To safely test whether a circuit is live or dead, first (as with any electrical work) turn off the power, not just at the switch but at the main panel or subpanel.

Next, use a neon tester (as pictured at left and enlarged at right) to ensure no electricity is flowing through. Touch a hot wire or its terminal with one of the tester’s probes; touch a neutral wire or its terminal with the other probe. (Or, you can touch the other probe to the grounding conductor or the grounded metal box.) If the circuit is live, the tester will buzz, ring, or light up, 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 the metal tips of the tester to live wires could cause a short circuit and very possibly give you quite a shock.

To test whether a receptacle is live or dead, simply insert the tester’s probes into the slots, as shown at right. If the tester makes noise or lights up, the receptacle is still conducting electricity and it is likely there is a malfunction in the lamp or appliance that was plugged into it.