaton


David Brearley / SolarPro magazine / Ashland, OR /

Primary Category: 

[Lawrence, MA] Solectria Renewables has developed its ARCCOM source-circuit combiners to meet the arc-fault interruption and rapid shutdown requirements of NEC 2014. The combiners feature string-level arc-fault detection and a contactor disconnect that allow the devices to detect and interrupt series arc faults. The units also provide remote shutdown functionality. Solectria offers the combiners with a 24 Vdc external power supply, a fire-panel 24-volt output supply or an optional 120 Vac power supply. The ARCCOM combiners are available with 16 or 24 fused inputs and are ETL listed to UL 1741 for 600 Vdc or 1,000 Vdc applications. The enclosures are NEMA 4 rated for vertical or horizontal outdoor mounting.

Solectria Renewables / 978.683.9700 /

Primary Category: 

The NEC recognizes a variety of conduits and tubing that hold wires and cables. How do you select the right raceway type for a particular application, and how do you design and install it efficiently, in a Code-compliant and long-lasting manner?

PV systems, like other electrical power systems, use electrical conductors to route power from sources to loads. It is often necessary to enclose these conductors and protect them along their path. The 2011 NEC lists several methods of getting conductors from here to there, including about 20 different types of raceways and almost as many types of cable, a multiconductor assembly with a covering or jacket.

In this article I focus on raceways commonly used for PV systems. In Part One, to aid in specification and selection, I describe various types of raceways and discuss the differences among them. In the next issue, Part Two will present practical design considerations regarding specific applications of given raceway types and cover installation techniques.

Definitions and Jargon

Unfortunately, the topic of raceways is an area full of trade shorthand and jargon. I can clear up some of this terminology.

Solid or stranded electrical wires are generally known as conductors. Individual conductors can appear by themselves, as in USE-2 underneath a PV array, or several can be assembled in the factory into a cable or installed together in the field into a raceway.

Conduits, tubing and even square wireways are all types of raceways, according to the NEC. However, the NEC does not consider auxiliary gutters raceways, although they are similar to square wireways. While Code does not define the terms conduit and tubing, it does define the term raceway and includes the types of conduit and tubing discussed in this article. For clarity, I use the term raceway as defined in Article 100 to generally indicate “an enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars.”

The trade often refers to particular raceway types with shorthand. For example, among the common flexible raceways, flex usually refers to type FMC (flexible metal conduit; see NEC Article 348), liquidtight usually refers to type LFMC (liquidtight flexible metal conduit; see NEC Article 350) and Sealtite usually refers to type LFNC (liquidtight flexible nonmetallic conduit; see NEC Article 356).

The real confusion happens with the nonflexible circular raceways: These common raceways are rigid (not flexible), but the term rigid often refers to type RMC (rigid metal conduit; see NEC Article 344). Thinwall refers to type EMT (electrical metallic tubing: see NEC Article 358), which in turn is slightly confusing because it is called tubing instead of conduit. Fortunately, both tubing and conduit are types of raceway. Schedule 40 and Schedule 80 usually refer to PVC (polyvinyl chloride) conduits, as per NEC Article 352. Steel or galvanized are ambiguous terms because either could refer to RMC, IMC (intermediate metal conduit; see NEC Article 342) or EMT. The term rigid is even more ambiguous because it could include both metallic and nonmetallic raceway materials, such as PVC. Technically, RMC can also be made from stainless steel, red brass or aluminum, but the vast majority of RMC is galvanized steel.

This article—and hopefully PV project specifications and plan sets—refers to the various raceways by their NEC designators. If you are bidding on a project with drawings or specifications calling for an ambiguous raceway type such as “rigid,” make sure to get formal, written clarification through the Request for Information (RFI) process to determine the intent of the specification. If you assume one type of raceway and the intent was for the other, you may substantially over- or underbid.

Raceway Options

PV systems are generally similar to other electrical power systems, but they do have certain features that affect raceway selection and installation. For example, the bulk of a typical PV system is installed in an exterior location with high exposure to sunlight and other environmental phenomena.

Different raceway types have different attributes, and it is incumbent on the system designer to specify the product most appropriate for a given project and application. In general, the three most common nonflexible raceway types are EMT, RMC and PVC.

EMT. EMT is a thin-walled, rigid raceway. It is almost always made of steel. Corrosion resistance comes from electroplated zinc on the outside and an organic coating on the inside. The pipe is not threaded, so exterior fittings are compression type and interior fittings are setscrew type. Installers can readily bend EMT up to trade size 1¼ inch in the field with hand benders. EMT is lightweight and relatively inexpensive, and offers substantial protection from mechanical damage. Therefore it is a very common raceway for both PV systems and general electrical applications.

RMC. RMC is a thick-walled, rigid raceway almost always made of galvanized steel. The manufacturer threads the ends of each length, and typical assembly involves threaded couplings. RMC is heavier than EMT and more difficult to bend. When cut, RMC requires field thread cutting. While it provides a high level of protection against mechanical damage, it is significantly more time-consuming to install than EMT. It is often used in locations where mechanical protection is required, such as shallow trenches, aboveground areas in close proximity to vehicular traffic, utility service entrances and high-traffic roof areas.

RMC’s almost identical cousin, IMC, is interchangeable in application with RMC. It has a slightly thinner wall than RMC and is always made of galvanized steel. The steel used for IMC is stronger than that used for RMC, so despite the thinner wall, it provides equivalent overall protection. IMC is about two-thirds the weight of RMC and has a slightly larger cross-sectional area available for conductor fill. Many in the field report that IMC is more difficult to bend and to thread properly than RMC, as well as less readily available in most areas.

PVC. PVC is a polymeric (plastic) rigid raceway. It typically comes in two thicknesses: Schedule 40 (standard) and Schedule 80 (thicker wall). The material has a high inherent corrosion resistance. Lengths of PVC raceway are coupled using PVC cement. PVC can be field-bent by careful heating or assembled with prebent elbows. PVC raceway is low cost and lightweight, and can be installed quickly. It is most often used underground, where it is not subject to impact damage or sun exposure.

Impacts on Raceway Selection

Choosing the most appropriate raceway for a particular application depends on a variety of considerations, including cost, durability, mechanical characteristics, thermal expansion, bonding requirements, voltage losses and embodied energy.


The material cost per foot for RMC is about twice that for EMT. RMC has a wall thickness about 2.5 times that of EMT, so a 10-foot stick of 1-inch RMC weighs 16 pounds, versus a 10-foot stick of EMT at 6.5 pounds. RMC costs more to ship and handle. Further, RMC needs to be threaded on both ends—an additional cost. PVC material costs are similar to those of EMT.

The labor involved in installing EMT and PVC is similar, but using RMC is more time-consuming because bending is more difficult and cut ends require thread cutting in the field. Where installed aboveground, PVC requires two to three times as many supports as EMT or RMC, which adds cost for materials and labor to install the supports. For a rooftop installation, the pier supports can be quite expensive, so the increased quantity of supports required for PVC may add significant cost.

