There are times when you need to trace an outlet to a circuit breaker. Maybe you need to replace the outlet. Maybe you need troubleshoot. Or maybe you are adding additional outlets and want to make sure you don’t overload the circuit. In this blog post, I will describe two ways to determine what circuit an outlet is on. I’ll also tell you how to know if two outlets share the same breaker.
The hard way to trace an outlet
The traditional way to trace an outlet to a circuit breaker is to plug a radio or something else that makes noise you can hear into the outlet. Power it on, then walk over to the electrical panel. Flip breakers until you hear the radio go off. That’s when you know you found the breaker.
This works but it can be tedious. You will also interrupt power to parts of the house that you may not want to interrupt. The upside, of course, is all you need is a radio or something else that is semi portable but plugs into the wall and makes noise. You can probably come up with something.
Be sure to annotate the room on the diagram on your panel. I also like to take the wall plate off the outlet and write the outlet number on the inside of the plate with a permanent marker.
The easy method requires a tool. The tool also lets you quickly find if two outlets are on the same circuit, so you may want the tool.
The easy method to find what circuit breaker an outlet is on
Tools are available to help you trace an outlet to a circuit breaker by sending a signal over the wires. You don’t have to interrupt the power at all. These devices, frequently called a circuit finder, consist of two parts. The transmitter plugs into the outlet, and the other is a receiver in the form of a battery powered wand. Plug the transmitter into the outlet you need to investigate. Then walk over to your breaker box, press the button and position the receiver over a circuit breaker, on the side facing away from the opposite row of breakers. The receiver lights up and makes a noise when it detects the signal over the wire from the outlet. If you get no response, move on to the next breaker until it lights.
If your breaker box is labeled incompletely or inaccurately, a circuit finder makes the process of determining which outlet is on which breaker much less intrusive and painful. It gets even easier if you have a helper. One of you can stand at the panel with the receiver while the other moves the transmitter from outlet to outlet. Then you can update the labels on the breaker based on what you find. I also recommend taking the wall plate off the outlet and writing the breaker number on the inside of the wall plate. That saves you from having to walk to the panel the next time you need to know.
Mapping lights to a circuit breaker works similarly. Some circuit finders come with an adapter that screws into the light socket to convert it into a two prong outlet. If yours came with the adapter, screw the adapter in, then plug the transmitter into the adapter. Then you can map the light fixture to the panel using the receiver. If your circuit finder didn’t come with one of those adapters, you can buy a suitable adapter for a few dollars at any hardware store. They just have a two prong outlet on one side and and Edison style threaded connector on the other side.
Trace or map what outlets are on the same circuit breaker
You can also use a circuit finder to see if two outlets are on the same circuit. Plug the transmitter into an outlet. Then walk over to the other outlet with the receiver. Turn the receiver on and position it over the second outlet. If the outlet is polarized, position the receiver over the thin prong. That’s because the thin prong attaches to the hot wire. But if you can’t tell which is which, just check both sides.
You can use this same trick to figure out if an outlet and a light switch are on the same circuit. Plug the receiver into the outlet, then check the light switch with the receiver.
Where to get the tool
Name brand circuit finders cost around $50 and large home centers like Home Depot sell them. You can also get an off-brand clone at Harbor Freight for closer to $25.
For occasional DIY use, the inexpensive clone unit is fine.
There is evidence the house I live in was remodeled at some point in the past, and as a result, I have rooms with outlets that aren’t necessarily on the same circuit, or adjacent rooms that have some outlets on a circuit in common but other outlets on a different circuit. Having a circuit finder made it much easier for me to map those outlets to make it easier to work on my house when I need to. For me, the time it saved was well worth the $30 I paid for the tool.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.