Commissioning and O&M Tools

Do you ever wonder what tools solar professionals carry when they are performing quality control, commissioning, or operations and maintenance activities on commercial and utility-scale PV systems? We did—so we found out.

We contacted PV project managers, commissioning agents, operations and maintenance (O&M) managers, service technicians and so forth—more than two dozen pros in total, representing every region of the country—and asked them questions like these: “What are your favorite meters, power tools and hand tools? What torque wrenches or drivers do you use? What is your most valuable tool?” In other words: “What’s in your tool bag?”

In this article, we summarize some of the survey results, emphasizing test and measurement tools used to verify that systems are installed and operating correctly. We provide typical retail price ranges for test and measurement device models in brackets, when available online. We also provide some helpful application notes along the way.

Electrical Power Testers

Surely we are not the only pros who occasionally suffer from a serious case of meter envy. Besides being the eyes and ears of the field technician, meters are fun and flashy. They can also be a significant investment. So before talking about some sexy meters, let us first cover some important business.

Electrical test meters must be able to withstand both the expected steady-state voltage of the system you are measuring and any transient overvoltages (short-duration surges or spikes: for instance, those caused by a lightning strike or electrical motor starts and stops). All meters produced since 1997 are identified with an overvoltage installation category (CAT) rating in accordance with the International Electrotechnical Commission (IEC) standard 61010-1, which details requirements related to the construction of low-voltage (<1,000 V) test and measurement equipment, as well as allowances related to their conditions of use.

As shown in Table 1, IEC 61010-1 defines four basic overvoltage installation categories for meters: CAT I–CAT IV. The technical basis for overvoltage installation categories is the relative threat presented by high-energy, lightning-induced voltage transients. Within each category, there are five possible working voltage designations: 50 V, 150 V, 300 V, 600 V or 1,000 V. All listed electrical meters are marked accordingly and should be used in accordance with their overvoltage installation category and working voltage designation.

Clamp meters. Not surprisingly, clamp meters received the highest number of “most valuable tool” votes in our survey. While some clamp meters measure current only, most models also perform many of the basic functions offered by a digital multimeter. Using a clamp meter is the best way to quickly compare source- or output-circuit currents. You can also use clamp meters to verify that no electrical current is flowing in a dc circuit before opening a non-load-break–rated disconnect—such as a module quick connect or a touch-safe fuseholder—to avoid pulling a potentially dangerous and destructive arc across the contacts.

The clamp meter of choice is the CAT IV Fluke 376 AC/DC True RMS Clamp Meter [$360–$450]. This meter is capable of measuring ac and dc voltages up to 1,000 V, which is an increasingly important feature given the trend toward higher PV utilization voltages. The fixed jaw is big enough to fit around a single 750 MCM conductor or two 500 MCM conductors, and can measure up to 1,000 A ac or dc. This meter is sold with a flexible meter attachment, the iFlex, which improves wire access and extends the ac current measurement range to 2,500 A. The Fluke 376 is a workhorse meter, a direct replacement for the now-discontinued 600 V–rated Fluke 337 clamp meter, which several survey respondents still carry. If you are in the market for a new clamp meter or need a multimeter that can measure up to 1,000 V, the Fluke 376 is an excellent choice.

Some survey respondents also carry CAT III-600 V–rated clamp meters, such as Extech Instruments’ MA220 and EX730 models and Klein Tools’ CL2000. While the Extech MA220 [$90–$110] lacks some of the Fluke 376’s bells and whistles—like the ability to record maximum, minimum and average inrush currents—and has lower voltage and current ratings, it is also more compact and affordable. The Extech MA220 can measure up to 400 A ac or dc and retails for roughly one-quarter the price of a Fluke 376. The Extech EX730 [$120–$190] can measure up to 800 A ac or dc and can capture peak inrush currents and voltage transients. The Klein Tools CL2000 [$130–$150] is a 400 A clamp meter with an integrated noncontact ac voltage tester; this meter is 1,000 Vdc rated for CAT II applications.

Several survey respondents also use clamp meters with a smaller current measurement range and a correspondingly higher degree of accuracy and resolution, which is useful for verifying signals in data acquisition systems or measuring leakage current on equipment-grounding conductors. The Fluke i30 AC/DC Current Clamp [$400–$450] is a CAT III-300 V clamp that plugs into any Fluke multimeter and can measure current from 5 mA to 30 A dc, or 30 mA to 20 A ac, with a resolution of 1 mA. The Fluke 80i-110s AC/DC Current Probe (100 A) [$630–$700] is a CAT II-600 V/CAT III-300 V current clamp that plugs into a Fluke multimeter or scope and can measure current from 1 mA to 100 A dc, or 1 mA to 70 A ac. Fluke’s 771 Milliamp Process Clamp [$520–$550] is designed to measure current on 4–20 mA signal loops with a resolution of 0.01 mA.