In the end, galvanized-steel RMC costs about twice as much, in terms of both labor and materials, as galvanized-steel EMT and PVC. For project-specific analysis, RSMeans publishes annually updated construction cost data based on national averages, which is useful for estimating material and associated installation costs. RSMeans’ Electrical Cost Data ebook includes a comprehensive list of electrical systems and equipment, as well as a brief section on PV applications (see Resources).


Several factors determine a raceway’s durability. For high-quality PV systems, the common functional requirement is that the raceway system protect conductors for the system’s lifetime. This requirement means that the raceway system itself should remain in good condition, without loss of key properties, for the average 25-year life of a PV system. Here are a few considerations to keep in mind for a long-lasting raceway.

UV resistance. UV exposure does not affect the material properties of metal raceways, but you need to evaluate all polymeric raceways—including PVC, LFMC and LFNC—for their resistance to UV degradation. The PVC used for electrical raceways includes additives intended to make the finished product relatively stable in sunlight. In practice, PVC raceway exposed to UV undergoes a reaction, often referred to as browning, in which the outer layer weakens and discolors. According to tests by PVC manufacturer organizations, this does not affect the tensile strength and modulus of elasticity, but it reduces the impact strength. One study by the Uni-Bell PVC Pipe Association, The Effects of Ultraviolet Radiation on PVC Pipe (see Resources), shows a continuous decline in impact strength over a 2-year test period. The study states that it is intended to examine the UV exposure of pipes stored temporarily (up to 2 years) in the sun but eventually installed underground. Clearly, this intended use is quite different from permanently installing PVC on a rooftop, where raceways may be exposed to UV radiation for 25 years or longer.

The relevant UL standard for rigid PVC electrical raceway, UL 651, and the UL standard for polymeric materials used in electrical equipment, UL 746C, describe Weather-Ometer testing that includes only 720 hours of accelerated UV testing. This is roughly equivalent to 2 years of full sunlight exposure, depending on location. There is some interest among experts concerned about long-term outdoor performance of nonmetallic raceways in extending this testing for longer periods, which would make it more pertinent to PV rooftop installations.

You can limit UV exposure by painting polymeric conduits a light color with water-based latex paint appropriate for exterior use. You must thoroughly clean the conduit before applying the paint. Painting is a good solution for short lengths of exposed PVC, LFMC or LFNC, such as when you use PVC underground with short stubs emerging into sunlight before terminating in the bottom of an enclosure, or when you use a short section of LFMC or LFNC as an expansion joint on a rooftop conduit run.

Chemical resistance. Whereas PVC suffers degradation when exposed to UV, it is quite resistant to corrosion from other environmental forces. Steel, however, is susceptible to oxidation in the presence of water, which it is commonly exposed to on rooftops, underground and in other exterior locations. Salt water, commonly found in the air near coasts, is even more corrosive.

Fortunately, steel raceways are commonly manufactured with protection against corrosion, most often in the form of galvanizing. Both EMT and RMC are made of galvanized steel, which provides enough corrosion protection for all but the harshest environments. In highly corrosive marine areas, however, electroplating or even hot-dip galvanizing may not be enough long-term protection for steel raceway. In those locations, you should specify RMC in stainless steel, which is very expensive, or more commonly RMC with a PVC coating. However, assuming UV exposure in addition to salt-water exposure, the PVC coating will degrade and eventually allow salt water to access the steel.

Another corrosion-resistant option is aluminum RMC. Aluminum oxidizes, but in contrast to steel oxidation (rust)—which tends to weaken the metal and flake off, exposing more steel to further oxidation—aluminum oxide forms a strong, protective layer for the underlying aluminum. In a corrosive environment, stainless steel or aluminum fittings should be used with any aluminum raceway.

Chemical resistance can also be a factor where raceways are installed in direct contact with earth or encased in concrete slabs or piers. In these environments, PVC provides the best corrosion resistance. The NEC permits you to install IMC and RMC in potentially corrosive environments where the raceway is “protected by corrosion protection and judged suitable for the condition”; see NEC Sections 342.10(B) and 344.10(B)(1). EMT is granted the same permissions, yet the corrosion protection must be “approved as suitable for the condition”; see NEC Section 358.10(B). Corrosion protection tape is often used on IMC, RMC and EMT in corrosive environments and is generally a good practice on sweeps where the raceways emerge aboveground. PVC-coated RMC is another alternative where additional corrosion protection is necessary.

Fire resistance. Steel survives high temperatures longer than PVC. I hope that your installations never experience an external fire or an internal arcing fault in the raceway—but if any of them do, you can breathe easier if you have specified steel raceway.

Mechanical Characteristics

In general, stronger raceway materials and thicker raceway walls provide better mechanical protection for conductors. Thus, all else being equal, steel is stronger than aluminum, and aluminum is stronger than PVC. Thick-walled steel RMC and IMC are stronger than thin-walled EMT. In underground installations where the raceway is subject to physical damage, NEC Section 300.5(D)(4) explicitly allows RMC, IMC and Schedule 80 PVC. It does not allow EMT and flexible conduits.

Interestingly, NEC Section 358.12(1) disallows EMT where “subject to severe physical damage,” (emphasis added) whereas Section 352.12(C) disallows PVC “where subject to physical damage unless identified for such use.” The UL White Book makes it clear that Schedule 80 PVC is identified for use where subject to physical damage, but Schedule 40 PVC is not. However, the Code leaves “subject to physical damage” and “severe physical damage” up to interpretation. Commonly, areas above ground are interpreted as subject to physical damage if there is any chance of vehicular presence, such as in driveways, parking lots, warehouses with forklifts and so on.

Many AHJs require at least Schedule 80 PVC where the raceway emerges from underground, whether or not there is  exposure to vehicles, and further require RMC when there are vehicles present. For PV systems, another common location potentially subject to physical damage is the rooftop. During installation and maintenance of rooftop equipment, including both the PV system itself and HVAC or window-washing equipment, there may be significant foot traffic on the roof. Raceways installed a few inches above the surface tend to get kicked and stepped on with some regularity, especially where the raceways cross walkways. These areas may require more robust raceways or physical protection such as ramps or steps.

In addition to losing impact strength with increased UV exposure, PVC becomes brittle in cold temperatures, making it subject to damage. At the other temperature extreme, both NEC Section 352.12(D) and UL 651 Section 1.2.3(a) limit the use of PVC to ambient temperatures up to 122°F (50°C) only. According to Thermal Expansion and Contraction in Plastics Piping Systems PPI TR-21/2001, published by the Plastics Pipe Institute (see Resources), even at 100°F (37.78°C), PVC loses 40% of its stiffness, or elastic modulus. Further, according to the same publication, PVC’s effective stiffness decreases significantly with increased duration of loading, so a PVC raceway tends to sag more over time. Metal raceways do not have any practical temperature limits, either hot or cold, and do not exhibit effective loss of stiffness under extended loading.

One common loading application for raceways is a horizontal run supported at certain intervals. Stiffer raceways show less deflection for a given span between supports, and stronger raceways allow longer spans without exceeding the yield stress or failing. The Code takes raceway stiffness into account when dictating minimum support spacing. PVC must be supported every 3 feet for sizes up to 1 inch, every 5 feet up to 2 inches, and a maximum of every 8 feet for 6 inches. In contrast, EMT of any size requires supports every 10 feet, and RMC can span 10–20 feet between supports, depending on its size.

