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Old 08-30-2009, 12:51 PM   #1
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100 amp Attached Garage Sub Plan


Here's my project, looking for oversights. Thanks !

Recently upgraded the main panel from 60A Federal Pacific to 200A CH, passed all local inspections. Then, National Grid upgraded overhead from pole to POA. 21 single pole slots remaining.

The main panel was upgraded so the garage could be isolated with it's own sub. Today, the attached garage and adjacent room share a single 15A circuit !!!

New garage sub panel (HOM12L125C) is rated for 125A, room for 12 single poles. 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.

Part of application is through a crawl space under the adjacent room, presently 12 ft of 1.5" schedule 40 conduit. Conduit is suspended from the floor joists (three feet above grade). Crawl space is insulated and considered part of main house envelope, plastic over the earth.

Between crawl space and main panel is basement.

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

Three THHN #2 copper (black, white and red)
One THHN #6 copper (ground)

Ground in sub panel will be isolated (not bonded with neutral).

No need for 240V in the garage at this time. Planning for three 20A circuits (outlets) and two 15A circuits (lights).


Will be talking with AHJ in next few days...


Thoughts ?

KB

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Old 08-30-2009, 01:01 PM   #2
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100 amp Attached Garage Sub Plan


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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Old 08-30-2009, 01:35 PM   #3
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100 amp Attached Garage Sub Plan


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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Old 08-30-2009, 05:43 PM   #4
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100 amp Attached Garage Sub Plan


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

Last edited by KevinBeamer; 08-30-2009 at 05:46 PM.
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Old 08-30-2009, 08:11 PM   #5
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100 amp Attached Garage Sub Plan


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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Old 09-05-2009, 08:57 AM   #6
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100 amp Attached Garage Sub Plan


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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Old 09-05-2009, 05:26 PM   #7
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100 amp Attached Garage Sub Plan


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.
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Old 09-05-2009, 06:45 PM   #8
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100 amp Attached Garage Sub Plan


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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Old 09-05-2009, 10:37 PM   #9
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100 amp Attached Garage Sub Plan


Yes, same as the sub-panel.
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Old 09-06-2009, 09:00 AM   #10
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100 amp Attached Garage Sub Plan


Quote:
Originally Posted by kbsparky View Post
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.

Quote:
Originally Posted by KevinBeamer View Post
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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Old 09-06-2009, 11:30 AM   #11
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100 amp Attached Garage Sub Plan


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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Old 09-13-2009, 11:59 AM   #12
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100 amp Attached Garage Sub Plan


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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Old 09-13-2009, 12:04 PM   #13
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100 amp Attached Garage Sub Plan


Quote:
Originally Posted by KevinBeamer View Post
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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Old 10-02-2009, 10:21 PM   #14
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100 amp Attached Garage Sub Plan


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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Old 10-03-2009, 07:44 AM   #15
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100 amp Attached Garage Sub Plan


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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100 amp Attached Garage Sub Plan-dsc09199.jpg   100 amp Attached Garage Sub Plan-dsc09200.jpg   100 amp Attached Garage Sub Plan-dsc09204.jpg   100 amp Attached Garage Sub Plan-dsc09206.jpg  

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