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Posted by aemeijers on July 26, 2007, 4:49 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.
>>
>
At 250 feet, I'd set a second meter and a seperate service, assuming there
is a line near enough. Or are you fed out at the road, and this is the back
forty, and you'd have to pay for another pole? Yes, the upfront costs would
be higher, but if you use much juice out there, it'll be more reliable, and
would certainly scare the eventual purchaser of the place less.
aem sends...
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