Major Issue with UPS

[Anonymous user]

OK, so my question is not necessarily about the UPS itself but trying to pick the brains of people in the field to get some ideas on how my issue happened. We were having a regular maintenance on a 50kva UPS. The unit was put into bypass for 15 minutes while some of the maintenance was being done. Before the technician put it back into UPS mode, my 2 IT rooms being fed through that UPS shutdown. The main 225 amp breaker feeding the UPS tripped and my day got a hell of a lot longer. This was a major issue because these 2 rooms is essentially our data center and houses everything. So the technician said he didn't do anything and that he was in bypass, which it was, and that he wasn't responsible for what happened. We checked the main breaker which was tripped, flipped it back, everything came up, and then he flipped the UPS back into UPS mode. So he was saying a couple of different things like it could have been a spike from some equipment and that the main breaker which has never been service couldn't handle the spike and tripped.

No breakers tripped on any outlets, only the main breaker so that's why I'm confused because every outlet has it's own breaker, plus a main breaker within that panel which I'm assuming these two breakers would have tripped first before the main feeder. I'm trying to get some idea's on what type of event could have caused this breaker to trip. Could it have been something the tech did inside the unit? Would he have seen a spark or something? Could it have been something like equipment surging or something like that?

[BillP]

What are the Voltages of UPS Output ?
What is the Mains Voltages?
If there is difference between Mains and UPS output Voltages then your Main Breaker will trips some time (Not trips at every Outage or Battery Shifting)
when you shift UPS on Bypass Mode breaker trips due to difference of Voltages between UPS Output and Mains Volts.

[Anonymous user]

What was the UPS loading before it was bypassed?

Also there are two things that are different. 1) UPS being internally bypass 2) UPS being externally bypass.

Externally bypass is always the safest way if you want to work on the UPS.

Just a separate note that all electrical connections will become loose over time and heat. There could be a loose connection somewhere that could cause the spike.

[BillP · Accepted solution]

Good day,

if the 225A breaker feeding theUPS trips, the no matter what the voltage is, you're in trouble. and big time. now I do not understand exactly what do you mean by "UPS IS BYPASS". if the UPS tech had done something wrong, the UPS would have not started up again( I guess the UPS is up and running) and you would have seen damages, sparks, you name it. Get yourself and engineering firm to inspect your electrical network for that part.Somebody must have done a huge short to trip the breaker. Equipements in your room are ok, no damages?

M

PS
As to see if there are problems in your room, you should check the UPS event log for overloads...still something is rotten here...it does not make sense....!?!?!?

Message was edited by: mihail@cpeinc.ca