Help - 1200A Electronic trip circuit breaker Tripping

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Sparky2791

Sparky2791

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Northeast, PA
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Electrical Design
Have a project with a 1200A Eaton main circuit breaker 120/208V 3 phase in a meter stack with nothing but thermal magnetic circuit breakers down stream. The main circuit breaker keeps tripping and no one can figure out why. There was no coordination study completed for the project. Since we are not coordinating with any other electronic trip breakers downstream, largest breaker downstream is a 200A. Would the settings for the 1200A breaker be best set at maximum levels. In this type of set up what determines the settings for the breaker?

Also heard that since it is located outside there is the possibility that the leads on the CT's used for these settings can corrode and cause continuous nuisance tripping of this breaker regardless of the settings. Breaker is only about 1 1/2 years old. My only other thought is to individually meter each stores main panel to determine if a faulty piece of equipment is causing the problem. Any suggestions?
 
LibertyEngineering said:
Have a project with a 1200A Eaton main circuit breaker 120/208V 3 phase in a meter stack with nothing but thermal magnetic circuit breakers down stream. The main circuit breaker keeps tripping and no one can figure out why. There was no coordination study completed for the project. Since we are not coordinating with any other electronic trip breakers downstream, largest breaker downstream is a 200A. Would the settings for the 1200A breaker be best set at maximum levels. In this type of set up what determines the settings for the breaker?

Also heard that since it is located outside there is the possibility that the leads on the CT's used for these settings can corrode and cause continuous nuisance tripping of this breaker regardless of the settings. Breaker is only about 1 1/2 years old. My only other thought is to individually meter each stores main panel to determine if a faulty piece of equipment is causing the problem. Any suggestions?
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You should have done the coordination study.
I've been there and got slapped in the face with a problem like that. Ours was a 3200A main PCB and the biggest feeder breaker downstream was just a 600A MCCB. A fault on that 600A feeder caused the 3200A main breaker to trip ahead of the 600A circuit breaker. The analysis results told us that the fault current level was high enough as sensed by the main breaker ETU and that 600A's instantaneous trip setting was longer than the trip time of the main breaker. When we plotted the TCCs, the 3200A and the 600A, curves crossed at the fault point level.
 
If nobody did a coordination study, then probably nobody adjusted any trips on the breaker. They come from the factory set to minimum. So the long-time-pickup might be set as low as 600A!
 
JoeStillman said:
If nobody did a coordination study, then probably nobody adjusted any trips on the breaker. They come from the factory set to minimum. So the long-time-pickup might be set as low as 600A!
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The Long Time should be factory set at the rating you purchased. The other settings would be at minimum.

By default many, if not most, 1200A and larger breakers are shipped with Ground Fault even though it is not required on 208V systems. The factory minimum settings would not even coordinate with something as small as a 30A breaker.

Pay for a coordination study.
 
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JoeStillman said:
If nobody did a coordination study, then probably nobody adjusted any trips on the breaker. They come from the factory set to minimum. So the long-time-pickup might be set as low as 600A!
Click to expand...
There are situations where the installed breaker does not have provisions for adjusting instantaneous trip settings/ fixed. The solution we did for our past problem was to have the 600A CB replaced with a better unit that could coordinate with the main breaker.
 
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