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Old 12-02-2009, 06:26 PM   #1
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Sub-Panel Wire Size and Conduit Questions

I plan on installing a 60 amp sub-panel in my detached garage. I'm going to use #6 individual connectors. There are a few questions I still have.

Can the hots be black and red or do they both have to be black? I ask because I have the wire but only enough to run one red, one white and one black.

What size does the ground running back to the main panel and the ground rods have to be?

Should I use green wire, bare copper or is either acceptable?

From what I understand I need to have a main breaker panel, a main lug is not acceptable? Am I wrong thinking that the 100 amp breaker in the box I get is fine as it is protected by the 60 amp breaker in the main panel and is only functioning as a disconnect?

The conduit will be going through a patch of ivy and under a cement staircase. From what I understand on this I should use schedule 40 PVC conduit buried at 18". Then I want to back fill 6'' and add the warning tape. Is this correct?

Am I required to have a tracer wire? The warning tape I have is the metallic type that you can tone out.

Can I put a 3/4 galvanized air line in the trench below the conduit?


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Old 12-02-2009, 06:32 PM   #2
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1 black, 1 red, white & green wire is OK
I used a #8 green as my ground back to main panel
I've been told #10 would be OK
(2) 8' ground wires....#6 min to the rods, I used #4 bare because I had some leftover
100a breaker in the panel is fine - that's what I did, I always use a min breaker handle
Not sure on depth I'd have to check...mine was at 30" - had a backhoe here
I did the warning tape at about 6" depth I think


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Old 12-02-2009, 08:06 PM   #3
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#6 {16mm˛} Red and Black and White and Green if the breaker is under 60 amp you can use #10{6.0mm˛}

For depth wise in PVC conduit you can have shallow as 18 inches however check with your local codes they may required more deeper if you have deep frost area. Shed 40 will cover most case unless up the wall where you will think it will get damaged then get shed 80 PVC but becarefull with size due thicker wall so the size I will recomed is get in one inch that will cover in case you have to upsize normally I know 3/4 inch will work most case but once you get over 16mm˛ { #6 } you will have to bump up to larger either one inch or 1 1/4 inch conduit.

Oh yeah good tip get expanding sleeve so that way if you are in deep frost area when frost can heave the ground or building etc that way the sleeve will move but will not pull or compressed the pipe like big time and rip anything apart along the way.

But one item you have to use THHN/ THWN most case it will be dual rated in pretty good percentage of time.

Make sure you keep the netural and ground seperated at the subpanel.

You want air line between the house and detached garage ? yes you can do that but one issue make sure you have good drain trap when you get the air pipe come out from ground.

From time to time get air brake dryer { air brake antifrezze stuff } can and pour down the line that will help to prevent get water frozed up and it will pick the water up.


Last edited by frenchelectrican; 12-02-2009 at 08:09 PM.
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Old 12-02-2009, 11:48 PM   #4
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So I'll use #8 green for my ground to the main panel. I'd rather spend the extra $10 and be sure it's large enough then risk having to change it after. Better to be a size to big then a size to small.

For the #6 to the ground rods can I strip the insulation off the leftover pieces of #6 and use that? I only have to go a few feet so it's not a big undertaking like trying to strip 120' for the run to the main panel.

Unless someone knows for sure I'll ask the electricians about depth the next time I see them. We put water at min. 48" and gas at min. 32". Our frost line is realistically 10"-12" so it should be safe at 18". I'll have to ask and find out for sure though.

The conduit will come up the wall about a foot. It will be located in an area where the risk of damage is next to nothing. It will be in an ivy bed that sees no traffic. The house end will come in underground.

The wire type is THW which can be used in buried conduit. I'm going to use 1-1/4 conduit so if I ever want to up it to #4 and a 100amp breaker I don't have to dig again.

Yes, I have water separators and filters on my air lines already, that's a must for painting. It's a pain to roll out 100' of air hose and put them away again every time I need air in the house or front driveway. I also want to eventually put the compressor in a separate shed and pipe the air into the garage, then to the house, then to the driveway. That's a whole different project though. My concern was just about them sharing a trench. I know we've done it with gas (36") and electric (18") and passed inspection so I don't see why an air line would be different.

Last edited by Tmb9862; 12-02-2009 at 11:54 PM.
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