How To Use a Voltage Tester | Ask This Old House

In this video, Ask This Old House host Kevin O’Connor and master electrician Heath Eastman discuss the different uses for voltage testers, as well as test some of Heath’s favorite models.

Kevin O’Connor meets master electrician Heath Eastman at the shop to discuss the different types of voltages testers and their uses. Heath has four types of testers to show Kevin, including a non-contact pen tester, a full-size multimeter, a miniature multimeter, and a plug-in tester. Heath explains how each tester works, which scenarios they’re best for, and how he uses them in his work line.

A contactless voltage tester is shaped like a pen or marker, and it can indicate whether a wire or outlet has voltage feeding it. They’re quick and easy to use, and they can help an electrician or homeowner locate live circuits. However, they don’t tell the user how much voltage the outlet or wire has, and they’re not always completely accurate.

A full-size multimeter might be overkill for homeowners, but they can tell an electrician a lot about an outlet, switch, fixture, or circuit. These voltage testers have two contact points or probes that the user can touch to the wires in a circuit to determine the amount of voltage, amperage, and resistance on the line. If the pen tester alerts to a circuit having a charge, a contact tester is the best way to find out why.

A homeowner doesn’t necessarily need a full-size multimeter, but a small contact tester can do much of the same work. These scaled-down meters have two contact points or probes, and they explain the voltage on a system in ranges, such as 24 volts, 48 volts, 120 volts, and 240 volts. They’re more affordable than full-size meters and much more compact. They’re also one of the only options for 2-prong outlets.

Receptacle testers are compact and easy to use, and they provide a lot of information. While they don’t explain how much voltage a receptacle is experiencing, they do explain if there is an open ground, an open neutral, or an open hot. They can also indicate polarity, or whether the hot and ground are reversed, or (more commonly) if the hot and neutral are reversed. These testers will only work on 3-prong outlets, and they can test GFCI outlets, as well.

They All Have Their Merits
All types of voltage meters have their pros and cons, and it could be worth keeping a few types of testers in your tool bag. While the receptacle tester is the only tester that tests polarity, it can’t quantify voltage or test two-prong outlets. Pen testers or contactless testers don’t explain voltage either, but they’re fast and easy to use. For the best results, have a few of these testers on hand before doing electrical work.

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From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. Ask This Old House helps you protect and preserve your greatest investment—your home.

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How To Use a Voltage Tester | Ask This Old House

[jstasiak]

A very important point about non-contact voltage testers (NCVT) was not mentioned: Prior to using a NCVT, it is extremely important to test it on a known “live” voltage source to verify that the tester actually works. This needs to be done each and every time it is used. If the tester fails to illuminate when testing, it could be because the tester has a low battery or is defective. In that case, it would fail to warn you about an actual “live” wire. That is why you need to verify that it actually detects voltage before using it for decision making. I cannot overemphasize the importance of doing this.

[HenrysHowTos]

So many appliances are wired as reverse polarity, Ive been zapped so many times by everything from DVRs to Stereos. Always completely unplug any appliance before removing the cover and working on it!

[loumonte]

Great info. It will probably save someone's life.

[GerardoRitchey]

That's one of the better explanations for why getting the polarity correct in the outlet is important. I bet this was a follow-up to the previous video they did on this, where Heath used to washing machine example and it was hard for some people to understand what he meant when he said that it could be off, but power could still be running to it.

[Danny-fshk]

Kevin is an excellent host. He asks great questions that us novice folks need answers to. 😂

[kingssman]

I would love to see a followup vid on using the multimeter to test a light switch or continuity check when power is off.

[devgupta]

Thank you TOH for covering something seemingly basic but could “trip” up any homeowner. I’m definitely adding a reverse polarity tester to my tool bag.

[TheBr]

Going to sign the paperwork for my first house which is an older house. This is invaluable information, thank you.

[mrjack]

Bought the 2 simple ones he mentioned about a year ago. Work great when I moved into my new house and replaced light fixtures. Great peace of mind.

[ronk]

Before you test a live circuit with a multimeter, put the meter on the lowest ohms setting and touch the leads together. They should read zeros across the display. If not, one of the leads is broken. After you confirm you have zeros on the display, the put the meter on ac and test the circuit.

[ronh]

Great information and comments. The 3 prong GFCI tester is definitely a good one to have. There is a new version out that also has an LCD screen that actually gives you a voltage readout on the screen that comes in handy. I believe it is made by Klein….

[ElectricGears]

Something super important about those contactless voltage testers that was not mentioned is that they are very short range and they are blocked by a Ground or Neutral conductor. If you use one on a jacketed wire like NM-B (Romex), you can tell which side the Live conductor is on. The same with an extension cord with it's twisted conductors. You can follow the twist down the cable. *This means a quick tap will not necessarily cause it to light up so you might cut through a live cable.*

[Dredpath]

Thank you for this video! I feel that new people in the trade need to have a basic understanding of how electrical testers work! Heath is a great electrician and I hope to meet him someday! Keep up the great work ATOH!

[SoniaBDorsey]

This has been the most educational video for me. Thank you so much for sharing this.

[libertarian]

As an electrician I carry a number of tester with me, including the first 3 types. I also have receptacle testers, one which tests and times GFCI trips as well as an AFCI tester; if you’re going to get a receptacle tester spend the extra to get a GFCI tester at a minimum. Also be careful with sum of the cheaper non-contact and direct contact testers as you can actually get sum parasitic currents/voltages on a line that can be too low to indicate yet still enough to hurt you. I carry a less expensive contact tester as it’s easier than pulling a meter out and unwrapping the leads but a decent True-RMS multimeter is something every homeowner should have. These aren’t expensive things, in fact I use these things along with some cheap tools and a tool box as a home warming gift for family and friends as these are a must have along with screwdrivers, pliers, and a hammer. Giving the basics also saves on having to go help people as they’re in the position to help themselves.

[_pudu]

excellent communication between the two and great information and questions asked. great video and interaction

[henrytherd]

Can you have a more detailed video about the multimeter tester? ty

[nscaledelights]

Wow that was an awesome explanation of how to test for electricity. Next time Im in Home Depot Im picking up one of those 3 prong testers.

[NathanMaharaj]

So informative. So useful. Just talked myself out of a full multimeter to instead get the simplified one that just shows different expected household voltages.

And as a bonus I now know why wiring a receptacle with correct polarity matters.

[Tractorman-xjgt]

Good stuff from Heath, as always - have used a couple of these - the "little guy" is worth its weight in gold - has indicated a reverse polarity in one of my kitchen outlets - highly recommend getting one...