Learning, Wiring,

How to Tell Which Wire is Hot Without a Multimeter

A multimeter is one of the best devices to use to check the polarity of electrical wires. But what if you are caught in a situation where you have to tell which wire is hot and you don’t have a multimeter on hand? We have you covered.

As an electrician with over 15 years of experience in home and office wiring and having done a ton of jobs that involve identifying electrical wires, I discovered that many people really don’t know how to tell the difference and try to carry on work by guessing which wire is hot sometimes leading to accidents. So, I decided to shed some light on the question with this guide.

How to Identify a Live Wire

Because sometimes different colors of wires will be used for different situations it’s best to be absolutely sure what wire is the live wire and not use color codings. That is why we’re going to teach you to create a homemade tester to find out whether the wire you have is the live wire. Of course, if its a common device and came with a manual you can often find the live wire in color-coded wire diagrams, but well assume you have already tried this and are working with wiring that was either installed by someone else or a device that doesn’t have this kind of color coding in which case building a homemade tester is best.

Step 1: Build a Tester

wire tester

You will need a couple of wires and a lamp if you do not have a tester. There are many ways to build a tester, but a bulb tester will suffice.

Strip off the insulation coating from the ends of both wires using a stripper to about ½ inch deep. Connect one end of the first wire to the metallic neck of the bulb and the other end to a plug that goes to the socket.

Note that there is no issue if you connect the black, red, or any other color first. The tester only needs to connect to a live wire and light up. That’s all.

Start by grounding one wire (that is) connected to the bulb, and then connect another wire to the wire that you want to check polarity.

Step 2: Unscrew the Box Cover

electrical box with capped off wires

Here, you will have to remove the cover of the box using a screwdriver. Do not touch any wires to avoid electrical accidents. Removing the cover enables you to access the wires and test them.

Step 3: Do Not Interrupt the Wire Connections

wire diagram of neutral, earth, live

Avoid altering the wire connections. Wire harnesses have various standard color codes. Black wires are live or hot in the electrical fixtures (USA), the white wires are designated neutral, and ground wires are coded green. It is wise not to interchange / alter the wires in any way to avoid confusion.

Step 4: Connecting Your Tester

connecting one of the two wires

Now connect one of the two wires you attached to the lamp to the ground (GND) – it is usually green or yellow. Go ahead and attach the other wire to the wire whose polarity is under test.

If the bulb/lamp lights, the wire is hot. If not, the wire is either neutral or ground. But you should be sure. So, test if the lamp is working in a different socket.

Finally, disconnect the tester and mark the hot wire with ink or tape.

There are many other alternative ways you can verify a hot wire. For instance, you can also use a non-contact detector. Follow the procedure below to use a detector.

testing the wires on the metal box

  1. Hold the non-contact detector near the wire you are testing.
  2. Identify a light on the detector to turn on.
  3. The detector will beep if there is any voltage flowing through the wire.
  4. Mark the hot wire – where the detector beeps.

Safety Precautions When Handling or Testing a Hot Wire

An electrical check like this can be a matter of life and death. Hence one needs to be vigilant and cautious to avoid catastrophic events. Read the following safety guidelines to be safe when testing for a live wire in your wiring harness. (1)

Always Get Ready with Your Safety Gear

electrician stripping off the bare copper wire

Fetch your safety goggles and have them on while experimenting. It will protect you from electrical sparks that are harmful to your eyes.

Also, avoid touching metallic surfaces in the electrical box when testing a live wire. 

You should wear insulating gloves to protect your hand from poking wires and electrical shock. Working with insulated pliers and other equipment is wise.

Cover the Switches

Be sure to cover switches and breakers when working on a circuit. That way, people will know that you are handling the circuit. If you do not, someone may turn the switch or the breaker on, exposing you to danger.

Wrapping Up

Hot wires are extremely dangerous. Handle them with extra care. Do not assume which wire is positive or negative, check them first. Have your safety gear on whenever you are looking for the live wire to avoid electrocution. (2)

Take a look at some of our related articles below.

(1) catastrophic events https://www.sciencedirect.com/topics/earth-and-planetary-sciences/catastrophic-event
(2) electrocution – https://www.sciencedirect.com/topics/medicine-and-dentistry/electrocution

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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