Why is breaker tripping?

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lfloyd

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Is there anything that can occur on the line side of a breaker that would cause it to trip?I have a situation where an 800 amp main in a 480/277 service is tripping where there is no evidence of overload or ground fault. Some are trying to blame the utility company or an emergency generator.
Is that a possibility or would the absence of overload and ground fault/short circuits indicate a faulty breaker?
 
Does it have magnetic trip adjustment? Does it supply motor(s) that may have high enough starting current to trip it - that is part of what magnetic trip adjustment is there for if it has it.
 
No magnetic trip adjustment but it does feed several large motors.
I'm told everything on the load side of this installation has been thoroughly checked out and the blame is being directed to the line side of the main.(utility power or generator)
How can you trip a breaker from the line side?
 
A couple months ago on a weekend, I reset a 800A main in the absence of any measurable fault or any sign of overload (all workers off for the day) .

A couple of hours later the main tripped again and fortunately the 30A breaker supplying the faulty humidifier tripped as well. When the HVAC system called for humidity, the contactor closed in on the faulty heating element.

I would not look upstream for your fault. The fault may be hidden from you by a contactor and could be brought in again. It could be a needle in the haystack.
 
jeremysterling said:
A couple months ago on a weekend, I reset a 800A main in the absence of any measurable fault or any sign of overload (all workers off for the day) .

A couple of hours later the main tripped again and fortunately the 30A breaker supplying the faulty humidifier tripped as well. When the HVAC system called for humidity, the contactor closed in on the faulty heating element.

I would not look upstream for your fault. The fault may be hidden from you by a contactor and could be brought in again. It could be a needle in the haystack.
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Speaking of HVAC systems, I find a lot of two stage units that during hot weather like we are having kicks in that second stage, and since the compressor hasn't been run a lot, ends up locked up and tripping the main if the settings are low. Just something else to consider, especially if it trips during the hottest part of the day.
 
Has there been any monitoring of voltage and current, what are conditions at trip time, what is peak demand, is there significant amounts of harmonic currents present - do the large motors have variable speed drives, are they started across the line, any heat building up in a termination to the breaker in question - line or load side. There is a lot of possibilities, you said everything was checked out, yet you did not tells us what checks were done, so we have no idea just how thouroughly it was checked out.
 
lfloyd said:
...an 800 amp main in a 480/277 service is tripping where there is no evidence of overload or ground fault.
Click to expand...
Have checked the line voltage when the breaker tripped? May be the breaker provided with any under voltage relay is tripping on low voltage.
 
lfloyd said:
Is there anything that can occur on the line side of a breaker that would cause it to trip?I have a situation where an 800 amp main in a 480/277 service is tripping where there is no evidence of overload or ground fault. Some are trying to blame the utility company or an emergency generator.
Is that a possibility or would the absence of overload and ground fault/short circuits indicate a faulty breaker?
Click to expand...

You need to provide much more info for us to help, otherwise we are guessing. Could be several things on the line side like a UV relay but not likely on such a small breaker. What type of breaker and trip unit? What has been checked to say no evidence of overload or ground fault?
 
I'll put it this way:

The chances that it is something on the LINE side causing ONLY THIS BREAKER to trip are far far slimmer than something on the LOAD side. If you had for example a grid glitch that caused a brief outage and if it came back on almost immediately, and if you had some big spinning loads, then if their motors had not had time to collapse the magnetic fields, the regen from those big spinning loads that can occur because the restoration of power is at a different frequency than the regen can cause a severe transient that can trip the magnetic trips of the breaker. Notice there are a lot of "ifs" in there and by the way, you could STILL consider this a load problem, because all you have to do to fix it is to not allow loads to stay on after an outage.

Or how about this: the likelihood that the breaker is DOING ITS JOB and preventing a fire because of some yet undiscovered but perfectly plausible issue on the load side are far greater than it being defective or getting fooled by some "phantom" even on the line side.

Before wasting a lot more time, I'd find out if a coordination study was ever done. If it was, then immediately check ALL other protective devices down stream of this breaker to make sure they are EXACTLY as depicted in that study. The one that is not the same or the one that is new and not included is the first place to look for undiscovered problems. If there was NO coordination study done (as I suspect), then that may be problem #1. You may have a down stream protective device that is set to trip at a level higher than the setting of this breaker. That's exactly what a "coordination" study prevents, it's intended to make sure that protective device settings are coordinated so that faults are cleared at the lowest (closest) possible level.
 
Jraef said:
I'll put it this way:

The chances that it is something on the LINE side causing ONLY THIS BREAKER to trip are far far slimmer than something on the LOAD side. If you had for example a grid glitch that caused a brief outage and if it came back on almost immediately, and if you had some big spinning loads, then if their motors had not had time to collapse the magnetic fields, the regen from those big spinning loads that can occur because the restoration of power is at a different frequency than the regen can cause a severe transient that can trip the magnetic trips of the breaker. Notice there are a lot of "ifs" in there and by the way, you could STILL consider this a load problem, because all you have to do to fix it is to not allow loads to stay on after an outage.

Or how about this: the likelihood that the breaker is DOING ITS JOB and preventing a fire because of some yet undiscovered but perfectly plausible issue on the load side are far greater than it being defective or getting fooled by some "phantom" even on the line side.

Before wasting a lot more time, I'd find out if a coordination study was ever done. If it was, then immediately check ALL other protective devices down stream of this breaker to make sure they are EXACTLY as depicted in that study. The one that is not the same or the one that is new and not included is the first place to look for undiscovered problems. If there was NO coordination study done (as I suspect), then that may be problem #1. You may have a down stream protective device that is set to trip at a level higher than the setting of this breaker. That's exactly what a "coordination" study prevents, it's intended to make sure that protective device settings are coordinated so that faults are cleared at the lowest (closest) possible level.
Click to expand...

Agree 100%, especially

The chances that it is something on the LINE side causing ONLY THIS BREAKER to trip are far far slimmer than something on the LOAD side.
 
One last point. In case UV relay is provided in the breaker, check whether it has any time delay arrangement also. The breaker may be tripping due to wrong setting of the time delay of UV relay.
 
As others have said, a load side cause or faulty breaker is much more probable than a line side cause. One possible line side cause is capacitor switching transient if the breaker is tripping on ground fault and the GFI is monitoring the neutral to ground bond. See this link for more information.
 
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