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Old 08-30-2012, 09:43 AM   #1
xbanone
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Default 100 amps to shop. What wire size?

I just had an electrician install a 200a service upgrade to my house. I would like to run a 100 amp feed to the new shop. I have a 100a panel in the shop and will have to go about 100-120 feet distance underground. What cable do I need to ask for at the electrical supply house? I will have 3 conductors and a ground. #3 THHN? What should I expect to pay for copper?
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Old 08-30-2012, 09:48 AM   #2
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Default Re: 100 amps to shop. What wire size?

Here's some good info. Post # 7 & 9.

http://www.garagejournal.com/forum/s...d.php?t=162740
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Old 08-30-2012, 10:03 AM   #3
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Default Re: 100 amps to shop. What wire size?

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Originally Posted by 930dreamer View Post
Here's some good info. Post # 7 & 9.

http://www.garagejournal.com/forum/s...d.php?t=162740
Thanks,

according to the chart, #4 copper or 2AL for 100 amps. Is voltage drop something I should consider at this distance?
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Old 08-30-2012, 10:19 AM   #4
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Default Re: 100 amps to shop. What wire size?

Distance is a factor.
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Old 08-30-2012, 10:22 AM   #5
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Default Re: 100 amps to shop. What wire size?

For a feeder the #2 Al is good to 90A not 100A. #2 Al used as service entrance carrying the whole load to a dwelling can be used at 100A. That chart is for 3 wire service entrance. You are doing a 4 wire branch/feeder circuit, which is a different chart/table. It's a NEC thing. If you can be happy with 90A use Mobile Home Feeder 2-2-2-4 or 2-2-4-6.

http://www.southwire.com/products/MobileHmFeeder.htm

The #2 is fine for the 120', it will be less than 3% at 90A @ 75C.

Last edited by pattenp; 08-30-2012 at 12:10 PM.
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Old 08-30-2012, 02:44 PM   #6
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Default Re: 100 amps to shop. What wire size?

And 95 and a half plus of the time it will never see much load, I like the 90A with alum also.
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Old 08-30-2012, 04:17 PM   #7
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Default Re: 100 amps to shop. What wire size?

Just ran 50' to a 100A subpanel in my garage. Used #4 Copper. Pulled 4 legs through 1 1/2" PVC conduit.
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Old 08-30-2012, 04:44 PM   #8
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Default Re: 100 amps to shop. What wire size?

Hope you are feeding it from a max of 90A breaker, because #4 Cu is rated at 85A.

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Just ran 50' to a 100A subpanel in my garage. Used #4 Copper. Pulled 4 legs through 1 1/2" PVC conduit.
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Old 08-30-2012, 09:24 PM   #9
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Default Re: 100 amps to shop. What wire size?

I ran #2 copper to my garage. Menards didn't have #3 in stock and the other vendors in town wanted more for #3 than I paid for #2 at Menards. It handles the 100a breaker with room to spare.
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Old 08-31-2012, 02:42 PM   #10
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Default Re: 100 amps to shop. What wire size?

I did a similar project earlier this year and was wanting #4 Cu thhn/thwn, but the cost of #2 Al XHHN was literally about half of what it was going to cost for Cu. I did the entire project for the cost of what #4 Cu would have been.

90A breaker > 4 cond AL to a subpanel in detached garage (on 100A "main disconnect")

I had a single 15A circuit prior to this but anything with a motor would heat up really quickly, voltage would drop to around 100 VAC, it was horrible. Things are much happier now that I have an actual sub panel setup. V-drop is next to nothing under the same loads I was putting on it before.
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Old 08-31-2012, 08:29 PM   #11
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Default Re: 100 amps to shop. What wire size?

Just got a price from local electric supply. #2 copper is 1.37 per foot. Menards is 1.89.
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Old 08-31-2012, 09:10 PM   #12
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Default Re: 100 amps to shop. What wire size?

Most economical is 1/0 al SER.
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Old 08-31-2012, 09:17 PM   #13
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Default Re: 100 amps to shop. What wire size?

Quote:
Originally Posted by Dave Maxwell View Post
Just got a price from local electric supply. #2 copper is 1.37 per foot. Menards is 1.89.
Wire other than romex is where the supply houses have the box stores beat by a mile. Panels and breakers usually seem to be cheaper at HD, Lowes, etc. YMMV
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Old 08-31-2012, 09:34 PM   #14
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Default Re: 100 amps to shop. What wire size?

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Just got a price from local electric supply. #2 copper is 1.37 per foot. Menards is 1.89.
#2 AL mobile feeder is running about 1.80/ft. That's a 4 wire cable - not a single wire. It's what I used for mine - it was 1.47/ft when I bought it. I fused my 100A panel at 75A in the panel at the meter.

Error - 70A is what's in the can.
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Last edited by Falcon67; 09-02-2012 at 09:24 AM.
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Old 08-31-2012, 11:25 PM   #15
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Default Re: 100 amps to shop. What wire size?

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Originally Posted by Falcon67 View Post
#2 AL mobile feeder is running about 1.80/ft. That's a 4 wire cable - not a single wire. It's what I used for mine - it was 1.47/ft when I bought it. I fused my 100A panel at 75A in the panel at the meter.
Where are you finding 75A fuses or circuit breakers? 75 is not a standard size, 70A is.
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Old 09-01-2012, 08:55 AM   #16
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Default Re: 100 amps to shop. What wire size?

That would be okay, except for the fact that SER can't be run under ground.

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Most economical is 1/0 al SER.
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Old 09-01-2012, 08:55 PM   #17
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Default Re: 100 amps to shop. What wire size?

Pipe it.
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Old 09-01-2012, 09:15 PM   #18
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Default Re: 100 amps to shop. What wire size?

Mine is about 90 ft overall from main panel to sub in shop.
We used #2 copper to feed the 100A sub panel.
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Old 09-01-2012, 10:48 PM   #19
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Default Re: 100 amps to shop. What wire size?

Quote:
Originally Posted by fnsane View Post
Most economical is 1/0 al SER.
Quote:
Originally Posted by pattenp View Post
That would be okay, except for the fact that SER can't be run under ground.
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Originally Posted by fnsane View Post
Pipe it.
338.12 Uses Not Permitted.
(A) Service-Entrance Cable. Service-entrance cable (SE)
shall not be used under the following conditions or in the
following locations:
(1) Where subject to physical damage unless protected in
accordance with 230.50(B)
(2) Underground with or without a raceway
(3) For exterior branch circuits and feeder wiring unless
the installation complies with the provisions of Part I of
Article 225 and is supported in accordance with 334.30
or is used as messenger-supported wiring as permitted
in Part II of Article 396
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Old 09-02-2012, 09:23 AM   #20
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Default Re: 100 amps to shop. What wire size?

Error - its a 70. 220,221 - whatever it takes

It was in stock and plenty big enough IMHO. I worked out here all day yesterday, cut some stuff on the lathe, built a mobile stand for the handsaw- bet I didn't pull 10~15A peak all day.
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Last edited by Falcon67; 09-02-2012 at 09:28 AM.
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