Skip to main content

Getting to Know Your Circuit-Breaker Panel

Written by
Home Controls
Published on
March 25, 2008 at 8:05:00 AM PDT March 25, 2008 at 8:05:00 AM PDTth, March 25, 2008 at 8:05:00 AM PDT

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.

Understanding 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!