With a couple of simple testing devices, you can check for wiring problems including …
- Whether power is present at a device or fixture.
- Grounding continuity.
- Defective receptacles, switches, and fixtures.
- Whether outlets are properly wired.
A voltage tester should be in every electrical do-it-yourselfer’s toolbox. Consisting of two probes connected at a plastic housing that contains a small neon bulb, a voltage tester lights up when it detects an electrical current. It also can detect which incoming wire is the hot wire and the presence of a grounding conductor. The probes of the tester either are inserted into a receptacle’s slots or are held against the terminal screws that secure the wire to the receptacle. If the probes do not detect a current when inside the slots but do detect one when held against the terminal screws, this indicates that the receptacle itself needs replacement. If there’s no current at the screws, there’s a problem with the circuit.
Note: With back-wired devices, the probes are inserted in the slots next to the wires. The receptacle will have to be removed from the box. To safely remove the receptacle, turn the power off at the panel first, then remove the screws securing the receptacle, pull it out, and, finally, test it.
After removing the cover plate, be sure the switch is in the “Off” position. Place one probe on the metal box that holds the switch; if the box is plastic or nonmetallic, place the probe on the white or neutral wire. You’ll have to remove the switch from the box in order to reach the neutral wire; be sure to turn the power off first and then turn it on again for your test. Place the second probe on each of the black wires, or on the terminal screws holding the wires if they’re side wired. One of them—the line side or black wire supplying power from the circuit—should light up. If neither of them does, there is a problem with the circuit.
After you find the line side, turn the switch to “On” and place the probe on the other black wire, which is the load side, while keeping the other probe on the neutral wire. In the “On” position, the switch completes the circuit and the load side carries power to the light fixture. If the tester doesn’t light up, the switch is faulty and needs to be replaced. You test a fixture by holding the probes against each of the terminal screws with the light switch “On.” If your test shows a current, but the light isn’t working, you need either a new fixture or new light bulbs.
Note: With back-wired devices, the probes are inserted in the slots next to the wires. The receptacle will have to be removed from the box. To safely remove the receptacle, turn the power off at the panel first, then remove the screws securing the receptacle, pull it out, and, finally, test it.
After removing the cover plate, be sure the switch is in the “Off” position. Place one probe on the metal box that holds the switch; if the box is plastic or nonmetallic, place the probe on the white or neutral wire. You’ll have to remove the switch from the box in order to reach the neutral wire; be sure to turn the power off first and then turn it on again for your test. Place the second probe on each of the black wires, or on the terminal screws holding the wires if they’re side wired. One of them—the line side or black wire supplying power from the circuit—should light up. If neither of them does, there is a problem with the circuit.
After you find the line side, turn the switch to “On” and place the probe on the other black wire, which is the load side, while keeping the other probe on the neutral wire. In the “On” position, the switch completes the circuit and the load side carries power to the light fixture. If the tester doesn’t light up, the switch is faulty and needs to be replaced. You test a fixture by holding the probes against each of the terminal screws with the light switch “On.” If your test shows a current, but the light isn’t working, you need either a new fixture or new light bulbs.
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