How can I determine which outlets belong to which circuit?

I'm putting in a powerline Internet adapter for my house (something like this). My mom said it has two circuit breakers, but she has no idea how the house is divided between them. Going across breakers causes too much interference and is bad for the connection, but sometimes the Internet works well and sometimes it doesn't so the signal here is noisy.

Is there an easy way to determine which outlets in my house are on the same breaker? Powerline aside I'm also just curious to find the answer.

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Are you sure there are only two breakers (it seems very few), or do you mean two service panels? – Niall C. Sep 7 '11 at 2:22

Most houses should have one circuit breaker box, that has a dozen or more circuit breakers (and thus a dozen or more circuits). Some houses have more than one circuit breaker box, with a dozen or so circuit breakers in each one.

Having two circuit breakers in a house is very very unrealistic, and probably not what your mom meant (she probably meant two boxes). While the layout can vary, inside the circuit breaker boxes that I'm used to you'll find two vertical columns of switches - the switches are the "circuit breakers". Each switch is a breaker, designed to 'break' the circuit (switch itself off, cutting the power) if something goes wrong (pulling too much power on one circuit at once or receiving too much power). But if something goes really wrong, like a lightning strike, the breakers help but don't eliminate the problem and damage can still result to things plugged in when the lightning strike occurs.

To test the circuits, just do it the old fashion way:

1. Turn on the lights in every room.
2. Make sure every outlet in a room is already powered.
3. Turn off the one circuit breaker. (If it was already off, skip it)
4. See what lights turned off. Make a note that breaker N turns off the lights in room X.
5. Test each outlet using a super-high-tech outlet-testing-device compatible with any USA outlet. Make a note that breaker N turns off the outlets on the North wall of room Y.
6. Turn the circuit breaker back on.
7. Repeat 3-6 for the next circuit breaker.
8. Type up and print out the notes and tape it to the inside of the circuit breaker box's cover.

This works easier with two people: One flips off a switch, the other one yells that the lights went out in room XYZ.

Skip switches that look twice as large than the others - those would be dedicated to your clothes dryer (the machine that dries your clothes and goes with your washing machine), and possibly your air conditioner. You don't need to test those ones because you already know they don't go to anything you're interested in.

Any switch that was already off, you should just leave off. Don't turn them on even "just to see" what they go to: just leave them off.

Any switch that was already on, make sure you turn it back on when you are done.

If you can see visible wiring in your circuit breaker box: Don't mess with anything. Everything should be covered and not visible, and only the switches should be visible - but if someone left the inside facing off of your box, you shouldn't mess with the box until the facing gets installed properly.

Note that if this was my house, you'd be out of luck: Every room's outlets are on a different circuit (almost - some walls share a circuit with the rooms on either side of the wall), and the lights are separated from the outlets. It'd be easier to just run wire along baseboard and through walls then tricking it to run along live power lines.

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You can get a circuit breaker finder which is a module that plugs into an outlet to send a signal that can be picked up by the other half. The plug-in component appears to only work when the power is turned on. The receiving unit is designed to work at the breaker panel, but I wouldn't be surprised if it worked on other outlets.

Of course this is overlooking the cheap and easy answer: turn off one breaker and see what's still working.

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Beat me to it, I was going to suggest simply turning one off too. ;-) – Conor Boyd Sep 7 '11 at 2:47
plug in a radio, turn it up and listen for it to go off when you flip a breaker. Too easy. I own one of those circuit testers, work good, but a little pricey for a single use. – shirlock homes Sep 7 '11 at 10:03