Insulation resistance testers. The single most popular meter is the Fluke 1587 Insulation Multimeter [$590–$700]. Its popularity attests to the fact that insulation resistance testing is not only a critical system commissioning activity, but also useful for tracking down faults. The Fluke 1587 combines the ability to measure insulation resistance up to 50 GΩ, using 50 V, 100 V, 250 V, 500 V or 1,000 V test voltages, along with typical multimeter functionalities, including the ability to measure voltage up to 1,000 V ac or dc. Note that the Fluke 1507 Insulation Resistance Tester [$475–$525] is similar to the Fluke 1587, minus the multimeter capabilities.

Survey respondents also mentioned insulation resistance meters from Megger and Ideal Industries. For example, the Megger MIT420 [$620–$760] is a CAT IV insulation resistance and continuity tester with internal data storage for test results; it has a test voltage range of 50 V to 1,000 V and a maximum insulation resistance measurement range of 200 GΩ. At a more modest price point, Ideal’s 61-795 Hand Held Insulation Tester [$300–$345] offers three test voltages (250 V, 500 V or 1,000 V) and a maximum insulation resistance measurement range of 4 GΩ.

IEC 62446, “Grid-Connected Photovoltaic Systems—Minimum Requirements for System Documentation, Commissioning Tests and Inspection,” requires insulation resistance testing to be performed on PV array conductors during system commissioning. According to IEC 62446, you should determine the test voltage using the guidelines in Table 2, based on the dc system voltage (Voc x 1.25). Before performing insulation resistance testing at these test voltages, isolate any surge-protection devices from the circuit you are testing and remove all other electronic equipment from the circuit. While you can use disconnects to open ungrounded conductors to inverters, you need to physically lift grounded conductors. As a result, you typically perform insulation resistance tests before landing and torquing grounded conductors.

Always check with the module manufacturer before performing insulation resistance tests on PV source circuits. While many manufacturers are amenable to these tests, some do not approve of them. The best practice is to get the manufacturer’s approval in writing. Ideally, the manufacturer can provide you with a white paper detailing its approved testing procedures.

Many EPCs perform insulation resistance tests on all the strings in a combiner box at the same time, rather than on individual strings. As a result, it can be difficult to know an exact target value for the resistance, which varies based on temperature, humidity and the number of modules you are testing. For example, as the surface area of glass increases, the expected resistance value decreases because more module-level leakage current paths are placed in parallel.

Experience is often the best guide when determining an acceptable resistance-test value range and identifying outliers. With that in mind, it is a good idea to document baseline values, which you can then use as a basis of comparison in the future. When you perform insulation resistance tests, document the test voltage, humidity, temperature and test duration so that you can perform future tests in the same manner or normalize them against these baseline test conditions. If your baseline conductor temperature is 20°C and you are subsequently testing the same circuit when the conductor temperature is 30°C, you would expect the new insulation resistance measurement to be lower.

If you take insulation resistance test measurements on insulated conductors, you will find they are much higher than measurements on PV source circuits. In many cases, new conductors with good insulation peg the meter at its maximum resistance value; a minimum acceptable value is likely around 2 GΩ. Unfortunately, an acceptable test result is not a 100% guarantee against callbacks. For example, a skinned conductor in a conduit may initially test out as good; however, once moisture infiltrates the conduit, a conductive path may form between the damaged conductor and a grounding conductor, resulting in a ground fault.

Digital multimeters. While current clamps and insulation resistance testers can incorporate some of a multimeter’s functions, most survey respondents also carry a general-purpose multimeter. Compared to an all-in-one meter, a dedicated multi-meter often offers additional measurement functions or improved resolution and accuracy. The most popular multimeters are the Fluke 179 [$300–$320] and the Fluke 87V [about $400]. While these models have similar features, the Fluke 87V offers improved accuracy and resolution. The basic dc accuracy of the Fluke 87V is 0.05%, versus 0.09% for the Fluke 179.

PV Characterization Testers

While you will find the meters we have discussed so far in most electrical supply houses, PV system commissioning and O&M also require some specialty electrical test equipment to characterize PV modules or source circuits. The most popular products in this equipment class are commissioning and safety testers, and portable I-V curve tracers.

