# 100 amp Attached Garage Sub Plan



## kbsparky (Sep 11, 2008)

You only need #3 THHN to support 100 Amps, with a #8 THHN ground.

But, if you upsize to a #2, then you will be required to upsize that ground to a #6 as originally stipulated.


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## J. V. (Jun 1, 2007)

The panel itself will be 120/240 regardless if you need 240 or not. If you go with #2 you can use all black wires and mark (marking tape) them as needed. Sounds like you have a plan. Your AHJ always has the final word, so run any questions by him first. Good Luck and have FUN.

ps.....#6 should be green.


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## KevinBeamer (Aug 30, 2009)

I decided to use a CH Pro 125A 8/16 main lug sub in the garage so my main and sub use the same breakers, making them interchangeable.

kbsparky, I am upsizing the wire because of the distance (almost 70'). 

Regarding voltage drop, do you think 3-3-3-8 would be OK at this length ? It would cetainly be cheaper.

J. V., Yep on taping the wires. Probably like you, THHN #2 around here (perhaps everywhere) only comes in black. I found a nice package of "GB" 6 colored electical tapes at HD for $3. 

I noted there's no 240V requirements at this time, but understand the sub is being fed 240V (from a 2 pole breaker in the main).

Need to ask the AHJ if he requires solid or stranded ground (or doesn't care either way).

Thanks for the feedback. I'll post pictures as the project progresses.

KB


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## kbsparky (Sep 11, 2008)

68 feet should be no problem using #3 circuit conductors. We would use a #4 for the neutral on such an installation, making the wires 3-3-4-8. You really don't need a full sized neutral unless you don't have any line to line loads.


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## KevinBeamer (Aug 30, 2009)

The town inspector said he will accept 2-2-2-8 THHN in 1.5" conduit for 100 amp service 70' from the main panel.

I was planning to feed the sub panel through the right side. Is this typically acceptable or must the wires from the main panel enter at the top or bottom of the sub panel ?

KB


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## kbsparky (Sep 11, 2008)

You can feed the sub-panel from the side if that is convenient. Back side, left side, right side .... Any side but the front side. :jester:


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## KevinBeamer (Aug 30, 2009)

Thanks kbsparky. Can I do the same at the main panel ?

As you can tell, I'm getting closer to starting the physical work.

KB


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## kbsparky (Sep 11, 2008)

Yes, same as the sub-panel. :yes:


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## AndrewF (Dec 29, 2008)

kbsparky said:


> You only need #3 THHN to support 100 Amps, with a #8 THHN ground.
> 
> But, if you upsize to a #2, then you will be required to upsize that ground to a #6 as originally stipulated.


While this is supposedly code, it really is up to your inspector.



KevinBeamer said:


> The town inspector said he will accept 2-2-2-8 THHN in 1.5" conduit for 100 amp service 70' from the main panel.
> 
> KB


My inspector had me run 2-2-2-6, which proves that one needs to check with their local inspector. I sure wish I could have run #8, but he wanted at least #6.


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## J. V. (Jun 1, 2007)

Looking back at the original post. Where is the main service panel located? Did you say on the pole? If it is on the pole, that would change everything. Please let us know. It's important!


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## KevinBeamer (Aug 30, 2009)

The main service panel is located in the basement of the house.

The sub panel is located in an attached garage.

I am planning to pipe and wire the whole thing from main panel to sub panel (68 feet).

AHJ has agreed to 2-2-4-8.

Will post some pictures soon...


KB


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## Scuba_Dave (Jan 16, 2009)

KevinBeamer said:


> Planning on a 60A breaker in the main, but want wire large enough to support 100A in the future. The choice of a 60A breaker in the main is the price difference for the 100A breaker ($15 vs $94) and current requirements.
> KB


That's weird, a 100a breaker here (Square D) is only about $50
I was going to run a 60a sub also, but opted for 100a


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## KevinBeamer (Aug 30, 2009)

The sub panel in the garage is done.         

I measured the following at the sub:

120v AC from either hot to ground (isolated)
120v AC from either hot to neutral
120v AC at four single pole breakers 
240v AC at both hots
0.1 ohms from ground to neutral

Thanks everyone for your advice and suggestions.

I will post pictures in the morning...


KB


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## KevinBeamer (Aug 30, 2009)

Pictures attached...

Actual plan:

Attatched garage sub panel CH Pro 125A 8/16 main lug, isolated ground
60A breaker in the main with wire large enough to support 100A in the future.
2-2-4-8 THHN in 1.5" 80 ft conduit


KB


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## jbfan (Jul 1, 2004)

Looks great!



Good Job.


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## zpm (Jan 6, 2009)

KevinBeamer said:


> 2-2-4-8 THHN


Technical foul. 250.119. #8 black remarked green.

Some may say you've got too much copper showing on the lugs.


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## KevinBeamer (Aug 30, 2009)

jbfan, Thanks. And thanks again to everyone in this thread for their oversight and direction.

zpm,



> Technical foul. 250.119. #8 black remarked green.


I only needed 80', so buying a 250' spool of green #8 was a huge waste of money when a role of six colored tapes costs $3.

In the end, there's no question which side of the main panel and sub panel are neutral / ground.



> Some may say you've got too much copper showing on the lugs.


Maybe. AHJ will be the final judge.

KB


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## Scuba_Dave (Jan 16, 2009)

But by NEC code you are not allowed to remark wire smaller then #4
I buy green by the foot, not rolls for my house


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