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Old 11-26-2008, 08:06 AM   #1
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60AMP Subpanel Wire Size/Type Question


Newbie here. I do woodworking in my garage as a hobby and have several tools there. With 2 electric space heaters on I keep tripping the existing circuit and need to upgrade. I want put a subpanel in my garage which is attached to my house via a breezeway. I live in PA.

I will be starting from an existing 200AMP Square D QO panel where I plan to install a 60 AMP breaker. Wire will run roughly 50' through my basement ceiling, run 10' under ground (easier than going through upstairs walls) in conduit, then run 15' in the garage. So roughly 80' total. I plan to attach it to a 100AMP subpanel, probably QO120M100C (OK?). What size and type of wire will I need? Will I need conduit with this wire in the house, or just underground?

I am considering 6-3NM-B ($2.56/ft at HD) and stripping the cover off the underground/conduit section (HD suggestion). A second option is 6/3THHN ($2.32/ft at local elec store). I'm trying to stay with 6AWG due to cost, 4AWG is a bit over my budget. Will either of these work?

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Old 11-26-2008, 08:22 AM   #2
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60AMP Subpanel Wire Size/Type Question


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stripping the cover off the underground/conduit section (HD suggestion)
No need to do this.
Quote:
QO120M100C
That load center comes with a 100 amp main breaker installed. You don't need a main breaker in your sub panel. You can use a cheaper main lug panel since it's protected upstream.

You need to keep the neutral and ground separate in the subpanel too. This panel just has one neutral bus.

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Old 11-26-2008, 08:44 AM   #3
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You can not use nm-b for the underground part. You must use 6/3 uf , or transition to conduit underground.
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Old 11-26-2008, 08:52 AM   #4
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You can not use nm-b for the underground part. You must use 6/3 uf , or transition to conduit underground.
I plan to use conduit underground.
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Old 11-26-2008, 08:55 AM   #5
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I plan to use conduit underground.
You still can not use nm-b outside. You must use uf(then you do not need conduit), or use thwn and use conduit all the way from panel to panel.
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Old 11-26-2008, 08:58 AM   #6
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No need to do this.
That load center comes with a 100 amp main breaker installed. You don't need a main breaker in your sub panel. You can use a cheaper main lug panel since it's protected upstream.

You need to keep the neutral and ground separate in the subpanel too. This panel just has one neutral bus.
Any idea what QO load panel will give me at least 12 slots that will be cheaper? I'll probably putting in 2-240 lines (4 slots), 2-120 (2 slots) for just the heaters, some separate lines for some machinery, and a room for expansion?
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Old 11-26-2008, 08:59 AM   #7
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60AMP Subpanel Wire Size/Type Question


Just a couple comments...

Gigs suggestion of a main load center without a main disconnect in the garage may not fly...first check with your AHJ as to whether your garage is still consider 'detached'...the breezeway may not make it 'attached'. If it's considered 'detached', it will need a main disconnect and a ground rod or two. If it's 'attached' it won't need either of those.

To add to jbfan's comment of transitioning to underground conduit...the underground wires have to be rated THWN. Most THHN type wire is multi-rated (THHN/THWN/MTW, etc.) but check it first. You can run NM up to a junction box and then transition to a conduit run which would have the THWN wires in it.
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Old 11-26-2008, 09:00 AM   #8
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60AMP Subpanel Wire Size/Type Question


Using that panel will be fine. The wire will be protected by the breaker in the main panel, and the 100 amp breaker just becomes a disconnect for the garage.
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Old 11-26-2008, 09:01 AM   #9
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You still can not use nm-b outside. You must use uf(then you do not need conduit), or use thwn and use conduit all the way from panel to panel.
Thanks. Would appreciate more comments from others on this. I'll be using conduit for the 10 feet outside whatever I go with.
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Old 11-26-2008, 09:01 AM   #10
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I plan to use conduit underground.
Doesn't matter... you cannot use type NM cable in a wet location, which underground in conduit is. And it is never acceptable to "strip the cover off" of NM to make it acceptable for use in conduit. Another "HD suggestion" that is totally wrong.

If this garage is detached, you need a panel with a main breaker, a four wire feeder, and a ground rod. If it is attached, you may substitute a main lug panel, you still need a four wire feeder, but no additional ground rod is required.

I would use 6/3 NM for the portion inside, transition to THWN for the conduit portion (3-#6, 1-#10), and continue in conduit to the subpanel; OR run 6/3 UF the whole way, with no conduit underground.

You guys type too fast!
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Last edited by HouseHelper; 11-26-2008 at 09:04 AM. Reason: slow typer
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Old 11-26-2008, 09:05 AM   #11
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...first check with your AHJ as to whether your garage is still consider 'detached'....
I don't believe they have codes in my area. I am out in the country. Don't plan on having inspectors.
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Old 11-26-2008, 09:07 AM   #12
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[quote=HouseHelper;190384]OR run 6/3 UF the whole way, with no conduit underground.
quote]
If I go with UF, can I put the UF in conduit for appearances sake. It will be running on the outside of my building for 2 feet before it hits the ground.
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Old 11-26-2008, 09:09 AM   #13
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Using that panel will be fine. The wire will be protected by the breaker in the main panel, and the 100 amp breaker just becomes a disconnect for the garage.
I do want a cutoff in the garage. Good to keep the equipment safe from minors (if my daughter ever has kids).
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Old 11-26-2008, 09:10 AM   #14
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[QUOTE=xv144;190390]
Quote:
Originally Posted by HouseHelper View Post
OR run 6/3 UF the whole way, with no conduit underground.
quote]
If I go with UF, can I put the UF in conduit for appearances sake. It will be running on the outside of my building for 2 feet before it hits the ground.
Yes. You must protect the wire where it enters the ground, and where it exits the ground.
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Old 11-26-2008, 09:24 AM   #15
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[quote=HouseHelper;190384]I would use 6/3 NM for the portion inside, transition to THWN for the conduit portion (3-#6, 1-#10), and continue in conduit to the subpanel; OR run 6/3 UF the whole way, with no conduit underground.[quote]

This sounds reasonable. If I go this way I'll have to price the THWN and UF and see how things work out.

You guys are great.

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