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Given the option, is it better to bring power to your switches first, then run wires to your lights? Or is it better to bring the power to your lights first, then run wires to your switches? Or does it matter?

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    No. I'm quite serious: if you're even considering this question, please hire a professional before you kill yourself by putting power where it shouldn't be. – Carl Witthoft Mar 9 '17 at 18:26
  • @CarlWitthoft I just finished talking with a journeyman electrician about how to rewire a job that was previously done poorly. He threw out some suggestions that didn't seem to be the most economical, and I'm not sure if that has anything to do with him being near retirement and maintaining some older practices, or if there's more to it than that. – ShemSeger Mar 9 '17 at 18:34
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    If you run hot to the lights first, then they are hot even if the switch is off. If you do any sort of work on the wiring without turning off the breaker, you stand a good chance of ending your existence. – BillDOe Mar 9 '17 at 20:49
  • If the line comes into the box of the light fixture, there would obviously be hot wiring in the box, but the light fixture itself would not be hot if the switch is off. The hot of the fixture is wired to the switch in the wall and if this is off, then one can work on the fixture without turning off the breaker. Personally, I like to have the line in the switch box, but my experience is so limited that I probably don't realize that in some cases other considerations make it convenient or even necessary to have the line in the box for the fixture. – Jim Stewart Mar 9 '17 at 23:11
  • @BillOertell even in that case, the always-hot wires from source and to switch-loop will be pushed up into the back of the box. The wires you disturb to change the fixture will be de-energized if the switch switches hot and it's off. Nonetheless, the vast majority of users here will shut off the breaker when doing such work. – Harper - Reinstate Monica Mar 9 '17 at 23:25
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For new installations, the important thing is really getting neutral to the switch location.

  • NEC requires it (in most cases) as of the 2014 edition

Chapter 4 Equipment for General Use

Article 404 Switches

404.2 Switch Connections.

(C) Switches Controlling Lighting Loads. The grounded circuit conductor for the controlled lighting circuit shall be provided at the location where switches control lighting loads that are supplied by a grounded general-purpose branch circuit for other than the following [...]

  • It allows you to use more advanced switches (timers, motion sensor, lighted, and/or 'smart' switches)

To get a neutral to the switch you generally either need to:

  • Run power to the switch first
  • Run a 3-conductor (eg 14/3) between the switch and power location (carrying neutral, hot, and switched-hot).

Given 14/3 is more expensive than 14/2, in most cases, I'd say run power to the switch first unless it's substantially father away from the power source than the lights (eg: the power-supplying wire passes your lights, then you have to double back with power to the lights).

If you only have a couple situations where you need this, it may not be worth it to buy a spool or some bulk 14/3, so it's ultimately a judgement call.

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Since neutrals are now required at switch locations, it's theoretically "better" to bring the circuit to the switch first. However, it likely depends on the cost difference, and ease of installation between the two methods. Without more detail, it's impossible to say for sure.

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  • So it depends sometimes on individual situations? I have one switch at the top of a set of stairs that someone wired to the lights, switches, and receptacles in two rooms in my basement. If you flick the switch, the power goes dead to both rooms. I want to rewire it so the receptacles still have power when the lights go out, and so you can turn the lights on in each room independently, as well as wire in a 3-way switch at top and bottom of stairs. – ShemSeger Mar 9 '17 at 18:42
  • Right now the power goes to the light in the one room, then to a receptacle, then to the switch in the second room, and finally to the light in the second room. My plan was to install a new 3-way switch at the bottom of the stairs, and wire it directly to a 3-way switch at the top of the stairs with 3-wire cable, then rewire the power downstairs so the receptacle always has power, and you can turn on the light in the second room without having the light on in the first. – ShemSeger Mar 9 '17 at 18:55
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    @ShemSeger You should ask a new question for that specific scenario – mmathis Mar 9 '17 at 18:58
  • @mmathis I'll draw up a wiring diagram then post it as a new question. – ShemSeger Mar 9 '17 at 19:01
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The question of "is it better" was actually determined by what the NEC code says. In a nutshell... the hot or supply wire needs to run into the switch box WITH its mated neutral wire first. The reasoning is that many of the new switches have circuitry in them that require a neutral and "end running" the switch doesn't provide that. Technically, and for liability purposes, if you touch it, it MUST be brought to code. However, in the scenario you brought up, all of that will be determined by exactly where that circuit is fed from. If you are doing a 3 way switch, and following code, it has to be in one of the switch boxes. The outlet for that circuit can be tapped out of the box that has the hot but that hot won't be in a light fixture box.

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  • You can provide a neutral on a switch loop, no problem -- just requires putting in a cable that's one wire fatter than you're used to. – ThreePhaseEel May 1 '18 at 11:39

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