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I have 10awg THHN service wires running from 30A breaker in my main home electric panel to a subpanel in a small detached yard shed.

The 100A main breaker in the subpanel (I'm using as panel shutoff, has lugs listing wire capacity from 6awg to 3awg.

While I'm relatively sure those large lugs will clamp on small 10awg service wires - I'm wondering if this is something an inspector may not pass ?

If so what are options to ensure the large breaker lugs clamp on 10awg service wires so they will satisfy any NEC code rules ?

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  • Not going to propose this as an answer because I don't know electrical codes, but maybe somebody else here could weigh in: What if you ignore the 100A main breaker, and back-feed a smaller, dual-pole breaker in the panel, and use that for your shutoff switch? Nov 1, 2021 at 0:39

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Just get some 6 AWG by the foot at any big box or electrical supply house. Black or red (or anything but white or green) for the hots, white for the neutral. 3 wire nuts (just make sure they can handle 10 AWG and 6 AWG) and you're done. About $ 5 total, if that much. Do not switch out for a smaller panel - the savings are minimal and then you don't have spaces you may need in the future.

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An inspector will/should flag that. The lugs are UL listed for that wire size, 6 AWG to 3 AWG, not 10 AWG. Since the #10 has a 30 AMP breaker in the main panel, You could splice some 6 AwG to the 10 AWG and run the 6 AWG into the lugs if room permits. Otherwise, get a smaller subpanel. Depending on the panel configuration, you might be able to get smaller lugs/ breaker for the subpanel.

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