Breaker making noise before tripping

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Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC
I was working on a short circuit today on a 3 phase 480 volt circuit. I thought I isolated the short and reset the breaker.


I heard a humming almost growling noise when the breaker closed for about 30 seconds. I am assuming this was vibration from excessive current flowing through the solenoid inside the breaker? The breaker opened shortly thereafter.

Is that normal? I've certainly have never heard that before. Should I plan on changing out the breaker or wait and see.

Its an Square D PowerPact HG 060 HGA36020YP. Pretty sure its thermal magnetic.
 

mike_kilroy

Senior Member
Location
United States
That noise sure can be unsettling! I've heard similar from breakers... first time when I was about 10, helping my dad with a breaker issue... he reset it, had panel cover loosely back on when it began very loud growling. He quickly stuck his finger thru the door pull ring and yanked it open. It did but the end of his finger flew past me where it sliced off from ring against sharp door edge! 50 years later and I still get anxious if I hear a breaker make noise!

Sent from my SM-G900V using Tapatalk
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
There is no "solenoid" in a breaker that would make noise. The mag trip might be sort of like a solenoid, but would not hold in for 30 seconds. As the others said, it's more likely the cables rattling in the conduit from the high current, because the magnetic fields in those conductors try to push away from each other.

First time I encountered it I almost had to go home and change pants...

The second time was at a sawmill on a 500HP starter for a gang saw where there was a loud banging sound from the starter cabinet. I knew what it was, but nobody believed me. Opened the enclosure door and turned it on, the unstrapped 500MCM conductors danced around in there like spaghetti.
 

Tony S

Senior Member
The second time was at a sawmill on a 500HP starter for a gang saw where there was a loud banging sound from the starter cabinet. I knew what it was, but nobody believed me. Opened the enclosure door and turned it on, the unstrapped 500MCM conductors danced around in there like spaghetti.

I had the same on a similar sized motor. Somebody in their infinite wisdom had removed all the strapping from the conductors to make the work they doing easier. They didn’t put the strapping back when they had finished.
 

kwired

Electron manager
Location
NE Nebraska
If it lasted for 30 seconds, you either have a relatively high impedance fault or low available fault current because of higher impedance in the circuit - long circuit run, small conductors, smaller capacity source, combinations of all of those will contribute to that happening. Higher impedance means less current flows during a fault and it takes more time for the overcurrent device to respond, if it is taking 30 seconds your device is likely tripping on thermal overload rather then magnetic trip because the current level is not high enough to get into magnetic trip range.
 

Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC
It is good that you have never heard that before.

Let us know what you have found to be the problem, BEFORE you test the breaker again.


Replaced the shorted wiring in the conduit and closed the breaker. Worked like a charm.

Thanks everyone for their posts. Nothing conclusive about the breaker noise. Might have been wire whip. Conductors were burned in half.
 

kwired

Electron manager
Location
NE Nebraska
Replaced the shorted wiring in the conduit and closed the breaker. Worked like a charm.

Thanks everyone for their posts. Nothing conclusive about the breaker noise. Might have been wire whip. Conductors were burned in half.
When you have high level of current flowing there is higher magnetic fields around conductors, including the conductive components in the breaker. You get noise from conductors in raceways and even from breakers during motor startups at times.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
There is no "solenoid" in a breaker that would make noise. The mag trip might be sort of like a solenoid, but would not hold in for 30 seconds. As the others said, it's more likely the cables rattling in the conduit from the high current, because the magnetic fields in those conductors try to push away from each other.

First time I encountered it I almost had to go home and change pants...

The second time was at a sawmill on a 500HP starter for a gang saw where there was a loud banging sound from the starter cabinet. I knew what it was, but nobody believed me. Opened the enclosure door and turned it on, the unstrapped 500MCM conductors danced around in there like spaghetti.

I disagree. The mag trip element acts the same as a solenoid and can make a humming noise based on the amount of current flow and as the current increases it can "growl." As stated by Kwired in post 7 this happens when the current level is just below the mag trip point and the breaker eventually trips by the thermal element.
see the explanation here:
http://www.tpub.com/neets/book3/8j.htm
 
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