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This is what my downstairs 3 way switch looks like: enter image description here

The new smart switch requires a neutral, but it appears that the white wire is the hot wire, I checked with a non-touch voltage tester and it is, in fact, hot. There is nothing else tucked inside the switch box, so am I basically missing the neutral wire?

The upstairs switch box does contain the neutral wires, but none of the cables have voltage unless I flip the switch downstairs.

Is my assumption that the hot (downstairs) box is missing the neutral line? The house was built in 2005, I thought newer houses had neutrals by code.

Just 2 feet up is the thermostat which I believe does contain a neutral since it has power, would be it okay to somehow piggy back off that neutral?

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    Uh, thermostats use a 24V system, it is completely different and incompatible. Check out the partner 3-way switch and sketch out the entire circuit, we should be able to help one way or the other.
    – Harper - Reinstate Monica
    Commented Jul 20, 2017 at 7:06
  • @Harper is it true that if a pair of 3-way switches is controlling a single fixture (or set of fixtures), and the line feed enters at the fixture, then there may be no neutral in either switch box? But if the line feed enters at one of the two switch boxes, then there must be be both an always hot and a neutral in one of the switch boxes. So the original poster should examine the other box and determine whether the line feed cable enters at one of the switch boxes or enters at the light fixture box.
    – Jim Stewart
    Commented Jul 20, 2017 at 17:30
  • @JimStewart yes, exactly what you say there.
    – Harper - Reinstate Monica
    Commented Jul 20, 2017 at 18:03
  • @Harper: This is what my upstairs receptable looks like: i.imgur.com/UjUs57J.jpg None of the lines are hot unless the downstairs switch is wired and switched. Can i use a splice a hot wire from the neighbor switch and use the previous black traveler ( the one that sent 120v upstairs ) to send neutral downstairs? ( This might not work since i am assuming the white hot wire going into the downstairs switch is coming straight from the breaker, if the hot goes to the fixture first, then i don't think i can be be done
    – user1957413
    Commented Jul 20, 2017 at 19:01
  • You should not have a white wire coming directly from the breaker. White is for neutrals and can be a switched hot, but should not be an always hot.
    – Jim Stewart
    Commented Jul 20, 2017 at 21:55

3 Answers 3

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Yes, that box is missing the neutral.

The National Electrical Code did not add that requirement until 2011.

Smart switches require a source of constant power to work. Therefore, they trickle a small amount of current on the neutral while they are working. They used to trickle this current on the equipment ground which was decided to be unsafe by the code making community. However, these older style switches that do not require a neutral are still available and can be installed in your situation.

Return the switch you have and look for a "no-neutral required" type of switch. Depending on how "smart" you want your switch to be, you can find occupancy / vacancy style switches that do not need a neutral and use the equipment ground instead. Similar to this one.

Harper is correct in his observation that thermostats use a low voltage system that is powered by the HVAC system through a transformer. You cannot get a neutral here.

Good luck and stay safe!

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  • Do these no-neutral required smart switches trickle a very small current (~ 1 mA) to ground?
    – Jim Stewart
    Commented Jul 20, 2017 at 12:19
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    Some of them leak a less-small current through the bulbs - which means trouble with modern LED bulbs (ignoring obsolete CFLs). I consider "leaks through bulbs" switches to be bad news, and "needs ground not neutral" switches to be fakers. It's easy enough to find "needs neutral" ones, and they are well behaved.
    – Harper - Reinstate Monica
    Commented Jul 20, 2017 at 18:05
  • @JimStewart That is what I was told at a Code conference, that is why the NEC has now started requiring the neutral to be at switch locations where people are likely to want an occupancy / vacancy / smart switch.
    – ArchonOSX
    Commented Jul 20, 2017 at 18:41
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You're trying to solve this upside-down. You are locked into the idea of putting the master in the lower box. The wires just aren't there for that.

The lay of the land is telling you to put the master upstairs.

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  • Also, I believe that even in current Code, the neutral is only required at one location in a multi-way switch setup
    – ThreePhaseEel
    Commented Jul 20, 2017 at 23:55
  • @harper I am trying to put the master up stairs, the problem is that i have no power upstairs. So to recap, upstairs i got neutrals. Downstairs i got the hot white wire, but no neutral.
    – user1957413
    Commented Jul 21, 2017 at 2:37
  • @user1957413 the light and 3-ways aren't wired like a triangle. Read more on how 3-ways are wired,
    – Harper - Reinstate Monica
    Commented Jul 21, 2017 at 13:12
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Thirty-five years ago I installed a programmable timer in place of one switch of a pair of 3-way switches that controlled a single outside fixture. An always hot was available in this box. (Probably the instructions said the timer must be installed in the box with the always hot.)

I think it may be that the box with an always hot will also have a neutral, but there will certainly be a neutral if the line feed enters at that box. If the line feed is entering at the box of the controlled light fixture it may be that a neutral will not always be available.

The instructions were to use a supplied jumper across a particular two of the three contacts of the other switch. And the instructions claimed that despite being jumped in this way the second switch would function as a 3-way switch.

Cannot the new smart switches be used this way? In any pair of 3-way switches one box will have an always hot so put the smart switch there and leave the old switch in place and use a jumper if necessary. New smart switches may not require a jumper like my old programmable switch did.

When I did this 35 years ago I was perfectionist and doubted that the puny jumper (looked like #18 stranded wire) would be the best practice. I realized that the jumper turned the 3-way switch into a 1-pole switch so I replaced the 3-way with a 1-pole switch. (I put two wires under a single screw of the 1-pole switch.) The circuit worked perfectly as if there were two 3-way switches.

This timer (which also was a two position dimmer) was only rated for incandescent lights, and when I switched to LEDs I removed it and put the original 3-way mechanical switches back in. I actually reinstalled 50-year-old mechanical switches in my house!

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  • These new "smart" switches don't behave like regular ones. They work in a master / slave configuration, with the slave just acting as a remote to the master. The master usually has the 5 wires. ( line, load, neutral, traveler, ground ). The slave only uses 2 wires. The neutral to trickle down some small voltage to run the internal electronics and a "traveler" wire which only acts as an on / off signal using small amount of voltage. ( You don't run 120v thru the traveler like a regular switch, in fact there is sticker in place warning you about that otherwise you end up frying it).
    – user1957413
    Commented Jul 20, 2017 at 20:20
  • Is the slave a special switch or just an ordinary 1-pole switch? Since the slave has only two wires I presume neither is a neutral, right? Or is the slave also a powered device that needs a neutral? Which connections are required for the slave?
    – Jim Stewart
    Commented Jul 20, 2017 at 20:44
  • Slave needs a neutral because yes, its a powered device. It takes a small amount of voltage of the neutral to run the internal electronics. The other cable ( usually the red traveler ) is used as the signal cable to tell the master to turn on and off. Here a link that shows how various configs are wired. community.smartthings.com/t/faq-ge-3-way-wiring/74962
    – user1957413
    Commented Jul 20, 2017 at 22:10
  • @user1957413 , if the slave takes two wires only and one is a neutral and one is a signal to the master, what about a hot at 120 V? To be powered the slave would seem to need an always hot and a neutral. Is the red that is used for a signal also supplying power to the slave say a low steady current maybe even at a low voltage? In which case no high power hot is needed for the slave?
    – Jim Stewart
    Commented Jul 20, 2017 at 22:45
  • Right there is no high power going to the slave at all. The slave just tells the master to turn on / off using the traveler. The 2 blacks ( load and line) are twisted together
    – user1957413
    Commented Jul 21, 2017 at 2:42

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