This WHOLE thing is wrong from the get go, and for several reasons.

1) You CANNOT feed a detached structure with more than one circuit. For this purpose a multi-wire circuit is considered one circuit.
It is being proposed to run MANY circuits to this garage. NOT good.
I am still uncler if this is detached or attached. If it is attached then this does not apply.


2) Derating was brought up. For all practical purposes, over NINE CCC's (current carrying conductors) you must start to derate #12 THHN. It is involved as to why, but ten or more CCCs and you must derate to the point where you are under the "standard" 20 amps for #12.
Keep in mind, the neutral of a MWBC (multi-wire branch circuit) does not count as a CCC nor do grounds.
It is being proposed to run WAY more than nine CCCs.
For instance, if he runs ten MWBCs, for twenty circuits, this is 20 CCCs and he MUST derate those circuits to 50% of 30 amps, or 15 amps.
IF this is an attached garage, then you would have to run several smaller conduits with up to eight circuits, (even MWBCs) in each to allow each circuit to stay 20 amps.


I can understand trying to save money and using something you have on hand, but butchering a job and doing things ALL wrong is NEVER a good way to go.
If you are insistent on using the THHN you then have go the multiple conduit run route provided the garage is attached as I said.

Quote:

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Originally Posted by EPMiller

I believe you will have to have 1 green grounding conductor for each circuit, so you will have to buy that wire.

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NOT true, you need ONE ground per raceway, based on the largest circuit conductor.
So you can have 100- #12 wires in a conduit and you would only need ONE #12 ground.

Quote:

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Originally Posted by stanfortyman

<snip>
NOT true, you need ONE ground per raceway, based on the largest circuit conductor.
So you can have 100- #12 wires in a conduit and you would only need ONE #12 ground.

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Thanks Stanfortyman. I will file that fact for future reference if needed. :)

As to the original question, I think the garage is attached, and he did mention 6 or 7 circuits. That would be 12 or 14 CCCs, so he would get into derating unless he did the multi wire branch circuit setup.

EPMiller

Heck, he could do four MWBCs in a 1" conduit and be all set.

Strat, that makes no sense to me. I believe that he is limited to one supply cable into the detached garage. So that means one breaker off the SEP (100 amp - two phase) to supply 120/240 on the sub panel.

LRA has to determine if the sub-panel can be on the outside wall of garage.
All receptacles inside the garage need to be GFCI protected.

Tommy, it appears that you believe I think you to be an idiot. That is absolutely untrue. I don't know anything about you. If I appear to be rude, I apologize, I'm from Da Bronx, NY and we are speak two languages. Manhattan English and Bronx speak. I promise you I am not trying to be rude. My concern is that you are not approaching this situation wisely so I ask you questions first to determine what you know or don't know.

Had replied but didn't send post, but I said, "I thought it was attached, then reread
"through my attic of underground"? Others felt it was attached also. Myself it was confusing , and I should have asked him to clarify.

Tommy,

I went back through all the postings and discovered that your garage is attached. That's a different ballgame. I was under the impression that your garage was detached. I apologize for my error.

I'll go back and start over.

Strat,

The phrase, "through my attic of underground"? is a typo.

It should read, "through my attic or underground."

Wow!