second guessing wire size due to voltage drop...

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emahler

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We have to run a 20A 120V circuit from a UPS panel to a remote communications panel...

the load is 10A
the distance is 650+/-

when i did the calculations, I come up with a #4 to keep the VD at 2.8%

anyone got a different answer?
 
bob said:
K varies with temperature. 10.5 at 25C to 12.8 at 75C.
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I looked in several books that I keep on hand and
found the following:
Southwire Power Cable manual list the volume
resistivity of copper at 20C = 10.371, 25C = 10.571 and in another book it lists copper at 12.57 at 50C all ohms-cmil/ft. If you know the resistance R1 and Temp1(initial temp)then
R1 = DC resistance
R2 = R1[1+a1(T2-T1)] T1 = 25C and T2 new temp
where a1 = 0.00385 at 25C for copper
and a1 = .00395 for aluminum
or an equation most used is
R2 = [{234+T2}/(234+T1)] for copper
R2 = [{228+T2)/{228+t1)] for al
 
that could be...it's a distribution facility...100+ overhead doors, always open...

anyway, the point is moot...just got an email that the calculated load is actually 16A...so now we are at #1....

oh well, how am I gonna get #1 around the screw terminals? maybe I should use back wired devices?
 
emahler said:
anyway, the point is moot...just got an email that the calculated load is actually 16A...so now we are at #1....
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emahler said:
the distance is 650+/-
Click to expand...

OK, so now your looking at about 2000' of 1 AWG copper and 650' of 1.25" EMT. (250.122(B) requires the EGC for this circuit to be 1 AWG unless you choose to use the conduit as ground)

IMO you should start thinking about other options, I don't know pricing, but you sure do. Is all that copper and pipe going to cost less then two - 2.5 KW transformers, say 120 x 480 (or 600) and 650' of 3/4" and some 10 or 12 AWG?
 
iwire said:
OK, so now your looking at about 2000' of 1 AWG copper and 650' of 1.25" EMT. (250.122(B) requires the EGC for this circuit to be 1 AWG unless you choose to use the conduit as ground)

IMO you should start thinking about other options, I don't know pricing, but you sure do. Is all that copper and pipe going to cost less then two - 2.5 KW transformers, say 120 x 480 (or 600) and 650' of 3/4" and some 10 or 12 AWG?
Click to expand...

material wise is roughly a little more for the transformer set up...labor wise would be a little less...

probably a wash overall...but it might be a little more profitable to go this way...thanks for the idea...i will look into it deeper today...
 
actually, a quick punch into Celtic's posted calculators, at 277V i still need a #4 and at 480V we still need a #6....

not sure if it would be much of a savings....
 
emahler said:
actually, a quick punch into Celtic's posted calculators, at 277V i still need a #4 and at 480V we still need a #6....

not sure if it would be much of a savings....
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Then I think your doing it wrong. :smile:

16 amps at 120 volts is 1.92 KW

1.92 KW at 480 is 4 amps.

I doubt very much that you need a 4 AWG to carry 4 amps @ 480 volts 650'. :smile:
 
iwire said:
Then I think your doing it wrong. :smile:

16 amps at 120 volts is 1.92 KW

1.92 KW at 480 is 4 amps.

I doubt very much that you need a 4 AWG to carry 4 amps @ 480 volts 650'. :smile:
Click to expand...

i thinks you are correct...thanks
 
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