1

If you need to test a circuit breaker with a multimeter and you're working in a live breaker box with 240v, what is the best safety equipment to use (eg: gloves, shoes, shield, etc)? It doesn't seem right working with those small multimeter lead handles with bare hands, but most contractors seem to have no trouble doing this. I am being overly paranoid, or is there a better way?

6
  • Isolate the supply, remove breaker, test then refit or replace.
    – Solar Mike
    Aug 15 '20 at 5:47
  • Hello, and welcome to Home Improvement. If an answer is helpful, please click the large check mark next to it to accept. And, please take our tour so you'll know the details of contributing here. Aug 15 '20 at 12:11
  • 1
    You are being overly paranoid. 240V is no more dangerous to work with than 120V (in the North-American split-phase system) since it's still only 120V to ground. As Jasen writes in his answer, a CAT-III rated multimeter and a sensible amount of common-sense and caution is all that's required.
    – brhans
    Aug 15 '20 at 14:18
  • One of my personal rules when working on a live panel is whenever possible use only one hand at a time. Not always possible, and when not, I'm extra careful. You can probably position the multimeter probes between your fingers of one hand to test the breaker. Aug 15 '20 at 14:29
  • 1
    A fully engaged brain is the big one.
    – Ecnerwal
    Aug 17 '20 at 23:13
2

Most important equipment is the right multimeter.

If you're working on your panel you want CAT III or higher.

https://en.wikipedia.org/wiki/Measurement_category

These will typically come with anti-slip probes which will help your confidence some.

1
  • And don't forget about the NRTL listing and labeling to go with the claimed CAT III rating Aug 15 '20 at 17:35
2

You'll want the right meter, for sure

The most important thing when probing on mains circuits is to use the correct meter, as Jason alludes to. You will want a CAT III/300V meter if you live in an apartment or flat where you don't have feeders or branch circuits that run out to lampposts, outbuildings, or such; if you do have wiring runs buried in your yard that you need to work with, you'll need to up that to CAT IV/300V. Furthermore, this rating needs to be backed up with independent testing and the provenance provided by listing and labeling; many bottom-of-the-barrel meters claim to have a CAT III rating, but don't come close to meeting the requisite IEC 61010 standards for it.

Beyond that, it's mostly a matter of going slowly and carefully, so you can think ahead of what you're doing, and thus keep your fingers away from energized bits. If you have alligator-clip attachments for your probes, a procedure of "turn power off, set up measurement, turn power back on, take measurement, turn power back off again" can be used, but may be problematic in terms of remembering what you last did with the breaker. Of course, if you're trying to test a circuit for liveness with a multimeter, you'll want to check it on a known-working circuit first to make sure it isn't going to lie and tell you the power's off when its not.

1

In addition to the CAT3/4 answers, I would like to add that in many cases you might not need a multi-meter.

If all you want to do is determine/test whether a circuit is live you can use a contactless voltage meter:

enter image description here

With one hand you hold the tester and press the tip lightly against a line wire or a screw/terminal and it will beep when live/hot. The tip is isolated, not metallic, and there is no electrical contact.

And if you need to know whether it's 120V vs 240V, and/or you want to make sure the neutral makes a circuit, e.g. at an outlet, you can use a 120/240 tester:

enter image description here

This device has two lights, one to indicate 120V and another to indicate 240V.

A multimeter is great for measuring the voltage and/or current -rather than determining whether the line is hot-, but comes rightfully with some concerns about safety and requires a little more carefulness, as you seem to be aware of.

0

The best safety equipment is your brain. As long as you don't touch anything you shouldn't, it'll be fine. And because you seem so concerned about it, that means you will be extremely careful when doing it. Just do it, and don't touch anything. It's really not that hard to not touch the busses.

1
  • 1
    Sorry, but "el cheapo" meters can blow up in your hands and face even if you are doing all the right things -- they just aren't built to take a knock on the head from an AC line surge. Aug 17 '20 at 23:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.