Double Wire Circuits

[Pavel314]

This is a theoretical electrical question, not something I actually plan to do. Say somebody wants to run a new circuit from the breaker box to one special outlet, like for a microwave oven or window air conditioner or something like that. Being an ecconomical sort, this guy decides that instead of buying the proper gauge wire for the job, he'll use up some 14 gauge wire which is lying around from a previous job, but run two hot lines and two ground lines in parallel, as diagrammed below.

Box: Hot ==================== Load Outlet Box: Ground==================

So we have two black 14g wires running from the hot connector on the breaker to the outlet and two white 14g wires running back from the outlet to the ground in the box. Two questions:

1. What gauge single wire would this be equivalent to in current carrying capacity? That is, would this be the same as running a single

10g or 8g or what? Maybe 14g / 2 = 7g?

1. This seems to be very unsafe but I'm not sure why. It's probably against every wiring code everywhere. What's the danger with this set up?

Again, I'm not going to do this, I'm actually going to go out and buy the proper gauge wire for my project, but this popped into my head and I wondered what the rest of you thought about it.

Paul

[jamesgangnc]

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Load Outlet

The danger would be that one half of the circuit could fail and the remaining half would be overloaded.

In your example it's probably ok to run a microwave on a 15amp circuit with a single piece of 14/2. But I would run 12/2 on a 20 amp myself. A dryer would be a better example.

[dpb]

You _could_ look up the wire size tables, but -- two 14's are the area of between one 12 and one 10. A14 = 0.003, A12 = 0.005, A10 = 0.008

The prime danger is one of the loss of connection or disparity in the quality of connection to one of the two conductors as most terminals are not designed for more than one wire under the connector.

It would be possible to do so by pigtailing ends to a third conductor for the connection.

AFAIK the arrangement is not condoned by NEC; where specifically it says it except under the workmanship clause I've no idea since it's patently silly as two wires of smaller size are more costly than the one larger.

But, if the ends were stranded, functionally there would really be no difference between the it and stranded wire of equivalent area.

As above, it's not "the right way" for the safety issue in the connections, mostly which is at least one reason for it not being Code-acceptable.

--

[Tony Hwang]

Hi, Since you mention theory, if you make the length of wires EXACTLY same to even the load current and make sure two wires always stay connected TOGETHER, it'll be OK.

[jamesgangnc]

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Load Outlet

I think you're both wrong. A single lead failure results in an overload on the remaining lead. And I think this is banned by the code which would require that a conductor connected to a breaker be rated to carry the load of the breaker. In otherwords an inspector would fail me for connecting 14/2 to a 30amp breaker. Even though two pieces of 14/2 could carry 30 amps.

[Tony Hwang]

Hi, I said it based on theory not on real life practice. OP mentioned theory.

[Jules Richardson]

That's essentially the way it's done in the UK; wiring is run such that outlets sit on a ring circuit rather than a radial from the service panel (consumer unit in UK parlance). See:

I'm sure it violates all sorts of rules this side of the Pond :-)

cheers

Jules

[jamesgangnc]

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Load Outlet

Even in the theoretical world it would still be bad because of the potential for a single lead failure. Safety aside you would also end up with reduced voltage at the load in the event of a single lead failure. In the case of a load like an AC this could lead to compressor failure.

[Tony Hwang]

Hmm, What is the definition of theory?

[Doug Miller]

Hold it right there, cowboy.

If you don't know the difference between neutral and ground, you have no business mucking about with 120VAC.

Code violation. Conductors are not allowed to be run in parallel below a certain size -- I think 2/0, but I'm not sure without looking it up.

[jamesgangnc]

Only the brits could come up with something like this. Seems the wiki article spends more time on the problems associated with it than anything else.

[Doug Miller]

Right here:

"... conductors of size 1/0 AWG or larger ... shall be permitted to be connected in parallel..." [2008 NEC, Article 310.4(A)]

Anything smaller than 1/0 AWG is not allowed to be run parallel.

[Doug Miller]

No, it's not "OK". It's a Code violation.

[HeyBub]

I once asked a college English teacher how he could smoke in the classroom when there was a sign over the door reading "No Smoking Permitted by order of the Campus Fire Marshall."

He rudely informed me that if I didn't want to smoke, I could remain in the room.

He would say the bit you quoted says nothing about anything smaller than

1/0.

[Pete C.]

As someone else noted, it's a code violation only below a certain wire size - 1/0. Above that size parallel conductors are permitted and fairly common, but that size puts such cases outside of nearly all residential applications.

[George]

It is quite common to do so with large size wire (1/0 and larger). One reason is because skin effect diminishes the ampacity increase you get by increasing size and the other is that it is just plain difficult to work with large cables.

[trader4]

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Load Outlet

In theory, whether the wires are exactly the same length or not matters not a wit.

[Pavel314]

I know the difference in my own mind but since I rarely discuss electrical wiring with others I may use the wrong term occasionally.

Paul

[terry]

Yes and even then UK allows 'spurs' off such a ring-main circuit. In other words like a 'radial' off a ring circuit!

However relative to the 13 amp rating of their outlets and use of fused plugs their ring and 'spur' wiring is AIUI heavier than would be used in North American practice. Don't know why we couldn't use ring circuits here in NA. A relative has encountered them in commercial oil rig practice!

[terry]

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Two 14AWGs in prallel!!!!!! I'd only do it as a temporary measure and remove before I left; because not easily understandable (Code or not) by someone working on it in the future. Therefore potentially dangerous. BTW I seem to remember measuiring the AC current draw of a microwave recently and it was I think about 11.36 amps, using a cheap clamp on. Voltage here is usually very consistent at 119 to 120 volts on each of the the two legs. So 11.36 x 120 =3D 1363 watts, that's still less than 80% of a 15 amp outlet? Also BTW we inadvertently plugged a second mid size m.wave into the other half of the outlet (Wired with #12 AWG from a 20 amp breaker) into which our big old timer m.wave is plugged. And then forgetting we switched on both, at same time! And it hasn't tripped the breaker yet, to our intense surprise. Only short term use mind you a few minutes here and there but definitely simultanaeous use of both microwaves! And outlet is NOT Edison wired, only single pole breaker! Wouldn't do the two 14s in parallel as permanent measure though.