Switch leg with no neutral run

Hi there. New to SmartThings and I purchased 21 light switches (Leviton Z-wave DZ15S) from Smarthings shop. I had checked a few switches and all had neutral. Now that I am installing I am finding all my rooms have switch leg setup with only two wire. I am wondering what my options next to tearing apart walls and rewiring are?

If the neutral is up in your fixture box you can install in-wall relays and dimmers there instead. There are a few companies that make them, aeotec tends to be one of the more popular ones.

Or you can look into Lutron caseta switches, which don’t require a neutral wire. They need their own bridge though, which communicates with SmartThings cloud-to-cloud (but works pretty well).

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It’s the best solution so you can use anything on the market, including your Leviton’;s but requires a lot of work.

As Mark says


Doesn’t that depend on the load?

Can you believe that I didn’t know this?!

I thought all relays needed to have a Neutral, but were still useful because they could be placed at the fixture if necessary! Direct neutral connection is still the requirement for other micro-relays, right… Like Monoprice?

Thanks for such quick replies. I will look into the Relays and Fibaro 2 dimmers. I will update when I decide how I am doing it. It’s an LED fixture so the device needs to work with LED. Still deciding if I should return a lot of these switches or sell on the open market as I got a pretty good deal at just over $30 a piece from SmartThings store.

If I were you, I would have a look at the lighting fixture as sometimes it is very quick and easy to install the Leviton (or other smart device) there, and that will save a load of extra faff with returns and a different device to manage/configure (plus possible complications below). To do this you want to find the Live/Neutral (one cable in and one cable back out to another room) and you will also find the cable which goes to your switch - then its just a quick juggle of the cables (though make sure you know what you are doing!).

Bear in mind this (maybe interesting for you @tgauchat too) :

Devices which dont need a neutral will constantly pull a small amount of current through your bulb, that way the bulb can be ‘off’ (or nearly off) and the device can still have power to run. If you have halogen/incandescent bulbs then this small current will not be noticeable and the bulb will appear off (and use minimal extra power), however if you use CCFL or some LED bulbs then this small current can often turn on the bulb with a dim brightness.

If you have a problem with the LED/CCFL glowing, even when it should be off, then you will need to add a bypass in parallel with the bulb. The bypass (basically a resistor and capacitor/inductor network tweaked to match the smart switch device) allows a small current to flow through it instead of the bulb, hence the bulb stays off when it should do.

The smart devices which support this ‘no neutral’ specification are typically not relay devices because relays need a fair bit of current to actually turn them on. Hence the background current to power the smart device cant turn on the main bulb. Instead they will typically be transistor based (something like an IGBT or perhaps a Triac though that is a bit harder to dim).


Cjcharles: Are you saying to install the light switch itself right at the light fixture? I am not sure exactly what you mean? Would it be in series with the room switch then?

that’s a good point, and the bypass assembly from Aeotec is typically about $20, really expensive considering the cheap components. So the “2wire/no-neutral” Aeotec Nano Dimmer with bypass is more like $60-70 for the hardware. It would be nice to know what the bypass component values and arrangement are, which could probably be home-made fast for $1 .

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I expect these are only R+C in series, and the time constant could be determined without chipping it apart from the current and a step-change voltage like 1.5v or 9v battery . Getting fuzzy on the relationship of current to voltage across the C (C= dV/dQ ? ) so might have to graph it or something. Time constant is much less than 1 second anyway so it might be hard to measure without a scope

It probably passes less than 0.5 watt. I don’t think it’s really fussy - I’ll put the nano and some RC bypass on my basement lights (fluorescent and no neutral of course) and see how it goes.

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I have a scope but I’d imagine even then it will be hard to measure and deduce exactly what is inside, as you would probably need to measure at the frequency that the Fibaro actually draws the background current as it won’t be a pure mains frequency…

I am not certain what the problem is. Maybe I don’t understand but try this.

There are a couple of different ways of setting up a house.

  1. Return all of the neutrals (normally white) from the light to a box then wire them all together so you only have to deal with sending out the hot (normally black) from the switch.

  2. Run two wires through the switch and tie the blacks an the whites together at some location like the breaker box.

So if you have two wires going to the light. One is the hot and one is the neutral.
The hot goes to the line and load side, then I just cut the neutral side, strip the two ends and put them into the neutral on the new zwave or zigbee switch. Electrically it is the same.

I have quite a few switches set up like this. I have a little table lamp set up as a test rig near the Smarthings hub, when setting up a new switch, I just wire it up as described (make certain not to cross the hot and neutral) and energize so the device is already on the network before I install in a remote location.

See if this works for you.

This is a quick sketch of the two common wiring setups in the UK and with some small changes it will apply to the US too (e.g. Live (L) = Hot).

Live/Neutral In/Out are the wiring ring that goes from your fuse board (or RCD) to a few lights (or lighting circuits) before returning to the fuse board. E.g. the wire might go from RCD to lighting circuit 1, then loops off to lighting circuit 2, then off to lighting circuit 3 before going back to the RCD. The In/Out wiring will be at the switch or at the light, with some small differences possible.

The Smart device might therefore sit behind the switch or above the light. If you have a smart switch (i.e. it is part of the switch rather than a separate smart device), then it isnt possible to put it in the ceiling (without modification). But hopefully this is helpful for understanding anyway.

The top pictures have the In/Out wiring at the light and the only wires at the switch will be the Live and Switched Live.
The bottom pictures have the In/Out wiring at the switch, hence the only wires in the ceiling at the light will be Switched Live and Neutral.

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That’s because yo have 220V AC and you have neutrals at the fixture.

You do have neutrals at outlets.

Any in wall relay will work with LEDs, but will not dim. There are Vision, Enerwave, Monoprice, etc.
You do have neutral at the fixture so installing the relay there is very easy and with minimal wiring changes.