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  • Help with wiring house to garage to pole barn

    Originally posted 09-30-2018 6:43 PM
    By: dirtbilly


    Hello people, looking for some confirmation and or direction to wire from house to detached garage and pole barn from main panel in house. So my situation is I have a 200 amp service in my house and would like to pull 100 amps to my detached garage and then to my pole barn I only have 3 spaces left in my service panel. at first I was thinking pulling 3 #2 THNN and a bare copper #4 ground to the garage and use either a feed thru panel or just install a 100 amp breaker in that sub panel and then on to the Pole barn, however in order to avoid having to run conduit (1 1/4)under a 12 foot wide driveway I was wondering if I could pull 100 amps from main panel to a sub panel in the crawl space and from there use breakers to pull separate 100 amp wires to each garage and pole barn. Thoughts ? is it legal to use a sub panel in this manner ?

  • #2
    Originally posted 09-30-2018 11:58 PM

    Depends on the crawl space. Is this space really a short basement, or is it truly a crawl space with a dirt floor where you'll be on your hands and knees? If its the latter, it may be a legal location for a panel but it is a crappy choice. Why not just put a new panel next to your main panel and put two 100A breakers in it (fed from a 100A breaker in the main panel)? Then, run those two 100A feeders through your crawl space and send one to the garage and the other to the pole building.

    Do you really need 100A in each location? It is difficult to use that much power. Things would be cheaper and easier if each feeder was 60A (or maybe 50A to garage and 100A to pole building). Have you done a load calc for either area?
    Mark
    Kent, WA

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    • #3
      Originally posted 10-01-2018 7:07 AM
      By: dirtbilly


      Thanks for the reply Mark, so the details of my site are as follows: the wall with my existing panel is an outside bedroom wall that is spray foamed insulated so adding a sub next to it would require removing drywall from the wall and digging out foam, the rim joist is very close to the first joist at the floor. making running wires very difficult there. When I built the house I installed a piece of conduit from the panel into the attic and another in a interior wall from the attic into the crawl for future runs. The crawl space is 4 feet high from a plastic covered dirt floor. As for the 100 amp service I always figured if you are going to spend the time and money to run a circuit might as well spend the little extra and put in capacity that you or a future buyer might want.

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      • #4
        Originally posted 10-01-2018 8:40 AM

        4 feet high is not high enough for a panel. You need at least 6 feet of head room so you can stand in front of the panel.

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        • #5
          Originally posted 10-01-2018 12:55 PM
          By: dirtbilly


          I see, are there junction boxes that would allow me to splice inside ? perhaps one with lugs to split 1 circuit into 2 ? in that case I would consider a 60 amp #4 wires

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          • #6
            Originally posted 10-01-2018 6:51 PM

            Can you merge one circuit in your panel to another one to free up another slot so you have your 4 slots you need? If not, you can put a double pole breaker in the main panel and run it to a junction box in the crawl space where you split it to two different destinations. I'd use all the same size wire in this case if that's your plan (either 60A or 100A).

            When wires are #4 or larger, box sizing is based on conduit size and not wire size. If it comes in 1 side and out the opposite wall, then you need a box whose wall to wall length is 8X that conduit size (e.g. 8 x 1.25 is 10"). If there are multiple conduits, that can cause an increase in size. I would look for a 12x12x4 junction box to use for this splice. I'd use either two split bolt connectors on each wire or a split bolt and a butt type splice that uses set screws. The splice hardware available at Home Depot will be bare metal, and I've never seen the insulated Y type or multi splice hardware there. So after you make up your splice, you need to wrap it with rubber splicing tape (4 lapped wraps) and then cover that with vinyl electrical tape (2 lapped wraps). Basically, the tape needs to end up 1.5x as thick as the insulation you took off.

            For the ground wires, install a 5 hole ground bar in the splice box and put the 3 grounds on it (one incoming and 2 outgoing).
            Mark
            Kent, WA

            Comment


            • #7
              Originally posted 10-05-2018 8:02 PM
              By: dirtbilly


              First off thank you to all that replied, so after trying to make my original plan that I had laid out years ago work I decided to take a step back and take a fresh look and I think I have a better solution. Since my house service panel is mounted to an outside wall I will remove a knockout on the back of the panel and go thru the wall with conduit to the outside trench to barn, garage etc. My question now is since I have a 200 amp main panel can I pull 100 amps to the barn and 60 amps to the garage from the main panel (install 2 new breakers in my main panel) or should I run 100 amps to the barn install a sub panel and then install a 60 amp breaker from barn to the garage ? just not sure if adding a 100 and 60 amp breaker to my main panel is ok ? that would be the most economical and trouble free way to run if I can.
              Last edited by TransferGuy; 03-19-2019, 02:49 PM.

