Dedicated Circuit

Hi jea48
electrician said that with 100amp service everything on the electrical panel is on the same “phase”. While I have a dedicated circuit it still is subject to influences of the rest of the house.
I don’t know if this is accurate or true. Need to do some research on this.

@ audiosaurusrex


I think you misunderstood what the electrician said.

In the typical US residential neighborhood the houses are fed from a single phase step down isolation type transformer. The secondary winding is center tapped. From the two outer most leads, legs, of the winding there is a voltage potential of 240Vac nominal. These two leads, legs, are called the Hot Ungrounded conductors.

From either of the two Hot Ungrounded leads, legs, to the center tap lead, leg, there is a voltage potential of 120Vac nominal. The center lead, leg, is intentionally grounded, connected, to earth at the electrical service equipment panel of the house making it the Grounded Conductor, the Neutral Conductor.

The winding is called a Split Phase secondary winding.

So yes there is only one phase but there are two 120Vac Lines.
Line 1 (L1) and Line 2 (L2). The two Hot 120Vac Lines, legs, are 180 degrees out of phase with one another.


Can one Line, leg, have loads that are connected to it putting AC noise back on it that are noisier than the other Line? Yes it can. Can the noisy Line still have an affect on the Other Line? Yes but to a lesser degree. Depends.

Best thing to do is not install the branch circuit breaker for a dedicated line for audio or video equipment in close proximity, (therein directly across from or directly above or directly below), to a know circuit that has a noisy load/s connected to it. The further away the better. (Note: Directly across from is the same Line as the dedicated circuit breaker. Directly above or directly below the dedicated circuit breaker is the opposite Line, leg.

Here is a good video on how a transformer with a split secondary winding works.
https://www.youtube.com/watch?v=eVamt9IdQd8

@ jea48,
Thanks very much, I really appreciate the detailed response and learned a great deal. So when my electrician installed the 20amp circuit breaker it is in fact right below two other 20amp breakers for the air conditioning units 20amp breakers,(two of them).
So should this be moved to the other leg or down further with separation between them? I think when these guys work they like to keep things all together nice and neat.

So when my electrician installed the 20amp circuit breaker it is in fact right below two other 20amp breakers for the air conditioning units 20amp breakers,(two of them).

120V window air conditioners? If yes one is fed from the same Line as your dedicated circuit and the other A/C unit from the other Line in the electrical panel.

I wouldn’t have installed the breaker for the dedicated circuit directly below the two A/C breakers.

With that said.....

Is the dedicated circuit for your audio system picking up noise from the two A/C branch circuit breakers? Maybe, maybe not. Depends on the quality of the electrical components used in A/C units. Can you hear any difference from your audio system when the compressor in the two units cycle on and off?

I guess you could try listening some late evening, when it has cooled down outside, to your audio system with the A/C units turned off. Then listen again with them turned on. Have someone else turn them on so you can listen to your audio system when they are powered up.

jea48,
so I just looked at the breaker panel again. The dedicated circuit is right below my mini-split air conditioning breakers which are dual 30amp. Haven’t used the air yet this year (chilly New England) so not sure If it will generate any noise.
If it does, bummer, have to get electrician back here. Tried to do my homework but should have talked to you first :-(
thanks for your expertise!