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

earlydean,

I disagree with your _literal_ interpretation of the NEC, though not on your read of intent, nor the safety of the installation that you describe.

310.4 is written to _permit_ parallel conductors sized 1/0 AWG or larger, and then has several exceptions that permit smaller conductors to be paralleled. (310.4 Exception 2 clearly matches what you describe, but only for limited types of circuits.) The pretty clear _implication_ is that parallel conductors smaller than 1/0 AWG, not covered by the exceptions, would therefore be prohibited.

I do not find any _explicit_ prohibition of smaller parallel conductors. Since the NEC is supposed to be a permissive code, this itself causes some problems with interpretation

300.3(B) has its own problems. It does not explicitly permit switch loops (and most switch loops don't have a neutral), and 'circuit' is not defined in article 100 ('Branch circuit' is defined, but 300.3(B) clearly applies to feeders as well as branch circuits.) The common _understanding_ of 300.3(B) is that the net current flow of all conductions in a raceway must balance out to zero, thus permitting switch loops. But this is not what the code actually says.

-Jon

Earl


I disagree with that statement for the same reasons Jon pointed out.

If parallel conductors smaller than 1/0 protected at the single conductors ampacity where generally allowed there would be no reason for exception 2 of 310.4.

IMO the only conductors permitted by the NEC to be run in parallel are either 1/0 or larger or fit one of 310.4s exceptions.

But I do see Jon's point that with a permissive code getting a firm grip on this issue is tough.


Jon IMO 300.3(B) specifically allows for switch loops without the grounded conductor included.


IMO when the CMP put in the words 'Where used" they mean for that potion of the circuit, not the entire circuit.

As far as the advantage of a ring circuit under the NEC that would be reduced voltage drop.

Have a great Holiday gentlemen, Bob

I do not see where 310.4 mentions the size of the overcurrent device. It does mention the size of the conductors, with a few exceptions, and there are other exceptions in the NEC as well, but none of those exceptions permit what Earlydean has mentioned in his post.

wouldn't a low voltage relay be a safer way to go to turn the fan on?

plus if fed from each units panel phasing could become an issue if apt #1 fed off L1 and apt #2 fed off L2 when both units turn on switches they will trip cb's.

maybe i am not up to speed with topic but seems possible to me

my 2 cents anyway.

h20

The installation I have described occurs only in single family homes and the fan and multiple switch locations are only fed by 1 individual circuit.

We always put some form of disconnect at the fan either a switch or cord and plug connect it. I really can't see any danger at all in this installation but I believe it is a violation of 310.4 due to its wording.

If we just focus on the definition of Conductors in Parallel: "electrically joined at both ends", it seems to me to mean those conductors run together strictly for the purpose of allowing a larger amount of current in the feeder than allowed in any one conductor. This is made clearer if we look at the other rules for paralleled conductors (same size, terminations, length, etc.)

Just like grounded vs. grounding conductors, the ending of a word or the context of the wording makes all the difference. "Conductors in parallel" or paralleled conductors are different from parallel conductors or conductors that happen to have a parallel circuit arrangement. (Is there any difference between the grounding of a receptacle and the grounding of the service? One goes to an equipment ground, the other to earth. We can't tell that from the one word "ground".)

Did anyone notice that if we hook up two or more lights on a single switch, that they too are connected in parallel? Is this forbidden? NO!

Actually I think it may be prohibited even though I am guilty of doing it as well.

Also that very question is the topic of this thread, the only difference was the load was a motor not a light.

Bob

Lee,

Since you said that you don't see any danger in this installation, do you believe that this installation violates the _wording_ of the code, or do you feel that it violates the _intent_ of the code?

IMHO if this install is done with multiple 'switch loops', then it is safe.

Does anyone see an electrical safety issue with this sort of installation?

Let me propose a different installation for consideration: start with a standard install of the exhaust fan with a _single_ switch. Now run two conductors from the first switch to a second switch, and wire the second switch in parallel with the first switch. If _both_ switches are on, then you have a parallel circuit pathway. However one of the circuit pathways is through the first _switch_, and the second pathway is through _wires_ and the second switch. In other words, with this arrangement you don't have parallel circuit pathways in _wires_.

IMHO this proposed installation is electrically the equivalent of having multiple switch loops feeding the fan. However there is now a code distinction: the 'parallel circuit pathways' are through devices (switches) rather than through the wires. Article 404 does not have any restrictions on paralleled switches So if you belive that this installation violates 310.4 on a technical violation of the wording, but is not actually dangerous, that I've provided an electrically similar installation that falls under different code rules. *grin*

-Jon (who should be cooking now)

Not in the least, I only question it's code compliance.

Bob

There is so much of the NEC that is subject to the intent of the CMP that wrote that section. What is our interpretation and what is the inspector's interpretation often differ. As Shakespeare put it: "Aye, there's the rub!" (my apologies for misquoting)

Perhaps that is why there is a purpose statement: " The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity." If we use this as a guide, can we go wrong?

[This message has been edited by earlydean (edited 11-24-2005).]