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NFPA 70E 120.5(7) Requires test instruments be verified as working satisfactorily on any know live source prior to and after the verification of an absence of voltage.

Unverified voltmeters can be deadly

Many electrical workers have created dangerous arc flashes, or have been shocked, even electrocuted, because the voltmeter they were using was broken and gave an incorrect reading. In some cases, the electrician turned the meter to the wrong setting or installed the test leads improperly when the meter was applied to the circuit, it indicated an absence of voltage even though the circuit was still energized.

This is why NFPA 70E Article 120.5 requires that the meter be verified as working properly prior to, and after, testing conductors or circuit parts that are thought to be de-energized. This is accomplished by plugging the meter in to a known live source such as a 120-volt outlet.


Live-dead-live (L-D-L) testing

If the meter does not indicate the expected voltage from the known source, we know there is a problem with the meter. This process is commonly referred to as a live-dead-live test.

Often it can be hard to find a 120-volt outlet or other live source to verify that the meter is working properly. Safety can also become an issue if guards are removed or circumvented so a live source can be accessed. Therefore, we suggest equipping yourself with a proving unit. This is a handy little tool fits very nicely into an electrician’s tool bag. It runs on batteries and has an output of A.C. and D.C. voltages (usually between 50 and 240 volts depending on the brand.) The electrician pulls it out of the bag, tests their meter prior to and after the absence of voltage test, he or she is on their way quickly and safely.

Use simple methods to ensure safety from electrical  hazards

Having performed electrical work in industrial facilities for most of my adult life, I understand that rules that make things complicated and/or time consuming tend to be overlooked. Especially if you’re in a production environment where equipment downtime needs to be kept to a minimum. Workers may feel time pressure and simply skip the live-dead-live test. By giving them this simple tool, very little, if any, time is added to the job scope. This makes this rule less objectionable, consequently the de-energization process will get done efficiently and correctly, keeping employees safe every time.