Getting to Know Your Circuit-Breaker Panel

Technical Notes

With the popularity of using the powerline for lighting control such as UPB and X10, the time will come when things don’t work and troubleshooting will be due. An example would be where devices work in one part of the house, while others in a different location don’t work at all. This problem usually means a lack of signal in one part of the house.

CircuitBreakerUnderstanding Phases

Before going any further, let me clarify some of the jargon associated with this subject. In a typical residence, the electrical power to the home’s load center, or circuit breaker panel, is 120/240-VAC, single-phase, and comes in on three wires. Two of the wires are hot, with the third being the neutral wire. The two hot wires, Line 1 and Line 2, when measured with an AC Voltmeter across L1 and L2, will show a potential of 240 VAC. If either L1 or L2 is measured with respect to neutral, the potential will be 120 VAC.

L1 and L2 are loosely referred to as phase 1 and phase 2 by the powerline community, and for sake of this topic, L and phase will mean one in the same. Phase coupling is a term used to describe a device that allows powerline signals to pass between the two electrical phases.


  • Take a look at this circuit breaker panel. Note that the left and right row of circuit breakers do not indicate that the left row is on L1 and the right is on L2. Adjacent breakers on the same row are on opposite phases.
  • Here’s another breaker panel, but this time with a few added phase coupling devices. See how the couplers are across 240 VAC?

So that’s how your read your circuit-breaker panel, with a little bit of powerline troubleshooting to boot. Now go out there and flip the lid on your panel and take a peek inside!

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10 Comments on Getting to Know Your Circuit-Breaker Panel

  1. Thanks for your blog. I am actually looking to looking to install 220V outlet and a circuit breaker for my electric dyer. Your blog was very helpful in understanding how the circuit breaker panel is put together and works. Keep up the good work.

  2. Hi there, Joe,

    Thank you. I am glad to have helped you out.

  3. Hey Now! That is a great post … thanks a million … couldnt figure out how i wasnt getting a 220v reading on my two hot dryer slots … they are on the same phase … move the breaker over one slot and now you are on two phase … Baba Bouie,
    Baba Bouie, Baba Bouie … Thank You

  4. Hi, WowDan!

    You’re welcome! Good to hear that your dryer is now connected properly and is working. I’m am quite pleased that the information I have provided is helping you and others with your DIY installations.

  5. How do I find a circuit that is off and should be on, is offto the left or the right?

  6. Thank you for clarifying certain things and not assuming everyone knows everything about electrical wiring. I am trying to become more aware of the wiring in my house for safety precautions. Your blog is helpful!

  7. I have a little experience with residential power, but I am stumped in regards to some LED lights I purchased. They are rated 90vac to 260vac, 40w, but they only have 2 wires. Normal one wire is the hot and the other the neutral for 110vac. I want to supply 220vac, but I am stumped on how to supply the 220vac to the lights 2 wires from the supply panel. Do I tie in L1 and L2 to the hot wire and neutral on the light? Do I use a 14/2 cable since the neutral is not used? Am I out in left field?

  8. I am hooking up a current sensor for a micro-controller project. If I have two black and one white wire coming in to the panel box, do I need a sensor on each of L1 and L2?

  9. Thanks for breaking down the difference between circuit breakers. I’m currently working on the electrical to finish my basement and so this information was helpful to me. I especially liked your examples of how to measure the voltage.

  10. Thanks for helping me understand that circuit breakers will enable a part of the house to work and can also turn off the electric source for another part. With that in mind, I’ll be getting one for my house. This is because I need to cut costs since I am a single mom which means that I do not have someone with me to support my kids’ needs. I have three kids, so you can just imagine how big my expenses can be. This will allow me to turn off a part of the house to keep them from using too much electricity.

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