3000 amp versa trip breaker keeps tripping.

[iwire]

Looking for suggestions here.

The company has a customer with a 3000 amp 208Y/120 service. The breaker is a GE with a Micro-VersaTrip unit controlling it.

The breaker has tripped a number of times recently and like all good customers they just keep resetting it.:roll:

In looking at the info I can get from the VeraTrip it shows it has tripped 7 times on the short term pick up with the last trip happening with a current of 17.1 kA on phase C.

There are only two feeders from this breaker that I feel could allow a 17.1 kA fault, one is a 700 amp feeder to a stage dimmer rack, the other is an 800 amp feeder to a chiller.

The breaker holds fine for weeks at a time, trips, gets reset and holds for weeks again.

How can I find the cause of this tripping





?

 

[cdslotz]

What type of breakers are the 700 and 800A?
Is there a copy of the original coordination study?

 

[ron]

A 17kA fault would likely have some burn marks somewhere along the feeders or terminations.

Since the trips occur so inconsistent, maybe start by having primary injection tests done for the breaker. Make sure it is working properly.

 

[petersonra]

Hang some kind of recording device(s) on the downstream branch circuits and see which one is the source of the short circuit.

 

[iwire]

What type of breakers are the 700 and 800A?
Is there a copy of the original coordination study?

Just the bottom of the line breaker with one adjustment each that is maxed out.

Yes, there is a study and the setting of the main seem to match.

A 17kA fault would likely have some burn marks somewhere along the feeders or terminations.

That was my thought as well, particularly after the fith or sixth time.

Hang some kind of recording device(s) on the downstream branch circuits and see which one is the source of the short circuit.

I cant get them all, right now I have one on this breaker.

 

[ATSman]

I would first confirm that it is a legitimate fault using a 3 phase recording device as suggested. Make sure the meter is fast enough to record a Short Time or Instantaneous fault (less than 10 ms.)
If nothing is recorded during the next trip then it sounds like nuisance tripping caused by a faulty trip unit that can be replaced.
We had a similar situation with the same type of breaker. The breaker was tripping and showed a GF LED indication on trip unit. Our recordings showed no downstream GF, we replaced the trip unit, end of problem.

BTW, as stated in other posts, high current testing WILL ONLY PROVE that a breaker trip unit is functioning properly at different current levels and trip times. It WILL NOT PROVE that a trip unit WILL NOT TRIP due to nuisance tripping (miss-firing.) If this is the case then replacement is the only solution.