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.

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