Is this thing going to kill me?

September 3, 2012 5:03 AM

I want to get a voltmeter. I think that is what it's called. Can you recommend one?

I want one of those thingies that measures electricity being carried to wires after you've cut the breaker, so that you know for certain you're not going to kill yourself swapping out an overhead light. It's like a little probe thing, and it's to measure current.

Some of these look right but there is a price range from about nine dollars to about a hundred. I just want the right thing at the appropriate price, and I actually don't know what that is.

Maybe useful: I would like a good quality, easy to use piece of equipment that isn't overly fiddly. I am pretty much interested mainly in the question of 'will this kill me? Y/N' and have limited plans for it. That said, I want to feel confidant that the thing isn't some cheap piece of crap because the correct answer to that question right is important.

I'm not going to do anything wacky or weird. I understand electricity can kill me, but I want to be able to swap out a ceiling fixture without calling an electrician for it, or swap out the weirdly unseated dimmer switch in the dining room. Also, secondarily, while my knowledge is limited Mr. Llama's is better and I want us to own one, because if it is owned it will be used.

posted by A Terrible Llama to home & garden (12 answers total)

I've had success with AC voltage detectors- you poke it in electrical socket (or near a potentially live wire) that checks that the current isn't flowing. It doesn't need to be wired into the circuit the way a voltmeter does, but it only works for AC (household) current.
posted by jenkinsEar at 5:14 AM on September 3, 2012

You might be able to get by with a simple voltage tester, like this one. I own a very similar model that I got from Lowe's, and I'e found it handier to carry around and use for household repairs than a multimeter. The wire leads snap into the case so you can use it to check voltage at an outlet, or be removed so that you can test wires or non-outlet stuff.
posted by Shohn at 5:20 AM on September 3, 2012 [1 favorite]

A voltmeter is a tool for measuring voltage, which you don' t need to do. You just need a simple voltage tester, which lights up if it detects voltage and does not light up if it doesn't detect voltage. You don't need anything with an LCD display.

Any big-box hardware store will be able to help you out for just a couple of bucks.
posted by jon1270 at 5:23 AM on September 3, 2012 [2 favorites]

If you're looking for a multimeter, ladyada's recommendations are the Mastech MAS830L (< $20) or the Extech EX330 (< $55). The cheaper ones are perfectly fine and safe; they just tend to be less robust.

(I have the stupidly expensive Agilent U1242B, which would be waaayyy overkill for what you need.)
posted by scruss at 5:24 AM on September 3, 2012

I have one of these http://www.specialized.net/Specialized/catalog/searchresults.aspx?keywords=vc200 and it works well. $10.

Around here we can also buy cheap analogue multimeters -- voltage, current, resistance. for around $10. I have one in the car permanently, even though I normally use more expensive digital meters at home or at work.
posted by wrm at 5:43 AM on September 3, 2012

So, here's the thing, in order for any tester like this to be useful, you have to already know which wires should be carrying the current, otherwise you'll get a false negative (shows no current when there is, in fact, current somewhere in the box).

This is especially true of houses where a madman* did the wiring previously and hooked up the negative to the metal housing, so you get a shock if you touch the switchplate and the faucet at the same time (ask me how I know!).

Given that, I know you'll read this next sentence and be all like "Psha, naw, that's too much trouble, I'll have to reset my clocks and shit..." but, seriously, do it: If you're going to messing with wiring don't bother trying to hunt sub-breakers. Grab a flashlight and turn off the main breaker to guarantee you won't die doing simple tasks.

*Not as rare as you would think.
posted by odinsdream at 5:49 AM on September 3, 2012 [2 favorites]

You do not need a voltmeter. You definitely don't need a multimeter. Those are gear you use for working on (mainly) electronics, where you're trying to ensure that the voltage is 2.5V instead of 3.8V. In fact, many many of the multimeters I've worked with were not rated for 120VAC and would have caught spectacular fire the moment you plugged them into a wall socket.

You want something I've heard called a "socket tester". Something like this.

If you're using it for house wiring, a voltage detector might be a better option. You don't even have to make contact to detect the current.
posted by Netzapper at 5:51 AM on September 3, 2012 [1 favorite]

In the old days, they made little gizmos with a neon lamp and two leads, like this
.
which is all you really need, but the more modern variations look intriguing. It is a good idea to familiarize yourself with where you should expect to see voltage, in any case, and be particularly careful to test pairings where you should NOT see voltage. For example, you should see no voltage between neutral (white) and ground (green or unjacketed) - ever. As in, that's sufficiently dangerous that you MUST figure out why you're seeing it, or call an electrician to figure it out. Seeing voltage between hot (black) and neutral or hot and ground means the circuit is live. Red or other colors generally mean switched. If there seems to be more wire in a box than necessary, beware that another circuit may be passing through it, and it is possible for that circuit to still be live.
posted by jgreco at 6:15 AM on September 3, 2012

As stated before, get the magic wand voltage detector. You just stick it into the mess of wires and if any of them are live, it beeps. There's no chance of being electrocuted: the wand is entirely plastic and you never need to make contact with bare wire.
posted by davidpriest.ca at 7:55 AM on September 3, 2012

Given that, I know you'll read this next sentence and be all like "Psha, naw, that's too much trouble, I'll have to reset my clocks and shit..." but, seriously, do it: If you're going to messing with wiring don't bother trying to hunt sub-breakers. Grab a flashlight and turn off the main breaker to guarantee you won't die doing simple tasks.

This. I was working with a fan/light setup that had two switches. The circuit was dead. I started digging around in there and notices a spark when I cut a wire. Wait, what? Digging into an attic crawl space some previous owner had decided properly setting up two switches and one live feed for a light and a lamp was too complicated so they ran a piece of Romex from another circuit with the wire and T-splice just hanging in the air and two separate live circuits in the same box. SURPRISE!
posted by Kid Charlemagne at 8:28 AM on September 3, 2012 [1 favorite]

Far more years ago than I care to remember, I sold all kinds of similar gear at Radio Shack, including inexpensive multimeters that did fine with 120VAC.

Most Radio Shacks are now cell phone stores named Radio Shack, but you might get one where they teach the punks enough electronics to show you what they carry.
posted by Mad_Carew at 10:47 AM on September 3, 2012

Most run-of-the-mill $15 multimeters will have a range that's good for 120VAC, but I agree that what you really want is one of those little neon testers (I assume they're still made; they never wear out and I think one of the ones I have predates WWII) or one of the more modern equivalents.

And yes, never assume that the last person to work on the wiring wasn't trying to kill you: check all the wires, even if they're supposed to be grounds.
posted by hattifattener at 11:27 AM on September 3, 2012 [1 favorite]