I've got a Cutler Hammer C-series breaker that trips for no apparent reason. It's a RDC frame, 1600A, with 310 Digitrip, and GFEP.

6 months ago it tripped 2 or 3 times over a few days. We thought it might have something to do with when different equipment came on-line but couldn't find a problem. The problem went away on its own.

About 2 weeks ago, it tripped again. and has done so 3 more times, including today. Can happen at any time during the day but we don't think it's happened over night. Monitoring equipment on the switch gear shows that we've never had a current draw of more than 700A so it seems like it must be tripping due to a ground fault and not over current. Ground fault interrupt rating is 200A.

I would think we'd notice a 200A ground fault somewhere but nothing stands out. We reset the breaker and it's fine for a few days.

We've checked for current on the ground path and we have seen a fraction of an amp that comes and goes but we're chalking that up to coupling and haven't seen anything near 200A.

I've got the manual for this breaker and I'm going to read through it tonight but I'm hoping somebody has seen this before and can point me in the right direction. If it is a ground fault. I don't know how we're going to find a ground fault that shows up for a few seconds every few days.

Any insight is appreciated.

Thanks

That is too large a breaker to casually switch out. Perhaps the manufacturer has some resources available - a visit by their rep, perhaps?

Last time I had that problem it was a faulty A/C unit. Rod

I've seen that also, 800A.
When the 2nd compressor would kick on,so that made it random,since 2 comps weren't always needed.This was an older RTU that did not have an alternator in it.
It would bypass the units OCPD and trip the main distribution.

Is this a 480Y277 volt system?

If so trivial ground faults on ANY 277V lighting circuit will give you trip level currents.

BTW that GFCI trip at the MAIN will not normally trip the branch circuit -- beware.

Derived circuits -- ie those run off of an isolating transformer -- are not going to be at issue; typically 480 delta to 208Y120.

The reference to a 200A GF interrupt rating should NOT be taken to mean that 200 amps has to be shorting to ground before it trips. Instead, that rating means that the equipment can tolerate such shorts and trip correctly. GF protection that only kicked in over 200 instantaneous amps wouldn't be any kind of life-saver for anyone or anything.

Pinched hot conductors, especially in site-lighting, have been the normal culprits for me. In these winter months photo-cell triggered contactors might have your short appearing with a passing cloud.

Concentrate on 277V to ground circuits.

If it's a Digi-Trip, you should have a flag showing ground fault, instantaneous, short time, or long time trip. The flag shouldn't clear until you press the reset button.
Joe

I forgot to ask if the breaker had a UV trip option installed. Also, if the breaker hasn't been maintained for a while, it's probably time to rack it out and hook it up to the test set. Remember to check all 3 channels. I've seen breakers not meet spec until the dials were exercised.

I had a 1600A 480/277 GE trip out suddenly and also for the 200A faults. In Sept. I adjusted the tolerance dial small screwdriver knob on face of CB and "knock on wood" it hasn't tripped off yet.

Time to hook up a power quality analyzer and start recording data. If the breaker has not been calibrated in the last 3 years, might want to look at that, too. Can it support secondary injection testing?

Steve.,

You did bring up a good poing with secondary injection as far from my experince the secondary injection is done best when the 1600 amp brekaer is drawed out { removed } and do the test and really one thing I will addressed to OP is get the power monitor and record for next couple days to see if the surge or dip of voltage show up ditto with current drawage.

Now for ground fault you have to check it very carefully with it I will not set the GFI over 200 amp the most any higher you have to get the RFI from the manufacter to advoid any issue with the set up.

I have see plenty 277v ground fault show up from time to time and you will have to look at the 277 lighting circuit that useally most common curpits.

Merci,Marc

A 277 GF caused by a bad ballast within 'older' lighting fixture caused a 2000 amp main to go out on GF. Now, that was one very unhappy facility mgr. Tracking it down was brutal; no tripped lighting CB. We went thru all the feeders initially. On-site the next day, the fried ballast was discovered. BTW, none of the 20 amp lighting circuits were tripped, and they all tested OK. The ballast was 'open' on the line feeds, and open on the output.

John,
Was the ground fault trip setting ever set after the main was installed? They often come from the factory set at the lowest setting and it is not uncommon to have the main trip on ground fault without tripping the branch breaker when the main is left at the factory setting.

The main was tested and 'set' by a factory tech from Siemens after initial install & energization. Factory tech returned after this incident & checked; all was within previously set range.