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Running wire to detached garage xgtfour 10-29-2006
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Posted by xgtfour on October 29, 2006, 1:28 am


I'm wiring up my detached garage for 220v/50amps for a TIG Welder and air
compressor. The plan is to change the breaker in the main panel for the
220v/30amp to a dryer outlet that is not being used to a 60amp breaker.
I'm planning on running some new 6 AWG copper wire, 8 AWG neutral, about
75 feet to the garage into a subpanel with a 50amp breaker.

My problem is the routing of the wire. The wire will start out from the
main breaker, go up to the attic, down another wall, to the outside via a
1" Schedule 80 PVC piping. Here it will go into the ground, minimum of 18"
deep. This is where I get stuck, the outside wall of the garage is
surrounded by a 3 foot section of concrete. Is it permissible to run the
PVC on top of the concrete floor to enter the garage wall?

Or is the only way to somehow cut the concrete and lay the pipe?

Thanks in advance!

Darius


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Posted by RBM on October 29, 2006, 7:10 am


There may be a few other things left out, such as ground conductor, ground
rods, and expansion couplings. Can you not come out of the ground at the
garage and use an LB condulet to go through the siding?


> I'm wiring up my detached garage for 220v/50amps for a TIG Welder and air
> compressor. The plan is to change the breaker in the main panel for the
> 220v/30amp to a dryer outlet that is not being used to a 60amp breaker.
> I'm planning on running some new 6 AWG copper wire, 8 AWG neutral, about
> 75 feet to the garage into a subpanel with a 50amp breaker.
>
> My problem is the routing of the wire. The wire will start out from the
> main breaker, go up to the attic, down another wall, to the outside via a
> 1" Schedule 80 PVC piping. Here it will go into the ground, minimum of 18"
> deep. This is where I get stuck, the outside wall of the garage is
> surrounded by a 3 foot section of concrete. Is it permissible to run the
> PVC on top of the concrete floor to enter the garage wall?
>
> Or is the only way to somehow cut the concrete and lay the pipe?
>
> Thanks in advance!
>
> Darius
>



Posted by xgtfour on October 29, 2006, 9:41 am


Thanks for the reply, I will be running a seperate earth grounding rod for
the garage. I could come out of the ground but I would have to go across 3
feet of concrete before I get to the garage wall. I've never seen PVC just
laid out across the ground on concrete before.

Posted by Pete C. on October 29, 2006, 10:18 am


xgtfour wrote:
>
> Thanks for the reply, I will be running a seperate earth grounding rod for
> the garage. I could come out of the ground but I would have to go across 3
> feet of concrete before I get to the garage wall. I've never seen PVC just
> laid out across the ground on concrete before.

Buy yourself a copy of the NEC code book (assuming you're in the US),
there are quite a few things you've mentioned that don't match code
requirements.

First off for a sub panel you need to run four wires, the two hots,
neutral and ground, you can not rely on a separate ground rod at the
garage (though you can add an additional ground there if you want). The
neutral should be the same size as the hots, the ground can be slightly
smaller (see code tables). You should be using schedule 40 PVC conduit,
schedule 80 is rarely ever needed.

If the issue is that the concrete foundation wall of the garage is 3'
high before you reach the wood / siding area, then yes, you can run
schedule 40 PVC conduit up along the cement before an LB into the sided
area. If it's in an area with the likelihood of being physically damaged
you need to provide some additional protection around it, or use rigid
metal conduit for that section. In some areas expansion slip joints are
required where you transition from underground to a structure for
protection from frost heaves.

It's not clear from your post whether you are intending to direct bury
the wire, or continue the conduit underground. I strongly recommend
conduit the entire way so you can re-pull wire if needed in the future.
I also recommend a larger than minimum conduit size to provide for
easier pulling and future upgrades. As a last thought, consider spending
the money up front to just run a full 125A sub panel (max allowed by
code), the cost difference is small unless it's a really long run and
you'll appreciate having the larger capacity panel in the garage.

Pete C.

Posted by RBM on October 29, 2006, 11:21 am


The current NEC allows you to do it with a separate driven ground rod and no
continuous ground from the main panel, but only under certain conditions,
which include that NO other metallic conductors of any type go between the
two buildings, such as water lines, telephone line, CATV, etc. You'd be
better off just running the appropriate ground conductor along with the
feeders. You will have to drive a separate ground as well, for the garage
panel. If you are going to have three feet of exposed PVC on top of the
cement, I would use Sch 80 for the extra protection, if not galv

> Thanks for the reply, I will be running a seperate earth grounding rod for
> the garage. I could come out of the ground but I would have to go across 3
> feet of concrete before I get to the garage wall. I've never seen PVC just
> laid out across the ground on concrete before.



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