Every DIYer should have these three inexpensive electrical testing devices. They're handy even when you aren't doing electrical work.
Introduction
Electricians tend to have sophisticated testing equipment that many DIYers wouldn't know how to use even if they could afford to buy it. Still, electricians aren't the only people who need to test electrical wires. Remodeling contractors and DIYers often encounter the need to disconnect or relocate electrical wires and devices before they can get on with the job they're doing, which may or may not be electrical in nature.
Instead of expensive testing equipment, all these folks usually need are three simple testing devices that together cost about $20. They are a non-contact voltage tester, a circuit tester and a continuity tester. I have all three in my toolbox, and I wouldn't go anywhere without them. Maryland contractor Yaeir Moinzadeh feels the same way, even though he spends most of his time doing roofing. Electrical wiring extends through every part of a building, and it's hard to avoid, even on the roof.
Besides being inexpensive, these testing tools are easy to use, but there's always a possibility of misusing them, and because you're dealing with electricity, the consequences can be severe.
Here are some tips and best practices for DIYers doing basic electrical work who might not be familiar with these essential testing devices.
Tools Required
- Non-contact voltage tester
- Circuit tester
- Continuity tester
Project step-by-step (13)
Step 1
The Non-Contact Voltage Tester
Every electrical current generates a magnetic field, so a non-contact voltage tester can detect current in a conductor without actually touching it, even if the conductor is insulated. It has an LED that illuminates — and it may also produce an audible beep — when it detects a live current.
A non-contact voltage tester has a battery, and Moinzadeh stresses the importance of doing a live test before you use it to ensure the battery is good. “Start by testing on a known live circuit, then on a dead one, and then finally back to the live circuit. This way, you can make sure that your tester is working properly.”
“It is critical to remember,” he continues, “that in certain conditions, like with wet insulation, these testers can give false negatives. They also usually won’t detect voltage on grounded conductors or neutrals.”
Step 2
Test a receptacle with a non-contact voltage tester
When an appliance doesn’t turn on, you can use a non-contact voltage tester to confirm whether the receptacle into which it’s plugged has power. You can also use the tester to ensure the power is off before working on a receptacle.
- Insert the tester’s nose into the hot prong of the receptacle (the smaller one). If the receptacle has power, the LED will illuminate, and you’ll hear a beep (if the tester is so equipped).
- If you plan to work on the receptacle, turn off the breaker, then use the tester to confirm that the power is off.
Step 3
Test for hot wires with a non-contact voltage tester
Sometimes, when you’re working on a receptacle, switch or light fixture, you’ll find extra wires in the electrical box. You can use a non-contact voltage tester to determine if any of them are live.
- Unscrew the device from the electrical box and pull it out.
- Insert the tester deep into the box and move it around. If it illuminates or beeps when you move it near a particular wire, that wire is live.
- Locate the breaker that controls that wire and turn it off. Then, use the tester to confirm that the wire is no longer live.
Step 4
Test switches with a non-contact voltage tester
Use a non-contact voltage tester to diagnose a faulty switch.
- Unscrew the switch from the box and pull it out.
- Move the tester close to one terminal and then the other. If the tester indicates power to the switch, but the switch isn’t working, it needs to be replaced.
- Turn off the breaker for the circuit, then use the tester to confirm there are no other live wires in the box before you disconnect the switch.
Step 5
Test light fixtures with a non-contact voltage tester
When a light fixture isn’t working, a non-contact voltage tester can help you determine whether the fault is in the fixture or the circuit.
- Remove the bulb and test the contact in the bottom of the socket for voltage. Make sure the light switch is in the ‘on’ position.
- If no voltage is present, unscrew the fixture from the electrical box.
- Pull it out and test the other wires in the box.
Step 6
Test cables with a non-contact voltage tester
When you encounter electrical cables inside a wall you’re working on, you can use a non-contact voltage tester to determine whether or not they are live. Just move the probe close to the cable, and it will beep or illuminate if the cable is live.
- Note: This works only with plastic-sheathed cables, but that’s most of the cables you’ll find in a typical residential building.