Commissioning and safety testers. Seaward Group USA offers a suite of testing tools specifically for PV applications. For example, the PV150 Solarlink Test Kit [about $2,000] is designed to meet the IEC 62446 commissioning test requirements. The PV150 installation tester is an all-in-one tester that verifies or measures ground continuity, insulation resistance (at 250 V, 500 V or 1,000 V), Voc, Isc, Imp and Pmp. The test kit includes the Solar Survey 200R, which is basically a souped-up irradiance meter (more on irradiance meters later). The Solar Survey 200R measures real-time irradiance and temperature, and then wirelessly transmits these data back to the PV150, which can store up to 200 complete test records internally. Seaward provides USB connectivity for the data dump to PC and also offers proprietary software [about $250] for generating professional reports.

I-V curve tracers. Paul Hernday’s article “Field Applications for I-V Curve Tracers” (SolarPro magazine, August/September 2011) provides a detailed explanation of how I-V curve tracers work and how you can use them to commission and troubleshoot PV arrays. These tools are essential for gathering data for module power warranty claims. They are also commonly used to benchmark large-scale PV system performance, to quantify the impacts of soiling and to refine plant production models over time—often at the request of project financers.

The most popular I-V curve tracers for field applications are the HT I-V 400, the Solmetric PVA-1000S and the TRITEC TRI-KA. The professionals we interviewed did not have a clear favorite, perhaps in part because each tool addresses a slightly different need based on criteria like portability, internal memory storage or battery run time. Cari Williamette, a master electrician at Ecovision Electric, notes: “If I need to power through a bunch of I-V curves to gather the data, I grab the TRI-KA; if I need to analyze curves in the field, I go with the PVA or I-V 400.”

HuksefluxUSA distributes the HT I-V 400 in the US. This CAT II-1,000 Vdc meter has a maximum current measurement range of 10 A. It has a 128-by-128-pixel LCD and is sold with an external reference cell and temperature probe, which you must physically connect to the meter to capture irradiance and module temperature. The meter’s internal memory capacity is 256 kilobytes, equivalent to roughly 200 I-V curves. The HT I-V 400 measures about 9.25 by 6.5 by 3 inches and weighs less than 3 pounds.

Solmetric’s PVA-1000S [about $5,500] is a portable I-V curve tracer with a maximum current measurement range of 20 A. This CAT III-1,000 V meter is sold with a wireless reference sensor that measures irradiance and module temperature at a range of up to 300 feet. The primary user interface is via a laptop or tablet (not included in the kit) that communicates with the PVA-1000S using a wireless USB adapter. The largest of the three I-V curve tracers mentioned here, this unit comes with a shoulder strap for transportation. In addition to offering a higher measurement voltage range, the PVA-1000S also offers improved accuracy over the PVA-600 [about $4,700], Solmetric’s 600 Vdc–rated I-V curve tracer.

The TRITEC TRI-KA [about $6,000] is available in the US via SkyBlu Energy as part of a complete kit that includes cables, sensors, sensor-mounting hardware, software and padded case. This CAT II-1,000 V/CAT III-600 V meter has a maximum current measurement range of 15 A. It has a 3.2-inch color LCD and is sold with a wireless irradiance and temperature sensor. The Secure Digital (SD) card memory storage capacity can hold more than 4,000 measurements. With physical dimensions of 8.2 by 4 by 1.6 inches and weighing in at just over 1 pound, this is truly a handheld I-V curve tracer.

Solar Power and Thermal Testers

In addition to having electrical and PV characterization testers in their tool bags, most of our survey respondents also carry an irradiance meter and an infrared (IR) camera or thermometer.

Irradiance meters. If you want to estimate real-time system performance with confidence or field-check a pyranometer in a data acquisition system, you need a handheld solar irradiance meter or pyranometer. In field applications, having laboratory-quality equipment is less crucial than having reasonably accurate, durable equipment that can stand up to local conditions.

The most popular devices are Daystar’s DS-05 Solar Meter, Apogee Instruments’ MP-200 and Seaward’s Solar Survey 100. The Daystar DS-05 [about $160] is a compact and lightweight meter that can measure between 0 and 1,200 W/m2 with an accuracy of ±3%. The Apogee MP-200 [about $410] is a pyranometer sensor with a handheld meter that displays and stores measurements; it has a measurement repeatability of less than 1% and can be used as a calibrated standard to check monitoring system sensors against. The Solar Survey 100 from Seaward is an all-in-one device that includes an irradiance meter, an inclinometer, a compass and two channels for measuring temperature.

