Wednesday, Apr 02, 2008 at 21:11
colly rivers is the go.. copy of it below here.
There is 'rounding up' discrepancy in most published AWG/ISO conversion tables (not in
mine). Use one AWG gauge size larger (ie. numerically lower) than the conversion shows. For example, ISO 2.5 is AWG 13 (not 14 as usually shown) etc. Using ISO gauges is easy. The actual gauge number (eg. 1.5, 2.5, 4.0, 6.0, 10 etc) is the actual cross sectional area of the conductor, in sq.mm.
Another very easy way to work out the voltage drop for any given length of cable, current flow, and cable size is the simple formula shown below. I always use this in conjunction with my published tables. This formula is simply:
Voltage drop equals (cable length (in metres) X current (in amps) X 0.017) divided by cable cross-section in mm.sq.
For example: 10 metres X 5 amps X 0.017 = 0.85. Divided by (say) 2.5, the voltage drop is 0.34 volt. This is just acceptable.
The above, and wire-tables indicate voltage drop across a single conductor. For chassis (earth) returns, the resistance of the return path can be ignored. Where there's another conductor for the return path, the total cable length must be taken into account. In other words, if there's a separate conductor for the earth return that's ten metres of cable, so you do the sum as if it were ten.
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