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I just bought a house and will be doing some electrical work (such as replacing old light switches with smart switches).

But I’m a newbie, and I want to make totally sure that I don’t shock myself.

From videos and articles, it seems like I should shut off either the main breaker to the whole house and/or the breaker to the area of the house that I’m working on, and then I should wave a NCVT near the wires that I’m considering touching (and get alerted about whether they’re live / hot).

Klein Tools ET45VP Voltage and GFCI Receptacle Tester comes with 2 different tools for $14.97

Klein Tools NCVT1P Voltage Tester, Non-Contact Voltage Detector Pen, 50V to 1000V AC costs more ($19.97) but seems to do less.

What is the difference between why someone would use one tool instead of another (Why would someone buy a NCVT if a Voltage Tester with leads is available cheaper?)?

It seems like a voltage tester with red and black leads provides more information.

Is a NCVT just more convenient?

And maybe I'll never need to read precise voltages?

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  • While there's nothing inherently wrong with shutting off the main breaker to the whole house, it's a bit overkill. It's also somewhat counter productive if you happen to be doing work in the winter, because you've shut off your furnace (even if it's gas, it needs electricity to operate). I've been DIYing electrical work in my own house for 30 years and never touched the main breaker.
    – FreeMan
    Aug 23, 2022 at 12:28

3 Answers 3

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An NCVT is the tool of choice for checking every wire before you work. It does not substitute for a multimeter (lots of uses) or for a 3-light tester (specifically for testing 120V receptacles). But it provides an extra, and important, level of safety when you are working on:

  • Light switches
  • Hardwired light fixtures and appliances
  • Receptacles (120V or 240V)
  • Junction boxes

The proper way to use an NCVT is:

  • Check against something "on" - make sure it lights/beeps
  • Check against the wires you think are off - make sure it does not light/beep
  • Check against something "on" - make sure it lights/beeps

In addition, when using on something like a light switch that you have never worked on before, test after removing the cover plate but before turning off the breaker and before removing the switch or working on any wires. It should light/beep. Then turn off the breaker you think is the right one and do a test as described above to make sure it is now off. If you don't test it first when it is "on", you may not be testing in the right place when you think it is "off" and have a false sense of security.

Klein is a good brand. There are others. In general the safest thing is to buy from a regular retailer (Home Depot, Lowes, your local Ace franchise, etc.) Amazon is perfectly fine if you get the right stuff. But Amazon makes no guarantee that everything they sell is UL/ETL/etc. listed, and that is important when you are dealing with tools to be used with potentially live wires.

Definitely do not get a "screwdriver tester". They have an actual metal screwdriver blade which (along with other possible problems) makes them much more dangerous than an all-plastic case NCVT such as the Klein (and similar) models.

Also keep in mind that due to a variety of reasons, the labels on a breaker panel may not match reality. This is especially the case for switches in boxes that contain multiple switches. It is possible to have two switches in one box that are on different circuits and have crossed neutrals that result in live wires on both switches when one breaker is turned off. Best practice is to turn off breakers until your NCVT shows nothing live in the box you're working on.

Klein (and others) now offer NCVTs that include other stuff - laser pointer, flashlight, distance meter, infrared thermometer. I recommend keeping it simple - just a tester. I don't see the point (except for convenience) of a laser pointer, most people have a flashlight in their phone (and likely separate flashlights besides - I highly recommend headlamps for hands-free lighting), etc. Really the only "extra" that makes sense to me is the dual-voltage range (the additional range is something like 12V - 48V) but even that is unnecessary for most people - you just need to know if there are any 120V or 240V hot wires waiting to bite you.

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    Thank you so much! That's helpful info.
    – Ryan
    Aug 22, 2022 at 22:32
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Well they're all somewhat dodgy - on a house you don't really know, it's best to cut the main, so you don't get nailed by historic stupidities, either miswiring or the once-legal practice of not handle-tying MWBCs.

The 3-light tester has a huge problem with its label, only "correct" and "open ground" are accurate. The rest are wrong and misleading, because the label is tuned for wiring mistakes in brand new wiring, and never considered wiring failures in old but previously functional wiring. We sadly see people (in defiance of all common sense) swapping the hot and ground wires on all their outlets because a $5 tester told them to, /facepalm.

The contact tester has a reputation for flagging on phantom voltage. One nice thing about 3-light testers is they can tamp down phantom voltage for you so you don't get misreads from other tools.

The limitations of non-contact testers are legendary. They don't flag when they should and flag when they shouldn't. Less likely to be tripped by phantom voltage, though.

