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#193048 03/17/10 01:24 AM
Joined: Aug 2006
Posts: 356
Niko Offline OP
Member
Table one of Ch 9 says if we have one conductor we can fill the conduit to 53%, 2 conductor to 31% and more than 2 conductors the conduit can be filled to 40%.
My question is why 31% for 2 conductors and 40% for more than 2 conductors? what is rational behind it.

An IAEI instructor once told me it is because of the heat dissipation. But he did not explain in details why?

Thanks.


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Niko #193049 03/17/10 01:41 AM
Joined: Jul 2004
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It just has to do with how they pack into the pipe. Three takes up less room than 150% of 2 and it is volume we are speaking of.
Heat really doesn't enter into it. You derate "x" number of conductors the same no matter what size pipe it is in.


Greg Fretwell
gfretwell #193053 03/17/10 09:14 AM
Joined: Feb 2008
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ask your instructor to elabroate.Then come tell us.

Rewire #193057 03/17/10 03:44 PM
Joined: Aug 2006
Posts: 356
Niko Offline OP
Member
Rewire,
the instructor was at a seminar. so i don't have access to him anymore.

I have posted the same question at Mike's site http://forums.mikeholt.com/showthread.php?t=123904
but i am still not 100% confident on my understanding.


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Niko #193059 03/17/10 07:23 PM
Joined: Jun 2004
Posts: 1,273
T
Member
It's the radius of the conductors...

Do the math.

It boils down to the straight geometry of circles.

The conduit/EMT is the big circle...

Now how many circles can you fit inside leaving enough room to pull in without excessive force/ruining the insulation.

That's all that's involved.


Tesla
Tesla #193061 03/17/10 08:26 PM
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Posts: 165
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Last edited by Rewire; 03/17/10 08:27 PM.
Rewire #193076 03/18/10 12:44 PM
Joined: Dec 2002
Posts: 326
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Expounding on Tesla, 3 conductors can line up in a straight line so all the diameters add up. 4 or more and bundle collapses (the conductors don't ever twist up to line out in a row. Thus the binding issue for 3 conductors.

sabrown #193122 03/19/10 08:32 AM
Joined: Feb 2008
Posts: 165
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just when it all makes sense they bring in nipples


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