How to Safely Test an Electrical Circuit

Whenever you work on an electrical circuit, it is very important to first make sure that the circuit is turned off--not just at the switch, but at the main panel or subpanel that controls the electrical circuit. Then, before working on the circuit, you must check the circuit or device to double-check that it is indeed off.

To safely test an electrical circuit use a circuit tester to ensure no electricity is flowing through. Holding the insulated parts of the probes, touch the bare metal end of the black probe to the grounding conductor or the grounded metal box, and then, while holding the probe there, touch the bare end of the other probe to the terminal or bare wire that is normally "hot" (live). This is typically a black or red wire or a white wire wrapped in black tape to designate that it is on the "hot" side of the circuit. If the circuit is live, the tester will light up (or otherwise signal the presence of electricity, depending on the kind of tester you are using).

Always hold the probes of the tester by the insulation around them. In the event that the right circuit was not turned off, or if the system shorted out, the wires in the circuit could still be hot. Touching wires with your fingers or any metal tool could cause a short circuit and very possibly give you a serious shock.

To test whether a receptacle is live or dead, you don't need to remove the device's faceplate. Simply insert the tester’s probes into the slots, as shown at right. If the tester lights up, the receptacle is still conducting electricity.