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So, i have a single switch by the garage door controlling the overhead lights like so:

existing

and i would like to add a switch by the other door (shown) and wire it for 3-way control of the lights.

I'm pretty sure wiring power-switch-switch-lamp (with 14/3+G between the switches to accommodate 2 travelers) is okay (right?), like so:

idea1

but is it also okay to run a hot out to a 3-way switch and bring both travelers back in the same 13/3+G cable, then route along to the other switch and then to the lamp, like so?

idea2

If so, what about doing that with both switches, like so?

idea3

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  • What is the purpose of the junction box? You would still need to run 14/3 between the switches in any case - why make additional splices?
    – Comintern
    Nov 16 '15 at 4:49
  • @Comintern, it would be required in the last picture, but in the 2nd-to-last, it was just to save running two cables to the left switch.
    – Rob Starling
    Nov 16 '15 at 4:54
  • Don't you have an existing wire there? If the top picture is the existing wiring, you should only have to run a single 14/3 to the new switch.
    – Comintern
    Nov 16 '15 at 4:59
  • The existing wire is ancient cloth-covered stuff and I'm not attached to it :)
    – Rob Starling
    Nov 16 '15 at 5:01
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    I believe that if you check you'll find that that current code requires that there be a Neutral wire at each switch box. This means that neither of your last two pictures are acceptable. You will appreciate the presence of that Neutral wire if you ever at a future time go to install "smart" type device in one or both of the switch locations that requires a neutral connection.
    – Michael Karas ♦
    Nov 16 '15 at 7:16
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Michael Karas is correct the 2011 NEC added the requirement for a neutral at all switch locations IF they are inaccessible after installation. If your garage has open framing and will not be drywalled then you don't have to do this.

However, it is always better to have the neutral at the switch for future use. You may want to install a switch with an occupancy sensor or add a receptacle next to the switch. If you don't have a neutral the occupancy sensor has to trickle current on the ground and that is what the NEC is trying to eliminate.

If you stick with your second drawing (first one with the 2 three ways) then you will have the neutral available at all locations. Less boxes less splices = simpler installation.

Wire is cheap compared to a simpler installation and less headaches.

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I can't vouch for code, but basically what you have here is a variation on the difference betwenn running wire first to the switch and then to the load, or first to the load and then running a "switch loop" out to the switch and back. Either is reasonable, though switch loops require that you make sure all the wires are labelled clearly as being on the hot side of the circuit. My guess is that all are acceptable, but that's arguing from common sense, not from knowledge of code.

Recommendation: The opinion that really matters is that of the indpector, so I'd take this question to your Local Authority Having Jurisdiction and ask them which of these they would or wouldn't aporove.

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    makes sense. also, the li'l black slashes on the white wires (shown gray for clarity) were meant to indicate "re-designated black via electrical tape, sharpie, and/or heat-shrink markers)
    – Rob Starling
    Nov 16 '15 at 6:23

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