DIY and Pro Help With Your Home Projects

How To Test An AC circuit

Circuit Tester in Outlet
Before you ever touch any AC circuit, make sure that the circuit is totally powerless. Many houses have serious hidden electrical problems including outlets that are wired to 2 breakers in the main junction box. The older a house gets, the more amateur renovators (and some professionals) change the wiring and they can do some crazy things. Therefore, it is very important that you make sure that there is no power in any area where you are working. Jumpers and crossed wires can make updating AC wiring a scary thing.

When in doubt, use the main breakers to disconnect electrical power from the entire house. Even this is not 100%. There is still capacitance in the appliances and wiring that could shock you.There is also the chance that someone has jumpered around the mains (or power meter) to save on their power bill or just cut corners. You may have to reset your VCR when you switch the mains, but it could save your life. In any case, you should test the circuit before and after switching the power at the breaker box.

Testing a Circuit

Before disconnecting the power, check the outlet using an outlet tester. You should see standard power (2 yellow lights) before disconnecting the power at the mains. Then once you have removed the power, the lights will be out. It is a good practice to know the source of the power and then remove the source. If you only test the outlet after turning off the power, you could be testing a a switched outlet on another circuit. In this example, someone could flip the switch, while you are working, and electrocute you.

The best option is to spend the 8 dollars and buy an outlet tester (show here) or a neon circuit tester (that can also test switched and exposed wire). Insert the outlet tester into the outlet and confirm that you have power (2 yellow lights). Flip the breaker and confirm that you have not power (no lights).

You can also use a multi-meter to test any circuit in your house. Switch the meter to AC voltage to test the difference between hot and neutral or ground. If you see any voltage, then the circuit may be partially hot. [You can only test AC current if the meter is in series and measuring the resistance of a live circuit will only destroy the meter so don't try these options]

Simply measure the voltage (using one of these 3 tools) before AND after switching the power so that you can be confident that the circuit is safe to touch.


Electrical work is highly dangerous. Let us help you find a great Electrician to do this job for you.

Need More Information? Check out our other articles on home wiring and electrical projects.

The information on this site is provided for reference only and is provided "AS IS", "AS AVAILABLE" with no guarantee of accuracy. Information comes with no warranties, express or implied. Use the information from this site at your own risk. See our disclaimer for more details.