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morsecarpentry · Sep 9, 2008, 04:32 PM

I am running 100 amp service from my panel in my basement 250 feet underground in 2" conduit to my polebarn. I am just trying to get all the supplies I need but do not know what wire I need.

donf · Sep 11, 2008, 10:08 AM

Sorry for the delay here but I missed your entry.

For a 100 amp feeder, I would suggest you use a 100 Amp breaker. The conductors should be 3 #1 AWG (Copper) THWN conductors plus a #8 THWN conductor for ground.

I do not believe that these conductors will fit into a Trade Size 2 conduit.

I can check when I get home and have access to the NEC Code Book.

By the way, what type of conduit are you planning on using? I also need to make sure that my calcs are correct.

Tev · Sep 12, 2008, 01:20 AM

I assume you used PVC.

If you have 1AWG wire and 2" schedule 40 PVC you can run 7 wires in it, for schedule 80 you can run 6 wires, so you will be fine with 2".

donf · Sep 12, 2008, 06:24 AM

For grins, I priced out THWN #1 copper wire. The best price I found was $835 for a reel of 250 ft.

So simple math, says that you would need 3 reels of #1 THWN wire ($835 X 3 = $2,505) plus a reel of #6 AWG copper THWN (ground) $635.

So just to get from here to there is going to cost $3,140. Plus the cost of a remote 100 Amp panel box. A grounding rod, an Equipment grounding conductor. One 100 amp dual pole single throw Breaker.

You may want to consider using an Aluminum feeder size #2/0 with a size #4 Ground.

Now, will they fit into a trade size 2 conduit? Yes and No.

Using Schedule 80 PVC size 2 you can get 3 #1 THWN copper and 1 #6 THWN for ground. If you choose to go to Aluminum then you will need to go to trade size 2 1/2 conduit.

Tev · Sep 13, 2008, 02:58 AM

Out of curiosity, how did you come up with those conduit fill numbers donf?

donf · Sep 14, 2008, 05:35 PM

From T310.16 - 90 (c) 150 Amp THWN copper = #1 AWG,
From T250.122 Min ground for 100 amp is #8 AWG. However I chose to use a #6 ground.

Chapter 9, T4 gave the Trade Size 2 Schedule 80 PVC total area as 2.874 sq.
in. For more than 2 conductors I can use 40% of the`total area. (2.874 X .4 = 1.150 <rounded up>

Chapter 9, T5 gave the #1 AWG wire at 0.1901 sq. in. per wire. You would need 3 #1 AWG conductors. 0.1901 sq. in. X 3 = 0.5703 sq. in.

Chapter 9, T5 gave the #6 AWG wire at 0.0726 sq. in. 0.5703 sq. in. + 0.0726 sq. in. = 0.6429 sq. in.

Since 0.6429 is smaller than 1.150 the four wires would fit.

I did not use the fill tables because I was using different size wires for the run.