ECN Forum Forums Code Related Discussion NEC & other Code issues Use of 90 degree rated cable

In Mike Holts "Masters Electrician Prep Book", he refers to the 90 degree column in T310-16 and states that this column is used primarily for ampacity derating. Has anyone else read or heard this?

Hi tmon,
yes , we are allowed to use the highest figure to start derating calc's from, i believe there was a code cycle to clear this up, but am at a loss this morning for an article...

It's always been that way.

Most earier Circuit Breakers ( small size ) were rated for 60º terminations.

Now many are rated for 60/75º terminations.

Usually only high voltage systems and bus work is the only items rated for 90º terminations.

Look at the labeling within panels and on equipment terminal info.

Also NEC 110-14(c) must be followed. Although is has only been in the NEC the last few cycles, it has always been in 110-3(b) and the UL White book has had the info for many mnay years, usually with-in the first 8 pages of text.

Glenn

thanks Glenn

tmon,

Welcome to the group!!!

Just wanted to point out one of the more "simpler" points on using the 90 degree column for derating is the reason we can put upto 9 current carrying conductors [#12 THHN cu] in the same raceway, and still have them rated at 20 amp max.
What is being done here is the 30 amps maximum for #12 in the 90 degree column is used for the derating number - so for 9 current carrying conductors, 70% of 30 amps is 21 amps.

Scott SET.