Forum Discussion

Jimbro's avatar
Jimbro
Explorer
Apr 30, 2019

add 2 30 amp 120v circuits

I hooked up a retired teachers airstream to the 20 Amp circuit from the goat pen. It proved to be inadequate for her. Now we are interested in traveling via airstream rather than our crowded Toyota Sienna. I have my own retired teacher wanting to stretch out.
I want to add 30 amp 120v service 50 yards from the farmhouse to a barn for our travel trailer which will double as a weekend guesthouse ...(pt A to B) I want to add a second 30 amp service 75 yards further to the retired teachers airstream. (pt B to C) all underground. What size wire do I need? A to B... and B to C? The box at point B would have a couple extra 20 amp circuits for barn lighting and light tools.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Apr 30, 2019
    RobWNY wrote:
    For that long of a run I wouldn't use anything smaller than #6


    Agreement 6GA. 0.39 ohms per thousand feet.. By the time you run down to the ground. bury it and back up to the box you are over 900 feet. So figure about 0.38 ohms times 30 amps = 11 volt loss at full load.. You might wish to go bigger still.

    Source document
    American Wire Size Chart
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Apr 30, 2019
    Electrical code only allows one power feed to an outbuilding (exception is for exterior lights, but nothing else can be on that circuit).

    The most economical cable is probably MHF 2-2-2-4 and can easily carry 60A the 150' to the barn where you must install a sub-panel (space, 12 circuit). From there you can run more MHF 2-2-2-4 to another 225' to another sub-panel. All of this would carry 240V. MHF is aluminum and cost a lot less than copper. (That last 225' in copper would probably require 6/2 copper which actually cost more)

    Do it right ! The cable and thesub-panels will cost about $500. Digging the trenches could be expensive. If the trenches are dug and the material is all on hand, a good electrician could do that job in one day.
  • cavie's avatar
    cavie
    Explorer
    Apr 30, 2019
    call an electrician. Not a diy project. google "voltage drop calculater" for wire size. I'm quick guessing #4 copper for the distance.
  • Jimbro's avatar
    Jimbro
    Explorer
    Apr 30, 2019
    What wire guage would the 50 amp between pt A and point B need to be?
  • wnjj's avatar
    wnjj
    Explorer II
    Apr 30, 2019
    It sounds like you want a sub panel at point B. That being the case, run 240V with a neutral (i.e. 4 wire including ground) to that sub panel. Then tap the “B” RV receptacle and one 20 circuit from one leg and the “C” RV receptacle and another 20A circuit off the other leg. The result is only 3 heavier wires needed from A to B instead of 4.

    Now the distances involved are quite far and you’re going to get a variety of answers, depending upon the worst case current draw. If RV C wants to run an air conditioner it’s going to take good size wire for that distance. Something like #4 or #2 copper.
  • RobWNY's avatar
    RobWNY
    Explorer
    Apr 30, 2019
    For that long of a run I wouldn't use anything smaller than #6

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