Replies

1. 
   BillHartmann | Oct 10, 2006 09:43pm | #1

   Yes, AWG is the size of the bare wire.

   But also note that when calculating conduit fill that you need to both AWG and the type of insulation. As conducit fill is based on the OD which and different types of insulation have different thicknesses.

1. 
   JohnSprung | Oct 11, 2006 01:10am | #2

   Isn't heat also a factor in conduit fill?   Insulation rated for lower temps requires looser fill so as not to get too hot?  

    

   -- J.S.

    

1. 
   BillHartmann | Oct 11, 2006 02:53am | #3

   NoThe conduit fill is simply a percentage of area. That is to allow for pulling wires without damage.Heat derating is a completely different subject.Depending on the number of equivalent current carrying conductors in a conduit or for cable bundled together then the ampacity of the wire is derated.*Equivalent current carry conductors. For single phase circuits you have two, the hot and neutral. For multiwire circuits you have the 2 (or 3 for 3 phase) hots. The neutral is not counted as it only carries the difference.

1. 
   JohnSprung | Oct 11, 2006 03:10am | #5

   Ah, yes.  I'm starting to remember now.  By staying below the point where derating kicks in, you pretty much always stay below the conduit fill limit, right?   

    

   -- J.S.

    

1. 
   BillHartmann | Oct 11, 2006 03:19am | #6

   No.For different size wires you need to calculate it, but for all the same size there are table of conduit fill.For 1/2" EMT with #12 THHN you can have 9 wires.In most cases that means derating.

2. 
   JohnSprung | Oct 11, 2006 03:33am | #7

   My code books are packed up for the move next weekend, but I think we're saying the same thing.  You can have nine THHN #12's in a 1/2" with derating, that's the fill limit.  There's a lower number than nine where you don't have to derate.  By staying below that lower number, you're cool -- as it were -- for both fill and thermal derating.  

    

   -- J.S.

    

3. 
   pm22 | Oct 11, 2006 04:20am | #8

   Don't forget that derating starts from the 90º column so actually it works out.

   ~Peter

4. 
   BillHartmann | Oct 11, 2006 07:16am | #9

   "Don't forget that derating starts from the 90º column so actually it works out."Depending on the insulation.But in general most is, but not all.

5. 
   BarryO | Oct 12, 2006 04:51am | #10

   This is a handy page for calculating conduit fill, provided you don't have too many different types:

   http://www.systemswestengineers.com/fill.htm

   I also have an Excel spreadsheet I got somewhere, for more complicated situations.

2. 
   rjw | Oct 11, 2006 03:06am | #4

   Thanks,Yesterday I ran across a box with 200 A breaker and unmarked copper feeds that just didn't look like the right size. (I get so used to seeing stuff sized properly, that when I see something like this, I tend to hesitate when the wire isn't marked.)I was able to pick up an unsecured wireless network and check the AWG sizes, and called it out as too small (the wires w/ insulation were 10mm)Just wanted to be sure.

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