Step 7
The Circuit Tester
Also known simply as a voltage tester, this device has two leads that must be in contact with a conducting wire and a ground or neutral wire to detect a voltage difference between them.
You can use this tester, as I often do, to determine whether or not a conductor is live. When you touch a live hot wire with the other, the neon test lamp should light. It confirms that the power is on and that you have a complete (good) circuit. If the light doesn’t come on, either the power is off, or you have a bad circuit.
A more specific purpose of this device is to determine whether a circuit, device or electrical box is properly grounded. You often have to check this when you replace older ungrounded switches with grounded ones, as now required by the National Electrical Code. It isn’t unusual to find an unused bare ground wire folded back into the box, and you have to test it to ensure it’s connected to the rest of the grounding system before hooking up your new switch.
“To check for voltage using double-prong voltage testers,” advises Moinzadeh, “it is better to test both ways. It helps you avoid false readings due to phantom voltages. In addition, it is a good practice to test a known live circuit before and after your actual test is performed to confirm the tester’s functionality.”
- Pro tip: Avoid touching a live hot wire and don’t let it touch anything else. Hold the tester leads by the insulated portion while making contact. Turn the circuit off again as soon as you finish the test.
Step 8
Test ground wires with a circuit tester
Circuit ground wires are usually bare (uninsulated), but sometimes they are coated with green insulation. Use this procedure to check whether a ground wire is actually grounded.
- Turn off the breaker that controls the circuit.
- Disconnect and separate the wires to a device with the circuit off.
- Turn the circuit back on.
- Touch the hot wire (black or red) with one lead and the ground wire with the other lead. The light will come on if the ground is good.
- Pro tip: Turn the breaker off when the test is complete. It’s dangerous to have live wires hanging loose in an electrical box.
Step 9
Test metal boxes with a circuit tester
Code requires metal electrical boxes to be grounded to prevent injury or fire.
- Test whether a metal box is grounded by using the same procedure you used to test a ground wire.
- Touch the metal box instead of the ground wire with the second lead. If the tester lights up, the box is grounded.
Step 10
The Continuity Tester
It’s difficult and dangerous to trace the routes of various wires with the power on. A continuity tester does it simply and safely with the circuits turned off. In fact, as Moinzadeh points out, the power must be off for the device to work.
A continuity tester has a probe, which contains a battery and a light bulb, and a wire lead. The battery allows the device to generate a small electrical current, and when you touch the ends to any continuous conductive path, usually a wire, with both the probe and the lead, a circuit will be complete, and the bulb will light.
- Pro tip: Make sure the device is working before conducting a test by touching the wire to the probe and verifying that the light comes on.
Working with several boxes and can’t remember which wire goes where? A continuity tester will help you identify them. Another great use for the continuity tester is to determine whether or not a switch is working.
Step 11
Identify circuit wires with a continuity tester
One way to identify circuit wires that run between a pair of electrical boxes is to use a test wire:
- With the power shut off, connect a test wire to a circuit wire in one box.
- Run the test wire to the other box.
- Clip the lead of the continuity tester to the test wire and touch the probe to the ends of the circuit wires in the other box. The bulb will light when you find the right wire.
Moinzadeh suggests an alternative approach:
“First, connect the tester to two wires at one end. Then, at the other end, touch pairs of wires together until you hear a beep. This allows you to identify the corresponding wires.”
Step 12
Test switches with a continuity tester
If a switch is bad, it’s because it has an internal disconnection, which may be caused by overheating or simply wear. You can use a continuity tester to diagnose this problem.
- Turn off the power and remove the switch.
- Clip one lead to one switch terminal.
- Touch the point to the other terminal and flip the switch on and off. The tester light will go on and off if the switch is good. If the switch is bad, the tester won’t light up at all.
Step 13
About the Expert
- Yaeir Moinzadeh is a contractor licensed by the Maryland Home Improvement Commission and the owner of Blue Rise Baltimore Roofing.
Originally Published: November 23, 2020
