A great thumb rule that I wish I'd seen (or noticed) long ago: Start from the easy to remember value for AWG 10 at 1 ohm per 1000 feet, the other gauges are all sized in dB. AWG 20 is 10/1000, 24 is 25/1000,
16 is 4/1000, 0 is 0.1/1000 and so on. The "real" numbers vary by manufacturer and specific part numbers, of course, but the thumb rule comes in handy for estimating.
As far as I know, NEC mentions 2 different figures for copper wire of each wire guage, likely with one of these figures varying with temperature and insulation type.
The one figure which varies with temperature and insulation type is ampacity. The other is maximum allowable overcurrent protection.
That's what I thought too, the actual ampacity for wire in air would be higher - and the NEC is probably more concerned with wire runs in hot attics with insulation and lots of dry combustibles around.
Not much of a concern when the wire is underground maybe.
I recently made a 0.001 ohm resistor using 10 gauge house wire. I thought I would need 12" to get the proper resistance, it was closer to 10" than the 12" I expected. Calibration was good at 75 degrees F. :-) Mikek
out
That's great! I never noticed.
Thanks Rich.
George H.
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