Live to Test Another Day, Part 3

April 7, 2015
You’ve got the right equipment, but do you dress the part?

In Part 2, we discussed the CAT rating for DMMs. It's important to understand that a meter rated for 600V may not be suitable for testing at a 480V service. Why? Because it must also have a CAT IV rating to be safely used there.

You can use a CAT III meter on internal distribution, such as feeders, but not at the service. And it's not the case that you can safely use a CAT I meter anywhere in an industrial plant during a shutdown. Incidental energy may still be available, so always use a DMM of the appropriate CAT rating for the location relative to the service; whether the equipment is energized or not.

Generally, there's no reason for industrial or commercial electricians to own or use anything other than a CAT IV DMM. If you have only CAT IV DMMs you will never be tempted to use the CAT III you have with you ("just this one time") rather than hike all the way back to the shop to get the CAT IV that you had meant to bring instead.

You’ve got the right equipment, but do you dress the part? Wear only PPE that’s rated for the incident energy you may encounter (e.g., the heat in cal/cm2).  Don’t use unrated or unmarked PPE. If its arc thermal performance value (ATPV) is unknown or insufficient, find other PPE.

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