Adding an outdoor sub panel - wire size, breaker size, ground rod???

Discussion in 'Electrical Forum discussion & Blog' started by Tim Fastle, Aug 26, 2018.

  1. Tim Fastle

    Tim Fastle Member

    Feb 10, 2017
    New Mexico
    Our property is 2 acres. I want to ad a small sub-panel near the front of the property (150 ft from load center) so I can run 3 - 20 amp circuits in order to have access to power in a number of spots for various things (a gate transformer, low voltage lighting, Christmas lights and power when doing odd jobs). I want them 20 amp circuit so I can run my small wire feed welder if/when needed out front (rarely). Each circuit will likely only have one outlet on it.

    My idea is to use a 30 amp 220 breaker to supply the sub-panel (pulling 4 #8 wires) and then run my 3 120v circuits from there. These outlets would be used rarely and, other than my welder, drawing fairly low power. I am fine if I am welding and someone helping me uses a drill and it throws the breaker at the main panel. Would this be approach be safe and acceptable or am I missing something? The distance from the supply panel to the sub is about 150' and the distance from the sub-panel to the outlets would be about 100' each. I calculated that I would need #8 wire for all of the circuits (feed and branch). One reason I am going this route is that I have quite a bit of the#8 wire I would need left over from another project and would like to use it as opposed to having to buy #6 to for a 40 or 50 amp panel.

    Also, I have done a lot of reading and seem to get conflicting information. Would I need a ground rod at this outdoor panel (on a pole, not attached to a building)? I gather I would not but am not sure.

    I came up with these wire sizes using an online wire size calculator. Since I will be bringing in 2 hots, a common and a ground, I used the source voltage as 240 which allows for smaller wire. From there I will run my 120 v circuits using 120 as my source voltage to calculate those wire sizes. Do my wires size calculations look to be correct?

    Sorry for so many questions but I want to have my plan fairly clear (and safe) before I start digging.

    Any input or help would be greatly appreciated!

    Thanks very much!
  2. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    IL leads me to think that your calculations are OK.

    I think your 120 volt outlets should be GFCI-protected.

    I think you could also put in a 240 volt outlet in case you get a new welder.

    I don't know if you need the extra grounding rod or not. I am not an electrician.
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  4. Tim Fastle

    Tim Fastle Member

    Feb 10, 2017
    New Mexico
    Thanks for the input Reach4. I do plan to use GFI plugs on all of the circuits and adding a 240v outlet is a very good idea. I just may do that!

    If anyone has any insight on the grounding rod it would be appreciated.

  5. Stuff

    Stuff Well-Known Member

    Mar 7, 2013
    Since this is a feeder the NEC only says you need a grounding electrode (grounding rods) if it is a structure or building. You might have local rules that override this so check with your building office.
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