I'm building a shed that will be housing a washer, dryer, hot water heater, and a freezer. The dryer and water heater both require 220V 30A and will be used concurrently. The washer and freezer use 120V 15A connections (not sure how much they actually draw), the freezer will run continuously. I'd also like a light fixture and a 3rd 120V outlet.

The main is 200A service. I have an existing subpanel (100A) that supplies my camper.

For the shed, I'm considering another 100A subpanel. The shed is 30 feet away from the main, and I'm going to bury the cable underground (with or without pvc conduit depending on recommendations here.)

Is 100A sufficient? Or overkill? What wire size would I need from the main panel to the subpanel?

I think I need to run 4 wires (two hot, a neutral, and an equipment ground). Is this correct?

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    No furnace or air conditioning listed. Keep in mind that, unless you are in an area with mild temperatures year-round, ordinary freezers (and even more so, refrigerators) are designed for conditioned space - e.g., 50 F to 80 F - and can fail miserably if too cold or too hot. – manassehkatz-Moving 2 Codidact Jul 2 '20 at 16:20
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    Remember that the panel rating is a max not a required amount, so a 100amp panel can be used with less draw on it. You may have a hard time finding a 60amp panel, and if you do, you may be full up with the circuits you're planning on installing today, leaving no room for future expansion when you want something else out there. Much cheaper to buy big today than to replace tomorrow. – FreeMan Jul 2 '20 at 16:47
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    Thanks, I hadn't considered that! In summer I was planning on using a portable window unit. In winter, I think I could get away with a space heater. It freezes here, but rarely. – C. R. Jul 2 '20 at 16:48
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    25A each for water and dryer, 10A for washer, 5A for freezer, all those cycle some, but you are looking at an 80 amp feed easy, 100A is not overkill. Yes, 4 wires and ground rods. Conduit or direct burial is dependent on how much you like digging. – NoSparksPlease Jul 2 '20 at 16:55
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    I had a customer I gave the same advice as my answer to you he went direct burial, not long after we upgraded his sub again direct burial several years guess what now he was upgrading again , we could get a 125 amp breaker Al wire and conduit at this size was cheaper and a 150a panel was cheaper and had more spaces than the 125 and the 150 came with ~6 120v breakers &3 240v breakers. He could have put in the 150 sub and conduit to start with he would have saved himself a massive amount and a lot of teasing from me, , pulling bigger wire later simple and the original wire can be reused. – Ed Beal Jul 2 '20 at 17:09

For the sub panel sometimes you can get a better deal on a 150 amp panel your panel really cannot be two large. Yes you will need a 4 wire feed but your main panel will dictate the size feeder wires , if I was doing this and could get a 125a breaker to feed my shop I would do it, however many panels will max out at 100 amp so size your feeder wiring on the size of your breaker. The size of the sub panel is not the controlling factor it’s the breaker in the main that feeds the sub your sub has to be at least that big but going bigger is usually considered better. Large feeders , most pros will pull aluminum no worry about voltage drop here and with large conductors conduit and individual conductors are the way to go the ground wire will be much smaller based on the size, yes the other conductors are based on size but grounds are a different table. You also need a local grounding rod for the sub.

So go big on the sub panel even If you only want 80 amps, use conduit PVC is easy to cut and glue schedule 80 above ground 40 below ground, IF you use a smaller wire size do your self a favor and over size your conduit 1-1/4” or 1-1/2” will make an easier pull with large aluminum and if you decide to go max size later it make using the existing conduit possible and a later upgrade simple. Newer code mandates all receptacles to be GFCI protected.

  • Wire sizes: If I assume 100 amps (dont want to go bigger, because I have that other 100A subpanel) I think I need 1/0 wires (aluminum) for the hots and neutral and 8awg copper for the ground. Does this sound reasonable? – C. R. Jul 2 '20 at 17:52
  • I am planning on a 150A panel if I can get it. – C. R. Jul 2 '20 at 17:55
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    I usually use #1 al on a 100 amp 1/0 is great . #8 copper sounds right but I don’t have a book handy , make sure to get a main breaker panel you need a local disconnect if not attached to the house. – Ed Beal Jul 2 '20 at 18:40
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    Ok I mean for your sub get a main breaker panel not a main lug only for the sub. – Ed Beal Jul 2 '20 at 19:17
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    10ka is the standard breakdown for a residential breaker but that is the correct one for a QO panel (my personal favorite) what is crazy is many times this value is not close when multiple homes connect to the same transformer most of mine are 25-65 at work except the mains off my transformers. – Ed Beal Jul 2 '20 at 21:41

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