Electrical Test Equipment
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Of the many tools you use to install and maintain a PV system, electrical test equipment may not be your first priority. But a PV system is only as good as the electrical energy it produces.
How do you know all circuits are working? How do you know the system is safe against shock hazards and fire? How can you be confident the system will continue working until the next scheduled maintenance? How can you find the problem when some part of the system stops working or when you are not sure whether it is working as well as it could be?
The answers to these questions can be found with electrical test equipment, which is essentially a set of measuring tools. The quantities that can be measured include voltage, current, resistance, capacitance, power, energy, frequency, power factor, phase angle and temperature. Many of these quantities can be measured in both ac and dc, and most can be logged over time. They can be measured with highly accurate equipment or with a simple tool that reports only presence or absence.
Perhaps your old analog voltmeter will do just fine. But here is a look at what this category of equipment could and should be doing for you, including examples of specific tools, what to look for, how and when to use them on PV systems and some idea of cost.
SAFETY IN TESTING
The first consideration when choosing and using electrical test equipment is technician safety. All those burdensome working clearance requirements in NEC 110.26 were designed to help make testing and maintaining energized equipment a relatively safe endeavor. Proper tools, procedures—such as lockouttagout— and personal protective equipment are necessary as well. Read and follow NFPA-70E, Electrical Safety in the Workplace, for more safety details (see Resources).
Be sure to read the test equipment manual thoroughly, both for safety and proper use guidelines, and for ideas for new and better ways to use the equipment. Also make sure your test equipment is appropriate for the application. ANSI/ ISA-S82 defines four categories of electrical test equipment user risk. The higher the available voltage and fault current in a given test location, the higher the category. In general, Category I is low-power electronics; Category II is branch circuits; Category III includes feeders and panelboards; and Category IV covers service entrances. All professional-grade, power electrical test equipment should be certified and marked on the device for 1000 V Cat III or 600 V Cat IV.
As with most tools, you tend to get what you pay for with electrical test equipment. Most high quality electrical test equipment is available through your usual electrical supply wholesaler. Almost everything is available for purchase online. Just beware of too-good-to-be-true prices. About five years ago, I monitored eBay for two months before finally snapping up a “new, in the box” Fluke 337 clamp meter for half of its retail price. It has worked at least as well as my other test equipment since then, but it felt like a gamble at the time. I could have wound up with a low quality knockoff or a genuine but refurbished brand-name product, out of warranty or out of calibration.
If you decide that your needs will be met by lower cost, consumer grade equipment, you can find these at the local hardware store or Radio Shack. Just do not expect consumer grade equipment to perform like a professional tool, out of the box or over time. Even if both tools have the same feature list, the professional tool offers extra value.
Durability. Test equipment almost always includes complicated, sensitive electronics, and it will not serve any purpose if those are damaged. A professional tool is designed to survive years of daily use and abuse, including being dropped, shoved into your tool belt, left in the rain and bounced endlessly in the truck. It will have to work reliably over a wide range of job site temperatures. So avoid equipment designed for laboratory use where possible. A professional tool will have proper fusing and input protection to protect you and itself from the occasional incorrect use and surprising surges you subject it to.
Accuracy. Professional equipment should have very high accuracy, repeatability and resolution (see sidebar). Even though a low quality meter might show three digits to the right of the decimal place for a voltage measurement, likely it is not very accurate in the millivolt range. High quality equipment will be backed by specifications, certifications and warranties that give you confidence in your measurements and the decisions you make based on those measurements.