Dimmers- why is the neutral required to make the switch work?

I understand why you need a neutral to complete a 120v circuit.

I just did a complete remodel of my home, 100% new electrical from service to every outlet.
There are several outlets in the kitchen that I have a junction box in the attic that goes from the power source, to the light, and a wire to the switch to interrupt the hot. This was done to reduce the amount of cables installed in a 4 gang box in a wall since there are some 12-AWG romex wires in there.

In this scenario, the black wire is the hot, and the white wire will carry current back to the junction box which ties the lighting circuit’s neutral to the line neutral as well as a switched hot. When this was done, I did not even consider the need for a neutral in the box for a Zwave/ Zigbee dimmer.

There is a common wire in the box that I can tap off of (ie power source for the garbage disposal switch) using a wire nut. Will this work - or does the switch actually read anything from the neutral?

All lights are LEDs. They are all can lights, but I would prefer to not swap the bulbs for halogens.

As long as the neutral you have in the jbox is from the same circuit the lights will be on then you are good with using that. BUT FYI it is a code requirement now that new electrical installations have a dedicated neutral at all switch locations specifically because of the new smart switches that require a neutral to function.


Interesting. I have one final inspection to go - no switches are installed yet, and I passed my R.O electrical already, so I bet I am fine with what I have fingers crossed - else I will be tearing out some sheet rock!

I have a piece of plywood setup with two different GE switches and just tied a separate common to the switch - but they ultimately pull off the same circuit so I wasn’t sure how true that scenario would be if I turn on the garbage disposal while the switch has a circuit closed (light on).

I see my setup all the time in commercial environments, even build outs completed within the last 12 months. Though, most residential environments don’t have junction boxes unless they are needed to split off a lighting circuit.

Good to know for future reference though, thank you!

They are not cheap but there are smart dimmers that do not require a neutral.

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This is what I was going to say. I believe it’s the NEC 2014 revision that added it. So assuming your city follows that and doesn’t have a city specific code…

As for the neutral requirement, smart devices are a load in series with the light. If the light is off, without a neutral you won’t have a complete circuit to power the smart dimmer circuitry. Afaik Lutron gets around it by trickle feeding the load and while not enough to turn on the lamp its enough to power the dimmer.

Also for neutrals it’s required to be bundled (same conduit or wire jacket) as the hot or switch leg. If you’re using another wire set in the same box, it’s not to code.


In my southern part of the US, I’ve not really run into this lack of neutral unless it was a really old house where they didn’t even have earth grounds on the plugs. The way I’ve always wired houses and seen things wired is the power line feeding the switch box has white, black and ground. Then the wire feeding out from the switch would feed the light(s) and would be a 12/2 w/ground wire as well. Makes things simple and just jump from box to box. Not sure why anyone would want to make things difficult on themselves and do it other ways.

NEC 2014 - Thanks. My city actually follows 2017. There is a state wide 2014 requirement as well.

Like I said in the original post, I understand what a neutral is for on a 120V circuit.
The neutral is already in place for the circuit, it just doesn’t go to a switch, it goes to a J Box

As far as code is concerned, I would like to see the section stating the neutral had to be in the same conduit/ wire jacket, as that isn’t possible. The jacket has to be cut to splice in a switch, and in my scenario I bypass the need for a neutral in the switch box anyway - it is in the Jbox, and it is all continuous.

If I pull a neutral off of a different circuit to go to the GE switch, it would not use that neutral to carry any current back and complete the circuit, the neutral in the jbox would close the circuit before it got to the switch. I’m still confused at why the switch itself requires a neutral to operate. Is it so that the switch itself gets 120v?

Smart devices have to have power for their circuitry and radios, so yes, it’s for the switch.

It’s so the radio in the smart switch can hear the next “on” command even when the device appears to be off.

Lutron does it a different way, which is why their Caseta smart switches don’t require a neutral, but they are an engineering company focused solely on lighting, and their method is patented.

There are a couple of the in wall micros that have come out in the last year or so and also don’t require a neutral, such as the Aeotec Nano model. I don’t know what method they are using or if they’re just not covered by the Lutron patent since they aren’t a wall switch.

In the past, there have also been people who used the micros elsewhere on the circuit, either at the fixture or in a junction box, whereever the neutral was located.

So there are some options in terms of device choice. I leave comments on Specific wiring setups to the electrical experts. :sunglasses: