State Park

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sab1987

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I need a little help with a wire size. We have a 150 amp 240 volt single phase breaker that is to feed three RV pedistals. The first one is 326' from the power, the second is 170' from the first, and the third is 170' from the second.
I could use some help on what size alum wire to run because the engineer is telling us to run 3-4/0 alum in parallel. We have talked with two other local electricans and we all disagree with the engineer but can't figure out what he is seeing. Do you agree or disagree? What size do you think? And how did you figure it? Don't forget about voltage drop. Please help.
Thanks.
 

roger

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Retired Electrician
Re: State Park

First,I must ask, why do all three of you disagree with the engineer? What formula or reason are you using to see a problem?

Roger
 

sab1987

Member
Re: State Park

:) When we figured out the amp draw at full load (50 amp) and the distance we have all come up with the same which is either 1-4/0 or
1-250. That would give us a max voltage drop of 10 volts.
Thanks,
 

roger

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Retired Electrician
Re: State Park

I do agree that his 3 x 4/0 AL is overkill.

It's almost as if he is thinking in the terms of each pedestal being a 50 amp load at the distance of 667' (I added 1' because I didn't like the other sum of the distances :D )

Even using 150 amps at the full length of 667' at a 5% VD I see no more than a 400 KCMIL conductor.

Using the formula CM = 2 x K x I x D / allowed VD

CM = circular mills
K = 21.2 for AL (the AL constant not exact K)
I = amps
D = Distance one way
VD = 240 x 5% = 12

Or 2 x 21.2 x 150 x 667 / 12 = 353,510 CM

You could also divide the total VD by three (number of loads) and do steps of 4 volts per load, (would equal total VD at last load) this could allow you to go to a progressively smaller conductor.


Roger

[ September 09, 2004, 02:41 PM: Message edited by: roger ]
 

lady sparks lover

Senior Member
Re: State Park

Call me the stickler, but isn't it 3% for feeder which feeds that panel/source of distribution, and 2% for the branch circuits fed from the panel/source of distribution? For a total of 5%?

I believe that's why he said that. Because any feeder from that breaker would have to meet the 3% criteria, and so I would have to agree with the engineer.

Correct me if I'm wrong! :)
 
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