Electrical – Wiring of a metal detached garage


I am looking to add power to my detached metal (enclosed carport) garage. With that said I am trying to figure out the most economical solution to wiring the garage. I would like to run the wire like normal unfinished detached garages with the wire running behind the metal studs and between the outside wall with 12/2 Romex. Behind Metal Stud This would then run each span (leg) of the garage inside the rib of the metal to give me power plugs for various things like power tools. Between legs in ribs My questions are…

  1. Can this be done and be NES compliant?
  2. Would I have to cover the wall surface to be compliant? (plywood or similar)
  3. Should I run it in PVC conduit (1/2 or 3/4)?
    3.a. Can I use Romex 12/2 in conduit or do I have to get THHN?
  4. At the subpanel do I need to connect a copper grounding rod for the sub?
  5. What is the better method GFI breaker or GFI plug at the start of each electrical run for safety?

Assuming when a house is put up for sale during an inspection a detached garage is not inspected does it really matter (within limits of safety) if I leave it exposed?

If you guys have any other advice on this please let me know.

Best Answer


Since the garage is detached yes a grounding rod is required. Last the ground wire from the rod is connected to the grounding buss and the metal frame of the box / the building. The grounded or neutral conductor is isolated from ground an insulated buss is normally available in a main lug panel or a main breaker panel, if the bonding screw or jumper is installed in a main lug panel it is removed.

Running cable behind metal studs of unfinished wall

Any NM-B or Romex running horizontally requires protection below 8 feet. In my jurisdiction even running down the side of the stud requires protection.

Although MC or metal clad is under the same requirements as NMB most inspectors will let this fly on an inspection so I would consider upgrading to MC wire it is a little more expensive but will look a lot better in my opinion than exposed NM-B.

Cable through conduit

Can you use NM-B or romex in conduit sure but why? It would be many times harder to pull (you cannot strip it) and if going to conduit THHN is cheaper and much easier to pull.

GFCI breaker or receptacle

As far as a breaker or first outlet it depends on the location to me because there is no difference in the operation or safety. The difference is in cost. Usually GFCI receptacles are cheaper than breakers. But again location comes up. By location if you have a separate room or a large area walking 30-50’ to reset a GFCI can become a pain when the receptacle is just a few feet away so many times I will use GFCI receptacles in a home and garage to save $ and have the reset close.

Hope I hit all your questions we normally ask that they be broken up but these are quite common for a detached building.