Trimmed Wires Violation Code

[Carultch]

19 strand conductor with 5 strands trimmed off. Logic says an adjustment factor of 14/19 (.7368) needs applied to the original ampacity you had with all 19 strands, right?

Not necessarily true, because ampacity is not linearly proportional to KCMIL.

 

[Coppersmith]

Not necessarily true, because ampacity is not linearly proportional to KCMIL.

I just looked at table 310.15(B)(16) and you are right but I don't understand why. Seems like twice as much copper should carry twice as many amps. Somebody enlighten me please.

 

[GoldDigger]

I just looked at table 310.15(B)(16) and you are right but I don't understand why. Seems like twice as much copper should carry twice as many amps. Somebody enlighten me please.

Twice as much copper has 1/2 the resistance, and so the same voltage drop.
But it has twice the current and therefore twice the heat, yet has a less than double surface area to dump the heat through.

mobile

 

[kwired]

I just looked at table 310.15(B)(16) and you are right but I don't understand why. Seems like twice as much copper should carry twice as many amps. Somebody enlighten me please.

Twice as much copper has 1/2 the resistance, and so the same voltage drop.
But it has twice the current and therefore twice the heat, yet has a less than double surface area to dump the heat through.

mobile

Keep in mind ampacity values in 310.15(B) tables are based on insulation temperature rating and not on what the conductor itself can carry. A 12 AWG copper conductor can carry a lot more then 20 amps but it is going to have some temperature rise.