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              • #8
                Originally posted 10-05-2018 11:15 PM

                Ultimately, the load on your main panel will most likely be the same, whether it is from the garage or the barn. Yes, it is possible to overload the main panel if the barn pulls 100 and the garage pulls 60, but if you do a load calc that shouldn't happen. And if it does, the 200A main will trip anyway.

                So I would run this whatever way is easiest and works best for you -- two separate feeders, or feed from one building to the next.

                You'll probably need an LB fitting to transition from the back of the panel down to the dirt. Don't skimp on conduit size. I'd use at least 1.5" for 100A and 1" for 60A. Pulling is easier and the LB boxes are larger so easier to feed into them.
                Mark
                Kent, WA

                Comment


                • #9
                  Originally posted 10-24-2018 9:26 AM
                  By: dirtbilly


                  Ok I have a plan now, just one more question: Can I run wires for 2 separate sub-panel's in the same conduit ? my plan is to run the 100 amp and 60 amp THHN wires in the same 2" conduit from the panel into the crawl space and then utilize a large pull thru / junction box to separate the 100 and 60 amp feeders into there own conduits. So 2" conduit in to the pull thru box and 1" out for 60 amp and 1 1/4" out for 100 amp. I will use THHN for hots-neutral and ground conductors to the sub panels and then solid copper from sub panel to ground rod.

                  Comment


                  • #10
                    Originally posted 10-24-2018 10:37 PM

                    Yes you can, but you have to apply a derating factor. You will have 4 current carrying conductors (neutrals only carry imbalance current, so they count as 0 in a 102/240V feeder). This results in an 80% factor you apply to the ampacity. Crawl spaces are almost always under 86F, so you most likely don't need to apply any factors for ambient temperature. If the wire you buy is labeled THHN, then it is 90C rated and you apply the 80% to that 90 degree ampacity. You didn't mention what wire sizes you were using.

                    The 90C ratings of copper wire are as follows:
                    #6 AWG is 75. 80% of that is 60 amps.
                    #2 AWG is 130A. 80% of that is 104 amps.

                    So #6 is right on the edge, and #2 has 4 amps to spare. If you're in arizona and the crawl can get over 86F, then I'd upsize the 60A feeder. If you in a cooler area and the crawl never gets over 70F, you have a little extra margin than the numbers above.

                    Note that one grounding wire can support the two feeders, so you only need one green wire in the 2" conduit. You size it for the largest feeder overcurrent device. A 100A feeder requires #8 copper. You can always go larger if you want (#6 is good to 200A for grounding).

                    The ground electrode conductor to the ground rod does not have to be solid. I'd use #6 if it isn't exposed to damage, #4 if it is. #8 would be the minimum required, but you have to run #8 in conduit (and PVC is easier), so it ends up making #6 or #4 cheaper and quicker.
                    Last edited by suemarkp; 03-19-2019, 03:00 PM.
                    Mark
                    Kent, WA

                    Comment


                    • #11
                      Originally posted 10-25-2018 6:48 AM

                      Most THHN wire is dual rated but make sure you have TWWN rated wires for the underground portion.

                      Comment


                      • #12
                        Originally posted 10-25-2018 9:45 AM
                        By: dirtbilly


                        Mark, I live in Michigan the 100 amp run is 235 feet so I planned on using #2 THHN for hot-neutral and the 60 amp run is 141 feet so I planned on using #4 THHN hot -neutral is this overkill ? and can I use #8 THHN for the ground between feed and sub panels for both ? I was under the impression you go up one size for ground so #2 hot would use #4 ground etc. Thanks again for your all your help.

                        Comment


                        • #13
                          Originally posted 10-25-2018 1:45 PM

                          If you upsize the conductors for voltage drop (which is what you're doing because of the long distance), you also must proportionately upsize the grounding conductor too. To me, the "normal" size for 60A is #6 cu and the normal size for 100A is #2 cu. The normal size ground is #10cu for 30 to 60A feeders, #8 cu for 61 to 100A feeders, and #6 cu for 101 to 200A feeders. Go larger than normal, and you're upsizing.

                          I'd be inclined to maybe upsize the 235 foot run. Maybe go to 1/0 for that. The 60A feeder is a toss up -- nothing wrong with going to #4 other than cost. If you upsize the 100A feeder from #2 to 1/0, you'd need to upsize the green ground to #6.
                          Mark
                          Kent, WA

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