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#37129 04/22/04 06:59 AM
Joined: Dec 2000
Posts: 4,289
Member
OK,
NEC'99 310-15(b)(2)(a)

Exception No. 3: Derating factors shall not apply to conductors in nipples having a length not exceeding 24 in. (610 mm).

So what exactly constitutes a nipple??

#37130 04/22/04 07:24 AM
Joined: May 2001
Posts: 717
G
Member
A pipe not over 24" is a nipple.

#37131 04/22/04 11:07 AM
Joined: Jun 2003
Posts: 1,143
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<<CENSORED>>

Never mind. George's answer is probably more appropriate for this forum!

#37132 04/22/04 01:12 PM
Joined: Aug 2003
Posts: 1,374
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Moderator
I like George's answer. It is easy to overthink this. A 90 degree bend can be a nipple if it is less than 24".


Ryan Jackson,
Salt Lake City
#37133 04/22/04 03:39 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
At first read you say why?

Why can I stuff 24" of pipe with wires and not derate?

I believe the answer lies in coppers ability to readily conduct heat.

Say you have a 24" nipple between a panel and a contactor enclosure, you will have conductors hanging out of both sides of the nipple acting like heat sinks limiting how hot the conductors in the nipple will get.

That's my story and I am sticking to it. [Linked Image]

After all there has to be logic behind this exception.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#37134 04/22/04 04:37 PM
Joined: Feb 2003
Posts: 939
F
Member
i am leaing more to bob's answer there .

yes any pipes included the ell sweep[s] if 24 inch or less but i am still consering about the abilty of heat build up in there.

and for short pipe nipples 24 inch or less.

I have see few place some peoples did use 24 inch pipes and jamed many romax[s] wire in the pipe and i have one call not too long ago and have to replace bunch of romax wire they were brittle in few spots.

Really IMO,, i dont know if they did change the code or not about derating the wires in the nipples at all but i wish they change the length limit to more like 4 inch or less that can clear up some of the mess we have to deal with it ..

merci , marc


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

#37135 04/23/04 08:36 AM
Joined: Dec 2000
Posts: 4,289
Member
I like both George and Ryan's descriptions.
(the elbow was what I was looking for).

We had an inspector proclaim that by (his own) definition a nipple must be a straight piece of rigid conduit. (Although he couldn't explain the term "offset nipple")

Thanks...S

#37136 04/23/04 10:00 AM
Joined: Aug 2002
Posts: 1,081
T
Member
Elbow and nipple:

[Linked Image from s91748743.onlinehome.us]

[This message has been edited by ThinkGood (edited 04-23-2004).]

#37137 04/23/04 11:05 AM
Joined: Jul 2002
Posts: 8,412
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Guy's if you want my input into the frey, a nipple as I understand it is a Male-Male Threaded coupling.
Ask any plumber what a nipple is, provided they are civilised, that will be thier answer.
Cue Russ!. [Linked Image]

#37138 04/23/04 07:45 PM
Joined: Nov 2002
Posts: 558
G
Member
That would be my thought too Trumpy.

If it doesn't have threads at both ends most plumbers wouldn't call it a nipple,just a 24" length of pipe.

Russell

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