Buzzing 150 amp breaker Square D circa 1967

[RRonke]

Customer called about buzzing sound from main breaker panel with underground service from remote pedestal feeding a basement panel. Main breaker sometimes sounds like a ballast with a few loose laminations. By tapping on breaker I either start the buzzing noise or cause it to stop. All external screws and lugs are tight. Square D is behind on building these and it will take about a year to get a replacement. Does anyone think this is an indication of future failure or potential hazard?
An interesting side note: When I opened the panel about a quart of fine dirt like you would find around ant hills started pouring out of the panel. Service wires feed in from the bottom so only the bottom two breakers had on of the fine dirt on them but the rest of dirt was piled up at panel bottom (no environmental seal). Thanks for any thoughts.

 

[Jraef]

ANY debris that gets lodged in between the contacts of the breaker will cause it to buzz. If it goes away when you tap it, that’s almost a confirmation of that issue.

Now that this has begun to happen, you likely have some carbon built up on the pole faces of those contacts and this will continue to get worse. There is not a lot that can be done; Molded Case Circuit Breakers are not designed to be disassembled and cleaned. It should be replaced ASAP. But given the situation, I would be looking for even a used replacement (although that’s often a craps shoot too) or at the very least, remove that breaker to a workbench, spray the heck out of the contact area with contact cleaner (if you can get the spray tube inside), then do a periodic thorough cleaning of the panel to remove that dust before it gets in there again.

 

[ptonsparky]

Do a FOP test across the contacts.
Turn all the loads off. Cycle the breaker several times. Turn loads on and repeat ,FOP.

 

[RRonke]

ANY debris that gets lodged in between the contacts of the breaker will cause it to buzz. If it goes away when you tap it, that’s almost a confirmation of that issue.

Now that this has begun to happen, you likely have some carbon built up on the pole faces of those contacts and this will continue to get worse. There is not a lot that can be done; Molded Case Circuit Breakers are not designed to be disassembled and cleaned. It should be replaced ASAP. But given the situation, I would be looking for even a used replacement (although that’s often a craps shoot too) or at the very least, remove that breaker to a workbench, spray the heck out of the contact area with contact cleaner (if you can get the spray tube inside), then do a periodic thorough cleaning of the panel to remove that dust before it gets in there again.

Thanks Jraef for your suggestions. At least I can give the cleaning a try and will look for a used breaker and will clean that too before installing if I find one.

 

[RRonke]

Do a FOP test across the contacts.
Turn all the loads off. Cycle the breaker several times. Turn loads on and repeat ,FOP.

Simple and good idea. Maybe some of the problem on the contacts will get knocked off. Thanks for the help!

 

[RRonke]

Do a FOP test across the contacts.
Turn all the loads off. Cycle the breaker several times. Turn loads on and repeat ,FOP.

Is the FOP just measuring the resistance across the contacts with a multi-meter? I can't say I have any experience doing a FOP.

 

[ptonsparky]

Is the FOP just measuring the resistance across the contacts with a multi-meter? I can't say I have any experience doing a FOP.

Use meter capable of millivolt AC measurements and check the voltage drop across the contacts. Use a hair dryer or similar as as load. VD should be comparable.

 

[ptonsparky]

Fall of Potential.