When derating conductors, do you determine the wire size according to the amperage after taking the 125% or before. For example, I have a load of 17.5 amps. If I take # 14 wire amp capacity in the 90 degree column and derate it 70 % I get 17.5 amps. Can I use this calculation or do I have to figure 125% of 17.5 amps. which would be 21.87 amps, which would mean I would have to use # 12 wire?? This is only an example, I would use # 12 wire anyway, but in some of my other calculations, it might make a real difference. I'm figuring out on this job, I'm doing what an electrical engineer should be doing if there had been a set of prints drawn out,like was orignally proposed by the inspectors. Somehow they didn't make the owner get it done like that, so now I'm having to figure it all out [Linked Image] Thanks..

I also have a situation that I need to run branch circuits to 7 pieces of machinery. I originally was going to run 1 1/4" conduit and run all in it. Now I realize that if I do that, I will have to derate to 50% which will make me have to run a # 3 wire for one machine that would originally have taken # 6 wire. I guess it would pay me to run separate conduits, at least where I will only have to derate 70% . Any other input on this? thanks again..

[This message has been edited by sparkync (edited 03-15-2005).]