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I have a shed which is a little less than 100 feet from my home breaker box. I currently am poor-manning it running a 100 foot extension cord out there. I have already purchased a branch electrical box and wired the shed. I am about to rent a trencher to trench for the electrical cable.

I would like to run 240v out there just in case I ever need it so I do not have to redo the job in the future. However, at this point I want 2x 20 amp circuits running out there for saws and things on one breaker & lights, tv, receiver etc on the other. I am going 20 amp vs 15 amp just to have some extra capability. If your opinion on this differs, I would like to know more.

So here is my main question. With a 3% voltage drop in mind, what wire do I need to run out there given the distance (100 ft) to obtain a max 20 amp 240v capability and/or 2x 20 amp 120v capability? Can I go with a smaller gauge electrical wire to achieve this or is 6/3 what I need to go with? I do realize that the most important part of the equation are the breakers installed on the home side. Those must be at or below whatever electrical cable I run out there. Would it be possible to run 1x 10AWG/3 UF-B electrical cable out there with 2x 20 amp breakers in the house?

The online electrical wire calculators are confusing me... I guess what I do not get on the 3 conductor cable is if the cable is capable of supporting 20 amp per hot wire or a total of 20 amp across all 3 conductors.

Is it reasonable to assume that a 100 foot 10AWG/3 Conductor wire is capable of carrying 2x 15 amp loads @ 120v or 1x 30 amp load @ 240v?

I do not plan on welding (due to wood shed/wood shed floor) or anything like that. I can also probably step down to two 120v 15 amp circuits as I can only operate a tool at once. i may want to install an a/c unit out there though at some point. probably 120v. the shed size is 12x20.

This install location is in east north Dallas. Lots of clay and rocks. If i can avoid digging an 18" ditch, I would definitely prefer it. I will not permit the install but do want to follow code and do so with the cheapest trenching method and electrical cable possible.

isherwood
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ThaKidd KG5ORD
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2 Answers2

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Sounds like cheap is a motivation, but there's a relationship between depth of dig and cost of materials.

  • At 24" of cover you can use plain cable such as UF.
  • At 18" of cover you can use cheapie PVC conduit or EMT.
  • At 6" of cover you can use Rigid metal conduit.

So as expensive as Rigid might be, it might be significantly cheaper than renting a trencher if you can hand-dig or hydro-dig with a hose to 6".

If you run conduit, you can use THWN-2 single wires instead of expensive, balky cable, and you can go cheap now and add more or larger wires later. If you use metal conduit, you don't need a ground wire.

Also if you are cheap, the first thing to shortcut is the 3% voltage drop thing - that was always an old wives tale, is usually computed wrong anyway, and is simply not needed. Also, 100' distances are within 3% even at statutory max current!

  • For 20A, use 12 AWG UF or THWN in 1/2" conduit.
  • For 30A, 10 AWG " " " 1/2" conduit.
  • For 40A, 8 AWG " " " 3/4" conduit
  • For 60A, 6 AWG copper ... ... 3/4" conduit or 4 AWG Aluminum in 1" conduit.
Harper - Reinstate Monica
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I'm not a certified electrician but I do have a man cave similar to what you are talking about. Mine already had 10 gauge wire running from the house panel to the shed. I added 100 amp six breaker panel made by square d and split my circuits. I am running a double 240 for a heater and welder not at the same time and I'm running a circuit for the air compressor, a circuit for the lights. A circuit for the other shed that's connected as well which I have a couple of freezers in.20amp circuit They are all 20 amp circuits except for the welder circuit which is a 30 inside. The house is a double pole 30. It's all 240 coming to the shed which is the way you want to go. You can split it back to 120 in the box in the shed, but I realize that 10 gauge wire is pushing it a little bit in my case when I check my amperage between the two hot wires. One is 16 amps and the other is 10 with the heater and the lights running but 6 gauge would probably be the way to go because then you're up around 80 amps or so capable and you should be okay for the future if you ever wanted to add on. Sounds like you're on the right track but just look up how to wire sub panels with certain things like grounding rods and so on. But you should be fine. Just pay attention. Good luck

RICH
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