Buried raceways are not susceptible to vehicle impact, and they are effectively supported along their length, but stronger raceways better survive localized compaction from heavy equipment, soil shifting and settling, and motion resulting from seismic activity.

Fittings and assembly quality. In addition to the material properties and geometry of the raceways themselves, the difference in fittings used to connect them creates significant variances in mechanical durability among assembled raceway systems. Typically, RMC is assembled with threaded fittings, EMT is assembled with either compression fittings or setscrew fittings, and PVC is solvent welded. All of these methods are long lasting and reliable, if you assemble them with excellent workmanship. However, some are more susceptible to field failures than others.

Solvent-welding PVC sections can be problematic in several ways. Bell-end raceway sections, intended to save labor and materials by eliminating a separate coupling piece, often do not have the tight tolerance required for a perfect joint. Even with good materials, the quality of a joint is highly dependent on the skill and attention of the installer. The mating surfaces must be deburred, cleaned and primed properly (if required), and the appropriate amount of the correct solvent cement must be applied evenly. Then the joint must be pressed together, rotated slightly and held for at least 30 seconds to prevent it from pushing itself apart as it cures. If the installer improperly executes—or ignores—any of these steps, that compromises the joint. Unfortunately, even close inspection does not reveal shortcomings until a few thermal cycles or a moderate amount of stress (including wire-pulling forces) cause the joint to fail, leaving the conductors susceptible to damage. Another minor downside to these welded joints is that they are not reversible. If a joint needs adjustment after welding, you need to cut out and replace the raceway section with the joint.

With exterior-rooftop EMT raceway used in PV systems, installers join sections of EMT using compression couplings. These fittings also rely on good workmanship and are difficult to inspect at a glance. To make a good joint, the tubing must be cut square, deburred and inserted cleanly through all of the rain-tight gaskets and compression rings. The fitting must be a compression fitting listed for use with EMT. Slightly larger compression fittings listed for RMC do not work. The installer must make the fitting wrench tight while ensuring that the tubing remains bottomed out in the fitting and, if the tubing has bends in it, that it does not rotate as the fitting nut is tightened. Again, if the installer forgets any of these steps or does them improperly, the joint may appear acceptable at a glance, but sharp exposed burrs or edges can damage conductor insulation during the wire pull or the fittings may pull apart when stressed. Setscrew fittings used for indoor applications of EMT have similar requirements and shortcomings.

The combination of the need for excellent workmanship with the difficulty of accomplishing a thorough inspection of an installed raceway system gives John Wiles, Code guru and senior research engineer at the Southwest Technology Development Institute at New Mexico State University, cause for concern: “The only time that we get reports of a conduit problem is when there has been a failure leading to a fire or other issue. As PV systems age, issues with improper installation of metallic conduits increase.”

The threaded couplings used to join sections of RMC and IMC are the strongest and most reliable of the various connection methods. Cut sections require more labor and tools to field-cut threads—again, after cutting the pipe square and deburring it. As long as the pipe ends have threads and you have selected the correct fittings, the mechanical integrity of the joint is all but assured once you have engaged enough threads. When you have made the joint wrench tight, only a thread or two is visible. These joints are easy to inspect visually, and they are tremendously strong.

Thermal Expansion

Most of us who have spent time on rooftops have often seen long runs of wavy raceway and broken sections. Wavy or buckled pipe does not usually result from the failure to set a straight string line when the pipe was installed, but rather is a clear manifestation of thermal expansion and contraction. All raceway materials are subject to thermal expansion, but some much more so than others.

Two results are common when high–thermal-expansion raceways are installed without properly designed and installed expansion fittings: First, when the raceway expands against fixed supports or terminations, it causes high stress on the raceway and fittings, which can cause buckling and cracking. Second, when the raceway cools and contracts, the resulting tensile stress can pull fittings apart. In either case, the raceway has failed and exposed the conductors it carries to damage.

The linear coefficient of thermal expansion is a material property. Basically, when the atoms in a material get warmer, they vibrate more and take up more space, thereby causing expansion of the bulk material. The coefficient for a given material is expressed in fractional change in length (strain) per degree of temperature change of the material. Common building materials expand on the order of 10 units of length per million units of length for every 1°F of temperature change, or 10 × 10-6/°F. A convenient way to express this change is in inches of expansion per 100 feet of length. For a 100°F temperature change—commonly seen on roofs—thermal expansion of common materials is as follows:

  • Steel 0.8 inches
  • Concrete 0.8 inches
  • Wood (parallel to grain) 0.3 inches
  • Aluminum 1.6 inches
  • PVC 4.1 inches

Calculating raceway thermal expansion. NEC Article 300, “Wiring Methods,” has a section that applies to all raceways called “Raceways Exposed to Different Temperatures.” Section 300.7(B) requires expansion fittings “where necessary to compensate for thermal expansion and contraction.” The raceway-specific articles come later in Chapter 3. Article 352 governs PVC raceways and has specific requirements for mitigating thermal expansion because PVC has such a high coefficient and causes a bigger problem if thermal expansion is ignored. Section 352.44 requires expansion fittings for PVC raceway when the expected length change due to thermal expansion is ¼ inch or greater. Table 352.44 lists the expansion coefficient for PVC and shows calculated length-change values for different assumed temperature changes.

For steel and aluminum raceways, it is up to the designer and the AHJ to interpret the definition of the “where necessary” language in NEC Section 300.7(B), although Code does provide an informational note after Section 300.7(B) that suggests using rounded multipliers for steel (0.2) and aluminum (0.4) based on the PVC chart in Section 352.44, because the coefficient of thermal expansion for PVC is approximately 5 times that of steel and 2.5 times that of aluminum. This is one of the primary reasons why PVC raceway is typically not specified for rooftop use in PV systems.

Among common raceway materials, steel has the smallest coefficient of thermal expansion, which makes it most similar to the steel, concrete or wood buildings it is fastened to.  Specifically, for rooftop raceway applications—which tend to be exposed to severe temperature changes—you can compare the raceway linear coefficient of thermal expansion to that of the roof framing. In most buildings, the roof framing, which is often insulated from the exterior or moderated by conditioned space below, does not experience as large a temperature swing as does a raceway installed a few inches above the roof surface. In addition, common roof framing materials have a relatively low linear coefficient of thermal expansion, meaning with less temperature change they tend to expand and contract less than rooftop raceways.

The equation used to calculate thermal expansion and contraction is:

delta L = alpha × delta T × L

where delta L is the length change of the raceway, alpha is the coefficient of thermal expansion of the material, delta T is the temperature change and L is the initial raceway length. This is always an approximation because alpha typically changes slightly with temperature. The NEC provides coefficients of thermal expansion for PVC, steel and aluminum raceways (see Table 1).

Consider a raceway running 200 feet along a parapet wall from a combiner box to a pull box (see Diagram 1). The location’s ambient temperature ranges from 10°F to 90°F. Assuming that the building has no expansion joints between the boxes, the building itself (and therefore the distance between the boxes) will expand by as much as 1 inch. Depending on the framing materials and the level of insulation and interior temperature conditioning, which reduces the temperature change to which the framing is exposed, the building may expand as little as ¼ inch. Since the raceway is a few inches above the roof surface and is exposed to direct sun, it can reach 120°F, for a total temperature change of 110°F (120°F − 10°F). For a steel raceway, the length change of the raceway would be 0.143 feet (0.650 × 10-5 × 110°F × 200'), or 1.72 inches, which is about ¾ inch to 1½ inch more expansion than the building itself will experience.

