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!

You are correct, it doesn't matter what size conduit you use, the derating requirements start with 4 current carrying conductors

Roger

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...

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.

Also note that you can put up to 20 CCC's in one pipe if you use #10 for 20A, and #12 for 15A. That approach is used a good deal in commercial work.

Especially if you're upsizing the wire for voltage drop anyway.

Are you still having misunderstandings with your same piece of 2" conduit and the same plant engineer?

That would apply only to the travellers. The switchleg conductor must be counted as a current carrying conductor.

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[This message has been edited by electure (edited 02-05-2007).]

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!

SolarPowered, what do you mean by CCC's? Something...Circuit Conductors. I need to know more about this. Thanks!

CCC = current carrying conductor