How to test circuits; circuit testing

When you are going to work on an electric outlet or switch, always turn off the circuit power at the breaker box or fuse panel. To determine which outlets and switches are on a circuit, see Circuit map. Then, to test that the power really is off, turn a switch on and off. Test a receptacle that you know is working by inserting the probes of a neon test lamp into its two openings: if the lamp lights, the power is still on; if it doesn’t light, it’s safe to begin work.

Frequent fuse blowing or circuit tripping may be caused by operating too many appliances and lights on one circuit. Unplug enough of them so that the circuit is not overloaded.

If the problem persists, try to trace the cause by unplugging all appliances and turning off all switches on the blown circuit. Turn on the power. If the breaker trips or the fuse blows, turn off the breaker or remove the fuse. Unscrew the cover plates on each switch and outlet. Look for broken wires and loose or missing terminal screws; fix or replace them.

If the circuit doesn’t blow, re-engage the power and turn on the switches one by one. If during this procedure, the circuit blows again, the problem is in the switch or the fixture you just turned on. To determine which, test the switch with a continuity tester; if the bulb lights, showing the switch is all right, then the problem is probably in the fixture. Remove the fixture; test it and repair or replace it. If no problem develops, plug in and run appliances one by one. If the cord, plug, or switch of an appliance turns out to be the cause of the blown circuit, replace or repair the faulty part. If none of these suggestions remedies the problem, call in an electrician.