ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Potseal 11
Recent Posts
600 KW 120/208 3 Phase Y protection
by Yooperup. 07/24/17 12:20 PM
1913 American Electrician's Handbook
by gfretwell. 07/20/17 01:08 PM
Green House wiring
by ghost307. 07/20/17 09:10 AM
Permit Snafus...AHJs and Contractors Jump in
by HotLine1. 07/18/17 08:06 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
239,345 Are you busy
174,811 Re: Forum
167,191 Need opinion
Who's Online Now
0 registered members (), 51 guests, and 4 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#127726 - 10/16/01 07:10 AM Why oh why?  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Why is only 31% conduit fill allowed for 2 wires, as opposed to 40% for 3?
I assume that it is precautionary, in the event that only 2 wires of a 3phase system are used, and the magnetic fields aren't cancelling. However, for all the commentary in the Handbook, this is not mentioned.
Anyone else.


Tools for Electricians:

#127727 - 10/16/01 02:44 PM Re: Why oh why?  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,878
NY, USA
Redsy,

My guess is that it would be because 2 wires together that took up 40% fill may be too tight to pull through a conduit because they would be like >> oo or 8 << and together might approach the inside conduit diameter with the 40% fill limit. It would be a tight one for sure! Straight pulls might not be so bad, but 360 degrees would be another thing.

Does that make sense?

Bill


[This message has been edited by Bill Addiss (edited 10-16-2001).]


#127728 - 10/16/01 08:49 PM Re: Why oh why?  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,311
Redsy,
I see FPN #2 70-561, to back up the angle Bill's offered. Other than that the #'s do make me wonder if any specific mathematical logic was followed.
CMP9,,,
35!
no..29!
34 ?...
30
31.., an' it's break time!
[Linked Image]


#127729 - 10/16/01 10:06 PM Re: Why oh why?  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Guys,
Ahh..
The jam ratio! Lots of thought went into this idea. I think it refers to 3 wires, though. Not two.


#127730 - 10/16/01 11:02 PM Re: Why oh why?  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,878
NY, USA
Redsy,

That's my best shot...

[Linked Image]
Bill


#127731 - 10/17/01 07:12 AM Re: Why oh why?  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Bill,

It's not anything that really concerns me. It's just something I have wondered about this in the past, and now, with this forum I thought I'd bounce it around.
Thanks.


#127732 - 10/17/01 07:22 AM Re: Why oh why?  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,311
Redsy,
We are, as electricians, always complying to code, and left wondering about the rationale. The handbook only goes so far, the only other resource would be a formal interpetation.
The thing is, some codes, and specifics , are probably so old there's no one left to explain it's orgin.


#127733 - 10/17/01 12:47 PM Re: Why oh why?  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
sparky,
A formal interpretation would be of no help in finding out the "why" as the NFPA requires that requests for a formal interpretation be submitted in a manner that will allow the NFPA to answer the question with either a "yes" or a "no". The only way that I know of would be to find the TCR (now known as ROP) and the TCD (now known as the ROC) for the proposal that became the rule.
Don(resqcapt19)


Don(resqcapt19)

#127734 - 10/17/01 07:55 PM Re: Why oh why?  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,311
Don,
Sounds like some serious archive searching, at least on this issue. It makes me wonder if anyone actually pursues code history to this extent.



Member Spotlight
MarkC10
MarkC10
CA, Inland Empire
Posts: 43
Joined: September 2013
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.014s Queries: 14 (0.003s) Memory: 0.7996 MB (Peak: 0.9670 MB) Zlib enabled. Server Time: 2017-07-26 10:48:27 UTC