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I have a 100 amp sub panel being fed a 6/3 cable. The main Panel has a two pole 60 amp breakers.

How many breakers can I have, or how many amps can I have? All the outlets/receptacles will be 120v. Can I use twins? What is my limit?

This is for a shed with power tools, fairly light use. I just want lights and 120 volt outlets attached to the Sub panel.

Thanks, -Greg

Edit please... I'm looking for direct answers, not what I should change. I have 6x spaces can I put 6x 20amp breakers? I had two electricians suggest I can't but wouldn't tell me why.

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  • Hi Greg: There have been tons of questions and answers posted here regarding all aspects of sub-panels. Have you tried searching for your answer. Also, welcome to SE and please take the tour so you can best know how to participate. – George Anderson Jul 2 '20 at 16:56
  • Hello, Thank you, I have been searching for a while, and my limited vocab may be hindering me, I couldn't find anything here or google, or an electrician that could give me a straight answer. All other post seem to be about how many amps a 6/3 can handle or how to build or wire, when I'm talking about an existing. – Greg Jul 2 '20 at 17:11
  • Can you post photos of the panel in question? Also, are we talking "average woodshop power tools" here, or some other sort of workshop space? – ThreePhaseEel Jul 3 '20 at 1:17
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If you’re thinking about twin breakers, it’s because you got too small a panel. Stop right now before you sink any more work into it, and get a much bigger panel. Spaces are dirt cheap right now, and it’s one place you should splurge.

And it’s fine for the subpanel busing to be much larger than the feed breaker. It’s a safety margin, 130 mph tires are safer than 85 mph tires even if you never drive 85 mph.

Your ability to use twin breaker depends on your local Electrical Code and any requirements it has for AFCI on any breaker or GFCI on 2-pole breakers. Those are not available in double-stuff breakers, so you must plan a full space for each of those circuits. Nowadays that will be most circuits, so I advise to just forget about twins.

Since you will certainly never use all circuits at once at full power, you can put quite a lot in a panel. Having 16 120V circuits would not be unreasonable.

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  • Agreed Harp. Why even consider tandem breaker in a new panel? And with AFCI/GFCI requirements now, hard to use according to code. We always seem to have to tell ppl over and over: "Buy the extra spaces now, they are cheap compared to upgrading later". Actually, they are cheap without considering the potential upgrade! LOL + – George Anderson Jul 2 '20 at 17:48
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    @GeorgeAnderson - remember, you've read a lot of posts by Harper, TPE, NSP and others making this recommendation. Most new people haven't read in depth or seen it 20 dozen times, so it hasn't sunk in yet. It's not you he's telling, it's the new guy for whom the message hasn't yet sunk in. – FreeMan Jul 2 '20 at 17:49
  • Ok, I can get rid of the twins that not the problem. I know, the 6/3 can handle 60amps per leg, but I am looking to see how many breakers I can put in it. I have 6x spaces can I put 6x 20amp breakers? I had two electricians suggest I can't but wouldn't tell me why – Greg Jul 2 '20 at 20:37
  • Well assuming a 20A circuit uses on average 1/3 of breaker trip (and that's a generous assumption), you can have nine 20A breakers per leg, or 18 breakers. So you are a long way from overloaded. A 6 space panel might be appropriate if you were loading up all six 20A breakers to near 16A each continuously, e.g. if you were running Bitcoin miners. – Harper - Reinstate Monica Jul 2 '20 at 23:00
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The 60A breaker feeding the 6/3 (I hope it's copper) will limit the current to the subpanel to 60A per 120v leg. The panel must be rated for a minimum of the size of the breaker feeding it. You can put as many breakers in the panel as the panel will hold, you just can't concurrently use loads that will exceed 60A per 120v leg.

Twins may or may not fit depending on the panel itself, but will mostly be prohibited by current requirements for AFCI and GFCI requirements due those style breakers needing full spaces.

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  • So I know, the 6/3 can handle 60amps per leg, but I am looking to see how many breakers I can put in it. Aye its copper. I have 6 spaces can I put 6 20amp breakers? I had two electricians suggest I can't but wouldn't tell me why – Greg Jul 2 '20 at 20:36
  • @Greg I can't tell you why, the 2017 and 2020 NEC 225.33 allows six breakers to serve as disconnecting means to a detached building. Many States and some cities adopt the Code with modifications, maybe you are subject to a modification that requires a single switch, that would mean you need two spaces to backfeed a 2p60 as a disconnecting means, leaving only 4 spaces. – NoSparksPlease Jul 3 '20 at 1:36

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