600-Amp Breaker Tripped

[jim dungar]

Just to reclarify, The breaker is not a main breaker. Someone had labeled that breaker by mistake. It front feeds from bus. Conductors leave the breaker and travel about 3' to another panel.

Thank you for the help.

Oh.

But that makes no difference to any of my comments.
Fix the coordination problem first.

 

[Tony S]

There’s been several suggestions of raising the I_i setting but no mention of the supply capacity. I certainly wouldn’t be raising I_i to x10 considering the MCCB has been in use for 14 years without fault. As has been said, I_r and T_r need to coordinated with both the up and down stream breakers.

I’ve used the same MCCB’s in the UK (Schneider here) and never had a problem with them. Considering the duty and conditions they were subjected to, they surprised me with their reliability. Induction furnaces aren’t the subtlest of things and definitely not environmentally friendly. The one failure was dirt (iron dust) jambing a shunt trip.

 

[mbrooke]

I could see it: If he's running nominal load of ~200A he only needs to make up 700A of inrush to dump that breaker, even a 35HP load might be enough to do that.

That said, I didn't see the bit about a bunch of little condensers, so I agree, not likely to see a large motor load in there. The plot thickens. That HVAC unit still running?

I see little compressors doing it. If all are running during a momentary that will trigger all of them to go into locked rotor. You should see the current spike when a recloser comes back in on a hot day

 

[Ravenvalor]

All of these replies have been helpful to say the least. I've got the customer contacting the electrical engineer who wrote up the drawings for the building. He will hopefully verify the coordination study and the trip settings. I've also got a company in town that rebuilds those circuit breakers. Their ballpark figure for a used certified breaker is $4,000.00. The customer is resting a little bit easier and frankly so am I thanks to your help.

 

[zog]

All of these replies have been helpful to say the least. I've got the customer contacting the electrical engineer who wrote up the drawings for the building. He will hopefully verify the coordination study and the trip settings. I've also got a company in town that rebuilds those circuit breakers. Their ballpark figure for a used certified breaker is $4,000.00. The customer is resting a little bit easier and frankly so am I thanks to your help.

There is nothing to rebuild in that breaker. Yours probably is working just fine but to be sure you want to test that trip unit, it's a 20 minute job. If there is a problem with the trip unit you can replace the trip unit for <$1,000.

 

[Ravenvalor]

There is nothing to rebuild in that breaker. Yours probably is working just fine but to be sure you want to test that trip unit, it's a 20 minute job. If there is a problem with the trip unit you can replace the trip unit for <$1,000.

I will definitely research testing this now.

Thank you,

 

[big john]

I see little compressors doing it. If all are running during a momentary that will trigger all of them to go into locked rotor...

That's where I was going with it, but I don't know what their version of "little" is. If they've got a half-dozen HVAC units then they're probably only a few HP each and I wouldn't expect the LRA on any one of them to be more than 200A.

I'm honestly leaning more towards a ground-fault at this point. If that breaker is working properly, I think the thing to do would be to compare the curves for the mains directly below it and try to get some selective coordination. That way if it happens again, it takes out a smaller feeder and maybe the problem can be chased down.

 

[mbrooke]

That's where I was going with it, but I don't know what their version of "little" is. If they've got a half-dozen HVAC units then they're probably only a few HP each and I wouldn't expect the LRA on any one of them to be more than 200A.

I'm honestly leaning more towards a ground-fault at this point. If that breaker is working properly, I think the thing to do would be to compare the curves for the mains directly below it and try to get some selective coordination. That way if it happens again, it takes out a smaller feeder and maybe the problem can be chased down.

Figured, you know your stuff. IMO its one of the two. The fact the smokes tripped would be a ground fault for me.