TRIPPING PENTHOUSE CIRCUIT BREAKER

[Coastalguy1]

We have a building which is 14 stories. The mechanical penthouse is located at the top of this building. It has a motor control center located in it. Periodically, the building will loose power from local power company. When power is restored the main breaker in the motor control center trips. What could be the cause of this?

 

[__dan]

If the normal running loading is high, up near the max rating, it could be the starting surge of everything starting at the same time. The main is not rated for group motor loads all starting at the same time. You would need "on delay timers" on the starter controls to stage motor load starting.

You cannot blow the main open under load too many times until the breaker is shot.

 

[petersonra]

Dan probably has it right.

I would find the largest loads and put time delays on start up for them. Its a good idea anyway, as you really do not want them trying to startup in the first few seconds after power comes back on.