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I'm a beginner at doing electrical work, and I want to make sure I'm not taking unnecessary risks.

Let's say that I'm preparing to work on some wiring. I have a non-contact voltage detector that beeps when held up to live wires. Next, I have turned off what I believe to be the proper circuit-breaker and my detector reads negative on the wires I'm about to work on.

Am I good to go, or are there still other electrocution risks that I need to be aware of?

If the latter, what other safety measures should I take?

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The following should be sufficient to determine that it's safe to work inside a switch box.

  • With the breaker(s) for this box turned on, touch the NCVT to the wallplate or insert it into the "hot" (narrower) blade socket of the electrical outlet you'll be working with. The NCVT should indicate live wiring. This is primarily a test of the tester itself; it should light on a known hot circuit.
  • Turn the breaker(s) that provide power to this box off.
  • Return to the box and repeat the test; the NCVT should not indicate live wires. If it does, you flipped the wrong breaker or didn't flip enough breakers to make the entire box "cold".
  • Open the wallplate, and touch the NCVT to all screw terminals on all devices in the box. The indicator should not light; if it does, you missed breakers (or there's a more serious wiring problem like shared neutrals).

At this point, I'd be confident of not getting hurt working on the box. If you REALLY wanted to be sure, you could take a multimeter and test the AC voltage between all terminals on each individual device; all readings should be zero. This may be necessary if you suspect a voltage leak (faulty breaker, miswiring joining unrelated branch circuits together); an NCVT requires 50VAC to indicate "live", but 45V can still give you a jolt with sweaty/wet hands (remember that a car battery, only 12VDC, is an effective instrument of torture).

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  • Thanks! Is there anything else I should do to be safe, such as wear gloves or rubber-soled shoes or anything? Or is that just silly? – anon May 5 '12 at 3:03
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    That's bordering on silly, IMO. As long as you can verify all wires are "cold", and prevent anyone from mistakenly turning breakers back on while you're working, you're fine to handle the wires with bare hands. Usually all you have to do is tell other members of the household "don't $%^& with the breaker panel", but if people are coming and going or several areas of the house are being worked on at once, you can put a strip of tape across the breaker with "NO" written on it. – KeithS May 7 '12 at 16:25
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It is possible for some electrical boxes to have more than 1 circuit running through them, so make sure you test all of the hot wires (black wires) in the box to ensure there is no electrocution risk.

I also like to put a piece of tape over the switch and/or breaker I am working on so someone doesn't walk by and flip it back on.

If you are replacing something and you aren't so familiar with the wiring, make sure you draw a diagram or a label the wires before removing them. You could create an electrocution risk if you wired it wrong.

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  • Agreed. It'd be nice if multi-circuit boxes were labeled like they're supposed to be...but... – Alex Feinman May 4 '12 at 20:13
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    I like the idea of taping the breaker and jotting down the wiring. Thank you! – anon May 5 '12 at 3:04

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