The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Correct rotation, wrong sequence
by Potseal
Yesterday at 03:14 PM
Industrail Control Panel bonding per 409.108
by sparkyinak
12/09/16 06:29 PM
Calling all Non-US members!! (Non-US only)
by aussie240
12/07/16 02:39 AM
Photo Upload Tutorial
by DanK
12/06/16 11:35 PM
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 11
HotLine1 9
Potseal 9
sparkyinak 8
Texas_Ranger 7
Who's Online
0 registered (), 8 Guests and 1 Spider online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#193048 - 03/16/10 11:24 PM Ch9 table 1
Niko Offline
Member

Registered: 08/17/06
Posts: 358
Loc: Campbell, CA
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.
_________________________
Be kind to your neighbor, he knows where you live


Top
2014 / 2011 NEC & Related Books and Study Guides
#193049 - 03/16/10 11:41 PM Re: Ch9 table 1 [Re: Niko]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
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

Top
#193053 - 03/17/10 07:14 AM Re: Ch9 table 1 [Re: gfretwell]
Rewire Offline
Member

Registered: 02/23/08
Posts: 167
Loc: Missouri
ask your instructor to elabroate.Then come tell us.

Top
#193057 - 03/17/10 01:44 PM Re: Ch9 table 1 [Re: Rewire]
Niko Offline
Member

Registered: 08/17/06
Posts: 358
Loc: Campbell, CA
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.
_________________________
Be kind to your neighbor, he knows where you live


Top
#193059 - 03/17/10 05:23 PM Re: Ch9 table 1 [Re: Niko]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
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

Top
#193061 - 03/17/10 06:26 PM Re: Ch9 table 1 [Re: Tesla]
Rewire Offline
Member

Registered: 02/23/08
Posts: 167
Loc: Missouri


Edited by Rewire (03/17/10 06:27 PM)

Top
#193076 - 03/18/10 10:44 AM Re: Ch9 table 1 [Re: Rewire]
sabrown Offline
Member

Registered: 12/12/02
Posts: 297
Loc: Ogden, Utah, USA
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.

Top
#193122 - 03/19/10 06:32 AM Re: Ch9 table 1 [Re: sabrown]
Rewire Offline
Member

Registered: 02/23/08
Posts: 167
Loc: Missouri
just when it all makes sense they bring in nipples

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals