Mystery Breaker Trip

[controlnovice]

Just received a call from one of our plants. PM explained that 3 or 4 breakers trip out to the point that they would not reset. These were replaced with new breakers of the same model (name withheld to protect the inoccent) approximately 6 months ago and have not failed since. He recently had a different breaker (same panel, same type/style breaker) begin tripping frequently. He disconnected the heat trace circuits on that breaker and it still tripped under no load.

This is for heat tracing and the breakers are 480/277V, 30A with 30mA GF. They are two pole with 277V on them.

My first thought was ground fault, until he said he disconnected the cable and the breaker still tripped.

Any ideas?

 

[jraef]

Condensation in the breaker box?

"Venditori de oleum-vipera non vigere excordis populi"

 

[bigbillnky]

jraef maybe on the right track. Did they try to remove and reseat the breaker or relocate it in the panel? Had this breaker tripped lately under a fault? You did not mention the brand, and "cheaper brand" breakers could be the cause of the problems you are having.

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[controlnovice]

Condensation was a guess of mine too. I asked him to investigate that further.

Would a small heater in the panel help if that's what we suspect? This isn't a breaker box, it's a NEMA panel.

 

[Alex68]

Possible harmonic disturbances?

 

[Alwaysexciter]

It could be Vibration. I had the same problem. Some breakers styles seem to be more prone to this then others. The ones I had were GE tri-pack MCB between 100 amps and 400 amps rated. Do you have any rotating equipment that could cause this.

Also, maybe the breaker is bad.

 

[jraef]

Condensation occurred to me because you said they were GF circuit breakers, and you had disconnected the load entirely.

Yes a small enclosure space heater is a good idea, espcially if the ambient temperature ever drops below the dew point, 40 deg. F. That is all it would take for internal condensation to form and provide a path to ground for the GF sensor to pick up. You can buy pre-made heaters with built-in thermostatic switches set to 40F, or you can buy a strip heater and a separate t-stat and do it yourself. Neither option is very expensive and the pre-made ones are simpler to install.

"Venditori de oleum-vipera non vigere excordis populi"

 

[DanDel]

I had the same issue at a customer's facility with brand-new Square D GF C/Bs. When a particular piece of equipment was plugged in, some C/Bs would trip in the same panel that did not feed the same load. As a matter of fact, some C/Bs in a panel in a different room would trip, and they didn't have any load wires connected!
I monitored the circuitry with an oscilloscope and found a current pulse into the neutral (apparently caused by a charging effect from the power supply of that particular device which was being plugged in) was causing the trips even though no load wires were connected.

 

[busbar]

 
Fab test jig using 7.5k? 30W [Ohmite F30J7K5] fixed resistor in series with a 5k? 25W [Ohmite RHS5K0] pot