David Nebenzahl wrote:
On 8/29/2009 2:49 PM EXT spake thus:

Also, just as a long wire needs to be a thicker gauge, compared to a
normal length of wire, to carry a fixed amount of amperages,

Saying "a fixed amount of *amps*" would do.

a very short length of wire can be rated to carry a larger amperage
at a smaller gauge than normally used.

That's not true. Conductors are rated at a certain current regardless of
their length.

Agreed. That was probably the nuttiest comment in this thread.

This is the rational used on appliance cords, and the internal wiring
in appliances. I have seen a formula somewhere that will determine
the exact gauge needed for a given length at a specific amperage.

As others have said, length is a consideration only to limit voltage
drop. Length has no relation to the current carrying capacity of the wire.

I was going to bring up the aspect of cords too, as our 20-amp circuits
have cords plugged into them that are rated at far less than that,
creating another potential source of fire.

The code is rather pragmatic. #18 fixture wires on a 20A circuit are
not a problem because the lamp socket can not have a bulb over the wire
rating. (Someone could screw in an adapter-to-plug and run a space
heater - the rules of natural selection would then apply.)

Apparently there are not major problems with overloading #18 extension
cords on 20A circuits - dead bodies are very effective at promoting code
changes, probably also effective at UL. If I remember right, a
consideration was that the available fault (short circuit) current at
the end of the #18 cord is high enough so a short will give
"instantaneous" operation of the circuit breaker/fuse (not time delay).
(That is not likely true for Christmas tree lights.) AFCI breakers may
also help (but the selling point was cords that had been abused, like
walking on them).

You might be upset with motor circuits, that can have a circuit breaker
significantly larger than the wire ampacity. Welder circuits even bigger
difference.

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