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Mach1 08-04-2007 01:15 PM

Another Garage Subpanel Q....
About a year ago, I wired my attached garage with a subpanel. My sub in the garage is only 15 feet or so from the main. I used 4 AWG THHN 90C for both hots and netrual, 6 AWG bare stranded for the ground. The conductors are installed in 1.25" PVC 90C rated conduit.

The table I looked at when I bought the wire said #4 was good for 95A (w/90C insulation) My breakers are the Cutler-Hammer BR type. Since there was no 95A breaker avaliable, I used a 100A.

In hindsight, I'm wondering if using the 100 Amp BR this was the right thing to do? Should I switch it to a 90A breaker? The only reason I can think of to change it to 90A would be because of de-rating due to conduit fill. Can someone help me out?


Parrothead 08-04-2007 04:01 PM

Derating isn't an issue here, since there are only three current-carrying conductors in the pipe. However, the wire you used is only rated for 95 amps, and they are protected by a 100- amp breaker. to make it legal, you're going to either have to up-size the wire to #3 or down-size the breaker to 90 amp.

BTW, since this is a subpanel, did you make sure to remove the bonding jumper in the subpanel??? Just a thought.

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