DIY subpanel install

Discussion in 'Electrical Forum discussion & Blog' started by J Eickholtz, Sep 16, 2018.

  1. J Eickholtz

    J Eickholtz New Member

    Sep 16, 2018
    Dorr, MI
    I'm new to the forum, hoping some knowledgeable guys can help me out. I'm pretty sure the only code I need to worry about is National Electric Code (NEC) and I have done the best research I can.

    Current situation:
    -100 Amp meter socket
    -100 Amp? panel for house.
    -30 amp breaker for garage, not sure the cable is big enough for that, but it's there.
    -Pretty sure the panel is overloaded and I don't think I have a Main breaker. Not sure how this got through, I guess codes were easier back in '69.

    -200 amp meter socket
    -100 amp panel for house
    -100 amp panel for garage (I want to weld @ 50 amps and have plenty of room for more)

    My current plan:
    -Power company has to install the new meter socket. If possible I will use the Siemens MC0408B1200T to eliminate my main panel. It is basically a meter socket that has spaces for large breakers.
    -If the power company uses their own socket, which I think they will, I'll use 4/0-4/0-4/0-2/0 Aluminum MHF wire to the main panel. Is there a better/cheaper wire I can use for this? Do I need a bare ground? The run will be pretty short; straight from the socket into the panel in the basement.
    -2 x 100 Amp breakers, 1 for each subpanel.
    -2-2-2-4 Aluminum Mobile Home Feeder (MHF) wire to each subpanel
    -House panel is now a subpanel.
    -2" metal conduit 6" under concrete from the house to the garage. I think I can go down to 1.5" conduit but I want some room just in case.
    -100 Amp subpanel in garage

    Running to the garage is a challenge. It's detached and there is nothing but concrete and HUGE trees between the 2. I plan to trench out the concrete and run metal conduit under the fresh patch. Do I need to go 4 inches or 6 inches below grade? Do I need Rigid Metal Conduit (RMC) or can I use Electrical Metal Tubing (EMT)? The MHF is safe underground if it's in conduit, right? I have to go all the way across the house (25+40=65ft) and then about 9-10ft underground to the garage.

    I have also thought about tunneling between the 2 buildings, starting from the basement and aiming for a 6"x30" patch of dirt next to the garage. Anyone ever tried something like this? I am concerned that there will be roots in there because the canopy from 2 trees intersects about where I need my conduit run.

    I could also exchange my main panel for a 200 Amp, then run my garage off that. Either way I have to buy a new 200 amp panel and a new 100 amp panel, but with my plan I don't have to re-wire every breaker in my house, and I can buy a 200 amp panel with le$$ breaker spaces.

    My last question is about inspection. Will they need to see the conduit before I cover it with concrete? What about after?
    Last edited: Sep 16, 2018
  2. WorthFlorida

    WorthFlorida Broad-Wing Hawk

    Oct 28, 2009
    Orlando, Florida
    A job this large and complicated it is best to hire an electrician to go over your work and do some or the work. It seems that you did your homework but a local licensed electrician will know what the local inspectors want to see.
    • PVC Conduit needs to be 18" below grade from the top of the conduit. Any part of it above grade must be schedule 80 if you use PVC for impact protection. The inspector does want to see the depth of the conduit. For metal as little a 6" but do check your local code. After a while metal conduit will corrode and difficult to get nearly a 100% water tight. Properly glued PVC conduit will be as water tight as possible. If you use metal conduit, coat the pipe with a driveway sealer where it will come in contact with concrete. It will minimize electrolysis of the steel conduit.
    • 1.5" will be tight for 2-2-2-4 MHF. It'll work but go to 2" for a little cost increase.
    • Grounding will be an important issue and there are code requirements for connections in panel that must be torqued. The inspector may want to see the proper torque. An experienced electrician should know these.
    • Power company will not transfer service or connect to your new panel without an electrical inspection and some may require a permit pulled by a licensed electrician registered with the power company.
    • Most power companies only make the connection at the "pole or mast" and plug in thier meter in your panel, everything else you provide.
    If a DIY does his own plumbing, you might get water on your head, if a DIYer does his own electrical and messes up, you get fire, electrocution or death.
    Last edited: Sep 18, 2018
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