Circuit Tester Instructions

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Things You'll Need

  • Probe circuit tester

  • Plug-in circuit tester

A circuit tester is one of the most important tools a homeowner or electrician can have to verify the integrity of electrical wiring and receptacles. Circuit testers have external probes or prongs designed to fit into the slots of an electrical outlet. The probes make contact with the exposed terminals of circuit breakers and switches, while the three prongs of a plug-in tester can be inserted directly into a receptacle in the same way as any electrical plug. Learning to use a circuit tester requires only basic electrical circuit knowledge.


Probe Circuit Tester

Step 1

Select a switch to be tested. Remove the switch cover plate screws by turning them counterclockwise with a flat-head screwdriver. Remove the cover plate from the wall.

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Step 2

Place one probe on the switch terminal screw to the right side of the switch, and the other probe on the left terminal.


Step 3

Check the circuit tester for an indication of power. This test verifies the presence or absence of electricity.

Plug-in Circuit Tester

Step 1

Insert the tester into the receptacle until it is fully seated. The tester should illuminate immediately with any combination of its three lights.


Step 2

Check the tester. If one yellow light in the middle of the three is illuminated, this indicates that there is an open or disconnected ground in the circuit. If there is no ground wire, this would also cause that light to be illuminated.

Step 3

Check the tester. If the yellow light on the far right is the only one on, this indicates that there is an open neutral wire in the circuit. Neutral wires have white insulation or white tape if the wire used as a neutral was a color other than white.


Step 4

Check the tester. If no light is illuminated, that indicates that the circuit has been turned off or the hot wire is disconnected. The hot wire in the circuit has black insulation.

Step 5

Check the tester. If the light on the left is red and the two to the right are yellow, this indicates that the hot wire and the ground wire crossed. The ground needs to be connected to the green grounding post of the receptacle, and the black hot wire should be connected to the brass terminal.


Step 6

Check the tester. If the light on the left is red and the light in the middle is yellow, this indicates that the hot wire and the neutral wires are crossed. The black hot wire must be connected to the brass terminal, and the white neutral wire must be connected to the silver terminal to be wired correctly.

Step 7

Check the tester. If the middle light and the light on the far right are both yellow, the circuit is wired correctly.


The use of circuit testers requires working with live circuits. Follow the manufacturer’s safety recommendations and instructions for the particular style of circuit tester you are using.



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