GCFI Breaker

[tw/nci]

We have a facility with a 1600amp squareD circuit breaker, that has the ground fault setting at 800 amps. We are experiencing intermittent trips on ground fault. We have checked out all of our motor loads, and tried to locate the problem. Would anyone have any tips on how best to locate a problem like this. Thanks for your help.

 

[brian john]

You really should find the issue prior to closing the CB on into a fault. BUT I also know in the real world this step is overlooked, especially with GFP issues.

2nd this IS NOT A GFCI circuit breaker the CB had Ground Fault Protection GFP.


YOU CHECKED OR YOU MEGGERED? You need to megger feeders and motors.

Is there any current on the main neutral to ground bond?

In order of tripping.

1. Careless electricians/construction workers during construction or remodeling shorting 480/277 vac circuits.
2. A defective device you are missing (see this all the time) You checked everything BUT the one item you overlooked.
2. Defective relay or sensor, This can be tested by a company with the equipment and knowledge.
3. Neutral ground issues as noted above.

If all else fails utilize a line disturbance analyzer monitoring phase, neutral and neutral ground bond a PIA but this will help determine if the issue is intermittent with the relay or sensor. If it is a fault move the CT to the load CB's, this can be time consuming but......

 

[hillbilly1]

If the ground fault main can be reset without it tripping again immediatly, meggering will not do much good because the fault is likely contactor controlled which will not show up until the load is energized. A likely load that will cause this is an A/C unit, probable second stage compressor because they generally are intermittent loads.

 

[tw/nci]

I currently have a Dranetz Power Visa monitoring the load side of the breaker monitoring all 3 phase conductors voltage and amperage but due to a broken current probe can only monitor voltage on the nuetral (grounded conductor) I am not picking up any excessive current draw on any of the phase conductors, or swells prior to the trip. Is it possible this could be an interference problem with the breaker? Or would you monitor the circuit differently

 

[brian john]

If the ground fault main can be reset without it tripping again immediatly, meggering will not do much good because the fault is likely contactor controlled which will not show up until the load is energized. A likely load that will cause this is an A/C unit, probable second stage compressor because they generally are intermittent loads.

Thats why we are professionals, we go beyond contactors and thermostats. A
complete inspection of the distribution system.

HVAC units and cooling towers, VAV boxes are the real PIAs

 

[brian john]

I currently have a Dranetz Power Visa monitoring the load side of the breaker monitoring all 3 phase conductors voltage and amperage but due to a broken current probe can only monitor voltage on the nuetral (grounded conductor) I am not picking up any excessive current draw on any of the phase conductors, or swells prior to the trip. Is it possible this could be an interference problem with the breaker? Or would you monitor the circuit differently

BAD CB, what type of CB?

 

[tw/nci]

the breaker is a squareD MP16H2

 

[brian john]

OHHHHHHHH! for my money I'd bet on the CB..
Cover all your bases on this BE SURE you have checked every possibility,

 

[hurk27]

To use a monitor to find a GFP problem you would want to monitor the current on the EGC down stream from the breaker, not the neutral, usually I put a current clamp on the MBJ next to the GFP current transformer, any one will do if the neutral clamp is bad, use the one for C phase. but I'm with Brian on the breaker being bad.

If it is indicating a GF when it trips, check the ground current transformer, and conductors to it, and connections to the trip unit.

 

[brian john]

99% of the time when I get to the point of frustration as I/we cannot locate the fault and resort to a monitor it is the CB, GFP relay or the CT.