1200A Main tripping

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finster1

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I was working in a restaurant and the 1200a main kept tripping instead of the branch circuits. Generator auto transfer kept tying back in...Having hard time locating source of problem. POCO Line voltage good 208v 3ph y...Shutdown main components running on three phase but still tripping....Restaurant active and needed some life line to a restaurant devices so I shut off what I could and still tripping. Even shutdown ac units still tripping. Many subpanels 400a 225a, 200a some 100a at least 10 separaTE SUB SYSTEMS. sIEMENS BREAKER 1200a main. Tryed reading to ground lines off breakers but with devices still attached and restaurant still operable kind of tough...Any suggestions. Left and told manager to continue to shutoff main 1 at a time untill he gets to the point that one of them doesn't cause a trip and that if all elkse fails maybe the shunt trip in the main was starting to fail of the shunt was being sent from the generator for some reason., but the timing of the trip usually 4 to 5 minutes after resetting made me believe it was from a faulty component in the kitchen or an ac unit
 
Is the 1200A main an electronic circuit breaker with adjustible settings for the time-current curve? I had a new building which had a large compressor that kept tripping the main. The factory setting on the main was lower then the branch breaker's curve which is why the main kept tripping.

Just because it takes 4-5 minutes to trip doesn't make me think there's anything faulty. Breakers are thermal-magnetic. The thermal part is why we don't load normal breakers over 80%. Because when you do, eventually the heat build-up in the breaker will cause it to trip. Have you used an amp probe on the main feeders and branch feeders?
 
1. Existing or new CB?
2. CB ever been tested?
3. While it is 208/120 is there GFP?
4. Are there aux trip component Phase Failure, UV relays?
5. Is there a shunt trip on the CB is this energized?
6. Defective trip unit!

And while it could be I doubt a NEW CB at 1200 amps is a thermal magnetic.
 
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With it taking 4-5 minutes before it trips, sounds like an HVAC unit with a bad compressor, they have an anti-short cycle timer that is probally delaying the restart for several minutes.
 
If a circuit breaker with a static trip OCP is defective it will trip on load pickup. and while I have no documentation (Zog Please) to backup this statement I have been told they default to the minimum settings. Or if there is a defective sensor in the CB almost any load can trip the CB depending on OCP functions.

With the CB off test all downstream devices (megger and visual), Temporary a FSS to support the customer load and test the CB, primary and secondary injection testing. Order new CB next day air.
 
With GE breakers with rating plugs, if the plug is removed or defective I think it trips at something like 10% of the breaker rating, but don't quote me on that, been a while since I've dealt with GE #$*@
 
brian john said:
If a circuit breaker with a static trip OCP is defective it will trip on load pickup. and while I have no documentation (Zog Please) to backup this statement I have been told they default to the minimum settings.
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Depends on the type of trip unit but that is generally true. If the OP gives us more details perhaps we can help more. He mentioned it was a siemens breaker but not what type or what type of trip unit, but the Siemens STII and III default to lowest settings.
 
I did not pick up on the Siemens (GOOD TROUBLE SHOOTER I AM not).

Had a Siemens with a open CT, and another one with the CT in backwards.
 
a) Can you check the load before it trips?

b) If it has an electronic trip module, try changing it.

c) IS the breaker hot? ( Symptoms of loose connections..)

Loose connections = hot terminals= hot breaker=thermal relay nuisance trips.

cheers.
 
Had a similiar problem with an 300amp cutler hammer with a thermal magnetic trip unit. This breaker was supplying a heavy motor load and after 3 months of being installed started tripping without blowing any of the fused motor circuits. After hooking up the fluke scopemeter to try and catch the high current draw and pulling my hair out (without any luck) I proceeded to inspect the breaker. Bottom line had a loose lug on the LOAD side of the breaker from the factory. It might be a good idea if you can on a down day to fully inspect the breaker eventhough it is new you can't rule this out as a possibility.
 
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Had a similiar problem with an 300amp cutler hammer with a thermal magnetic trip unit. This breaker was supplying a heavy motor load and after 3 months of being installed started tripping without blowing any of the fused motor circuits. After hooking up the fluke scopemeter to try and catch the high current draw and pulling my hair out (without any luck) I proceeded to inspect the breaker. Bottom line had a loose lug on the LOAD side of the breaker from the factory. It might be a good idea if you can on a down day to fully inspect the breaker eventhough it is new you can't rule this out as a possibility.
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FOP Fall of Pontenial. Long before I would use a scope meter, PROBLEM RESOLVED.
 
we had a 3000 amp 480v 3/0 main breaker with microversa trip GFPE trip before in the middle of the night. the problem that caused it to trip was an air compressor motor blew and tripped the GFPE. the megger will help you find those kinds of problems pretty easily
 
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