Nuisance tripping 1200 amp main gfp

[chris.doyle.391]

What do the pickup frame rating and the short time trip rating mean and what should the settings be. This is a 3 phase 480 volt Ncg 1200 amp Westinghouse breaker. The the breaker has opened at lunch time with minimal draw and at night when no one was in the building. Each phase is drawing only around 40 amps. The breaker was set at 0 time delay I turned that up and the problem hasn't occurred again since. The manual for the breaker is not very clear as the only manual I can find is online and it's slightly different with the frame rating adjustment. I included a photo of the breaker.

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[chris.doyle.391]

Nuisance tripping 1200 amp main gfp

Also I'm getting 1.6 amps on the ground inside the transformer. This 480v step down transformer has no independent ground and is not mounted onto the concrete floor. Sending residual power back into the frame and onto the ground of the switch gear I was wondering i mean theoretically that could trip the gfp, right? I don't think I'm picking up residual either cause I have 1.6 amps to the panels from the ground lug and .5 amps to the switch gear.


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[templdl]

What do the pickup frame rating and the short time trip rating mean and what should the settings be. This is a 3 phase 480 volt Ncg 1200 amp Westinghouse breaker. The the breaker has opened at lunch time with minimal draw and at night when no one was in the building. Each phase is drawing only around 40 amps. The breaker was set at 0 time delay I turned that up and the problem hasn't occurred again since. The manual for the breaker is not very clear as the only manual I can find is online and it's slightly different with the frame rating adjustment. I included a photo of the breaker.

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You have provided no information on your system nor the breaker itself.
Yes, 3ph 480v breaker. Is this being applied is a 480y/277 system?
Do you have an external neutral CT?
Is there a reason as to why the settings are set lower than the max? Has there been a coordination study done to suggest the be settings be set otherwise?
If you do have an external neutral sensing Ct has it been installed correctly? There is a terminal block on the left side on the breaker with terminals 1,2,N and G. Is the CT connected to N and G?

 

[kingpb]

The Long time setting is the continuous rating of the plug; i.e. 1200A

The short time trip rating is No. setting X plug rating; i.e. 8 x 1200 = 9600A
Unfortunately, I do not see a time dial setting ofr the short time p.u. If must be fixed and you will have to determine from manual.

Looks like the Ground Fault is set at 120A with a delay of 0.5 seconds.

Are these the right settings; as stated in other post it depends on what your system is and what the short circuit study says.

 

[coop3339]

Are you sure you don't have an intermittent ground fault?

 

[ron]

The reason this type of project would have required design drawings to be signed/sealed for permit, is because the answer to your question is that it depends. Someone would have to determine those ratings from the application, there is no one answer.

The pickup frame rating is likely the ground fault trip pickup value. The short time trip is the adjustment in the regular phase portion of the tripping characteristics that is in the short time region. Look on page 3 of the link. The long time and instantaneous for this breaker are fixed values and not adjustable, which is why there is no dial for them on the breaker. http://static.schneider-electric.us...100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf