Breaker buzzing when AC kicks on

A quick google tells me this may be an issue with the AC’s alternator or the breaker. Probably about a half-second buzz.

Anyone have some insight on this? Is it a danger?

One of the biggest reasons you may notice your circuit breaker or electrical panel buzzing, particularly when the AC kicks in, is due to a device in your HVAC system called an AC capacitor .

FYI there is no such thing as a A/C alternator.
Please don’t put that in your report. an alternator belongs in a car to charge the battery. a capacitor holds a large voltage charge used to start the motor, then it charges again.
there will be one inside for the fan, and one outside for the compressor.

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The thing that most often buzzez or chatters when the AC kicks on is the compressor contactor located in the condenser. Most often a poor electrical connection in the low (24v) wiring. could also be start capacitor. Will cause the contactor points to burn, should replace contactor as well.

ah, sorry that is what i meant.

and full disclosure, this isn’t for an inspection. its for a condo that I just moved into. The panel is in the bedroom and the buzzing is definitely coming from the panel itself.

There are also no AFCI breakers; i don’t know if that could contribute to a larger problem involving the buzzing?

If you all were me, would you insist the landlord sends an electrician? or is this just a nuisance? i don’t want to be an annoying inspector-tenant and not get my lease renewed, but I also want to be abundantly safe about electricity and fires.

edit: i couldn’t care less about the appliances.

Not having afci breakers won’t cause this problem. I see panels every day that have no afci breakers. It could be a loose wire on the a/c breaker. Causing small sparks that sound like buzzing.
I would report it to the maintenance guy at least. Could be a fire hazard.
Have you removed the cover? Examined the inside of the panel?

You probably shouldn’t as you are renting if you have not already.

Yeah just report it, as it’s your life we are talking about here.

yea, i resisted opening it. no insurance inspecting my own house.

landlord seems reasonable, ill just let him know im concerned about it

Sounds like a defective CB to me


If it’s a loud buzzing… it needs to be checked – from sizing of the components to actual load from the AC. It’s trying to trip and the question is why. It could be a failing breaker like Mr Goldenberg has stated.


What brand is it?

There’s also an unlabeled 70 amp breaker, I’m just realizing…

Circuit directory incomplete

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oh for sure, but like i said before, this is my own condo rental and not an inspection. I’m not going to give my landlord a list of everything I’d normally write up

I’d just let your landlord know what you are hearing, and that you’re concerned about something catching on fire. I’m with others it sounds like it is a bad breaker or loose connection, either is bad.

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yea, done. thanks for all the help!

A short buzz or hum can occur when current is first run through a breaker. Typically the buzz will be short or become a faint/slight hum.

4 Reasons Your Circuit Breaker Panel is Buzzing.

You can report your observation and refer, but I would move on.

Hope that helps.

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Respectfully, Once again to the whole group. We are hired and paid as Home Inspectors, not as Master Electricians, nor Electric Contractors. I personally hold a BSEE degree and over 40 years of field engineering experience (rights & wrongs) but in this case, and to restrain myself to the Home Inspection Minimum Standards of Practice, as well as to cover my legal liability shoulder, I will ONLY Note: Circuir Beaker Buzzing noise Noted during inspection. Recommended further evaluation by licensed Master Electrician or Contractor.” I don’t know how much are you charging for this inspection, my flat common rate is $399 and does not include electrical circuit analysis. I am not trying to impress anyone with my knowledge of HVAC or A/C Compressor starter Capacitor behaviors.
Feedback most welcome.


I call this “Staying in my lane” and I agree with you. Background knowledge will obviously make us all better inspectors, but it is important to resist the urge to do to much. Identify a defect and report what you see.

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In this case it is the guys own house, condominium, not an inspection he was performing. So most of us were just giving him some advice.

But you are correct we shouldn’t try to analyze the exact cause.


The buzzing on the breaker are the magnetic parts for short circuit. I would change the breaker.
I am not an electrician but have been selling breakers for 35 years