Mystery Breaker Trip
Mystery Breaker Trip
(OP)
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?
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?






RE: Mystery Breaker Trip
"Venditori de oleum-vipera non vigere excordis populi"
RE: Mystery Breaker Trip
Bigbillnky,C.E.F.....(Chief Electrical Flunky)
RE: Mystery Breaker Trip
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.
RE: Mystery Breaker Trip
RE: Mystery Breaker Trip
Also, maybe the breaker is bad.
RE: Mystery Breaker Trip
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"
RE: Mystery Breaker Trip
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.
RE: Mystery Breaker Trip
Fab test jig using 7.5k? 30W [Ohmite F30J7K5] fixed resistor in series with a 5k? 25W [Ohmite RHS5K0] pot