derating question.

[zappy]

We have 10' gutters, some are nippled together, some have longer raceway (emt) connecting them. So as more and more wires start to build as were pulling threw the emt, is the derating based on the one conduit with the most wires in it? I hope this makes sense?

 

[augie47]

I believe each conduit would stand on it's own. For example a #12 sharing a conduit with 15 ccc would have a different ampacity as the same #12 in a conduit with 22 ccc. I would think that rather than having to change wires sizes in most situations you would just size to the worst case scenario.

 

[Jim W in Tampa]

Can you keep the emt to under 24 inches

 

[don_resqcapt19]

Don't forget that if you have more than 30 current carrying conductors at any cross section of the wireway you will also have to derate. 376.22(B)

 

[sameguy]

code book is in truck and it is snowing, I think you can only fill nipples 60% even 24" and smaller.

 

[raider1]

code book is in truck and it is snowing, I think you can only fill nipples 60% even 24" and smaller.

You are correct for conduit fill for nipples up to 24" in length. (See note 4 to the Tables in Chapter 9)

Chris

 

[benaround]

Zappy,

I think you will find that more smaller conduits, with 9 CCC or less, is a better way to go

than fewer larger sized conduits, with over 9 CCC. jmo.

 

[rikthejman]

Theres a great example of gutter fill in Art 376 (NEC Handbook 2008) So, I guess if you are 24" or less on your EMT then you don't have to derate. Then you have to watch your fill (20% of cross section) and no derate until 30 CCC in the gutter. At least thats what I see from your question.