Breaker running warm (120F) under load -- normal?

[CarlosJr]

I was called back to look at a recently completed whole house rewire project. It has a newly installed Siemens load center with 20A AFCI breakers. The customer complained of flickering lights when he ran a 120V in-wall AC unit.

Steady state, the AC unit consumes approximately 1200-1350W according to a Kill-A-Watt meter and this causes a voltage drop from 110V -> 105V on its circuit. The voltage drop seemed high to me compared to other circuits in this residence that I tested under load. Not horrific, but high. I calculated that for the ~50ft run of 12/2 @ 13A, the drop should only be about 1V on each conductor = 2V. Popping the dead front off the panel and checking with an IR camera, I did see that the loaded circuit was about 120F. The load center is indoors so ambient temp is in the low 80s. And of course all of the other AFCIs in the panel run a few degrees over ambient to power their circuitry.

Could this be an installation/equipment problem or is it normal?

 

[Eddie702]

The temp doesn't bother me much that is around 50C. But the lights shouldn't flicker. I would check all the connections in the panel for that circuit, maybe try a different breaker, check the receptacle and where the breaker plugs on the busbar.

 

[LarryFine]

I suggest checking the circuit's total current. Most A/Cs want a dedicated circuit.

You have a panel full of the same breaker you can swap it with to compare it to.

It is at the top of a stack of warm breakers; maybe move the wire to a lower one.

Remember, troubleshooting is a process of elimination, so eliminate possibilities.

LEDs are usually sensitive to small voltage fluctuations. Maybe try non-dimming.

 

[BarryO]

I'd check how tight the connection between is breaker tabs and the panel bus bar. Pop them out and see how hard they are to re-seat.

 

[ptonsparky]

Do a Fall of Potential test!

 

[CarlosJr]

I suggest checking the circuit's total current. Most A/Cs want a dedicated circuit.

The room has a dedicated circuit and the only other thing on it is a TV + iPhone chargers. It's not oversubscribed but I did wonder if there was a potential installation defect.

AIUI the "dedicated circuit" boilerplate tag on AC units >=7.5A is just so the manufacturer can say they comply with 210.23 "Utilization Equipment Fastened in Place". Obviously on a greenfield installation you wouldn't want half the branch circuit capacity taken up by permanently-installed equipment. On retrofits, few customers are willing to pay for the extra home run unless their breaker is constantly popping.