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Old 08-15-2006, 05:39 PM   #1
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Help with wire sizing


I need to run 240V either 40A or 60A 70 feet throught PVC
conduit to a out building. I'm going to oversize the conduit,
since I have a bunch of 1-1/4", unless someone can say
why I should not use it. That should take care of the 40%
fill.

There will also be a 3-5' section of liquid tight (*)

Here's the questions

Since the conduit is burried, am I correct that the wire
has to be THWN, and can not use NM ?

What should the AWG be for 40A, and 60A ?

The out building is in the middle of a concrete slab, and eventually
will want to move it. I felt that is would be easier to terminate the
ridged conduit at the edge of the slap into a LB supported by
a section of UniStrut. Then put a LB on the building and connect
the two with carflex or similar.

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Old 08-16-2006, 04:53 AM   #2
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Help with wire sizing


40a and 60a is no 8 and no 6 respectively. But If you plane use alot of stuff in your shop all at the same time I would upsize one for voltage drop.

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Old 08-17-2006, 08:15 PM   #3
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Help with wire sizing


Hey pdxoregon , Im getting ready to do the exact same thing as you are planning, wiring my new detached garage I built.

I was gonna use either 1" or 1.25" pvc, I actually have a post on here now to see what others suggest.

Yes your wire has to be THWN inside the conduit. The conduit will fill with water over time from condensation. or you could run UF which is rated for direct burial.

Im gonna run 6-3 W Ground off a Dual 60amp breaker in my main panel with NM-B (romex) to the outside corner in my basement before I go thru the foundation, there I will run the romex into a juntion box and splice the wires over to the THWN, and start my conduit off the juntion box out thru the wall, buried 18" deep and into my sub panel in the garage. I also think its code where you will need to sink a seperate ground rod out by your out building.

The issue I had was, since I plan to run a low voltage alarm wire and a network cable out there (in seperate conduit), I have to isolate the grounds and Neutrals in my sub panel. Most breakers boxes have that option today by removing a screw or a bonding strap. So if u have any metal conductor running from your out building to your home other than your new feed, you will have to isolate the grounds and neutrals as well as this is now code.

Good luck to you, and let me know who u make out....

Last edited by stagger19; 08-17-2006 at 08:26 PM.
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