conductor grouping & NEC 300.3B

[iblittljn]

NEC 300.3 Conductors
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4).

Isn't the fundamental requirement of this section that single conductors shall be grouped together to mitigate the parasitic effects of magnetic and electric fields. One of the ways to achieve grouping is by using conduit/raceways etc. If a raceway etc is used, all conductors of the circuit must be contained therein.

There are other ways to achieve grouping of conductors to keep them in close proximity such as staples, straps or other acceptable wiring procedures. Wouldn't interlacing or weaving them together as in CAT V UTP cable assemble, achieve the same mitigation requirements?

From an installation concept, placing conductors into a conduit may be the defacto standard, but is it the only way?

Ian

 

[charlie]

Re: conductor grouping & NEC 300.3B

I was going to close this thread as a duplicate to this one but this is a different question that deserves discussion from an engineer's viewpoint.

 

[petersonra]

Re: conductor grouping & NEC 300.3B

the key is "acceptable".

the code defines what means of keeping the conductors in close proximity are acceptable. no other means are allowed.

 

[iblittljn]

Re: conductor grouping & NEC 300.3B

Then what methods are acceptable and what code section defines them? Are there even any others?

300.3b talks about keeping all conductors in the same raceway etc. but it does not state it is exclusionary. It does not say: Only the following methods shall be used to group single conductors forming one circuit.

 

[haskindm]

Re: conductor grouping & NEC 300.3B

This is an interesting question. 300.3(A) states that single conductors shall only be installed "where part of a recognized wiring method of Chapter 3." The only methods that I see in Chapter 3 that let you install single conductors that are not "enclosed" in some sort or wireway or cable are "knob and Tube" (restricted usage), Messenger supported wiring, and Open Wiring on Insulators. There is an exception for "overhead conductors" but that refers to Article 225 which is for "outside installations". 300.3(B)(2) allows the installation of single grounding and bonding conductors. Other than that we are restricted to using the wiring methods of Chapter 3. Unless you can convince the AHJ that the method you are contemplating meets the criteria of one of these wiring methods then it would be a violation of the NEC.
Let me know if I missed some loophole. An inspector once told me (and he was the AHJ at the time) that if I found that the NEC prevented me from doing something, I probably had not read far enough. Because somewhere there was probably an exception that would allow it!

 

[steve66]

Re: conductor grouping & NEC 300.3B

Wouldn't interlacing or weaving them together as in CAT V UTP cable assemble, achieve the same mitigation requirements?

Yes, that would fall under the "same cable" method listed in 300.3(B) (although much of article 300 wouldn't apply to Cat V).

Single conductors require a raceway or other wiring method per 300.3(A) anyway.

If you are trying to group cables by staples or straps, technically, the cables should be split where they enter a box. That would be a violation of 300.20A if the same current is split between two cables. And putting 2 cables through the same box connector is often a violation of the connectors listing.

Steve

[ August 17, 2005, 09:00 AM: Message edited by: steve66 ]

 

[luke warmwater]

Re: conductor grouping & NEC 300.3B

The IRC made it easier for you.

They put the 'allowable wiring methods' from Chapter 3 into one table. Table E3701.2

They even went farther and put those into a nice table called 'allowable applications for witing methods'. It's Table E3701.4

I don't know if there are any direct on-line links to these tables. If I find them, I'll post them.

 

[charlie b]

Re: conductor grouping & NEC 300.3B

Originally posted by iblittljn:Isn't the fundamental requirement of this section that single conductors shall be grouped together to mitigate the parasitic effects of magnetic and electric fields?

I think that is the main reason. I suspect, however, that a secondary reason is so that the wires don't go running off in different directions. If, for example, the hot and neutral of a circuit were run some distance apart, it would make it very difficult for a future electrician to locate the wires, in case there were a need to do any repairs or upgrades. Something along the lines of the "KISS principal."

 

[derf48]

Re: conductor grouping & NEC 300.3B

Ian, welcome to the forum! As you are an engineer and it seems new to the nec, remember that it is a construction manual, not an engineering design standard, much like the NESC. The end users of the NEC wear many hats, from the engineer and electrician down to the homeowner. The minimum standards contained in the code, if followed, ensure the practical safeguarding of persons and property from the hazards arising from the use of electricity. To achieve the desired end results of electrical safety, most times the NEC does not allow the user the freedom to "design". Most who use the NEC do not understand the why's behind a code section and therefore must be lead down the correct path. If the AHJ understands the intent of a section, and you fulfill the intent with alternative methods, then he has the ability to approve the installation. Of course that is a big IF!

Fred

 

[iblittljn]

Re: conductor grouping & NEC 300.3B

charlieB and derf48
Beautiful posts! Thanks.