Main Distribution Panel with a Loud Hum

[ATSman]

Breaker Humming

Breaker Humming

I'll ask again. What is ACTUALLY humming? Is the breaker vibrating? Is the lug vibrating? I think that we can all agree it's humming because of an overloaded panel or circuit, but what is physically happening when the hum occurs?

Thanks guys.

Working around circuit breakers for 35 yrs, this is my take on it. Since the main breaker is of the older vintage it is most likely a molded case frame with a thermal-magnetic trip unit. The thermal element reacts (slow trips) to overcurrents in the lower ranges (300%) while the magnetic element (fast trips) reacts to high currents (short circuits of 800-1200%.)
The humming is coming from the magnetic element (electro-magnet) of the trip unit. The greater the load current, the greater the magnetic field on the magnet........the louder the hum This is the same hum you hear coming from a starter contactor in an MCC bucket.
If the breaker is the larger air frame type then the same reasoning applies since they also use the manetic element in their trip units. Breakers with the newer type solid state trip units do not hum. They employ CT's that measure the load currents and electronics to shunt trip the breaker when the current exceeds rated levels.
I have had data center customers replace their breakers with the solid state version because the humming sound bothered them:smile:

 

[realolman]

......while the magnetic element (fast trips) reacts to high currents (short circuits of 800-1200%.)
The humming is coming from the magnetic element (electro-magnet) of the trip unit. The greater the load current, the greater the magnetic field on the magnet........:smile:

I like that... that sounds reasonable to me.

 

[GUNNING]

woo hoo!! Change order time!! $$$chiching$$$

 

[cowboyjwc]

I don't know, but I'm gonna take a WAG.
When current flows through a conductor, it causes a force perpendicular to the wire. I suppose that force could cause the conductor to move enough to cause a sound... But again that's just a WAG... I really don't know.

That's what I was thinking.

 

[zog]

The humming is coming from the magnetic element (electro-magnet) of the trip unit. The greater the load current, the greater the magnetic field on the magnet........the louder the hum :

My thoughts exactly. Did it go away when you replaced the breaker?

 

[danickstr]

50k lines hum

 

[zog]

50k lines hum

From domain alignment, just like transformers.