Electrical Tips and Tricks: Part 2 of 3 — Locating A Circuit In An Unmarked Breaker Box (Yes, it’s possible. And easy.)

A lot of electrical work starts with a simple concern: how can this work be performed safely–or, better, how can I sort this out without death or hospitalization.

A lot of electrical work starts with a simple concern: how can this work be performed safely–or, better, how can I sort this out without death or hospitalization.

In the last post, I showed a “voltage sniffer,” or non contact voltage tester. Which is an easy enough tool to use. You check for voltage, and turn off the power if it’s there. In the simplest of worlds, you simply shut off the power to the circuit you need to work on. To be even safer, you shut off power to the entire building. What if you can’t do that? What if you need the power on in other parts of the building, or you’re doing more than a simple repair?

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And what if you’re faced with something like this–an entirely unmarked breaker box.

Many people would give up here and call an electrician. (And unless you’re perfectly capable and understand electrical theory entirely, I would suggest you do just that. This post is only meant to entertain.)

But with the right tool it’s actually easy to locate a circuit in an unmarked box.

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This is a circuit breaker finder. It also has a receptacle tester integrated into the transmitter. This version, the Klein Tools ET310, is the best I’ve used. It’s also relatively cheap.

The receptacle tester is itself a very important tool.

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If you look closely, you can see the simple operation of this tool. You insert it into a standard receptacle, and the light pattern will tell you what’s going on with it.

In the case of this receptacle, not much is going right.

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This house I’m working on–which is, overall, an electrical disaster–doesn’t have ground wires in any of the circuits. In order to make things a little safer temporarily, I replaced two receptacles, adding a GFCI. (I won’t go into details about how a GFCI receptacle works, or how to wire another receptacle to a GFCI. You can find out more about that here and here.)

Before I do anything, I need to shut off the power. Due to the virus, many people are working from home. Shutting off the power to an entire house isn’t a great option. In many cases, you’ll also want light when working, and you might not have enough battery powered light to illuminate your work space. Here I needed to not only shut off power to this circuit without shutting off power to the entire house–I also needed to label the entire breaker box. Again, the wiring in this house is less than safe, and the ability to shut off the various circuits is necessary. (All of this is temporary until the funds are available to hire an electrician for a full rewire.)

To start, I insert a receptacle tester into each receptacle. One of them is the ET310 transmitter.

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This makes it easy to see the situation by simply glancing into the room. Then I go to the breaker box to scan for the correct breaker. It’s as easy this:

After shutting off the power to the circuit, I glance back into the room and see that the lights are off on the receptacle testers.

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I then test each receptacle, the light switches, and the light fixtures for power using the voltage sniffer. The power is entirely off to this room. (More work goes into mapping out the circuit and labelling the box, but for this post I’m only going to cover the basics. Again, you can find out a lot more by reading this book.)

The final result is nowhere near finished. This, again, is just temporary until the house can be rewired.

Having a GFCI and knowing the location of the various circuits helps quite a bit in the short term.

Extra: The transmitter doesn’t just plug into a receptacle. It can also be used to test a light socket, or even attached directly to wiring, using these accessories.

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