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re: the dreaded voltage drop
7 feb 2000
george ghio writes:
>below is a chart or wire sizes and amps showing the voltage drop.
>wire sizes in the dashed area should not be used as over heating
>may occure.
the problem seems more one of wasting precious pv power.
d inch copper wire melts at 10244d^1.5 amperes (f, below.)
(aluminum melts at 7585d^1.5 a, with 3148d^1.5 for iron and
1642d^1.5 for tin, as listed in table 39, "fusing currents
in amperes" on page 4-54 of the 1968 itt reference data for
radio engineers. i used to own an electric car with aluminum
wire links for the golf cart battery fuses, and lived in a
french house with wire fuses between binding posts...)
>voltage lost per 10 metre of route length twin wire
> cross sectional area of wire m sq. (square meters? :-)
approx. awg
b&s gauge 22 16 12 10 8 6 2 1
>amps- 0.4 1.8 2.9 4.6 7.9 13.5 32 49
>-------------------------------------------------------
>0.5 - 0.42 0.09 0.06 0.04 0.02 0.01 0.01 0.00
> 1 - 0.83 0.19 0.11 0.07 0.04 0.02 0.01 0.01
>1.5 - 1.25 0.28 0.17 0.11 0.06 0.04 0.02 0.01
> 2 - 1.67 0.37 0.23 0.14 0.08 0.05 0.02 0.01
>2.5 - 2.08 0.46 0.29 0.18 0.11 0.06 0.03 0.02
> 3 - 2.50 0.56 0.34 0.22 0.13 0.07 0.03 0.02
> 4 - 3.33 0.74 0.46 0.29 0.17 0.10 0.04 0.03
> 5 - 4.17 0.93 0.57 0.36 0.21 0.12 0.05 0.03
>7.5 ----------1.39 0.86 0.54 0.32 0.19 0.08 0.05
> 10 ----------1.85 1.15 0.72 0.42 0.25 0.10 0.07
> 15 ------o---2.78 1.72 1.09 0.63 0.37 0.16 0.10
> 20 ------o---------2.30 1.45 0.84 0.49 0.21 0.14
> 25 ------o---------2.87 1.18 1.05 0.62 0.26 0.17
> 30 ------o------o--------2.17 1.27 0.74 0.31 0.20
> 40 ------f------o--------2.90 1.69 0.99 0.42 0.27
> 50 -------------o-----o--3.62 2.11 1.23 0.52 0.34
> 75 -------------o-----o--------3.16 1.85 0.78 0.51
>100 -------------o-----o--------------2.47 1.04 0.68
120 f
240 f
330 f
480 f
680 f
1340 f
1600 amperes f
we might say wire overheats when the insulation temp reaches 180 c on a
40 c day. that's a 250 f temperature rise, with an area of about 2.7 ft^2
for a pair of small 10 m wires, and a still air film thermal conductance
of 1.5 btu/h-f-ft^2, or a total thermal resistance of 0.244 f-h/btu, so
we might say overheating occurs when 250 = 2x3.41vax0.244, or va = 150 w,
as noted in the first o's above...
nick
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