Main PV breaker tripping

[electro7]

I have a system with 4- 480V inverters that connect to a main PV panelboard. See the info below:

(2) 100K
Max output: 120.3A
OCPD: 175A

(2) 75K
Max output: 90.2A
OCPD: 125A

Main PV Panelboard OCPD: 600A
Main PV Feeder length: 630ft
Feeder conductors: 3 sets of 3/0 CU thwn

When the system is at full capacity, the main PV 600A breaker trips. With two DC switches off, which are 8 strings, the breaker stays. That is about 84% of the entire system.

This has happened from the initial start-up. We checked torque on the feeder connections and breaker to bussing connections.

A couple of the inverters can sometimes go into a "grid interference" alarm when the system is at full capacity.

I installed a data logger fluke 1730 meter the other day to test and troubleshoot. When the inverters were at full capacity, the peak amperage was 343A. The main 600A breaker tripped.

I've talked to the breaker seller, and he said we should replace it but that it may be too much heat on the breaker. The panelboard isn't in direct sunlight, although it gets hot here - 100°F plus. He was wondering about replacing it with a 700A instead. I have contemplated that since we are protected at the MSB by 600A fuses and a 600A breaker.

Any thoughts?

My initial is that it's a faulty breaker.

Oddly enough, when I was testing it with the fluke 1730 and it tripped, one of the inverters went dead and will not respond. I am in the RMA process for that with the inverter manufacturer.

Could harmonic distortion be an issue?

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[ggunn]

I have a system with 4- 480V inverters that connect to a main PV panelboard. See the info below:

(2) 100K
Max output: 120.3A
OCPD: 175A

(2) 75K
Max output: 90.2A
OCPD: 125A

Main PV Panelboard OCPD: 600A
Main PV Feeder length: 630ft
Feeder conductors: 3 sets of 3/0 CU thwn

When the system is at full capacity, the main PV 600A breaker trips. With two DC switches off, which are 8 strings, the breaker stays. That is about 84% of the entire system.

This has happened from the initial start-up. We checked torque on the feeder connections and breaker to bussing connections.

A couple of the inverters can sometimes go into a "grid interference" alarm when the system is at full capacity.

I installed a data logger fluke 1730 meter the other day to test and troubleshoot. When the inverters were at full capacity, the peak amperage was 343A. The main 600A breaker tripped.

I've talked to the breaker seller, and he said we should replace it but that it may be too much heat on the breaker. The panelboard isn't in direct sunlight, although it gets hot here - 100°F plus. He was wondering about replacing it with a 700A instead. I have contemplated that since we are protected at the MSB by 600A fuses and a 600A breaker.

Any thoughts?

My initial is that it's a faulty breaker.

Oddly enough, when I was testing it with the fluke 1730 and it tripped, one of the inverters went dead and will not respond. I am in the RMA process for that with the inverter manufacturer.

Could harmonic distortion be an issue?

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What breaker is it, exactly, that is tripping? Is it a main breaker on the inverter combiner panel? You don't need one; that panel can be MLO as long as you have OCP between it and the service. If you are backfeeding a breaker in the MSB, that is all the OCP you need, the disco can be unfused as well.

CAVEAT: Some AHJs will require you to have a fused disco although it is neither required by the NEC nor needed for functionality or safety.

 

[electro7]

What breaker is it, exactly, that is tripping? Is it a main breaker on the inverter combiner panel? You don't need one; that panel can be MLO as long as you have OCP between it and the service. If you are backfeeding a breaker in the MSB, that is all the OCP you need, the disco can be unfused as well.

CAVEAT: Some AHJs will require you to have a fused disco although it is neither required by the NEC nor needed for functionality or safety.

Yes it's the main in the PV combiner panel. I designed it with a breaker since it was at a separate structure.

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[jaggedben]

Does this breaker have a trip unit or setting and is it set properly?

Also if you are only getting 343 A then either the system is not at 'full capacity' of something else is off. Did you measure all phases?

 

[electro7]

Does this breaker have a trip unit or setting and is it set properly?

Also if you are only getting 343 A then either the system is not at 'full capacity' of something else is off. Did you measure all phases?

It does and was set at 2 when I bought it. The seller said put it to 8, and it still tripped. He then said go 10 (maxed), and it still trips. See attached photo.

I feel like I do smell some burnt electrical or plastic near the main breaker.

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[electro7]

With my situation I described would anyone be against installing a 700A breaker since the conductors are protected downstream at 600A with fuses and a breaker in the MSB?

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[jaggedben]

With my situation I described would anyone be against installing a 700A breaker since the conductors are protected downstream at 600A with fuses and a breaker in the MSB?

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No. But if it were me I'd kinda want to know what the actual problem is. If it's literally just a bad breaker then replacing with another 600A should be fine. If it's something else, the 700 will either trip or mask the problem.