For an aluminum raceway, the length change would be 0.286 feet (1.3 × 10-5 × 110°F × 200'), or 3.43 inches. Finally, for a PVC raceway, the length change would be 0.744 feet (3.38 × 10-5 × 110°F × 200'), or 8.92 inches. All three raceway types would require at least one expansion fitting—and PVC would require at least two-—as well as associated sliding supports and guides to allow the expansion fittings to operate properly.

When burying PVC pipe, the temperature change underground is generally assumed to be relatively small. However, if you assemble the PVC raceway and solvent-weld it out of the trench, in the sun, and then drop it into the trench and immediately bury it, it may develop high tensile forces when it cools to below-grade temperature after you have fixed it in place. These tensile forces may cause the weakest joint to pull apart underground, resulting in a failed raceway system. You can easily avoid this problem by allowing the assembled raceway to reach the cooler underground temperature before backfilling and compacting.

Bonding Requirements

Another difference between raceway systems relates to grounding and bonding. Polymeric raceways are not conductive, so they cannot be used as the primary or supplemental equipment-grounding conductor. In addition, they are nonferrous, so they have no effect on the impedance of fault-clearing circuits or dissipation of high-current surges to the grounding-electrode system. In contrast, steel raceways are conductive, which has two implications. First, it means they need bonding to prevent unintentional energizing of the raceway and subsequent shock hazard. For most PV dc circuits, as well as 480 Vac and above, installers must pay special attention to bonding any metal raceway because NEC Section 250.97 essentially requires the use of grounding bushings (with some exceptions) for all circuits above 250 V to ground. Second, the fact that steel raceways are conductive also means that they can provide either the primary or supplemental ground-fault current path to help clear faults by opening overcurrent protection devices.

You typically cannot use flexible steel raceways, such as FMC and LFMC, as the primary equipment-grounding conductor (EGC), except for very short lengths, whereas rigid steel raceways are permitted as the sole equipment-grounding conductor; see NEC Sections 250.118(6) and (7). However, best practice is to include an insulated EGC along with the current-carrying conductors inside the raceway so that the fault-clearing function of the EGC is not dependent on every fitting in the raceway system. Especially on a long run across a roof, where the raceway may be subject to all manner of challenges to its integrity, it is critical to install the nonraceway EGC inside the raceway. The addition of this “above Code” conductor also reduces the impedance of a potential ground-fault circuit and gives PV ground-fault detection devices a better chance of doing their job and preventing fires.

By definition, steel raceways are ferrous, which means they have magnetic interaction with both intentional and unintentional current flowing in the conductors inside the raceways. Among other considerations, this means that if any grounding electrode conductors (GECs) used in a PV system, including dc GECs, are contained in steel raceways, then NEC Section 250.64(E) requires bonding of both ends of the steel raceway to the GEC to prevent the raceway from restricting the flow of current from a lightning strike—or any high-current surge—to the grounding electrode and into the earth. Aluminum raceways have the benefit of being conductive without the drawbacks of magnetic interaction with fault currents. Therefore aluminum or PVC raceways are recommended for protecting GECs. See NEC Article 250 and especially the Soares Book on Grounding and Bonding, by the International Association of Electrical Inspectors, for more details on this topic (see Resources).

Voltage Losses

Choice of raceway material can affect the amount of voltage drop on ac inverter output circuits, especially with larger circuits (300-kcmil and above) and in newer systems with grid-stabilizing inverter features such as power factor correction. See “Voltage Drop in PV Systems,” SolarPro magazine, February/March 2010, for more information on voltage drop in general, and for a comparison of the effect on voltage drop of PVC, aluminum and steel raceways.

Embodied Energy

For certain projects, factors such as embodied energy and recyclability are important design criteria. In those cases, lightweight EMT steel raceway may be a better choice than aluminum or PVC. Steel has about ¼ the embodied energy of PVC on a per-kg basis, and about 1/8 that of aluminum. Typically, for a given size of raceway, Schedule 40 PVC is about 1/2 the weight of EMT, or about 1/5 the weight of steel RMC. Steel and aluminum are readily recyclable, whereas only a tiny fraction of PVC gets recycled.


Once you have assessed the benefits and limitations of raceway options for PV installations, raceway selection can proceed. Making the selection is quite valuable for bidding and estimating projects, yet the raceway system is only as good as the installation. Poor installation techniques can result in raceway issues that may damage conductors during the wire pull or raceway failures. Proper installation of the raceway system and the conductors it holds requires design, planning, preparation and execution strategies that I will expand upon in Part Two of this article in the next issue.


Blake Gleason / Sun Light & Power / Berkeley, CA /


Electrical Cost Data, RSMeans, 2013,

The Effects of Ultraviolet Radiation on PVC Pipe, Uni-Bell PVC Pipe Association,

Thermal Expansion and Contraction in Plastics Piping Systems PPI TR-21/2001, Plastics Pipe Institute,

Soares Book on Grounding and Bonding,  International Association of Electrical Inspectors, 2011,

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[Pleasanton, CA] AMtec Solar has expanded its EQUINOX array recombiner product line. Developed specifically for bipolar PV arrays, the new EQUINOX Bipolar Circuit Breaker Solar Recombiner Box features circuit breakers to provide individual disconnecting means to meet 2011 NEC installation requirements. The recombiner supports up to seven positive and seven negative circuits and offers breaker ratings of up to 400 A. The assembly is listed to UL 1741 for 600 Vdc or 1,000 Vdc applications. AMtec designed the NEMA 3R enclosure to provide adequate space to maintain a code-compliant wire-bending radius when working with large conductors, and allows for the removal of the side and rear wall panels if necessary. Options include Modbus RS485 current monitoring, ground-fault detection and surge protection.

AMtec Solar / 510.887.2289 /

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[Norcross, GA] Type VBII PV disconnect switches from Siemens are specifically designed for disconnecting three separate 600 Vdc circuits. Precisely aligned magnets are incorporated into each switch’s line base assembly to quickly and safely extinguish the dc arc caused by disconnecting an array under load. Products in the heavy-duty switch line are listed as UL 1741 PV Disconnect Switches and also comply with UL 98 requirements. Type VBII PV disconnect switches are available in fusible and nonfusible models with 30 A, 60 A and 100 A ratings in indoor or outdoor enclosures. Standard features include a factory installed ground bus and NEC-required labeling, indicating that line- and load-side conductors may be energized when the switch is open. In addition, the line- and load-side lugs are larger than those in standard disconnects to accommodate conductor upsizing due to voltage drop considerations.

