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I plan to install a Smart Switch to control an outside outlet.

The existing electrical box is in my detached garage and it does not have a neutral wire. The box currently only controls a single GFCI outlet and a few other outlets in the garage.

I want to pigtail the Smart Switch to it but all the Smart Switches claim to need a neutral wire so it can have continuous power. I don’t understand why it needs a neutral wire when the available wiring would provide continuous power to the smart switch.

Why does a Smart Switch need a neutral?

How do I provide one?

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    It is called a switch loop. Basically to power something (a light or outlet or smart switch) you need power in ("hot") and out ("neutral"). If it is panel -> switch -> device, then you have hot/neutral from panel to switch and switched hot/neutral to the device. But if it is panel -> device -> switch then you have hot/neutral from panel to device and from device to switch you have hot/switched hot. So when the switch is off you don't have a complete circuit at the switch. With a manual switch, no problem. But with a smart switch it doesn't have the power needed to turn itself on. – manassehkatz-Moving 2 Codidact Apr 24 at 18:29
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    Current flows in loops. It's not like air tools. It's more like hydraulic tools, you need that return line! Even moreso with electrical. On an old switch, the loop is always-hot to the switch and switched-hot back. No need for neutral, the switch doesn't need any power, you're the power. – Harper - Reinstate Monica Apr 24 at 19:23
  • Not all smart switches require a neutral. Some are ok without it, but they usually do require a ground (Such as Caseta). So, now that you know you're missing it, shop around. – JPhi1618 Apr 24 at 19:38
  • Since a smart switch needs so little power, it used to be allowable to use the ground as a neutral for a smart switch, but I believe that went away in the 2014 or 2017 code. – George Anderson Apr 24 at 19:43
  • What wiring method was used to hook up the switch to the light? (NM or UF cable? Armored cable? Conduit of some flavor?) – ThreePhaseEel Apr 25 at 0:38
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Current flows in loops

You know, with an air tool, you only need one hose. When the tool is done with the air, it can just release it into the air! Hydraulics could work that way if we were fish. But since we're not, hydraulic tools need a return line.

Electrical needs a return line too, and it's even more important because electrical power works on the difference of forces. So the return line has the same force as the supply line, actually (that's why we insulate it and keep it separate from safety ground).

So a load connects between hot and neutral (in our nomenclature.)

Now a dumb switch is human-powered. It needs no power of its own. So a dumb switch simply connects (or does not connect) an always-hot wire to a switched-hot wire. Those are the 2 wires in the switch loop before you.

So what options do you have?

Replace the "switch loop" with a /3 cable

The cable run between lamp and switch does not have neutral. We change that if we have ready access.

Unlikely, but if it's in conduit with loose individual wires, a white THHN neutral wire can simply be added, and done.

Generally, pre-2011 wiring will be a /2 cable meaning 2 conductors (black, white) + safety ground. Change that to a /3 cable which has black, white, red. You cannot simply toss in a loose single wire, because all related conductors must be in the same cable. The old cable can be up-cycled to other tasks if it's removed carefully.

In the /3 wiring, you must use white for neutral (it's not that way now). Then I advise using black for always-hot, and red for switched-hot (to the lamp). If you do that, the colors will probably match up with your smart switch.

Select a no-neutral smart switch (leaks through the lamp)

This is the option if you don't have a functional grounding system. This works the way traditional dimmers work - it relies on the very low resistance of incandescent bulbs to "leak" a small amount of power through the bulb to power itself.

This won't play well with CFLs or most LEDs, however that can be solved by adding one incandescent bulb, or paralleling a Lutron LUT-MLC "incandescent simulator" into the lamp wiring.

Select a no-neutral smart switch (that bootlegs ground)

You should never do this on your own. This, plus a trivial wire problem, would render the grounding system itself lethal. Not what you want!

And this only works if your grounding system is in good order clear back to the panel.

UL (Underwriters's Laboratories) writes the rules that appliances must follow to be certified as safe. Under very narrow rules, they allowed smart switches to power themselves by bootlegging the ground wire as a substitute for neutral. The rule limits current to 0.5 milliamps (not harmful if the above happens) and too low to trip GFCIs.

However NFPA (who writes the National Electrical Code) does not like this method, and outlawed it as of NEC 2020 (or to be more precise, outlawed sale of the devices as of Jan 1 2020). The good news is, only one US state has adopted NEC 2020. So they should still be available, but don't count on that supply to last.

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