I am going to install 4 LED downlights on a 3-way switch. My plan is to do panel-switch-switch-lights... similar to this image

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I will be using THHN inside conduit from panel to first switch, and from first switch to second switch. My question is do I need to splice the neutral in the first switch box, or can I just make it a continuous run from panel - through first switch box - spliced to NM-B in second switch box?

Alternatively, is it good practice to splice here (provides future capability) or bad practice (unnecessary point of failure)?

  • 2
    Do be sure to leave enough wire in each box that if someone changed to a switch that needed a neutral (i.e. a smartswitch, typically) in the future, they could cut the neutral and splice in a pigtail for that.
    – Ecnerwal
    May 19, 2019 at 3:34

3 Answers 3


To me the choices are equally acceptable. I don't see either as a good or bad practice. As long as a good splice is made it will last indefinitely. And sometimes I like less clutter in the box.


If your splices are failing, that is a technique problem. A competent wire-nut splice should be reliable.

It doesn't matter legally, you can either leave zero spare length, 18" of spare length so you can splice to it if needed, or actually fit a splice. You always have the option of running a replacement wire if needed since it's conduit -- that's why it's legal.


I'd leave loops of everything except the travelers in each box, especially if the incoming was at the light, where power would have to be brought through all of them anyway. That's assuming there isn't a junction box in the middle somewhere that might someday be a 4-way; then you'd need the travelers too.

Fishing a fifth wire down an EMT with four wires in it already can be tough. For total future-proofing, run and loop an extra live wire as well. Even if the client doesn't ask for it, when running a lighting circuit I run it as half of a MWBC. The other half is for me when I come back to do something else and I need power from there.

Those loops and the, easy to do now, extra wire can save the next guy a whole lot of work.

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