Siemens Industry / 800.743.6367 /

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[Lawrence, MA] Solectria recently introduced three new combiner modules with dc disconnect options. The disconnect feature is available in an eight-circuit combiner rated for 120 A maximum, housed in a NEMA 4X fiberglass enclosure; a 16-circuit combiner rated for 180 A maximum, also housed in a NEMA 4X fiberglass enclosure; and a 24-circuit combiner rated for 180 A maximum in a NEMA 4 polyester powder–coated steel enclosure. The CSA-listed load-break–rated switch is tested to UL 508 and is compliant with UL 1741 and the 2011 National Electrical Code.

Solectria Renewables / 978.683.9700 /

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In the summer of 2012, when we started working with Marvin Hamon and Greg Ball on the article “1,000 Vdc Utilization Voltages in Nonresidential PV Applications”, exactly one module manufacturer (MEMC) had publicly announced the release of a listed 1,000 V–rated PV module. Fast-forward 6 months, and over 200 different models of listed 1,000 V PV modules are available from 17 different manufacturers. It does not take a crystal ball to see where this is heading. More 1,000 V–rated products in every equipment class are on the way.

This article is intended to provide a representative snapshot of 1,000 V product availability at press time (February 2013). Since the certification and availability of products listed for 1,000 Vdc systems is changing rapidly, we do not expect this list to be comprehensive. In addition to the module, inverter, combiner and BOS product lines covered here, several manufacturers have initial or additional certification efforts either planned or under way.

PV Modules

While several module manufacturers have announced certification to UL 1703 for systems with maximum voltages of 1,000 Vdc over the last year, more have either quietly achieved this listing or have related testing and certification under way. We reached out to 65 module manufacturers that are active in the North American market for updates on 1,000 Vdc certification efforts, and discovered that roughly 25% of these companies either have listed 1,000 V PV modules or will soon. The following summaries include brief corporate backgrounds and overviews of specific product lines that are listed to UL 1703 for 1,000 V applications.

Integrators should be aware that during our research we identified instances where module specification sheets posted on a given company’s website were not up-to-date regarding 1,000 Vdc listing, even if the certification was complete. If you are planning to develop “in-front-of-the-fence” 1,000 V systems that require components to be listed to relevant UL standards, and you currently have preferred module suppliers that are not covered here, we recommend that you ask for updates through your regular sales channels.

Canadian Solar Founded in 2001 in Ontario, Canada, Canadian Solar is a publicly traded corporation that was listed on the NASDAQ Stock Market in 2006. The firm currently operates in 11 countries, with US sales offices located in San Ramon, California. In July 2012, Canadian Solar received certification to UL 1703 for maximum system voltages of up to 1,000 Vdc on four of its module lines. The certified product lines include UL 1000V CS6P-M (60-cell, mono, 245 W–260 W), UL 1000V CS6P-P (60-cell, poly, 240 W–255 W), UL 1000V MaxPower CS6X-M (72-cell, mono, 295 W–310 W) and UL 1000V MaxPower CS6X-P (72-cell, poly, 290 W–300 W). CSA Group performed testing and certification.
Canadian Solar / 925.866.2700 /

Centrosolar America Centrosolar America is headquartered in Scottsdale, Arizona, and its parent company, Centrosolar Group AG, was founded in 2005 in Munich, Germany. The publicly traded company introduced its modules to the US market in 2008 and recently listed its 60-cell polycrystalline E-Series module line to 1,000 Vdc. Intertek performed testing and certification to UL 1703. The 235 W to 265 W 1,000 Vdc– rated modules have a Q2 2013 projected release date.
Centrosolar America / 877.348.2555 /

Conergy Americas Conergy Group, a German module manufacturer, project developer and equipment wholesaler, was founded in 1998 and is listed on the Frankfurt Stock Exchange. Its US subsidiary was established in 2005 and is headquartered in Denver. CSA Group has tested and listed the company’s PH Series modules to UL 1703 for maximum system voltages of 1,000 Vdc. The 60-cell polycrystalline PH Series modules are available with rated power outputs of 230 W to 255 W. Conergy North America is scheduled to release a new PE Series module line in Q1 2013. Initially the product line will be listed for 600 Vdc applications, but the company plans to have the line listed for 1,000 Vdc applications in early 2013.
Conergy Americas / 888.396.6611 /

DelSolar Founded in 2004 at the Hsinchu Science Park in Taiwan, DelSolar is a joint venture of Delta Electronics and the Taiwanese Industrial Technology Research Institute. In September 2012, UL listed four of DelSolar’s module lines for 1,000 Vdc applications: D6C_B3A-WS (60-cell, poly, 230 W– 250 W), D6S_B3A-WSf (60-cell, mono, 250 W–260 W), D6C_B4A-WS (72-cell, poly, 285 W–305 W) and D6S_B4A-WSf (72-cell, mono, 300 W–310 W).
DelSolar / 888.880.8868 /

ET Solar Headquartered in Pleasanton, California, ET Solar is the US subsidiary of the privately held ET Solar Group, based in Nanjing, China. The company announced the launch of its 60-cell and 72-cell 1,000 Vdc–listed module lines at PV America East. The recently listed modules received certification to UL 1703 for 1,000 Vdc applications in January 2013. Intertek conducted the testing and certification. The relevant module lines include ET-P-WW (60-cell, poly, 225 W–260 W). ET-P-WB (72-cell, poly, 280 W–310 W), ET-P-WWG Anti-glare (72-cell, poly, 270 W–295 W) and ET-P-BBG Antiglare (72-cell, poly, 270 W–290 W, black frame and backsheet).
ET Solar / 925.460.9898 /

First Solar First Solar was founded in 1999 and is headquartered in Tempe, Arizona, with manufacturing facilities in Malaysia and Perrysburg, Ohio. The company launched its IPO in November 2006 and is traded on the NASDAQ Stock Market. For years, First Solar has been deploying its thinfilm CdTe PV laminates in utility-owned 1,000 V, behind-thefence projects. In October 2012, the manufacturer and project developer completed the UL listing of its Series 3 module line for use in systems with a maximum voltage of 1,000 Vdc. The Series 3 product line currently includes five models with power outputs of 82.5 W to 92.5 W.
First Solar / 877.850.3757 /

JA Solar USA Founded in 2005, JA Solar Holdings is headquartered in Shanghai, China. The vertically integrated cell and module manufacturer was publicly listed on the NASDAQ Stock Market in February 2007. The company’s US subsidiary, JA Solar USA, is headquartered in San Jose, California. JA Solar USA offers an extensive suite of nine module lines that Intertek or TÜV Rheinland NA listed for 1,000 Vdc applications per the UL 1703 standard, including JAM6 (60-cell, mono, 250 W–270 W), JAM6-R (60-cell, mono, 255 W–275 W, full square cells), JAM6-BK (60-cell, mono, 245 W–265 W, black frame and backsheet), JAP6 (60-cell, poly, 235 W–260 W), JAP6-BK (60-cell, poly, 235 W–255 W, black frame and backsheet), JAM5-L (72-cell, mono, 195 W–215 W), JAM5-L-BK (72-cell, mono, 190 W–210 W, black frame and backsheet), JAP6 (72-cell, poly, 280 W–310 W) and JAM6 (72-cell, mono, 290 W–325 W).
JA Solar USA / 408.586.0000 /

