Think DC first, or remember it is
Ohm's Law
V=IR
12= 90(R)
R= 7.5
Opps, no home work problems!
Even on the high side or average 14 V (what one might see on the dash)
14=90(R)
R= 6.42 even better
With respect, that's an irrelevance.So, put 120V in the equation, that would make things exciting!
Your forgetting that your only at 12V!
I just put a new alternator in my truck it is rated at 90 amps the wires coming from the alternator look like #14 wire how can this put out 90 amps?
Several automotive wiring spec's (this side of pond; SAE, mainly; Ford; Chrysler) state the max' insulation temperature rating of engine compartment wire at 125?C (257?F). AFAIK, there is no automotive spec' similar to 110.14(C) of the NEC....
And, given that the alternator is in the engine bay, you'd think that the wiring insulation would have to be rated for elevated temperatures thus making higher currents acceptable/permissible.
Automotive wiring is somewhat different in that the conductor lengths are relatively short and the wiring is designed for much higher temperatures as has been mentioned previously. The typical conductor sizing requirement for a 90 amp alternator is #8 if the conductor length is less than 5 feet and #6 if greater. I am quite certain that the wire is not a #14, it would not meet the manufacturer's specs for that size alternator.
Bob
Wire sizes vary from one make to another. I owned and operated an automotive electrical repair facility for over a decade and never could figure out the reason for that.
Below is a chart I found for wire size. It is generic, but as you can see, length is a factor. According to the chart, #12 is good for 100 amps if it's not too long.
http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm
Sometimes other factors like flexibility are figured in. Not always correctly, I might add. For instance, GM oversized the wiring in the door jambs for power windows and the like. They were huge, finely stranded and had thick insulation. Ford and Chrysler just used the same size as the rest of the circuit.
Well, GM's engineers botched the job. I repaired hundreds of broken door jamb wires in GM's over the years and almost none from any other maker.
I have a 2004 RAM truck that I have repaired the door jamb wires many times - but only on one door and it isn't even the driver door that gets the most flexing. I just butt splice them together when they break but have done so several times and more than once on same conductor in some instances.
Exactly why I have been using butt splices - don't want to take all that apart. This is rear door of a 4 door vehicle - kind of a pain when door lock quits or power window quits - especially if not all the way closed when it quits. Sometimes have lost speaker in that door.When you get ready to pull an entirely new conductor in, PM me and I will tell you how to do it. You have to remove the door and kick panel trim, but not any of the wiring harness.