Coordination Studies - Preview to the On-Demand Class

[@9999afshin]

Nice

[@510purple]

I work for a 3rd party testing company. I did infrared scans today and the electrician opening up the equipment for me dropped the cover onto the lugs inside the transformer and it tripped the panel feeding it. It also tripped the main breaker in the main electrical room. Why did a feeder panel trip the main?

[@Brainfiller]

Could be a couple of reasons. 1) Did the main have ground fault protection? Sometimes if it is ground fault, depending on the settings, the main may trip in addition to the feeder. 2) Higher magnitude faults can cause the instantaneous of overcurrent devices to trip. So it is possible that the current caused the feeder and the main to trip. To be sure, that would require reviewing the devices and the respective time current curves. Thanks for your comment. 3) I hope no one was hurt. That could have been disastrous. 4) NFPA 70E provides much needed guidance for safe work practices. Thanks for your comment!

[@510purple]

@Brainfiller thanks for responding. Thankfully, no one was injured. As for the main breaker, I'm pretty sure it has ground fault. And that would make sense because it was more of a ground fault than a short circuit.