A proving unit is a battery-powered portable device that serves as an electronic voltage source to safely verify the operation of an electrical test tools such as a digital multimeters (DMM) or clamp meter.
Proving units can be used to satisfy elements of the 2015 edition of NFPA 70E 110.4 (5), which states, “When test instruments are used for testing the absence of voltage on conductors or circuit parts operating at 50 volts or more, the operation of the test instrument shall be verified on a known voltage source before and after an absence of voltage test is performed.”
Typically, a “known voltage source” is a nearby power outlet or junction box or another panel but in situations where no voltage is available, like up-tower in a wind generator or at a remote pumping station, a proving unit can serve as the voltage source. Also, once absence of voltage and lock out, tag out (LOTO) are complete there may be no available power for retesting the test instrument on a known voltage source.
Here is how to verify the operation of an electrical test tool at 240 VAC or 240 VDC with the Fluke PRV240:
If the power indicator led does not illuminate, check the condition of the battery and replace if required.
An in-depth look at an indispensable tool