400A Main Breaker is tripping

[blakef223]

I have a 400A I-line molded case main breaker that is sporadically tripping, it has tripped twice in the last two weeks with anywhere from 2 days to a week between trips. The main feeds 4-30A feeder breakers and 1-40A feeder breakers. These feeders in turn feed a couple exhaust fans and some heater strips. The panel was installed prior to 1990 and the main has likely only been operated a few times, the issue supposedly started after the main was locked out. The interior of the panel appears to be free of any discoloration or obvious issues, the equipment downstream continues to run when the breaker holds and the trip indicator on the breaker itself doesn't register any fault conditions. I have tested the breaker by starting all the fans and heater strips at the same time and the breaker still holds. I am thinking it is an internal issue to the breaker that requires replacement but I wanted to see if anyone else had a suggestion before I recommend spending $20k on a new breaker(or $10k to downgrade to a 200A main). Please let me know if anyone has any suggestions, thank you.

 

[ATSman]

Before I would consider breaker replacement I would try and rule out the cause as being load related.
Does the breaker have GF protection? Have you taken any load readings with all fans and heaters operating (max load?)
Or connected a recording ammeter on all phases?
What are the breaker trip unit settings?
Give us the nameplate info: Brand, Model#, voltage, etc.

 

[blakef223]

I don't believe it has any GF protection on it. It's a squareD breaker with model number ME36350LI6453 with a 400A plug with model number RP100 operating at 480V. Trip settings are 1.0 for long time, 7 for delay, and 5 for instantaneous. I have connected an ammeter and it's reading approximately 92A give or take an amp for each phase. We have a few recording ammeters that I can try but I don't bleieve any of them have a battery life longer than a day.

 

[ptonsparky]

Have you taken a thermal image of the breaker while it is in operation for a few hours? A FOP accross the breaker?

 

[petersonra]

I don't believe it has any GF protection on it. It's a squareD breaker with model number ME36350LI6453 with a 400A plug with model number RP100 operating at 480V. Trip settings are 1.0 for long time, 7 for delay, and 5 for instantaneous. I have connected an ammeter and it's reading approximately 92A give or take an amp for each phase. We have a few recording ammeters that I can try but I don't bleieve any of them have a battery life longer than a day.

what does the "5" for instantaneous trip mean? 500 Amps? Might want to nudge that up a bunch.

 

[oldsparky52]

Does SQ D offer field support for this?

 

[blakef223]

Ptonsparkey I haven't done any thermal imaging on it but I will look into trying it. Petersonra I apologize the instantenous rating is 5xthe rating=5x400=2000A.

 

[jim dungar]

You have a 29 year old electronic trip breaker, possibly it is beyond its useful life.
You may be able to replace it with a more standard 350A breaker, especially if it is a 'plug-on' I-Line style.

 

[david]

I wanted to see if anyone else had a suggestion before I recommend spending $20k on a new breaker(or $10k to downgrade to a 200A main). Please let me know if anyone has any suggestions, thank you.

Before I spent $10,000 or $20,000 i consider the 6 throw rule and see about eliminating a main ahead of four breakers in a Main service panel

 

[petersonra]

I am thinking it is an internal issue to the breaker that requires replacement but I wanted to see if anyone else had a suggestion before I recommend spending $20k on a new breaker(or $10k to downgrade to a 200A main). Please let me know if anyone has any suggestions, thank you.

That sounds like a lot of money for one breaker. You might want to just remove the main and replace it with some 400A class J fuses.

 

[ATSman]

You have a 29 year old electronic trip breaker, possibly it is beyond its useful life.
You may be able to replace it with a more standard 350A breaker, especially if it is a 'plug-on' I-Line style.

Yeah Jim
Experience has shown that solid state trip units can and do fail after 20 or 30 yrs. We see it all the time.
In GFR systems especially.GE, Westinghouse, ITE, Hi-Z, etc. The old electrolytic capacitors would degrade over time and cause nuisance firing and tripping of devices.

 

[electrofelon]

Before I spent $10,000 or $20,000 i consider the 6 throw rule and see about eliminating a main ahead of four breakers in a Main service panel

That sounds like a lot of money for one breaker. You might want to just remove the main and replace it with some 400A class J fuses.

I agree, definitely look at other options. Had a bad 1200 main breaker once and replaced the whole switchboard (with a MLO panelboard) for less than what the breaker would have cost.

 

[zog]

I don't believe it has any GF protection on it. It's a squareD breaker with model number ME36350LI6453 with a 400A plug with model number RP100 operating at 480V. Trip settings are 1.0 for long time, 7 for delay, and 5 for instantaneous. I have connected an ammeter and it's reading approximately 92A give or take an amp for each phase. We have a few recording ammeters that I can try but I don't bleieve any of them have a battery life longer than a day.

That should have a Micrologic series B trip unit which is very prone to failure , usually from internal corrosion, I have a high success rate in repairing those trip units, usually runs around $750. Or you can replace with new, should be well under $10k , I'll have to decode your -6453 suffix, that's a odd one.

 

[ptonsparky]

Does that type of breaker even care about thermal conditions?

 

[zog]

Does that type of breaker even care about thermal conditions?

Nope, I'm sure it is the trip unit, a simple secondary injection test will verify that.

 

[blakef223]

Before I spent $10,000 or $20,000 i consider the 6 throw rule and see about eliminating a main ahead of four breakers in a Main service panel

David, what section of the NEC is that in? I can't seem to find it.

 

[ptonsparky]

Try 230.71

 

[blakef223]

Thank you for the responses everyone. We have a breaker testing and rebuild shop on site so I'm gonna look at getting the panel on a temporary generator while we pull the breaker and test it. If the breaker ends up being faulty I will definitely be looking into replacing it with a set of fuses, another panel, or seeing if i can find an adapter kit to make a different breaker fit since the replacement that squareD quoted came in at $19k. Zog I appreciate your offer on the repair but unfortunately my employer will not let us repair(or have anyone else repair) molded case breakers.

 

[oldsparky52]

Try 230.71

Would they need to get the equipment field inspected by a UL rep to keep the UL listing if they did this?

 

[Cow]

Thank you for the responses everyone. We have a breaker testing and rebuild shop on site so I'm gonna look at getting the panel on a temporary generator while we pull the breaker and test it. If the breaker ends up being faulty I will definitely be looking into replacing it with a set of fuses, another panel, or seeing if i can find an adapter kit to make a different breaker fit since the replacement that squareD quoted came in at $19k. Zog I appreciate your offer on the repair but unfortunately my employer will not let us repair(or have anyone else repair) molded case breakers.

I try not to purchase large framed breakers directly from the manufacturer unless someone is holding a gun to my head. Their markups are insane once they know you have their gear installed and you need parts for it. I don't like those games.

I try 3rd party resellers/testing firms, whether it's new or used/tested surplus first. If that doesn't pan out, then I head over to the manufacturer knowing what comes next, is going to be sticker shock.

20k for a 400 amp breaker is nowhere near reasonable.