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Old 08-18-2011, 03:53 PM   #1
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Garage subpanel


I have 200AMP service in my new home. I'm building a double detached 20x22 garage next year and I want to put in a sub-panel off of the house panel. Ideally I would like:

- Two 14AWG 15 amp circuits, one for lights and another for plugs
- A dedicated 20AMP 12AWG 110V receptacle
- A dedicated 220V receptacle

I've been told a 60AMP sub-panel would meet these requirements and allow for future expansion. I need to run approximately 40 feet of wire underground to the house in a 2ft deep trench, and approximately another 30 feet indoors to the existing panel.

What type of cabling would you recommend for both the outdoor run and the indoor transition?

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Old 08-18-2011, 04:19 PM   #2
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Garage subpanel


I will give you an answer for the USA but I believe it will also meet Canadian code. Run NM cable from the main panel (60 amp breaker) to a junction box above the trench. 1" PVC conduit from the house and terminated in a 100 amp main breaker panel in the garage. 3 runs of #6 THWN copper, 1 run of #10 bare or green. 2 ground rods bonded together to the ground bar in the sub. Separate ground and neutral bars in the sub.

There are other choices of cable and/or conduit, but I have given my preference.

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Old 08-18-2011, 04:22 PM   #3
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Rjniles you are right on the money except we don't need the additional ground rods. Your #10 ground is all you need.
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Old 08-18-2011, 06:51 PM   #4
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The neutral has to be white.
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Old 08-18-2011, 07:01 PM   #5
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Home depot has a 100 amp panel with breakers(interior panel)quite inexpensive too.also a 5/8 by 10 foot ground rod.clamp #4 sheilded copper....you need a breaker(main)at both ends.better ground is 20 foot 1/2 rebar in footing.2 # 6 black,1 #6 white.
are you going to drywall the garage?
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Old 08-19-2011, 10:03 AM   #6
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Garage subpanel


Thanks for all the great information.

Instead of running 3 individual THWN and an additional #10 ground, is there any already packaged cable ready for burial that exists?
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Old 08-19-2011, 12:17 PM   #7
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In most US locales, burial depth for wires in conduit is 18" for this senario.
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Old 08-19-2011, 04:36 PM   #8
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Yes you can purchase NMWU for what you want. Get 2 PVC LB and a piece of PVC pipe. Put an LB where it leaves the house and a piece of PVC down to the bottom of the trench, run the NMWU in trench and do the same thing with the pipe and LB where you come up into the garage.
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Old 08-20-2011, 10:55 PM   #9
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I was reading that 1 1/4" PVC might be a better choice here. What do you guys think?

Also - Can I use the LB as my junction box to switch to NM once it reaches the house?
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Old 08-20-2011, 11:00 PM   #10
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Originally Posted by darren View Post
Yes you can purchase NMWU for what you want. Get 2 PVC LB and a piece of PVC pipe. Put an LB where it leaves the house and a piece of PVC down to the bottom of the trench, run the NMWU in trench and do the same thing with the pipe and LB where you come up into the garage.
I'm also running natural gas in the trench and after speaking with the city I think the PVC with THWN is the better choice since I was told I won't need to separate the two services with a PT board and sand, just need to maintain a foot separation.

Just to verify - if I run THWN I'll be pulling four individual wires whereas the NMWU would be a single 6/3 coated bundle with bare ground?
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Old 08-20-2011, 11:03 PM   #11
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Garage subpanel


Quote:
Originally Posted by rjniles View Post
I will give you an answer for the USA but I believe it will also meet Canadian code. Run NM cable from the main panel (60 amp breaker) to a junction box above the trench. 1" PVC conduit from the house and terminated in a 100 amp main breaker panel in the garage. 3 runs of #6 THWN copper, 1 run of #10 bare or green. 2 ground rods bonded together to the ground bar in the sub. Separate ground and neutral bars in the sub.

There are other choices of cable and/or conduit, but I have given my preference.
Everything makes sense except the breakers. Why is the breaker in the house panel 60 amp but the garage sub panel 100 amp? Shouldn't they both be 60?
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Old 08-20-2011, 11:06 PM   #12
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Quote:
Originally Posted by vsheetz View Post
In most US locales, burial depth for wires in conduit is 18" for this senario.
Thanks. It's the same here - 18" for PVC, 24" for the direct buried cable.
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Old 08-20-2011, 11:08 PM   #13
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Originally Posted by Marbledust View Post
Home depot has a 100 amp panel with breakers(interior panel)quite inexpensive too.also a 5/8 by 10 foot ground rod.clamp #4 sheilded copper....you need a breaker(main)at both ends.better ground is 20 foot 1/2 rebar in footing.2 # 6 black,1 #6 white.
are you going to drywall the garage?
Like darren mentioned we don't need the grounding rods here. The city verified this for me too. Yes, I'm planning to drywall the garage. If I'm running a 60amp feed from the main panel, why do I want a 100 amp sub panel and not a 60?
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Old 08-20-2011, 11:23 PM   #14
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Garage subpanel


You mentioned in the original post "future expansion". The 100 amp breaker is a good start. The breaker in the main will be the determining factor in your capacity. You can upgrade later if you need, but from what you say the 60 AMP will be just fine.
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Old 08-20-2011, 11:27 PM   #15
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You mentioned in the original post "future expansion". The 100 amp breaker is a good start. The breaker in the main will be the determining factor in your capacity. You can upgrade later if you need, but from what you say the 60 AMP will be just fine.
With 6/3 whats the max amperage I can run? I don't mind spending more on the largest breakers for that wire size.

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