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Electrical101
Burned Switch

How to Troubleshoot Switches

Switches are used to turn lights or electrical devices on and off. Usually when a switch fails, a light or electrical device will not turn on. After determining that a light bulb is not burned out and a circuit breaker or GFCI is not tripped, the switch may have failed.

This troubleshooting page assumes the switch wiring is correct and switching has worked correctly in the recent past. If you think there is a problem with the wiring or if someone has worked on it but did not fix it, call an electrician.

How to Troubleshoot a Single Pole Switch

Troubleshooting a single pole switch is fairly simple.

  1. With power on, remove the cover from the switch and turn the switch off. Using a voltage detector (see picture below), place it next to the terminals on the switch. See if there is voltage at one of the switch terminals. If the tester detects voltage, turn the switch on and see if voltage is detected at the other switch terminal.
  2. One terminal (120 V) will always have voltage and the other will have voltage only when the switch is on. If you only detect voltage at one terminal when the switch is toggled, the switch has probably failed. Sometimes the switch terminals are connected to the back of the switch, and voltage cannot be detected while the switch is inside the electrical box. In this case, proceed to step 3.
  3. Turn off power to the switch at the circuit breaker. Unscrew the switch mounting screws and pull the switch out of the box enough to access the switch terminals. The switch wires do not need to be disconnected at this time. Using a continuity tester on the terminals, see if there is continuity when the switch is turned on. If there is no continuity, the switch has failed and needs to be replaced.

Neutral

Neutral

120 V

120 V

Voltage Detector on Switch

Check for voltage on switch terminal

Single Pole Switch

Place leads of continuity tester on the two terminals with power off

How to Troubleshoot a Receptacle Switch

If a lamp that is plugged to a switched receptacle does not work, it could be a bad light switch. Below is an example of troubleshooting a lamp with a good bulb that does not turn on.

Using an electrical meter, check for power at the switched part of the receptacle, or use a voltage detector to see if there is voltage on the lamp cord.

If there is power present at the receptacle and on the cord, there could be an open circuit in the lamp:

If there is no power at the receptacle or on the cord:

Notice the burn marks on a failed switch caused by an internal arc flash. If you hear a crackling noise inside the switch, it is caused by internal arcing and is ready to fail.

Voltage Detector on Lamp Cord

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