Breaker tripping

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  #1  
Old 07-30-07, 02:05 PM
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Breaker tripping

OK, I have a sub panel in the garage and have it feed from a 30 amp in the house panel...added a 15 amp (2 pole) breaker in the garage for a 220v compresor, plugging in the comp. to out it trips the main 30 amp in the house and not the 15 in the garage...would this be a short in the comp. wiring or a short in the wiring from 15 amp breaker (in garage) to its outlet.? I think it may need a bigger breaker (20 amp) in garage as it says its a 15 amp comp.? would that be right? thanks
 
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  #2  
Old 07-30-07, 02:18 PM
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I would guess you have a short circuit somewhere. When you have a short circuit, thousands of amps flow briefly, and it's a race to see which breaker trips first. In your case, the 30-amp breaker won the race, but the 15-amp breaker would not have been more than a few milliseconds behind it.

You may or may not need a 20-amp breaker in the garage. You should consult the compressor installation instructions. This change would not, however, mitigate your current problem. That's caused by something else.
 
  #3  
Old 07-30-07, 07:10 PM
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Are the breakers of the same brand? If not is the 30 amp a "QO"? Breakers have differing instantanous trip points and the normal starting current may get into this trip range. The "QO" has the lowest instantanous trip point of any breaker on the market....in fact QO means "quick opening". Note that my comment assumes that you get power to the garage, and the only time the breaker in the house trips is when you try to use the compressor.
Don
 
  #4  
Old 08-04-07, 11:05 PM
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Look at the nameplate and see what RLA's it has. You would take the RLA number of amps and mulitply it by 125% or 1.25 and size your wire up to the next size allowed for that amperage. You may have a faulty breaker if it is not tripping. If this happens when you first turn on the compressor, the inrush in the first few seconds may be too great for the wire and breaker.
 
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