Home Improvement: How to Test Various Electrical Fixtures and Switches

Testing three-slot receptacles. Check that your voltage tester works and turn off power. Place one probe in one receptacle opening; place other first on green screw, then in other receptacle openings, one at a time. Repeat for each receptacle opening. The tester should not light for any combination.

Remove receptacle with care. Test each of the four bare wires that were attached to the receptacle. Place one probe on a black wire and the other on a white wire. Check both sets of wires, testing all possible combinations. If power is indeed off, tester will not light.

There will be twice the number of wires as usual when two circuits run through one box. Be sure power is off to both circuits at the main panel and check them separately with the voltage tester before proceeding.

Once you are sure power is off at the service panel, keep the fuse in your pocket and label or lock the panel box so no one will accidentally turn the power on while you work.

Ganged receptacles. When more than one receptacle shares a circuit and an enlarged box, the receptacles are referred to as “ganged.” All receptacles may be wired through their sides, at screw terminals, or directly through the back, termed back wiring. To test a back-wired receptacle, first follow step one above then remove one receptacle completely, test bare ends of the exposed wires, and replace it. Repeat for any additional receptacles.

Testing ceiling fixtures. Turn off power at the main panel. Turn the wall switch that controls the fixture to “on” and pull fixture from box to expose wires. Remove black wire cap and test from exposed wire to the metal box.

Remove white wire cap and test from black wire to white wire, then from white wire to metal box. If power is off tester will not light during any of these tests.

Testing single-pole switches. Turn off power, remove cover plate and pull switch carefully from the box. Test each screw terminal while keeping one probe on the grounding wire or metal box.

If the main power is off, all wires should test as dead regardless of switch position. If the power is on, the tester will indicate the wire from the power source as live, whether switch is turned “on” or “off.”

If main power is on and switch is in the “on” position, the wire going to the fixture will be live. Repeat testing on both wires for “on” and “off” switch positions until all testing indicates power is off before proceeding.

Testing three-way switches. Turn off power. Remove cover plate. Keep on probe on the grounding wire or metal box and test each screw terminal.

Remove switch from the box. Keeping one probe on the grounding wire or metal box, test each exposed wire. If the circuit is not turned off at the service, panel, one of the wires may be live. Repeat test with all combinations of wires until all wires test as dead.