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Non-electrician here - I have a small detached garage 25ish feet from the main service on the back of my house.

In consulting with an electrician he said the simplest way to get power out would be mounting a sub panel on the back of the house right by the main service, then just run 4 12/2,14/2 wires underground to a junction box in the garage. Easy enough, however unconventional.

I passed rough in inspection yesterday but because there is more than one circuit to a detached building (despite the sub being on the house) the inspector wants to see a separate ground.

So, I’m thinking I’ll install a ground near the garage, and run it in the trench back to the sub-panel. I think I also need to have the ground from the main service per updated code, so that would mean my subpanel, mounted on the exterior of the house would have a ground coming from the main service AND a separate two rod ground.

So double grounds in the sub panel. The neutral bus won’t be bonded. Any issues?

Am I understanding that correct? All thoughts are welcome.

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  • Detached and they allowed 4 circuits ,,, don’t have my code book handy but I think that is a code violation. – Ed Beal Jul 18 '20 at 15:29
  • It sounds like you'll have to dig things up and start over from scratch. What are you trying to power in said detached garage BTW? – ThreePhaseEel Jul 18 '20 at 16:15
  • What is your location in the world ? As mentioned in multiple comments and answers 2 circuits are the max for a detached structure in the USA unless one of the few locations that doesn’t use the NEC. – Ed Beal Jul 18 '20 at 21:53
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The inspector should have red-flagged 2 or more circuits to the same outbuilding. That's not allowed.

There should be a subpanel alright, but it needs to be on the garage, and then the mandatory grounding rods are a straightforward matter.

The grounding rods are no substitute for a ground wire; they do different jobs.

Since Code does not allow multiple circuits to an outbuilding, it is difficult to advise how to attach them to a local grounding electrode system.

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Dang. Why on Gods Green Earth did your "electrician" suggest this? We get a lot of "sub-panel" questions here that are quite similar, but this one is new to me.

Why not simply place the sub-panel in the garage? Run a decent feed to it, oversize it (I'd get snipped by one of the big-3 here if I didn't mention that! LOL) It would be much more flexible for the future than running a bunch of circuits underground and probably even less expensive.

Regarding code compliance, in this weird setup, I'm not sure. Probably float (isolate) the neutral from the ground and install a couple of ground rods connected to the ground bar on the sub-panel.

But let me strongly suggest, even though you already passed rough in. Fix it now. Get a new, large panel for the garage, run a decent supply to it (50 amp minimum) that will support current and planned loads. You'll be much happier with it in the long run. Too late to save money on the runs, since they are already in.

I'll be nice considering what I'm thinking of your "electrician" and only say he gave you bad advice.

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    I fully agree I believe more than 2 circuits is a code violation for detached I can’t believe it passed rough. + – Ed Beal Jul 18 '20 at 15:31
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    Yes, Ed, at least in the USA it is not to code to have more than 2 circuits in an outbuilding without it's own sub-panel. I wonder when the OP is located. Maybe not in USA? + – George Anderson Jul 18 '20 at 19:55
  • I did not think outside the us but I did double check and you were correct I thought you were. – Ed Beal Jul 18 '20 at 21:50

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