I am going to be running wire underground to my shack about 300' away. I will need a 30amp a 20 amp and a 10 amp at the sub panel at the shack so 60 amps total. I assume I am going to need a 2 pole 60 amp break in the main panel. What wire am I going to need from the main panel to the sub panel?

Update - It is going to be a sugar shack about 20x20. I need 30 amps for a reverse osmosis machine, 20 amps for the pump im running most of the day then 10 amps for lights or whatever.

230 volts is what I run it on it draws 5.5 amps. 110 bolts is 7.5 amps. That is for the pump The reverse osmosis is 110v 30amps

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    That is a really long way to run wire. I am sure you have your reasons but I would think about alternatives.
    – DMoore
    Commented Sep 17, 2020 at 5:13
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    What are the actual loads you are serving from this panel? How many square feet is this shack, and is it going to be workshop space, a small dwelling unit, a storage shed, or ...? Commented Sep 17, 2020 at 11:42
  • Well, sort out what (if any) load is 240V and edit your question. If the loads were all 120V you'd only need a 30A 240V breaker to feed 60A of 120V loads - so it makes a RATHER big difference if one or more of the loads is 240V - or if there are additional loads. Likewise, the actual load of the vacuum pump that will be running all day (not just its breaker size) matters since as a continuous load it needs to be provisioned at 125% of that load. I'd suggest 1 AWG aluminum in 1-1/2" conduit for a start, but I don't know how much you are "good, and a little room to grow" .vs. "cheap as possible"
    – Ecnerwal
    Commented Sep 17, 2020 at 12:50
  • If you have a choice, you WANT your motor loads running on 240V, by the way. 1/2 the amperage, 1/4 the power loss in wiring .vs. running the motor.
    – Ecnerwal
    Commented Sep 17, 2020 at 12:52
  • The RO does not have a 240V option?
    – Ecnerwal
    Commented Sep 17, 2020 at 14:44

1 Answer 1


Subject to revision depending on your actual loads and how tight the budget is (cheap can be expensive later on, though) I would suggest:

3x 1 AWG aluminum (hot, neutral, hot) 1x 4 AWG Aluminum (but 6 AWG is technically acceptable if cutting it to the bone) Ground. That allows for up to a 100A feed - you may find some use for that, but it also allows for reasonable voltage drop at 50A and 300 feet.

Use 1-1/2" schedule 80 PVC conduit - trenches are expensive, conduit is cheap. If there's any odds you might want even more power at some point, consider 2" conduit. If you might yearn for telephone, intercom, or internet or camera coverage, put in an extra conduit for communications lines. If you are careful about placing the conduit and filling the trench you can save a few bucks by using schedule 40 where it's fully buried - if you are not willing to put the effort into being careful about that, schedule 80 all the way may save you agony. You need schedule 80 where it comes out of the ground anyway (unless you are running this overhead on poles - very retro but acceptable - subject to falling tree damage, though.)

If the shack is "yet to be built" put an UFER ground in the slab or footing, and drive a ground rod outside. Otherwise drive at least two ground rods outside, separated at least 8 feet. Use a 100, 125 or 200A panel at the shack (does not matter so long as it's "at least as big" as the feed breaker) and be sure to remove the bond and keep grounds and neutrals separated (grounds bond to the case, neutrals are isolated from the case.) You require both the grounding system at the "shack" and the grounding wire (connected to them) back to the main feed.

Or if you are SURE 60A is all you'll need and you want to go cheap-as-possible:

3x 4 AWG aluminum (hot neutral hot) + 1x 8 AWG aluminum (Ground) - gets about 6% drop but should still work, and will be less drop when not fully loaded.

That only gets your conduit size down to 1-1/4" - using a 10 AWG copper ground would get you down to 1".

So, the actual loads appear to be:

Vacuum pump needs 20A breaker, runs at 5.5A, 240V - continuous load (runs more than 3 hours) size for 7 amps (wire has to be sized for 20A due to the breaker, breaker presumably has to be that size to start it.)

Lights etc. 120V loads: 7.5A - use a 15A breaker, 14Ga wire, Provision for 9.5 since lights tend to be continuous loads especially in sugar season.

Reverse Osmosis - 120V at 30A.

So your "actual load at 240V" is 50A (minimum breaker size) to support the 20A 240 and the 30A 120, (the 15A 120 you get "for free" by putting it on the opposite leg from the 30A - you could even add a second one) and your "continuous" load is 16.5 between the lights and the vacuum pump, with the the RO bumping up to 35.5 A (again, the lights become "free" in terms of amperage [not power used] but you have the vacuum pump power added to the RO power, whatever that actually is (using the full 30A for now.)

If you go with the cheap option your RO will be dropping 5% or so if it pulls the full 30A - it probably uses a bit less. You could also pick a size between 4 AWG and 1 AWG to suit your price/performance/expansion or no-plans-for-expansion preferences. If your RO can be reconfigured to use 15A @ 240V you might be able to shrink the wire a bit more.

  • Would you be able to dumb this down for me a little bit. I am trying to do it cheap as I can. I was told if I run 30A 240V out of the main break I should be able to run 60A 120V at the sub panel in the shack. Is this true? Commented Sep 17, 2020 at 16:16
  • Yes, I already commented that 30A @240V gives 60A@120V, but that's not a smart approach if you can put both of your large motor loads on 240V (call it 230 if you like, but it's 240 for decades now.) By doubling their voltage and halving their current, you cut line losses from the 300 foot run by a factor of 4. It would appear that you could slide by on 30A@ 240 so long as you don't try to start the vacuum pump while the RO is on (appears to be fine if it's already running.) Might pay to split your 120V loads on two circuits for balancing in that case. Or step up to a 40A feeder.
    – Ecnerwal
    Commented Sep 17, 2020 at 19:06
  • Likewise, folks concentrating on "as cheap as possible" (the first time) tend towards 4-wire direct burial feeder (don't go to 3-wire, that's a code violation for decades now) and it's cheap, in every sense, including becoming expensive because it's more prone to break in the future. But it's cheap out of the gate...
    – Ecnerwal
    Commented Sep 17, 2020 at 19:09
  • See also: diy.stackexchange.com/a/195329/18078
    – Ecnerwal
    Commented Sep 18, 2020 at 13:40

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