IR cameras. Thanks to dramatic price declines, IR cameras are more available than ever and are increasingly incorporated into standard O&M procedures for PV systems. They can identify high-resistance electrical connections and thermally stressed over-current protection devices. They are invaluable for locating module issues such as cracked cells, faulty internal connections and defective bypass diodes.

While there are many IR cameras to choose from, the two most popular brands are FLIR Systems and Fluke, in that order. By far the most popular model is the FLIR i7—which Bill Brooks describes as “providing the best value for your money.” The other IR camera models represented are the FLIR E60, FLIR E8 and Fluke Ti200.

The FLIR i7 [$1,600–$2,000] is a lightweight and compact 19,600-pixel IR camera with a 2.8-inch color LCD and microSD card storage capacity for 5,000 images. The FLIR E60 [$6,000–$8,000] is a 76,800-pixel thermal camera as well as a 3.1-megapixel color camera that can capture picture-in-picture composite images. It has a 3.5-inch color LCD and can output enhanced (blended) thermal images that include visual details. It also accepts telephoto and wide-angle lenses, and it stores up to 500 sets of images. The FLIR E8 [about $6,000] is a 76,800-pixel IR camera as well as a 640-by-480-pixel color camera that can capture picture-in-picture composite images. It has a 3-inch color LCD and can output enhanced thermal images with visual details. It stores up to 500 sets of images. The Fluke Ti200 [about $6,000] is a 30,000-pixel IR camera as well as a 5-megapixel visible light camera with picture-in-picture or enhanced image capabilities. It accepts different lenses, and it has video and voice recording capabilities that are useful for making notes in the field. The top-of-the-line IR cameras that utilities use run upwards of $20,000.

IR cameras are not just a significant investment in hardware. Users also require specialized technical training to accurately capture, tune and interpret thermal images. For example, FLIR recommends the thermography training services that the Infrared Training Center (ITC) offers. ITC provides three levels of thermography training and certification. Each level is a 4-day course that costs about $1,900. A 2-day day training on thermography fundamentals costs about $1,000.

While Level I IR Thermography Certification is a reasonable goal for most PV technicians, a basic knowledge of settings and procedures can be sufficient for using IR cameras effectively in the field. Generally speaking, you are on the lookout for outliers in the results. For example, imagine taking an IR photo of two identical conductors in the same enclosure, carrying the same current and landed identically. If one terminal measures significantly hotter than the other, a loose connection is likely the cause of the difference.

The most difficult environment for taking an accurate IR image is outside. The surface of PV module glass can reflect both the extreme heat of the sun and the extreme cold of deep space (the sky). As a result, it is a common mistake to interpret the reflection of the sun on module glass as a hot spot. Another common error is failing to compensate for the emissivity of the object you are photographing. Emissivity is the relative ability of a surface to radiate energy as compared to a black body, an idealized construct with an emissivity of 1. The emissivity of metal surfaces varies considerably, based on whether the metal is polished or coated and so forth.

Interestingly enough, black electrical tape has a known emissivity of around 0.95, so it can be valuable for making accurate temperature readings once it has reached the temperature of a surface. You can put black electrical tape on a piece of aluminum as a way of accurately setting emissivity; you can also use this technique for measuring temperature on the backsheet of a PV module. Another way to calibrate emissivity is to compare a temperature taken via a thermocouple to the IR camera temperature, and then adjust the emissivity value on the camera until the two values match. Of course, neither of these methods is suitable for use with live electrical circuits.

IR thermometers. If you do not want to carry your $6,000 IR camera around a dusty jobsite all day but you still want to take basic IR temperature measurements, a humble infrared thermometer is just the ticket. Most of our survey respondents keep one in their tool bags or buckets at all times.

A basic IR thermometer is often nothing more than a 1- or 2-pixel, trigger-actuated thermal imaging device. These rugged and inexpensive devices are available from many manufacturers, in some cases for under $100. If you want one that runs on rechargeable lithium ion batteries, check out Milwaukee Electric Tools’ Laser TEMP-GUN M12 thermometer kit [$200–$230], which has a measurement range of –30°C to 800°C. If you prefer one that matches your Fluke gear, consider the Fluke 62 MAX+ [$90–$130], with a measurement range of –30°C to 650°C.