To answer your question, non-contact testers are non-contact which means you can test through insulation. FYI if you were brought up being taught that piercing wires is OK, that's wrong for AC power.

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  • Thank you SO MUCH for your answer! I'm now wondering what you'd recommend instead. My house was built in 1979. Its electrical panel was mostly unlabeled, and the few labels it did have seemed sometimes incorrect, so I'm trying to label it thoroughly. And I'm eager to install things like amzn.to/3Cnjt7w and amzn.to/3pCs3b5 so want to know how to be safe. If you have recommendations for what tools I can buy to eliminate risk (and what online videos or tutorials might help), I'd very much appreciate your thoughts!
    – Ryan
    Aug 22, 2022 at 22:06
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    @Ryan don't buy anything from 3rd parties on mail order. (Sold by: Amazon is semi-OK but mail order generally is risky). Everything needs to be UL, CSA or ETL listed. Honestly... I use very few tools. Tools don't think for you. I advise browsing books on DIY electrical and find a couple that speak on your wavelength, and read them through. You need a well-rounded primer, you can't Google it - Google only answers questions, you need the primer to know which questions to ask. Nobody ever said "Help, I have too many electrical skills" lol. Aug 22, 2022 at 22:13
  • Thanks for your tips!
    – Ryan
    Aug 22, 2022 at 22:22
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I don't own and don't miss a non-contact voltage tester. Not on my list to purchase. Never had one. But, I'm not you. I was once a newbie, and I managed to get through that without one to become older, wiser, and still willing to learn. If having one makes you happier, by all means get one.

I do use a 3-light+GFCI tester plug-in for 120V receptacles, a Kill-a-Watt meter for the same sort of receptacles, and a variety of multimeters. For labeling breakers, plug in radio(s) and/or lamps (the sort you normally use) are perfectly fine if you are methodical about tracking every receptacle and light to the breaker it lives on.

Throwing the main breaker should always work, and almost always does, except in weird, mostly illegal, edge cases (stealing power from the neighbors or the power company, improper solar setup not shutting down when it should, etc.) If you can't positively identify what circuit the part you are going to be working on is on, throw the main (after preparing things that won't like a power outage by shutting them down nicely.) Once you've sorted the labelling, that should be very rare.

One "simple if you can learn" technique is not to touch uninsulated wire ends. I don't advocate working on live wiring; I've seen a show-off licensed electrician blow a circuit while needlessly doing so and screwing up. But I treat all wires as live until verified otherwise, and sometimes even then. The vast majority of tools for working on electrical devices have insulated handles - use them. There's no need to touch the bare metal ends with your hands, or to use uninsulated tools. You do, however, need to keep control of where those ends are, at least until verified dead.

Knowledge is power: you should understand and respect electricity, not fail to understand it and fear it (which seems terribly common...) or fail to respect it and get hurt (also common.)

Also, don't work on electrical while drinking or otherwise impaired, too tired to think straight, or in a huge hurry.

And always, always always take "before" pictures before you disconnect any wires. There are dozens or hundreds of questions here that boil down to "if it was working when you started, you should have connected the new thing the same way the old thing was connected, but now that you've screwed up the wiring by disconnecting it all, or "fixing" something you didn't understand was correct, and now it doesn't work, it's harder to sort out correctly." Classic one is not understanding that white is hot in a switch loop, and you will find switch loops with white hots (or incorrect black hots and switched-hot whites) unless your house is very, very new.

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  • Thank you for your very helpful answer! The part about "before" photos is ringing true to me. I recently uninstalled a light above my sink, and I could have sworn I took "before" photos" but haven't found them... and I don't know that they'd help much now anyway because the kitchen painters carelessly painted over the wires and everything, which really annoyed me. But I'll figure it out when I have a moment. "Before" photos are a must, yes! (At least that area seems simpler than the more complicated switches I've posted about recently: diy.stackexchange.com/a/255223/20576 ) Thanks!
    – Ryan
    Aug 24, 2022 at 12:46
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    It's pretty easy to gently scrape the paint of the wiring, @Ryan, with a razor blade. Drag it so the cutting edge is trailing so that it doesn't actually cut into the wiring, and enough paint will come off to be able to identify the colors. Painting wiring seems to be a particular joy of house painters, while covering them with mud seems to be a hobby of the drywall crews... :(
    – FreeMan
    Aug 24, 2022 at 12:51
  • @FreeMan Good to know! Thanks so much for all of your tips!
    – Ryan
    Aug 24, 2022 at 13:28

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