MEMC Headquartered in St. Peters, Missouri, and founded in 1959, MEMC Corporation manufactures semiconductors for electronic devices as well as polysilicon, solar cells and modules for PV applications. The company launched its IPO in July 1995 and is traded on the New York Stock Exchange. In 2009 MEMC completed the acquisition of SunEdison, a well-known solar project developer that recently expanded into the residential installation market in the US. In April 2012, MEMC announced CSA listing of its Silvantis P290 module series to UL 1703 for 1,000 Vdc applications. MEMC now has two primary module lines that are certified for systems with maximum voltages of 1,000 Vdc: the 72-cell polycrystalline Silvantis P series with a rated output of 280 W to 305 W and the 72-cell monocrystalline Silvantis M series with a rated output of 305 W to 330 W.
MEMC / 636.474.5000 /

Motech Americas Motech Americas is the US subsidiary of Motech Industries, a public Taiwanese PV cell and module manufacturer founded in 1981 as a test and measurement equipment manufacturer. The US subsidiary is headquartered in Newark, Delaware, where it manufactures ARRAcompliant monocrystalline and polycrystalline modules. In October 2012, Motech Americas announced that its IM+ Series and XS+ Series modules had achieved certification for use in 1,000 Vdc systems. Intertek performed the related product testing and listing to UL 1703. The relevant models include IM60+ (60-cell, poly, 250 W–260 W), XS60+ (60-cell, mono, 255 W–265 W), IM72+ (72-cell, poly, 300 W–310 W) and XS72+ (72-cell, mono, 310 W–320 W).
Motech Americas / 302.451.7500 /

Phono Solar USA SUMEC Group, headquartered in Nanjing, China, is the parent company of Phono Solar USA and six additional Phono Solar subsidiaries that operate throughout Europe and Asia. The company conducts all module manufacturing in Nanjing. The US subsidiary is headquartered in The Woodlands, Texas. Intertek tested and listed two of Phono Solar USA’s primary module lines for 1,000 Vdc applications, including Diamond 235-265 (60-cell, poly, 235 W–265 W), Diamond 280-330 (72-cell, poly, 280 W–330 W), Diamond 190-210 (72-cell, mono, 190 W–210 W), Onyx 235-265 (60-cell, poly, 235 W–265 W, black frame and backsheet) and Onyx 235-270 (60-cell, mono, 235 W–270 W, black frame and backsheet).
Phono Solar USA / 281.909.0644 /

REC Americas REC Americas’ parent company, REC Group, is headquartered in Sandvika, Norway, and is traded on the Oslo Stock Exchange. The company produces polysilicon for the solar and electronics industries at two US materials plants located in Moses Lake, Washington, and Butte, Montana. The company’s wafer, cell and module production is located in Tuas, Singapore. REC Americas is headquartered in San Luis Obispo, California. In February 2013, the manufacturer completed the listing of its Peak Energy 72 Series modules to UL 1703 for 1,000 Vdc applications. UL performed the testing and certification process. The 72-cell polycrystalline product line includes five models with rated power outputs of 285 W to 305 W.
REC Group / 877.332.4087 /

Renesola Established in 2005, Renesola is a vertically integrated PV manufacturer that is active from polysilicon production to module assembly. The company has manufacturing facilities spread across three locations in China, with its US headquarters located in San Francisco. The company was listed on the New York Stock Exchange in 2008. In November 2012, UL completed testing and certification of several Renesola module lines for 1,000 Vdc applications including JCS-24/Bbh (60-cell, mono, 250 W–260 W), JCM- 24/Bbh (60-cell, poly, 250 W–260 W) and JCM-24/Abh (72- cell, poly, 300 W–310 W). Listed models with black frames and backsheets are also available.
Renesola / 415.852.7418 /

SolarWorld SolarWorld’s US subsidiary conducts ingot, wafer, cell and module manufacturing at its corporate headquarters and production facility in Hillsboro, Oregon. All modules produced at the Oregon location meet ARRA domestic content requirements. SolarWorld USA’s parent company, SolarWorld Group, is headquartered in Bonn, Germany. The Group launched its IPO in 1999 and is traded on the Frankfurt Stock Exchange. SolarWorld offers several products within its Sunmodule PV line that have received certification for use in 1,000 Vdc systems per the UL 1703 standard. Listed products include the 60-cell Sunmodule 255 W to 270 W monocrystalline models, as well as the 60-cell 250 W to 260 W Sunmodule Mono Black products. Intertek and/or TÜV Rheinland NA completed testing and listing to the UL standard for 1,000 Vdc applications.
SolarWorld / 855.467.6527 /

Suniva Headquartered in Norcross, Georgia, Suniva is a privately held US manufacturer of monocrystalline and polycrystalline PV cells and modules. The company’s Optimus product lines contain more than 80% domestic content and are ARRA compliant. In January 2013, Suniva announced the listing of the Optimus product models to UL 1703 for 1,000 Vdc applications. These lines include OPT-60-4-100 (60-cell, mono, 255 W– 270 W), OPT-60-4-1B0 (60-cell, mono, 255 W–265 W, black frame and backsheet) and OPT-72-4-100 (72-cell, mono, 300 W–315 W). Intertek performed the testing and certification for these recently listed product lines.
Suniva / 404.477.2700 /

Suntech Americas Suntech Power Holdings operates regional headquarters in China, Switzerland and the US. The company entered the North American market in 2004 and was listed on the New York Stock Exchange in 2005. Suntech’s US headquarters is located in San Francisco, with domestic module assembly in Goodyear, Arizona. In August 2012, the manufacturer announced the certification of its Ve-Series modules to UL 1703 for 1,000 Vdc applications. The 72-cell polycrystalline module line includes models with rated power outputs of 290 W to 305 W. CSA conducted the testing and listing on the Ve-Series modules to the UL standard.
Suntech / 866.966.6555 /

Trina Solar Founded in 1997, Trina Solar is a vertically integrated manufacturer of PV ingots, wafers, cells and modules that is headquartered in Changzhou, China. Manufacturing and R&D activities are conducted at the company’s Changzhou campus. Trina Solar was listed on the New York Stock Exchange in 2006 and operates 12 offices worldwide, including its US headquarters in San Jose, California. The manufacturer completed TÜV Rheinland NA testing and certification to UL 1703 for 1,000 Vdc applications in December 2012 for its TSM-PD14 and TSM-PD05 module lines. The 72-cell, polycrystalline TSM-PD14 line is available with power outputs of 285 W to 305 W. The 60-cell, polycrystalline PD05 line will be launched in the near future.
Trina Solar / 800.696.7114 /

Yingli Green Energy Headquartered in Baoding, China, Yingli operates more than 20 subsidiaries and offices worldwide, including US offices in San Francisco and New York. The company’s manufacturing activities include all aspects of the PV value chain, from polysilicon production to module assembly. Yingli was founded in 1998, launched its IPO in 2007, and is traded on the New York Stock Exchange. In September 2012, the manufacturer announced the listing of its polycrystaline YGE-U 72 Cell Series to UL 1703 for 1,000 V applications. UL completed the testing and certification. The YGE-U 72 Cell Series modules were developed specifically for utility-scale projects and are available with output ratings of 285 W to 305 W.
Yingli Green Energy / 888.686.8820 /


At least ten inverter manufacturers currently offer 1,000 V inverters that are certified to UL 1741. The majority of these companies announced the release of their listed 1,000 V inverter lines in 2012. Only American Electric Technologies (AETI), GE Energy and Nextronex were earlier to market. While most of the 1,000 V products currently available are intended for utility applications, several companies offer high-capacity inverters that can be interconnected at 480 Vac. Power-One is the only company at press time with listed 1,000 V inverters rated less than 150 kW in capacity. REFUsol plans to release 1,000 V versions of its 3-phase string inverters in 2013. It is reasonable to expect that many other companies plan to release listed 1,000 V inverters in 2013 and in years to come, and that product offerings will become more diversified over time.

