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hkstroud · Jan 19, 2012, 12:03 PM

What type and size wire, in PVC conduit, for 100 amp 120/240 volt sub-panel in free standing garage/workshop 120 feet from main panel? I assume 1/0 aluminum will be cheaper than #1 copper and ground must insulated. What size ground. What size conduit? Will 2" conduit be worth the additional cost over 1 1/2' as far as pulling? What would be trade name for wire, if any. Must neutral be white or can it be redesiginated with paint.

I have done my own research but would like to have confirmation.

tkrussell · Jan 20, 2012, 04:35 AM

Harold, assuming a worst case scenario with 80 amps at 240 volts, #1 aluminum XHHW will be fine. You may go to #1/0 if you desire.

Check prices. Sure, copper will cost much much more.

Equipment ground can be #4, increased due to increasing the line conductors for voltage drop.

So, three # 1 Al XHHW and one #4 Al XHHW would fit in minimum 1-1/4" Sch 40 PVC.

I would use 2 " Sch 40 PVC conduit to help with the distance, and would be more than adequate if you use #1/0 Al XHHW.

For the neutral, it must be marked white at both ends. We simply use white tape, and mark it before pulling so there is no mistake. If you can find white #1 XHHW, that would be great, but not necessary.

The #4 Al XHHW equipment ground needs to be green, again, if you can find green wire, great, but green tape at both ends is fine.

Be sure the new panel has a Main Breaker.

Drive at least one ground rod, check local codes, some states require a min of two 8 foot copper ground rods.

Connect the rod(s) with #6 copper wire, Al is not allowed, continuous from the equipment ground bar in the new panel to one or both rods, no splices or cuts.

You already know that the neutral bar needs to remain insulated and isolated from the metal panel box, no bonding jumper.

I hope this helps.

hkstroud · Jan 20, 2012, 06:09 AM

Thanks TK, yes it helps a lot.

This if for a friend. Main panel is in house garage and very full. Plan is to come out of the box with conduit, go down the inside wall. Go through the wall to the outside with a couple pulling ells. Then down and underground with a sweep.

I will probably have trouble finding a place in the main panel for the conduit. Could I come out of the main panel with cable, go down and through the wall, then make a connection in the pulling ell. If so, is there a fitting to close where the cable enters the pulling ell.

tkrussell · Jan 20, 2012, 06:59 AM

You can change from conduit to cable, for a short run use #2-4 SER cable, but you need to end the conduit with a 8 x8 or 10 x 10 PVC junction box and splice the #1 to the #2 in that box.

hkstroud · Jan 20, 2012, 09:53 AM

Thanks again TK.