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#4653 10/06/01 10:53 PM
Joined: Jul 2001
Posts: 40
glenn35 Offline OP
I am sure that some of you have had dealings with these breakers. The one I am referring to is something like a 2000 amp GFI.

Anyhow I had a trouble call because the breaker kept tripping when they would fire up a large motor. Forget exactly what size motor but it was big. The breaker would trip on (ground fault) but one time it tripped on instantaneous(?) My first suggestion was that the motor or the circuit feeding the motor was bad or going bad. The electrician said they had meggered the motor and the circuit and was OK. They wanted to blame it on the PoCo. They said that the breaker would read line and load as far as the GFI was concerned. Just being a lineman I thought surely this thing could not read the line side but what do I know. Without the motor or hardly anything running they were pulling around 300 amps per leg(277/480). I told them that if there were a problem with the trans bank then at 300 amps it would be showing something pretty visible that would be seen from standing on the ground. Arcing or melted insulation or something.
They replaced the "brain" for the breaker but still had the problem. THey had steady voltage the whole time even when the breaker tripped. The equipment they had would record the voltage and load and who knows what else.

I haven't been back to find out what the problem was or if they had resolved it. I know they had called for a temp disconnect to replace something else to do with the breaker but don't know what the outcome was.

Any ideas what the trouble could've been?

Oh and they had mentioned that they did not have this problem until we had a severe lightning storm the day before.


#4654 10/06/01 11:15 PM
Joined: Aug 2001
Posts: 599
I don't see how they could possibly blame it in the power Co. A ground fault breaker should be oblivious to what is happening on its line side. My first thoughts while reading this were that the settings were set to low. (time and trip curves) But you say they didn't have the problem until after a lightning storm? Did anyone think that maybe the breaker is doing it's job and they really have a ground fault? You say they meggered the motor but did they megger the feed to the motor. The lightning storm could be purely coincidental and the have a break down in insulation value on the feeds. Maybe a lightning strike caused the break down. All this is speculation but maybe something to try.

#4655 10/07/01 02:30 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Since the trip unit has been replaced, it is kind of hard to blame the breaker.

Maybe it is a low tech problem. Has anyone checked the neutral & grounding system & all bondng since the lightning storm? Most power quality surveys start with the grounding system.

If the problem isn't related to grounding/bonding, I'd look for electrical noise when the motor is starting. If it is a really large motor, maybe it has a solid state starter or drive that may have been affected by lightning.

I think the only way to get to the bottom of this will be with a power line analyser or recording meters that could narrow down the search.


Few things are harder to put up with than the annoyance of a good example.
#4656 10/07/01 05:23 PM
Joined: Jul 2001
Posts: 40
glenn35 Offline OP
Yes I think that they need to do more checking. And yes it is a very large motor. The amp reading's went from around 300 A up to a whopping 1700 or 1800 A when the motor was trying to start.

And they did megger the circuit feeding the motor as well.

But you know how some just want to cast blame and not really do anything to try and resolve the problem. Either laziness or a lack of knowledge is usually the cause when this happens.

The worst to usually do this is the phone comp or cell phone comp and their cell towers. Numerous times have I made trouble calls because their equipment read that there was a voltage drop and they call in lights out. Even if the ckt just operated one time. Too lazy to send there own tech out to check it out. I hate trouble shooting for lazy folk.
A little of subject eh? Sorry.

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