Advanced Energy (AE) Headquartered in Fort Collins, Colorado, AE Solar Energy has certified its AE 500NX-1kV inverter to UL 1741. Formerly known as the Solaron 500 kW 1kV, the AE 500NX-1kV is a 500 kW transformerless inverter that uses a 1,000 Vdc single-array configuration. AE also offers integrated 1 MW to 2 MW power stations based on the NX inverter platform. (See photo on p. 42.) A prewired PowerStation NX includes up to four AE 500NX-kW inverters, a medium-voltage transformer, a distribution switchboard, dc subarray combiners and dc disconnects. No additional weatherproofing is required, and a single truck can deliver a power station of up to 2 MW in capacity.
Advanced Energy / 800.446.9167 /

AEG Power Solutions Headquartered in the Netherlands, AEG Power Solutions Group is the sole subsidiary of the holding company 3W Power, which is based in Luxembourg and has US offices outside Dallas. In September 2012, AEG announced the certification of its 1,000 V Protect PV.500-UL inverter to UL 1741. TÜV Rheinland NA performed testing and certification. Using an appropriate transformer, the product can be adapted for use at 480 Vac or common medium-voltage levels. A 1 MW turnkey container solution is also available that integrates a pair of ProtectPV.500-UL inverters with disconnects, switchgear and a medium-voltage transformer. While the standard inverter enclosure is indoor rated, an outdoor enclosure system is available as an option.
AEG Power Solutions / 469.229.9604 /

AETI Headquartered in Houston, AETI is a publicly traded company specializing in power delivery solutions. It was one of the first companies to test a 1,000 V inverter to UL 1741. In June 2011, the company announced that TÜV Rheinland NA had validated the compliance of AETI’s Integrated Solar Inversion Station (ISIS) to UL 1741. The ISIS solution is available at two capacity levels (1 MW and 1.5 MW) and with two medium-voltage interconnection options (15 kV and 38 kV). When the solar inversion and utility interconnection platforms are supplied together, the entire assembly—inverter, step-up transformer and interconnection switchgear—is witness tested to comply with UL 1741 and ANSI C.37.
AETI / 713.644.8182 /

Bonfiglioli With world headquarters in Bologna, Italy, and North American headquarters in Hebron, Kentucky, Bonfiglioli specializes in power transmission and control in industrial, mobile and renewable energy applications. In November 2012, Bonfiglioli announced the certification of its 1,000 V RPS TL-UL inverter series to UL 1741. The RPS TL-UL system is modular and scalable from 367 kW to 1.4 MW. Power modules can be configured in a masterslave configuration to maximize conversion efficiency and extend component life or in a multi-MPPT configuration to accommodate subarrays with different PV technologies or orientations. Both floating and grounded array configurations are supported. The RPS TL-UL enclosure is rated for indoor installations.
Bonfiglioli USA / 859.334.3333 /

Eaton Headquartered in Cleveland, Eaton is a global diversified power management company. Eaton’s 1,000 V solar product portfolio includes two large power block inverters for utility-scale applications. A modular design ensures fault tolerance. The Power Xpert Solar 1,500 kW uses three independently isolated 500 kW power trains, whereas the Power Xpert 1,650 kW uses a three-by–550 kW configuration. Critical components are designed for reliability. Power electronics are located in a dust- and water-free environment and liquid cooled. Each inverter can be close-coupled with a step-up transformer in a configuration without skids that results in smaller pad sizes. The enclosure is outdoor rated. A coldweather package, which extends the minimum temperature limit from -20°C to -40°C, is available as an option. Listing to UL 1741 is pending on both products.
Eaton / 855.386.7657 /

GE Energy Headquartered in Fairfield, Connecticut, GE is a diversified global conglomerate with four primary business divisions. The company offers its solar solutions through the GE Energy division. In September 2011, the company announced that GE Energy’s 1 MW Brilliance Solar Inverter had received UL 1741 certification, making it one of the first high-capacity, listed 1,000 V inverters. The product is intended for multimegawatt PV projects. The 1 MW Brilliance Solar Inverter has a standard voltage output of 480 Vac and is optimized for direct grid connection via a mediumvoltage transformer. The enclosure is outdoor rated.
GE Energy /

Ingeteam Headquartered in Zamudio, Spain, Ingeteam specializes in electrical engineering and equipment manufacturing. The company’s US operations are located in Milwaukee. Inverters in the Ingecon Sun PowerMaxter U family are rated for outdoor installation and ETL certified to UL 1741 at 1,000 V. Inverters in this product line range in capacity from 375 kW to 880 kW. The Ingecon Sun PowerMaxter TL U inverter modules are transformerless for direct connection to a medium-voltage transformer. The Ingecon Sun PowerMaxter T U models (375 kW or 500 kW) are sold with a transformer for connection at 480 Vac. Integrated turnkey power stations rated from 750 kW to 1,760 kW are also available.
Ingeteam / 408.524.2929 /

Nextronex Headquartered in Toledo, Ohio, Nextronex develops and manufactures utility-scale inverter systems. In July 2010, the company announced that its Ray-Max 150 Solar Inverter had been certified to UL 1741 at 1,000 V, making it the first listed 1,000 V inverter available in North America. The Nextronex Ray-Max system is a modular power conversion system in which multiple 150 kW transformerless inverters are distributed alongside a high-current dc bus assembly. Since its inception in 2009, Nextronex has sold more than 20 MW of its Ray-Max solution, 98% of which is wired for 1,000 V operation.
Nextronex Energy Systems / 419.838.7889 /

Power-One Headquartered in Camarillo, California, Power- One is a global power conversion company with a focus on renewable energy applications. The company offers both string and central inverter products that are certified to UL 1741 at 1,000 V. The Aurora Trio is an outdoor-rated transformerless 3-phase string inverter with dual MPPT inputs that is available in two capacity levels, 20 kW and 27.6 kW. The Aurora Trio product line is currently the only 1,000 V–rated string inverter available in North America. The liquid-cooled outdoor-rated Aurora Ultra central inverter line is designed using multiple 390 kW power stages and is available in three different capacity levels: 780 kW, 1,170 kW and 1,560 kW.
Power-One / 805.987.8741 /

REFUsol Headquartered in Metzingen, Germany, REFUsol specializes in designing and manufacturing PV inverters. It has North American operations in Fremont, California. The company plans to release a line of 1,000 V 3-phase string inverters certified to UL 1741 in late Q2 2013. Like REFUsol’s current K-UL product line, the 1,000 V models will be available with output power ratings of 12 kW, 16 kW, 20 kW and 23 kW and are designed for a 3-phase 480 Vac interconnection. A 1,000 V–rated 10 kW inverter is also in the works that will interconnect at 208 Vac. The company also plans to release a line of higher-capacity central inverters certified at 1,000 V later this year.
REFUsol / 480.775.7744 /

