ECN Forum Forums Code Related Discussion NEC & other Code issues Conductors in parallel

Winnie,

I feel it violates the wording of the code only, not the intent.

I think the code should allow switch loops creating parallel conductors, provided that the OCPD is not greater than the rating of any of the conductors. Most of the article if referring to paralleled conductors with OCPD greater than individual conductors. IMO Exception NO. 2 should be reworded to allow this.

I've done this (in a commercial setting); therefore, it's legal.

Earl


To me that is 'the rub'.

We (electricians or inspectors) have no business trying to guess the intent of the CMP.

The only thing that matters is what is written in black and white.

It is the written work that is adopted into law not the intent of the CMPs.

Actually we don't have to guess the intent of the CMP. It is recorded in the ROP and ROC by NFPA.

try here: http://www.nfpa.org/displayContent.asp?categoryID=997
and here: http://www.nfpa.org/displayContent.asp?categoryID=998

earlydean WROTE: That does not change the fact that what the legislative body adopted includes only the language of the code itself. A court trying to sort out conflicting interpretations will look at the legislatures intent but not at the intent of non legislative CMPs. It is a legal absurdity to attempt to delegate legislative authority to anyone outside the legislature in question. The office of the California State Fire Marshal tried to adopt the National Fire Codes by reference without naming a year or addition in an attempt to avoid the costs of periodic adoption. I don't know if any court ever called them on it but I'm confident that the court would have depended on the editions of the various codes that were in effect at the time of the adoption by the legislature.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

I disagree with that, I see no reason the court would not start at the source.

Longtime lurker first time poster.

In Canada this is strictly not allowed. Conductors smaller than 1/0 can only be run in Parallel if they are in the same cable. COnductors 1/0 and larger can only be run in parallel if they are (among other things) of the same length and free of splices. (see rule 4-108 of the CEC if you are interested)

The issue that I see is that if you have conductors of different lengths, you have different impedances. Different impedances lead to potential phase differences at the load (i.e. where the conductors join back together) and the potential for overvoltage at the motor. At the very least you should ensure that the conductors are of the same length.

Steve

Steve the NEC rules are very similar for the same reasons.

SteveG,

I've got to disagree with you.

The NEC has similar rules about the use of parallel conductors, but these rules have nothing to do with phase differences affecting the _load_. They have everything to do with different conductor impedance leading to the parallel conductors not equally _sharing_ the current, and thus potentially overloading one of the conductors.

The current differences between the two paths depend upon the impedance difference of the two paths, so that small differences in length could lead to significant differences in current balance.

For the different lengths to have an effect on the _load_ requires such very long paths that the inductance and capacitance of the wire is a significant fraction of the load impedance. Straight voltage drop difference in the conductors wouldn't much matter; you would only have problems with energy stored in the conductors. In other words, over transmission line distances. Especially with 'switch loops' where the loop area is intentionally kept small and the inductance low, I don't see this as a problem for wiring inside of a _structure_, certainly not a home.

-Jon