Length of run

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  #1  
Old 04-07-07, 03:28 AM
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Length of run

Have a cabin in the woods, 400 feet from poco pole. Cabin is 24X30 with little need for more than 6-8 circuits, will need micro wave, lights and general purpose receptacles. No other requirement for electric expected.

Need some help in what size service wire to get for the 400 ft run. It will be in conduit (pvc) buried. Expect amps at house to be about 50-60. will use aluminum wire

Any thoughts

Thanks for your help
 
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  #2  
Old 04-07-07, 05:45 AM
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any thoughts? sure.

I'm thinking you are going to have to install a minimum 100 amp service due to the code requirement for single family dwellings requiring such.

I'm also thinking you will need minimum 4/0 aluminum conductors. I would suggest 250mcm though. Figured at 80 amps, the 4/0 is adequate. If you should end up loading your service to 90 amps, the 250 mcm would be needed.

btw: no water pump?
 
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Old 04-07-07, 05:53 AM
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You need a judgement call from the POCO as to if this is a Dwelling unit or not. A dewlling unit has perminant provisions for cooking and sleeping. The microwave may count. I know it sometimes does in hotels, when they provide them in the rooms.

If a dwelling unit use table 310.15 (B) (6). On this table 100 amp aluminum is #2

If not a dwelling unit use table 310.16. 100 amp aluminum is #1. 60 amp would be #4.

I used the 100 amp in the first because it is the lowest the table goes. I used 100 in the second because it may be the smallest size that you are allowed to install unless you get an exception from the AHJ.

Once you know the minimum size by code, you can then use a Voltage Drop calculator http://www.csgnetwork.com/voltagedropcalc.html to determine if this will be a concern. I used 130 feet at 60 amps on the number 4 wire and got less than 3 percent. A good rule of thumb is 3 percent from utility to main or sub panel, and 5 percent all the way to the load served.

Using #2 loaded at 100 amps at 130 feet I get exactly 3 percent drop.

I added the 30 feet to get you up the pole to the transformer at the utility end and up into your meter and main panel at the cabin. Wire lengths are measured as the wire flies, not the crow.
 
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Old 04-07-07, 05:55 AM
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Originally Posted by nap View Post
any thoughts? sure.

I'm thinking you are going to have to install a minimum 100 amp service due to the code requirement for single family dwellings requiring such.

I'm also thinking you will need minimum 4/0 aluminum conductors. I would suggest 250mcm though. Figured at 80 amps, the 4/0 is adequate. If you should end up loading your service to 90 amps, the 250 mcm would be needed.

btw: no water pump?
nap you quoted the numbers for a 200 amp service......
 
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Old 04-07-07, 07:00 AM
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Originally Posted by jwhite View Post
nap you quoted the numbers for a 200 amp service......
actually I didn't. I used this voltage drop calculator:

http://www.elec-toolbox.com/calculators/voltdrop.htm

the calcs came out to require the cables I suggested due to the voltage drop.(note OP's inclusion of a 400 foot run)

The reason I considered the 80 amp rating is the same reason one is allowed to use service feeders that are rated less than the actual service rating. A service is generally not utilized at it's full rating and the code does allow for this in 310-15(b)(6). I did not figure in the allowed undersizing of the grounded conductor as allowed by 310-16(6)
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I do agree that the AHJ may not require this to be treated as a dwelling but personally I would and recommended based upon that. It obviously is not a work shed or storage unit and is non-commercial in use so that, to me, leaves it as a dwelling (especially since it would basically be used as a dwelling unit) even though only intermittantly but then, my house in Hawaii is only used intermittantly as well but it is still considered a dwelling. (I wish)
 
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Old 04-07-07, 07:06 AM
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oops I guess I messed up .. should have used 430 foot.
my bad.
 
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Old 04-07-07, 07:25 AM
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Originally Posted by jwhite View Post
oops I guess I messed up .. should have used 430 foot.
my bad.
No big deal. I realized you missed that when you were speaking about a 130 foot run.
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any idea where everybody has gone?

You seemd to be MIA for a while and racraft, lectriclee (although he did post something yesterday, non-advice, more of a criticism of the current posters), and a hoard of others haven;t been around for some time.

I had seen our resident philosopher (Daveboy) had been suspended for something. Thought maybe the admin was cracking down exceptionally hard for some reason and suspended many more.
 
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Old 04-07-07, 07:34 AM
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I have been arround. I just normally dont post if I am just going to repeat what someone else has already said.

I see all the others from time to time. I just assumed that they didnt post if they had nothing to add either.
 
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Old 04-07-07, 07:41 AM
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I just assumed that they didnt post if they had nothing to add either.

Pretty much.

Spring is starting to break (slowly), Work is picking up a little and the yards a mess.
 
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Old 04-07-07, 11:32 AM
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that's good. I had though some of the best minds had left for one reason or another.

Good to see the two of you. Hopefully all the other major contributors are merely in the wings as well.
 
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