I need to put in about 10 feet of 3wire to install 3way switches. I have a huge roll of 2wire, but no 3wire, and I doubt I will need it in the future to justify buying a roll.
Can I run two lengths of 2wire (using only one conductor in the second length)? They would be right next to each other, going through holes together, so it seems to me that it should be as safe as 3wire.
Well, the SMART thing to do is just buy the wire you need (as another poster suggested.)
The DUMB thing to do is what your propose (using only one wire of the pair in one cable.)
If you insist upon using twice as much 2 conductor cable as 3 conductor cable) then ensure that the WHITE wire of each cable are connected at both ends. This is true whether you used a "switch loop" or you run the power through both switch boxes and then to the controlled fixture.
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Sure, you're right. I get carried away with frugality sometimes. (something to do with being unemployed?)
Locally, the inspectors wouldn't pass it. Electrically, there's no difference. I can't imagine the cost of 10 feet of 14/3 or 12/3 would be worth the hassle of dealing with two cables.
Jeff
I once had a conversation with someone I worked with who actaully believed this was a preferred method by electrical contractors so that they could reduce costs by buying and stocking more 2-wire cable instead of a smaller amount of 2-wire plus 3-wire. It must have been the contractor he was using!
Anyhow, here in Canada it is not allowed, and I suspect the NEC has a similar rule as we have:
12-106 Multi- and Single-Conductor Cables(1) Where multi-conductor cable is used, all conductors of a circuit shall be contained in the same multi-conductor cable except that, where it is necessary to run conductors in parallel due to the capacity of an alternating current circuit, additional cables shall be permitted to be used provided any one such cable includes an equal number of conductors from each phase and the neutral and shall be in accordance with rule 12-108.
Rule 12-108 starts off: "Conductors of similar conductivity in sizes No. 1/0 AWG copper or aluminum and larger shall be permitted in parallel provided..."
In other words, this is not allowed for 14/2 or 12/2 situations!!!
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