Burnt Breaker

[kingbambina]

Hi,

I need some help with investigating a burnt circuit breaker that feeds a compressor's motor. As you can see in the drawing attached, the voltage is 400V and a molded case circuit breaker that feeds the motor was burned at one phase only as an alarm was flagged of the motor overloading. As per the control circuit, I see that the breaker failed to open due to the overload but I cannot think of any reason why other than the phase that was damaged didn't age that well?

Any insight guys that can guide me on how to start this investigation?

Thanks

 

[retirede]

Guessing that’s an MCP which means magnetic trip only. It’s not going to trip on motor overload. It may have been undersized and/or that phase wire connection was undertorqued.

Not enough info given to say much more…

 

[ptonsparky]

Incorrect connection torque as stated. Frequently using it as a start/stop means while under load. Age. Nothing lasts forever.

Do a fall of potential across other breakers of this age, while under load. Or all of them. Might save some unexpected down time.

Safer would be a thermal scan

 

[kingbambina]

Guessing that’s an MCP which means magnetic trip only. It’s not going to trip on motor overload. It may have been undersized and/or that phase wire connection was undertorqued.

Not enough info given to say much more…

It's an ABB SACE MCCB and it's been installed since 2009. And yeah I can only think the reason for only one phase burning is that some loose connection is in there somewhere.

 

[kingbambina]

Incorrect connection torque as stated. Frequently using it as a start/stop means while under load. Age. Nothing lasts forever.

Do a fall of potential across other breakers of this age, while under load. Or all of them. Might save some unexpected down time.

Safer would be a thermal scan

You're right. We have similar breakers like this one and thermal scan might be a safe bet.