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Wire size for 250' to garage?????

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Wire size for 250' to garage????? over40pirate@aol.com 07-26-2007
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Posted by over40pirate@aol.com on July 26, 2007, 1:20 pm
I am trying to find out the wire sizes needed for a 250' underground
feeder from the main panel, to a sub panel in the garage. I would like
a 220, 50 or 60 amp service.
What type wire would be the least expensive/

Thanks, cliff


Posted by Doug Miller on July 26, 2007, 2:48 pm
>I am trying to find out the wire sizes needed for a 250' underground
>feeder from the main panel, to a sub panel in the garage. I would like
>a 220, 50 or 60 amp service.

At that distance, for the neutral and the two hot conductors, minimum of 6AWG
copper for 50A or 4AWG copper for 60A, and for the ground, minimum of 8AWG
copper at either 50A or 60A.

Grounding requirements are different in subpanels. You must make sure that:
- the subpanel has two separate bars for ground and neutral
- the two bars are NOT connected to each other (they ARE in the main)
- the neutral bar is insulated from the panel chassis
- the ground bar is NOT insulated from the panel chassis

You may also need a separate ground rod at the garage; check with your local
building inspector.

>What type wire would be the least expensive/

You'll need to make a few phone calls to find that out.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Posted by on July 26, 2007, 3:14 pm
wrote:
> I am trying to find out the wire sizes needed for a 250' underground
> feeder from the main panel, to a sub panel in the garage. I would like
> a 220, 50 or 60 amp service.
> What type wire would be the least expensive/
>
> Thanks, cliff

There will be a trade-off: more investment in copper will result in
reduced resistive loss in line over time.

J


Posted by M Q on July 26, 2007, 3:56 pm
over40pirate@aol.com wrote:

> I am trying to find out the wire sizes needed for a 250' underground
> feeder from the main panel, to a sub panel in the garage. I would like
> a 220, 50 or 60 amp service.
> What type wire would be the least expensive/

There are two issues here for wire size:
1) Minimum code required size for the current, regardless of length.
That would be 8AWG for copper and 6AWG for Aluminum, for either 50 or 60A.

2) Acceptable voltage drop at maximum current for that length:
My old 1990 NEC does not specify, but only recommends a voltage drop
percentage of 3% for the feeder or 5% including the branch circuit.
This would be based on the actual load, not the subpanel rating.
Also, if you will always have a balanced load, you can compute it
based on percentage of 240 V, and you may be able to get away with
a lesser wire for the neutral, if you may have a way unbalanced load,
you would have to compute it based on a percentage of 120 V.
Here is a bit of data:

AWG ohms/500' V drop @ 50A % of 240V
6 Cu .25 12.5 5.2
4 Cu .154 7.7 3.2
2 Cu .1 5.0 2.1

6 Al .404 20.2 8.4
4 Al .254 12.7 5.3
2 Al .16 8.0 3.3
1 Al .13 6.3 2.6%

You may find Aluminum to be cheaper for those wire sizes
even though you need a larger size for Al.

If you need to ask these questions, you probably should be talking
to you local building inspector because there are many other
code issues to do this right.


Posted by Speedy Jim on July 26, 2007, 4:15 pm
M Q wrote:

> over40pirate@aol.com wrote:
>
>> I am trying to find out the wire sizes needed for a 250' underground
>> feeder from the main panel, to a sub panel in the garage. I would like
>> a 220, 50 or 60 amp service.
>> What type wire would be the least expensive/
>
>
> There are two issues here for wire size:
> 1) Minimum code required size for the current, regardless of length.
> That would be 8AWG for copper and 6AWG for Aluminum, for either 50 or
> 60A.
>
> 2) Acceptable voltage drop at maximum current for that length:
> My old 1990 NEC does not specify, but only recommends a voltage drop
> percentage of 3% for the feeder or 5% including the branch circuit.
> This would be based on the actual load, not the subpanel rating.
> Also, if you will always have a balanced load, you can compute it
> based on percentage of 240 V, and you may be able to get away with
> a lesser wire for the neutral, if you may have a way unbalanced load,
> you would have to compute it based on a percentage of 120 V.
> Here is a bit of data:
>
> AWG ohms/500' V drop @ 50A % of 240V
> 6 Cu .25 12.5 5.2
> 4 Cu .154 7.7 3.2
> 2 Cu .1 5.0 2.1
>
> 6 Al .404 20.2 8.4
> 4 Al .254 12.7 5.3
> 2 Al .16 8.0 3.3
> 1 Al .13 6.3 2.6%
>
> You may find Aluminum to be cheaper for those wire sizes
> even though you need a larger size for Al.
>
> If you need to ask these questions, you probably should be talking
> to you local building inspector because there are many other
> code issues to do this right.
>


Possible typo: #8 Cu won't do it for a 60 Amp feeder.


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