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#74752 - 02/04/07 12:43 PM # of conductors in conduit  
kyelectric  Offline
Joined: Aug 2005
Posts: 64
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!

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#74753 - 02/04/07 01:00 PM Re: # of conductors in conduit  
Roger  Offline
Joined: May 2002
Posts: 1,716
You are correct, it doesn't matter what size conduit you use, the derating requirements start with 4 current carrying conductors


#74754 - 02/04/07 07:03 PM Re: # of conductors in conduit  
Tom H  Offline
Joined: Jan 2005
Posts: 74
Milford, Ct, USA
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 - 02/05/07 01:40 PM Re: # of conductors in conduit  
SteveFehr  Offline
Joined: Mar 2005
Posts: 1,198
Chesapeake, VA
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 - 02/05/07 02:07 PM Re: # of conductors in conduit  
SolarPowered  Offline
Joined: Jul 2004
Posts: 625
Palo Alto, CA, USA
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.

#74757 - 02/05/07 05:24 PM Re: # of conductors in conduit  
stevecheyenne  Offline
Joined: Nov 2006
Posts: 38
Yorba Linda, CA
Especially if you're upsizing the wire for voltage drop anyway.

#74758 - 02/05/07 07:50 PM Re: # of conductors in conduit  
electure  Offline

Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
Are you still having misunderstandings with your same piece of 2" conduit and the same plant engineer?
switched conductors (like in a 3-way switch) should only count as one conductor too,

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


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

#74759 - 02/05/07 08:13 PM Re: # of conductors in conduit  
kyelectric  Offline
Joined: Aug 2005
Posts: 64
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 - 02/05/07 08:16 PM Re: # of conductors in conduit  
kyelectric  Offline
Joined: Aug 2005
Posts: 64
SolarPowered, what do you mean by CCC's? Something...Circuit Conductors. I need to know more about this. Thanks!

#74761 - 02/05/07 08:24 PM Re: # of conductors in conduit  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
CCC = current carrying conductor


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