Power Tools

You should already have the heavy-duty work done come commissioning time, but you do have a lot of ground to cover in a short time. Therefore, most of our survey respondents leave their beefy power tools at home in favor of lighter and more portable products. J.R. Whitley, the owner of 690 Electric, notes: “I do miss my yellow DeWalt tools sometimes, but you can’t beat Makita tools for weight. My cordless Makita kit includes an impact driver, drill, reciprocating saw, band saw and flashlight.”

Haney at Next Phase Solar echoes this sentiment: “For maintenance and troubleshooting, I prefer smaller, more lightweight tools like my Hilti impact driver, which is still plenty powerful. Milwaukee makes a reasonably priced impact driver, but it is bulkier and heavier. I also carry a vacuum—for things like vacuuming metal bits out of enclosures—and leave every jobsite cleaner and safer than I found it.”

Digital Cameras

You need to carry a digital camera, but it does not need to be fancy. Nick Mshar, Strata Solar design and installation manager, notes: “The most valuable tool in my tool bag is a Canon PowerShot digital camera.” There is no need to spend much more than $100 for a camera that will spend the bulk of its days on hot, dusty, damp or muddy jobsites. Just make sure to get a decent-size memory card, one that allows you to capture and store hundreds of high-resolution images between downloads. If you want to read the fine print on a fuse back at the office—or get your picture on the cover of SolarPro—you need to take images at a reasonably high resolution. If you have enough memory capacity, you can just set your camera for the highest image quality and Bob’s your uncle.

Speaking of cover models, Whitley carries a Milwaukee M-SPECTOR M12 inspection camera [about $130; also offered as a complete kit with batteries for approximately $200]. He notes, “It’s a plumbing tool, really, but it has come in handy for seeing in some difficult locations.” The M-SPECTOR inspection camera has a 2.4-inch color LCD and a 3-foot flexible cable with a small camera head that fits inside ¾-inch openings. You can use the M-SPECTOR inspection camera to look under, over or around obstructions in tight places.

Portable Computing Devices

Most of our survey respondents consider computers indispensable for PV system commissioning and O&M. The most common field applications for computers include logging data, interfacing with data acquisition systems, troubleshooting inverters, running test and measurement device software, generating customer reports, and downloading equipment manuals or plan set details. Not everyone we surveyed relies on a computer in the field, however. For example, Strata Solar’s Mshar reports, “I keep my computer out of the field; it is most valuable to me in the office.”

Haney at Next Phase Solar uses a computer on every job. He explains: “At a minimum, we are logging what we did to generate a report for the customer. I also make it a habit to take screenshots so that I can reference them later, especially if I am doing something for the first time or making changes to a program. The application-specific programs that I regularly use in the field include proprietary inverter and tracker software, Campbell Scientific’s LOGGERNET datalogger support software, Modbus Poll, Fluke thermal imaging software and Solmetric PVA software. I also use general-purpose programs like Microsoft Office, Adobe Acrobat and Image Resizer for Windows.”

While most survey respondents carry Windows-based laptops, several use tablets from Samsung or Apple. The obvious benefit of carrying a native Windows device is that most specialty software programs are designed to run on that platform. If you want to take your expensive MacBook into the field, you need software like Parallels Desktop for Mac, which allows you to run both Windows and OS X applications simultaneously on your Mac.

If you are taking your computer into the field, you likely also need some means of Internet connectivity, such as a Wi-Fi hotspot on your phone. To get more than a few hours’ work out of your wirelessly connected cell phone and computer, be sure to pick up a 12 Vdc to 120 Vac inverter for your car or truck. While you are at it, pick up spare batteries for all of your new meters.


Brian Mehalic / Solar Energy International / Winston-Salem, NC /

David Brearley / SolarPro magazine / Ashland, OR /


“ABCs of Multimeter Safety,” Fluke Application Note,

“Testing Your Test Leads,” Fluke News Plus,

“Don’t Risk CAT IV Areas Without the Right Leads,” Fluke Application Note,


Apogee Instruments / 877.727.6433 /

Daystar / 575.522.4943 /

Extech Instruments / 877.439.8324 /

FLIR Systems / 800.464.6372 /

Fluke / 800.443.5853 /

Hilti USA / 800.879.8000 /

HuksefluxUSA (HT distributor) / 631.251.6963 /

Ideal Industries / 800.435.0705 /

Klein Tools / 847.821.5500 /

Makita / 800.462.5482 /

Megger / 800.723.2861 /

Milwaukee Electric Tool / 800.729.3878 /

Seaward Group USA / 813.886.2775 /

SkyBlu Energy (TRITEC distributor) / 858.255.1105 /

Solmetric / 877.263.5026 /

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