No matter what the size of the conduit, you always have to derate the conductors accordingly when you have over 3. Correct? So, like most people think, "put a bigger size conduit in and you can pull more wires!" For instance, putting 1/2" EMT in limits the # of conductors that can be pulled because of it's size. But really, even if I put a 1" EMT conduit in I can fit more conductors in but I have to start derating at 4-7 conductors. So even if I put a 2" EMT conduit in and I could physically fit alot of #12 THHN conductors inside I would have to derate the #12 THHN to 80% of its ampacity when I reached 4-7 conductors. If this is not correct please advise. Thanks!
Look in the code though, the normal use amperage and derateing amperage of some guages of wire are different. No code book here at home, but you derate from the higher amperage, still paying attenetion to the max amperage for that particular guage. If I remember correctly.
Code theory is so fun...
#74755 - 02/05/0712:40 PMRe: # of conductors in conduit
Are you talking small wires or large? For #12 THHN (90C), for instance, Table 310.16 allows 30A, but 240.4(D) restricts #12 to 20A maximum. For derating, though, you would use table 310.16, and would be able to put 7-9 #12 THHN conductors in a conduit before having to derate below 20A.
You do not have to count grounds for derating purposes, and may or may not have to count the neutral, depending what kind of circuit(s) you have. And I don't know if there is a code that explicely states it, but switched conductors (like in a 3-way switch) should only count as one conductor too, as only one will ever be considered a "conductor" at any given time.
#74756 - 02/05/0701:07 PMRe: # of conductors in conduit
Electure, I explained to the plant engineer that the larger size conduit does not mean that I can fill it all the way up. He wants to use it for "future expansion" but I told him about the code making me derate the conductors after 4. Anyway, I did everything legally, they just ended up eating alot of wire cost because I had to upsize the #12's to #10's and the #10's to #8's. Thanks for the input!
#74760 - 02/05/0707:16 PMRe: # of conductors in conduit