Solectria Renewables Headquartered in Lawrence, Massachusetts, Solectria specializes in manufacturing utility-interactive inverters. The company plans to release a new 1,000 V product line, the SGI XT-1000V Series, with power ratings of 500 kW, 630 kW and 750 kW. Based on Solectria’s existing SMARTGRID inverter series, the new models will be manufactured in the US, certified to UL 1741 and designed for direct coupling with external transformers for commercial or utility-scale applications. The company will also offer turnkey Solar Stations rated for 1 MW, 1.25 MW or 1.5 MW, which will integrate a pair of 1,000 V inverters with a medium-voltage transformer and switchgear on a skid, with or without an additional enclosure.
Solectria Renewables / 978.683.9700 /

SMA America Headquartered in Niestetal, Germany, SMA is the leading manufacturer of solar inverters worldwide. The company has North American headquarters in Rocklin, California, and in Toronto. In August 2012, SMA announced that the newest inverters in its Sunny Central product line were certified to UL 1741 at 1,000 V. The five models in the UL-listed Sunny Central CP-US product line are nominally rated at 500 kW, 630 kW, 720 kW, 750 kW and 800 kW. If the ambient temperature is under 25°C, these inverters can continuously operate 10% above their nameplate power rating. Sunny Central CP-US inverters can be coupled to any utility grid or 3-phase commercial service via an appropriate external transformer.
SMA America / 916.625.0870 /

Woodward Headquartered in Fort Collins, Colorado, Woodward is a technology provider to the aerospace and energy industries. In 2011, Woodward acquired IDS of Switzerland, a manufacturer of utility-scale inverters for PV and wind power plants. The company currently offers two UL-certified 1,000 V inverters rated at 250 kW and 500 kW, the SOLO 250 and SOLO 500, and expects to release additional models in 2013. Woodward’s central inverters are liquid cooled and utilize a modular powertrain that provides for multiple-MPPT inputs. Outdoorrated inverters are available as an option. The company also offers listed 1,000 V source-circuit combiners.
Woodward / 970.498.3455 /

Combiner Boxes

Combiner boxes were some of the first PV products to be certified at 1,000 Vdc to UL standards. In addition to the combiner box manufacturers profiled here, several of the inverter companies mentioned earlier—such as Eaton, Solectria and Woodward—offer listed 1,000 V combiners.

AMtec Solar Recently relocated from Hayward, California, to Pleasanton, California, AMtec Solar is a division of AMtec Industries, which engineers and manufactures custom control panels for a variety of industries. ETL is the Nationally Recognized Testing Laboratory used to certify the company’s 1,000 V–rated solar solutions to UL 1741. They include sourcecircuit combiners and subarray combiners with or without current monitoring and disconnecting features. Listed 1,000 V–rated circuit-breaker recombiners and load-break–rated safety switch cabinets are also available. AMtec Solar’s latest 1,000 V product offering is a bipolar recombiner with optional subarray monitoring.
AMtec Solar / 510.887.2289 /

Bentek Solar Based in San Jose, California, Bentek Solar is a designer, integrator and manufacturer of power distribution solutions for the PV industry. The company offers a wide variety of 1,000 V–rated source-circuit and subarray combiner box solutions for commercial and utility-scale projects. In addition to basic combiners, Bentek offers prewired combiners, disconnecting combiners, smart combiners, bipolar combiners, ungrounded combiners, circuit-breaker combiners and even theft-detection combiners. Bentek combiners are available in NEMA 4 steel or NEMA 4X fiberglass enclosures with lockable exterior doors and terminals rated for both aluminum and copper conductors.
Bentek Solar / 866.505.0303 /

Shoals Technologies Group Headquartered in Portland, Tennessee, Shoals is a provider of BOS solutions for the PV industry. The company offers a variety of predesigned 1,000 V–rated UL 1741 certified source-circuit combiner boxes for commercial and utility applications. Standard features include lockable, nonconductive NEMA 4X enclosures (fiberglass or metal) with finger-safe fuseholders. Optional features include dc disconnects, surge suppressors and wireless monitoring. The company’s SNAPShot Wireless Monitoring system is powered from the dc busbar and operates using a secure self-detecting and self-healing mesh network with a range in excess of 3 miles.
Shoals Technologies Group / 615.451.1400 /

SolarBOS Located in Livermore, California, SolarBOS specializes in providing configurable combiner boxes for the PV industry. SolarBOS uses ETL to certify its combiners to UL 1741. In addition to basic 1,000 V–rated source-circuit combiners, the company offers smart-string combiners, disconnect combiners, smart-disconnect combiners and multicombiners (two electrically isolated combiners within a single enclosure). SolarBOS also offers 1,000 V–rated subarray combiners with fuses only or with fuses and a non–load-break–rated disconnect, as well as a line of fuse boxes (with or without disconnecting means) that provide overcurrent protection without combining circuits.
SolarBOS / 925.456.7744 /

SunLink Headquartered in San Rafael, California, SunLink manufactures roof- and ground-mount racking systems, PV combiner boxes and wire management solutions. The company offers two product lines within its HomeRun combiner box family, both of which support 1,000 Vdc designs. The original Home- Run solar combiner box is available in 2,500 standard product configurations. Options include 4–48 poles, integrated disconnect switch, NEMA 3R, 4 or 4X metal or fiberglass enclosures, and string-level monitoring. SunLink’s most recent combiner box offering is the HomeRun LTE, which adds a lower price point, more compact enclosures and a streamlined set of features to the HomeRun line. SunLink works with ETL to certify its combiner boxes to UL 1741.
SunLink / 415.925.9650 / 

BOS Components

There is, of course, more to a dc collection system than PV modules, inverters and combiners. If you need 2,000 V– rated conductors for conduit or trench runs between source-circuit and subarray combiners, then traditional electrical suppliers can likely source what you need. If your needs are more esoteric or custom, then your purchasing agent is likely better off contacting companies that specialize in providing BOS components for PV power applications. For example, Bentek Solar, Eaton and Shoals can provide many of the unique 1,000 V–rated components used in high-capacity PV applications between the PV modules and inverters, including PV Wire jumpers and whips, interconnect systems, custom wire harnesses with or without in-line fuseholders, dc disconnects and so forth.


David Brearley / SolarPro magazine / Ashland, OR /

Joe Schwartz / SolarPro magazine / Ashland, OR /

Primary Category: 

The DC combiner product class is expanding rapidly as manufacturers new to the space and the OEMs of well-known brands release innovative new products. These SolarPro tables provide product specifications for combiners and recombiners available in the North American marketplace. Data for 148 products from 11 manufacturers are included.

CLICK on the images below for larger versions of the tables.
(The first table has PV Source-Circuit Combiner Specifications, the second has PV Recombiner Specifications)

CLICK HERE for the excel version (.xls) of the specifications

CLICK HERE for the article "DC Combiner Revisited" By Marvin Hamon, PE



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