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I'm trying to install this new Smart Switch I purchased from Amazon.

According to the instructions, I need a neutral connection. A short white neutral wire is included in a box as well.

The next photo shows the current configuration with my old switch. As you can see, there are

  • 2 black hot wires

  • 1 copper ground wire

AND

  • 2 unused white neutral wires.

Old Switch

I'm wondering if I can just randomly pick one of the two neutrals and directly connect it to the new switch.

OR

Do I need to use the short neutral that came with the new switch and do something with it (if so, specific instructions are appreciated)

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  • 18
    You really need to get help. You have yet to learn even the most basic "basics" with which to do electrical work, and you're as likely to do something dangerous. Hit up a library and home-improvement store and find an how-to electrical book that feels accessible to you, and read it cover to cover.
    – Harper - Reinstate Monica
    Sep 25, 2017 at 19:09
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    @HotLicks That is a keen and accurate observation, if slightly excitable. Seriously, though, that's spot on. Those neutral wires complete the circuit that is running through this box to the load on the (switched) black wires, and back to the panel on the white neutral wires.
    – Craig Tullis
    Sep 25, 2017 at 23:50

4 Answers 4

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22

Do I need to use the short neutral that came with the new switch

Yes.

(if so, specific instructions are appreciated)

The best instructions you should follow are those of the manufacturor of that switch.

But generally here's what you do.

  1. Remove the orange wire cap and add one end of the short neutral that came with the switch you bought. (It's called a pigtail btw)
  2. Connect the other end of that pigtail to the neutral terminal of the smart switch.
  3. Take the two black wires out of the old switch, and use a volt meter to determine which one is live when the breaker is on.
  4. Label it line, or 'from panel' if you want to be extra nice.
  5. Connect tha live black wire to the 'line' side of the smart switch.
  6. Connect the dead black one to the 'load' side of the smart switch.

This diagram shows the general idea. Ignore the shape of the hole in the wall. Also your switch doesn't have wires coming out of it it sounds, or you'd probably have a red one for the switched load. smart switch wiring

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    Because the OP did it wrong and came here for advice. He photographed the current (wrong) wiring. The diagram I showed is the correct way to wire it.
    – Billy left SE for Codidact
    Sep 25, 2017 at 20:55
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    From the OP's description it is a pre-existing switch, I suspect done by someone other than OP.
    – stannius
    Sep 25, 2017 at 21:03
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    Done! P.S. The one in my picture was the pre-existing non-smart switch installed by the previous owner of the house. They liked new stuff and installed a lot of switches with dimmers and timers everywhere, and some of them started buzzing and eventually died (probably due to wrong wiring?). Thank you for your help!
    – Aimo
    Sep 25, 2017 at 22:19
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    You're welcome! In my opinion fancy (functionality) switches that DON'T need a neutral are more likely to be of lower quality. Certainly if they have any active electronics, they ought to need neutral. Without neutral they're either stealing power through series connection with the load or god forbid, through ground. Either betrays bad design.
    – Billy left SE for Codidact
    Sep 25, 2017 at 22:33
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    To avoid shock, don't forget step 0. - Turn off the circuit breaker!
    – Ogre Psalm33
    Sep 26, 2017 at 11:33
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Those neutrals aren't unused. They complete the circuit that runs through the switch, through the load (light bulb), and back to the panel. (The fact that this is news suggests that you should do some study of the basics of house wiring before you continue, for safety.)

Simply add your smart switch's neutral pigtail to those neutrals and use a larger nut (yellow, red, or tan).

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Detailed, illustrated instructions should have been included with the device. If so, they will correspond with the advice presented in the other answers. I bought some home automation switches (INSTEON) to install in my house. Each came with an instruction sheet, so I would be surprised if yours did not.

Anyway... some key points:

  • Black wires are "hot" (120V) and lethal to touch exposed conductors when live
  • White wires are the return path; they should be at zero volts, but I'd never assume they are safe to touch (can always become live due to faults or errors; that's why there is a ground wire)
  • The "simple" switch only needs to interrupt the "hot" side to control the light; that's why the white wires are joined directly. The box in which the switch is housed is "on the way" to the light for both sides of the circuit.
  • The smart switch needs to be powered, so it needs a neutral (white) connection. All together, the smart switch should have 4 terminals: "hot" supply (incoming black wire, which by the way powers the device), "hot" switched (controls the load, the other black wire), neutral (completes the circuit needed to power the smart switch), and ground (for safety; normally carries no current). All the white wires get pigtailed together, all grounds get connected together (and to the metal box).

If all this is new/unfamiliar, best to get some expert help. It isn't rocket science, but you have to know what you're doing.

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    Let's say "potentially lethal". I've been zinged dozens of times while coiling up my dad's old cords or doing construction demolition. I get the desire to stress caution, but hyperbole is hyperbole. :)
    – isherwood
    Sep 26, 2017 at 14:11
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Simple answer:

  • turn off breaker to the switch
  • connect the short white "pigtail" wire to the neutral terminal
  • connect all the white wires together with a new wire nut
  • connect the bare copper (or green) wire to ground terminal
  • connect the black wires to the line and load terminals
  • turn the breaker on
  • try the switch (50/50 chance of working)
  • if it did not work...
  • turn breaker off
  • switch the line and load wires
  • turn breaker on
  • now it should work
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  • Since it is a smart switch, it is not advisable to feed current into the load side. Triac, SCR (FET based), or other solid state circuitry could fry if there is current to ground. There's no certain guarantee that the "el-cheapo" smart switch is mistake proof. Why not identify hot 100% instead of plug and pray. Its reckless.
    – noybman
    Sep 26, 2017 at 23:46
  • @noybman No, not reckless. I am actually familiar with the exact switch the OP linked to and reverse wiring will not harm the switch.
    – Justin Ohms
    Sep 27, 2017 at 17:50
  • It is reckless, the correct thing to do is to identify your hots and neutrals and ground then hook it up right the first time. Not guess.
    – noybman
    Sep 28, 2017 at 0:00
  • The neutral and ground have already been identified those are the white and the bare copper wires respectively. The only thing in question is which black wire is hot and which is load. For this switch it is fine to guess since it will not harm the switch. I have actual real world experience with this exact switch and can advise accordingly. FWIW I suspect the manufacture made the switch this way precisely because it would be installed in retrofits where load and hot would not always be easily distinguishable.
    – Justin Ohms
    Sep 28, 2017 at 0:23
  • I think you are missing my point, I am not missing yours. While I initially mentioned the chance (because there are things that will not tolerate a feed into a load), it doesn't actually matter. I am pointing out it is incorrect to guess. The correct thing to do is to identify the hot wire without guesswork.
    – noybman
    Sep 28, 2017 at 1:25

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