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Please see photos of sub-panel (in my detached garage) and the 50amp 2-pole breaker that feeds it.

If I am correct, I have almost 100amps @120v available in the garage, correct?

240v x 50amps = 12k watts

12k watts / 120v = 100amps

So I should be able to run a power tool on one 120v circuit (table saw, mitre saw, etc) plus a 120v dust collector on another, plus lights/chargers on another etc and shouldn't even come close to tripping that 50amp breaker. Assuming the power tools pull 12-15 amps or so each.

Is this correct?

My hope is that I can do all that and also add a (240v ?) mini-split...12k or 18k.

Yes, I will be replacing all the outlet circuitry with 12g wire and running them through the knockouts in the sub.

Main breaker

Sub-panel

enter image description here

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2 Answers 2

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You should be ok, the label on my 240v 18k says minimum circuit ampacity of 15A.

You didn't ask but you appear to have a Code problem in your main panel. The Code and Listing Lab specify installing and using as the label instructs, you have 3 brands of breakers and I've never seen a panel listed for more than one brand.

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    Brand alone is not definitive - type is what matters, and many types have changed ownership across several different brands over the years. That said, the three pictured breakers are all different, incompatible types (THQL, HOM, Q). At most, only one of them can be appropriate for the panel.
    – nobody
    Commented Oct 21, 2023 at 17:50
  • Yeah -- I've seen multi-listed panels show up on this site (early Murray stuff, mostly, although Milbank metering gear is also noted for being multi-listed/labeled), but I seriously doubt that the OP's panel is that. Commented Oct 21, 2023 at 22:50
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How much power you have in the garage really depends on how much power you have spare in the house. You need to start with a NEC 220.82 Load Calculation in the house. This is done in VA (~=watts) by the way, so you're not having to keep track of whether your amps are 120V or 240V.

Once you have that data, you know how much headroom is available for loads in the garage. Garage loads will have to fit within that.

There is load-shed technology which may help, e.g. suspend your water heater when garage loads get too high etc.

On your cables, I cannot tell if they are 14 AWG or 12 AWG. Yes, the sheaths are white, but until recently, 12 AWG had a white sheath. You will need to read the text on the side of the sheath.

Now your panel has breakers of every make. The bus stabs on different panels actually are different, and we see a lot of burn-ups on bus stabs - virtually all of them are "alien breakers" not rated for the panel. The reason to swap them is nobody likes a bus fire, and an emergency replacement of a main panel can be $4000. . Breakers are typically $8 per slot, so we're not talking a large expense here.

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  • This did cross my mind (spare power in the house). Figured I would at least refrain from doing laundry, cooking etc while I'm in the shed. The panel is pretty full but it is only me and my wife in this house. There's very effective passive solar heat and geothermal. Heating is also zoned.
    – Krewldad
    Commented Oct 22, 2023 at 15:39
  • ASSUMING there is enough headroom, is my math correct in that I shouldn't worry about tripping that 50amp breaker if running a few 8-12amp tools in the shed? Is your comment RE the different brand breakers referring to the sub-panel? Thanks for your input!
    – Krewldad
    Commented Oct 22, 2023 at 15:48
  • @Krewldad The problem is that you have to (within reason) plan for unusual situations. What if you decide to work in the shed to get out of the way while your wife is cooking Thanksgiving dinner? Commented Oct 22, 2023 at 15:49
  • Yes, 50A is plenty for typical one-person shop usage, especially if the 120V loads are reasonably balanced between the two legs. Commented Oct 22, 2023 at 15:49
  • That would be an unusual situation indeed. Would have to get Subway carryout. :^)
    – Krewldad
    Commented Oct 22, 2023 at 20:15

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