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Tripping 600A Main

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We went to a service call yesterday at an old tire shop. They lost utility power for about 8 hours a few days ago during some bad weather. Now, they are continually tripping their 600A main. Before their outage, they never had this problem.

After a little troubleshooting, we narrowed it down to an air compressor. The air compressor is turned on/off via a 100A disc. fused at 80 amps. This 100A disc. is fed from a 200A breaker in a subpanel, and the 600A main they are tripping located in an exterior panel. The 200A breaker is not tripping, nor are they blowing the 80A fuses.

Here's the other thing, the 600A main does not trip upon initial start up of the air compressor. It does trip however after the initial tank of air has bled out enough that the compressor kicks on to refill.

The starter on the air compressor seems to be brand new. Has the 600A main just gone bad?

Thanks for any help.
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Ambassador of Amps
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Did you do an amp reading at the 600A breaker? Are the connections tight? Any signs of overheating?

If its not getting hot, or not having an overload issue - then the breaker needs to be replaced.
 

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Donuts > Fried Eggs
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Does the 600A main have any adjustable settings?

Seeing how you have two much lower levels of protection, it's tempting to say that breaker is bad, but you need to have some current readings at the very minimum before you just go swapping parts.

It would also help to know exactly what model fuses are in the disconnect, and what the model number is on the breaker.
 

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11,734 Posts
Hope you tested before closing the breaker, since it could have been a short.

Anyways, is the breaker adjustable in any way? How old and what make? That fact the fuse aren't blowing nor the 200 sounds to me like the main itself is at fault with a possibility of the air compressor having a high inrush.
 

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Registered
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2,655 Posts
I'm just going to comment on a possible problem with the air compressor as others are taking care of the electrical part. It sounds like the air unloading valve is not working and the compressor is trying to start with head pressure.

ETA: when the compressor stops you should hear a short burst of air releasing from the cylinders and piping.
 
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