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I'm replacing two switches (which control separate lights) in a two-gang box with two smart switches (TP-Link HS200). To make my questions as clear as possible, I've sketched the current state as well as my plan for the smart switches:

Current State:

Current State

Future State:

Final Stalte

My questions are as follows:

  1. Does the future state look okay? Can I group all live and all neutral wires together per my plan?

  2. I live in Cook County, which requires conduit. Does this mean I can attach the grounds from the smart switches right into the 2-gang box and that's all I need?

  3. The smart switches don't distinguish between a line/load. Will they just figure this out? Or do I need to make sure I use the same one as a line/load for each since they'll be connected?

  4. Any guesses as to what the other orange/load wire is running up to? This room only has two lights, but I don't want to interfere.

Thank you for any advice you can provide-- as I'm sure is apparent, this is my first time with this!

  • In your second diagram one of the red wires should be black. (Either that, or in your first diagram the black wire should be red.) – A. I. Breveleri Mar 30 '18 at 1:09
  • It is not clear from your diagrams whether power enters via the orange wire at the bottom or via the orange wire at the top -- but it doesn't matter because you're not changing either one. – A. I. Breveleri Mar 30 '18 at 1:12
  • Hi-- you're correct, on the second diagram the one on the right should be black. My mistake! And I believe power enters from the bottom since the lights are on the ceiling. – user84147 Mar 30 '18 at 1:31
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To answer your questions in turn:

  1. Your future state with all the always-hots nutted together and all the neutrals nutted together looks spot-on, yes.

  2. You are correct -- metal conduit is a valid equipment grounding conductor (always has been and pretty much always will be save for some extreme circumstances that don't show up in residential work), so grounding to a metal box works in your case. Make sure to use a 10-32 machine screw into the matching hole on the box (vs. one of the mounting holes, which won't be tapped properly for this) -- you can get a bag of pre-made-up grounding-screw-pigtails, even.

  3. They're behaving like a normal switch here, so they'll figure this out on their own I reckon.

  4. That other orange wire is simply an always-hot running to some other switch, receptacle, or outlet on the circuit, likely in some other room.

  • Both ThreePhaseEel and Harper are correct. Little known fact NEC 250.126 will tell you the ground screw must be green. This doesn't make a ground less of a ground but if an inspector (AHJ) sees it he may flag it. Also, we used to use the conduit as a ground all of the time back in the 1970's and 1980's and it is still legal, but if the AHJ is younger he may be more comfortable if you run a ground wire since it is intrinsically safe and make you go that direction. – Retired Master Electrician Mar 30 '18 at 17:58
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1 You are using orange for always-hot. That is a fine choice*. Yes, that grouping of all always-hots (orange) together is correct. Ditto all neutrals (white).

2 If the box and all connecting conduit is metal and non-flexible, the conduit is a valid grounding path. You are always allowed to double it with a ground wire if you worry about the conduit's integrity, however the cause of your worry might be a code violation.

As far as attaching the grounds to "an empty screw hole", nope! Using a nail, wood screw or sheet metal screw is right out. You must attach the grounds to a very particular screw hole, specifically the one threaded 10-32, and you must use a 10-32 screw to do it. You can also drill and tap your own hole 10-32, or if you have access, you can use a nut and bolt to same effect. Home Depot sells cute little green 10-32 ground screws, with or without pigtails already attached.

3 you must obey the instructions when installing the smart switches. I don't find it terribly surprising that a smart switch doesn't care which is line hot and which is load hot. It only takes 1 extra diode and simplifies field installation.

4 Anytime you see an an always-hot and neutral exiting together on the load side, that simply means this is not the only load in the circuit. In the case of Romex switch loops, that hot+neutral is going to a future smart switch.

5 I would not make both switched-hot wires the same color. You will lose your mind. That's why there are 8 colors for hots: black brown red orange yellow pink blue and violet.


* unless you are coming out of a 240V 3-phase wild-leg delta panel: in that case, orange is reserved for the wild leg. That is the only place in the entire NEC where it calls out a specific color for a hot. Other than that, it only prohibits green white and gray.

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