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Electrical Wiring

QO Circuit Breaker buzzing under load

Bruce in Northern Virginia

9 years ago

I have a 200 amp Square D panel with QO breakers. Due to a kitchen renovation I am using my basement workbench as a temporary kitchen area. The workbench has a 20 amp circuit with two double receptacles. The 12/2 wiring and receptacles are only about 6 months old, but I don't know the age of the breaker in the panel. The wiring only goes across the basement about 25 feet, and there is nothing else on this circuit but the two workbench receptacles.

This morning the drip coffee maker was plugged in to one receptacle ( I don't know what the coffee maker draws after it stops perking.) and I plugged a 1500 watt hot plate into the 2nd receptacle and turned it on. I was close enough to the panel to hear the breaker start humming under load, and it then stopped after about 15-20 seconds.

Does this mean I have a breaker that may fail in the near future, or does the humming just mean I'm near the max amperage on the breaker? I think this breaker is an old one they reinstalled during the heavy-up, so I don't know its age.

Thanks,

Bruce

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Comments (5)

btharmy
9 years ago
So, you have a 1500w hot plate and a coffee maker (likely 1500w itself) plugged into the same circuit? Do the math. 3000w/120v = 25 amps on a 20 amp breaker.
ionized_gw
9 years ago
btharmy, the coffee maker draws much less power to keep the coffee warm after it is brewed.

Bruce, you were at max load in your testing regime when the hot plate was turned on. As the coil warms up resistance increases and current drops. I bet some of your other breakers buzz when a heavy load is on them. You are just not close enough to hear them talking to you.
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Bruce in Northern Virginia
Original Author
9 years ago
Thanks for the replies. It make sense that the breaker is near max amperage even if the coffee maker is just keeping coffee warm while the hot plate is running, but I've just never heard the breaker humming before.

Bruce
bus_driver
9 years ago
Can't resist the impulse for this old joke--
"but I've just never heard the breaker humming before." It doesn't know the words!
Valdemar
9 years ago
I vaguely remember going through a Siemens breaker catalog and seeing low-noise breakers there, which kind of implies that some amount of noise is normal in regular type breakers. I hear buzzing near my new Siemens panel, and I heard buzzing from the Zinsco panel it replaced.

This post was edited by Valdemar on Mon, Mar 24, 14 at 21:15

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