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Old 08-20-2009, 04:04 PM   #1
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wire sizing


I am building a home 3000' (yes, a half mile+) from the nearest road with a power pole. The home will have a 200A 240V load center.

I want to put AL wire in underground conduit. What size wire will I need?

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Old 08-20-2009, 04:15 PM   #2
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First I think I would see if the power co.is willing to run a line outto your place and how much would it cost to do so.Some power co.s will do this but you have to buy the poles etc and will add cost to your monthly bill for a set # of months or yrs.

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Old 08-20-2009, 07:18 PM   #3
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I have spoken to my power company, but I'm trying to price out the job myself and so was looking for wire size required for such a run.
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Old 08-20-2009, 07:21 PM   #4
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Get the specs from your POCO and call an electrician to get a price.

That run would have to be primary (high voltage) and then stepped down to secondary line voltage (120/240v) near the house (less than 250' away).

Your POCO can give you the specs on what wire you have to use.
Around here it would be a single run of #2 primary.
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Old 08-20-2009, 08:45 PM   #5
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Thanks Speedy- I will check on requirements with PoCo.
Can you recommend a low cost reliable transformer brand?
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Old 08-20-2009, 08:49 PM   #6
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Quote:
Originally Posted by bigbrotherjoe View Post
Can you recommend a low cost reliable transformer brand?
For the step down to line voltage?

That is a POCO transformer. Typically you supply the wire, grounding and pad mount. The POCO sets the transformer.
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Old 08-20-2009, 08:56 PM   #7
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Just to give you sort of an idea here, two parallel (6 wires) of 750 MCM aluminum will lose 8 volts at 100 amps at 3000'.

If this were installed, you'd notice the lights dimming quite a bit every time the A/C or well pump kicked on. Even the fridge, washer, or dryer would be noticeable.

You'd need two 4" conduits to pull these in. I know, the code says that 3-750's will fit in a 3", but I've pulled a LOT of big wire, I'd use the 4". I would have no problem with pull boxes every 1000', but I also have access to many thousands of dollars worth of wire pulling equipment. If I were pulling it in by hand (and had several good-sized guys to help), I'd put the pullboxes about every 200'.

You'll have to splice in these pullboxes, that'll add time and more expense than you think.

This would be a pretty spendy project, with questionable results. The POCO route is by far the best.

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Old 08-20-2009, 09:10 PM   #8
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Another alternative is see if the POCO will connect a single phase 480 volt service. Some will, some won't. To get 200 amps of 120/240, the 480 service will need to be 100 amps.

If they will, two 750 aluminum + one 4/0 (ground) will give about the same voltage drop, and you'll only need one 4". The wire, conduit, splices, etc., are the same with 240 or 480.

You'll need a transformer at the house to go from 480 to 120/240. A 37.5 KVA will do. It'll be somewhat spendy, but readliy available. It'll also be rather heavy!

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Old 08-20-2009, 09:12 PM   #9
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Rob,

Lots of good information there - The PoCo wants a hefty fee - over $20,000
They aren't installing anything I can't get at my supply house. I have access to a trencher and wanted to price it myself.
I'm now not sure if the PoCo included the cost of a step down transformer or any disconnects. I was trying to price Alcan 600v cable, but had no specs, likewise on sizing a pad transformer - do I need a 3 phase or 1 ?? 15Kva, 45, or 112Kva? Dry or Wet?
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Old 08-20-2009, 09:21 PM   #10
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There is another thread on this and the price per foot is comparable, but personal safety for a DIY job seemed to be a prominent concern.

PoCo also might want some assurance that you won't bring down their grid.

The difficult problems with this may not be technical; they may be legal.
If something goes wrong before, during or after installation, will you be the only one at risk? 60 hp is not small change.

And I suppose your risk-averse insurance company may/could even deny you coverage on your house.

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Old 08-20-2009, 09:22 PM   #11
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Quote:
Originally Posted by bigbrotherjoe View Post
I'm now not sure if the PoCo included the cost of a step down transformer or any disconnects. I was trying to price Alcan 600v cable, but had no specs, likewise on sizing a pad transformer - do I need a 3 phase or 1 ?? 15Kva, 45, or 112Kva? Dry or Wet?
The POCO provides, owns and maintains the transformer.

The rest of this ONLY your POCO can tell you. This part of the installation is under THEIR jurisdiction.

Besides, you need 15,000V cable, not 600v.
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Old 08-20-2009, 09:24 PM   #12
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Quote:
Originally Posted by bigbrotherjoe View Post

Lots of good information there - The PoCo wants a hefty fee - over $20,000
How much less do you think you are going to get away for??? Primary cable alone is over $2 per foot. And you are going to use a trencher for 3000' ?????

$20,000 sounds about right for 3000' of underground.
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Old 08-20-2009, 09:35 PM   #13
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The voice of reason rings through -
Through a few hours of research and discussion I've concluded you're right.
I won't save much - the $20K quote seemed high, but digging, conduit, cable, concrete, transformer - I can't seem to add up to less.

Thanks again.
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Old 08-20-2009, 09:39 PM   #14
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Plus they cover any problems & will replacefix anything
If you buy/install it you own it for life
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Old 08-20-2009, 09:41 PM   #15
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Quote:
Originally Posted by bigbrotherjoe View Post
I can't seem to add up to less.
I guess PoCo has Economy of Scale for everything; labor, materials, tools, equipment, insurance, all bought or rented at wholesale prices.

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