How to Detect Open Circuits in Old Houses

Test old house outlets, switches and sockets to detect an open circuit.

An open circuit in an old house is caused by the failure of a wire, switch or fuse/breaker. As an example, a simple open circuit is a fuse or a breaker that has been blown. You can readily check and correct such an issue by merely flipping the circuit breaker back to the "on" position or replacing the fuse. From there, wires are routed through the house to outlets, switches and sockets. You can test these for voltage; if no voltage is present, there is an open circuit along the electrical supply wire.

Things You'll Need

• Voltage tester
• Screwdriver
• Light bulb

Instructions

1. Determine whether the fuses or circuit breakers have been blown or tripped. Reset circuit breakers and replace blown fuses before beginning.

2. Test outlets for power. Insert the probes of a voltage tester inside the outlet receptacles. The voltage tester will light up if there is power in the circuit. If there is no power in the circuit, flip the breaker to the "off" position or remove the fuse. Remove the cover of the outlet receptacle and test for voltage by touching the probes on the voltage tester to the wires that connect to the receptacle. When you are assured that there is no voltage in the wires, flip the breaker to the "on" position or replace the fuse. Touch the wires again with the voltage tester probes. If there is voltage, the receptacle is bad and that was the cause of the open circuit. If there is no voltage, the wires between the breaker/fuse box have an open circuit.

3. Test a switched outlet in the same way. Test it by inserting the probes into the outlet when the power is on. If there is voltage, move to the next outlet. No voltage means there is an open circuit at the outlet, at the switch or in the wiring. Test the outlet wiring by turning the switch off, removing the face plate, turning the switch on and touching the probes onto the wires. If there is voltage, the outlet is the cause of the open circuit. If there is no voltage, test the switch. Turn off the breaker/fuse, remove the face plate, turn back on the breaker/fuse and test for power on the connecting wires. If there is voltage at the connecting wires, the switch is the cause; if there is no voltage, the wiring is the cause.

4. Repeat this procedure on every outlet and switch in the old house.

5. Test wired sockets differently. Screw in a brand new light bulb into the socket and turn it on. If the bulb light up, the circuit is good. If the bulb does not light up, check the supply wires to the socket, then check the switch if the socket wires show no voltage. Use the exact same procedures as outlined above during testing.

Tips & Warnings

• Always use caution when using an electrical probe. If you do not feel comfortable with this task, call in an electrician for the job.

References

• The Family Handyman: Circuit Tester: Test for Good Grounding
• All About Circuits: A Very Simple Circuit