Conductor sizing

[Codeman1]

I am reading Conductor sizing (11-19-99) by Mike Holt. Free stuff section.

On page 2 1st problem, Step 3: while correcting ampacity for #4 THHN conductor, instead of using 66 amp multiplied by the correction factor )0.80, the ampacity taken from 90 degree C column of 310.16 and multiplied by the factor 0.80.

Same method is followed in the 2nd problem at Step 3 on the same page.

I do not find any section saying that we have to use ampacity of 90 degree C column. The coorection table at the bottom of the Table 310.16 does not say anything about it. It just said mutliply the factor with the above ampacity to obtain the correct ratings.

Please clarify. Thanks. Aftab

 

[raider1]

Welcome to the forum.

110.14(C) permits conductors with temperature rating higher than specified for terminations to be permitted to be used for ampacity adjustments, correction, or both.

That means we can adjust the ampacity of 90 degree wire starting with the ampacity listed in the 90 degree column provided that the final ampacity does not exceed that listed for the temperature of the terminations.

Chris

 

[LarryFine]

Welcome to the forum.

What he said.

I do not find any section saying that we have to use ampacity of 90 degree C column.

It's not that we must, it's that we're allowed to. It's to our advantage in that it usually results in a smaller conductor.