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Seeking some advice on installing a sub panel in a detached garage. I have a 200amp main in my house and I plan on installing a 90 amp sub-panel in a detached garage approx. 100FT away from the main panel.

In order to avoid having to run a conduit in the house, I am planning on running 2-2-2-4 SER Aluminum cable from the main panel through a crawlspace into a metal junction box, then transition over to MHF. The MHF wire will run from that junction box through a rigid conduit buried 6” underground directly into the garage panel. Using Rigid over PVC due to the rocky soil making it difficult to dig 18” deep. I plan on installing a grounding rod next the garage which will ground the sub panel. Can I run the wire in this manner or does the rigid conduit need to be bonded back to he main panel?

Would I be better off running MHF the entire way and running it through EMT within the house from the main and transitioning to the Rigid conduit for the underground? Any advice would be greatly appreciated.

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    – Daniel Griscom
    Mar 5, 2020 at 11:58
  • What are you planning to use for the subpanel?
    – ThreePhaseEel
    Mar 5, 2020 at 23:46
  • The panel will provide electricity to the garage that will be used for lighting, regular power tools and a 60 amp breaker for an EV charger.
    – Peter L
    Mar 6, 2020 at 0:36

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You'll need minimum 1-1/2" rigid for MHF cable. That means 8" burial depth to give 6" cover. 12” cover under vehicle drives.

THWN or XHHW wires are a much better choice. It would allow 1-1/4 conduit and other wires in the conduit. Cable in conduit is silly as it makes for a very hard pull. The only reason to do it is if you wanted to transition from conduit to in-house wiring without any splices.

A wired ground, or Rigid as the ground, is fine. You need grounding rods also.

Remember at #2 wire size the splice box must be quite big.

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  • Thank you for your reply. I will look into possibly running separate wires in there, although I did run 2" rigid conduit to give me some more ease when pulling the wire. Does my conduit need to be bonded back to the main panel or is it fine terminating at the junction box?
    – Peter L
    Mar 5, 2020 at 14:48

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