Two-prong voltage testers are inexpensive, reliable, and available almost everywhere. Whatever tester you use, first test the tester on a circuit that you know is energized.
If the tester doesn’t indicate voltage on that circuit, the tool may be broken.
Testing Receptacles
When testing receptacles, grasp the insulated part of the tester and insert its probes into the receptacle slots. Never touch the bare wire tips of tester probes. If the tester lights up, there’s voltage present. Have a helper at the service panel flip circuit breakers (or remove fuses) till you find the one that controls the outlet and the tester light goes out. Use cell phones to communicate, which sure beats screaming between floors.
If the receptacle is faulty or a wire is loose, however, the previous test may not detect voltage present in the outlet box. To be certain, unscrew the receptacle cover plate and the two screws holding the receptacle to the outlet box.
Pull the receptacle out from the wall, being careful not to touch the wires, receptacle screw terminals, or metal outlet boxes. Touch the tester probes to screws on opposite sides of the receptacle (gold on one side, silver on the other). Then touch the tester probes to the bared wire ends on the opposite sides (black wires will connect to gold screws, white wires to silver ones). As a final test, touch the tester to the black wire ends and to the metal box.
Testing Fixtures
Remove a fixture by unscrewing the long machine screws holding it to the outlet box. Carefully pull the fixture out from the box. Test the screw terminals on the underside of the fixture as just described for receptacles. If a switch controls the fixture, test it as described in the next section. Unscrew the wire nuts, if any (support the fixture so it can’t fall), and then touch the tester probes to the exposed wires.
Testing Switches
To identify the circuit that serves a particular switch, turn on the fixture it controls and have a helper at the service panel flip breakers until the light goes out. If that test is inconclusive or you aren’t sure the switch is operable, remove the cover plate and the two screws holding the switch to the box. Test the wires leading to the switch:
Be careful not to touch the screws on the side of the switch or the wires leading to them. Switches interrupt hot wires, so apply the tester probes to each screw on the switch as well as to any group of wires spliced together.