 

[electro7]

No. But if it were me I'd kinda want to know what the actual problem is. If it's literally just a bad breaker then replacing with another 600A should be fine. If it's something else, the 700 will either trip or mask the problem.

Yeah, good point. If I keep it at 600A and it keeps happening, I'll have to investigate further. I mean, around 420A max output current of the inverters is well under 80% continous duty breaker which would be 480A. I wouldn't think it's the heat from the amperage. Do you agree?

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[jaggedben]

Yeah, good point. If I keep it at 600A and it keeps happening, I'll have to investigate further. I mean, around 420A max output current of the inverters is well under 80% continous duty breaker which would be 480A. I wouldn't think it's the heat from the amperage. Do you agree?

Yes, I agree. I mean, if everything is terminated and torqued and rated correctly and so on, there shouldn't be too much heat from the full amps.

 

[curt swartz]

When you say "seller" I take it you purchased this breaker used from someone? It looks like its been around for a while.
From your picture I can't read any of the breaker info. Are you sure this breaker has a 400 amp trip unit?
Have you tried to call Square D?

 

[electro7]

When you say "seller" I take it you purchased this breaker used from someone? It looks like its been around for a while.
From your picture I can't read any of the breaker info. Are you sure this breaker has a 400 amp trip unit?
Have you tried to call Square D?

I did buy it from a company that does sell reconditioned breakers. It's a 600A. It says 600A. Is there another way for me to check it has a 600A trip unit?

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[curt swartz]

I did buy it from a company that does sell reconditioned breakers. It's a 600A. It says 600A. Is there another way for me to check it has a 600A trip unit?

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Sorry, I meant to type 600 amps.

If this is a legitimate company selling reconditioned breakers they should have tested it before selling it to you. I would tell them either test it, get me a different one or give me my money back. If it is tripping at far below its rated current there is obviously something wrong whit it.

 

[electro7]

Sorry, I meant to type 600 amps.

If this is a legitimate company selling reconditioned breakers they should have tested it before selling it to you. I would tell them either test it, get me a different one or give me my money back. If it is tripping at far below its rated current there is obviously something wrong whit it.

Thanks. He has offered to give me another one and I think I'll stay with the 600A and not go to a 700A.

Thanks again guys. Really appreciate the input.

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[ggunn]

Thanks. He has offered to give me another one and I think I'll stay with the 600A and not go to a 700A.

Thanks again guys. Really appreciate the input.

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What is the bus rating of the panel? Even though it is protected at 600A by another OCPD it may get flagged as a violation if the rating of the breaker exceeds the rating of the bus. It would be ironic, seeing as the panel could be compliantly MLO.

 

[electro7]

What is the bus rating of the panel? Even though it is protected at 600A by another OCPD it may get flagged as a violation if the rating of the breaker exceeds the rating of the bus. It would be ironic, seeing as the panel could be compliantly MLO.

Good question. I assumed it was 600A but will double-check that.

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[kwired]

It does and was set at 2 when I bought it. The seller said put it to 8, and it still tripped. He then said go 10 (maxed), and it still trips. See attached photo.

I feel like I do smell some burnt electrical or plastic near the main breaker.

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Can't read things in that image but I think that blue adjustment dial is for magnetic trip setting. Should not effect continuous current trip point.

Did you take temperature of individual lugs or do any thermal imaging of this when in operation? If there is a "hot spot" that is probably indicating where the trouble is, if all three poles appear identical throughout then actual trip setting maybe isn't right for whatever reason, this assuming current is same in all three poles.

 

[electro7]

Can't read things in that image but I think that blue adjustment dial is for magnetic trip setting. Should not effect continuous current trip point.

Did you take temperature of individual lugs or do any thermal imaging of this when in operation? If there is a "hot spot" that is probably indicating where the trouble is, if all three poles appear identical throughout then actual trip setting maybe isn't right for whatever reason, this assuming current is same in all three poles.

I have not done thermal imaging yet. I'll do that as well.

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[Tulsa Electrician]

It should have said 600 in a tag right under the handle and on the trip unit Hard to see in the pic.

 

[Todd0x1]

That breaker looks like its been through some stuff. The amp rating sticker below the handle is missing. The other labels look like they might have been transferred off another breaker. Who knows what the heck this breaker is and what it has been through. These 'reconditioned' breaker guys buy their inventory from scrap yards and tweakers then make 'good' breakers from pieces of all different ones. AFAIK there is no legit reconditioning process for MCCBs. I know cost and leadtimes are an issue, but this is not somewhere to buy parts of unknown origin. Then theres also the issue of is the customer aware they were given some old recon breaker in lieu of the new one they would have expected?

 

[electrofelon]

Just yesterday I found out we have a PV main breaker that is tripping. Its a larger resi system, about 20kw so say 83 amps. 200A breaker keeps tripping. I haven't been there yet to investigate, but most likely just a bad breaker, I'll keep you posted.