Finding Line in 3-Way Switches

I’m in a relatively new house (built in the last 5 years) so I’m relatively confident there are neutral wires, and my plan is to install Red-series switches. But the house has fair amount of 3-way and 4-way switches. As I understand it, unless I use an Aux switch, I need to install the Red switch where the line comes in from the power source–which should only be one in switch per 3-way or 4-way switch. A few questions:

  1. Can I easily locate where the line comes in? (or is there any other way to easily determine where I could place the Inovelli switches)?
  2. In a new build, is it safe to assume there is neutral in every box?
  3. Does this wiring diagram mean that I can place the Inovelli in a place where the line doesn’t come in so long as I use an Aux switch where the line is coming in? And if so, does this option apply to 4-way switches as well?

I’m asking the above because I’m hoping that, before the electrician comes for the actual installation, I can figure out (1) where I can place the Reds and (2) how many aux switches I would need to buy to get proper placement of the Reds.

Can you turn off the power, pull both existing switches all the way out and take a picture of the wires. We can probably guess your configuration. The different wiring diagrams are in the link below.

1 Like

Yes, that is mostly true. If you are going to mate with a dumb switch, then the Inovelli must go in the box into which the power is fed. If you use Aux switches, then you can reverse those, except (I think) if the Line and Load are in the same box.

I’d start by looking at the wiring diagrams, link below, which I think you have based on your screenshot. It generally requires that you pull the switch to look at the wires “involved” at each switch. For example, in a 3-way, if you have a 2-wire and a 3-wire at both switch locations, then you likely have Line in one and Load in the other. Then you just have to figure out which is the Line box, using a meter.

I wouldn’t assume anything. If you’re in the US, the 2011 NEC requires a neutral at switch points. But your local codes with be the deciding factor. For example, do they adopt the 2011 NEC or have the implemented a variation.

BTW, there isn’t a requirement for a neutral at EVERY switch box. More than likely it’s a neutral where the power is being is being fed to the switch leg for a multi-way. But you don’t need a neutral at every box with an Inovelli/Aux or Inovelli/dumb configuration. If you go with multiple Inovellis instead of dumb or Aux, then there is a way to send what you need to the other switches.

That being said, it’s more likely than not that you have a neutral to a switch box. But you never know. I’m working with a guy in Canada whose house was built in the last couple years and he has a non-neutral switch loop. I’m not familiar with the codes up there, but just sayin’ . . .

Yes, but that’s what I referred to above. Note that this is where the Line and Load are in separate boxes. If you have a Line and Load in the same box, than this “reversed” thing won’t work with an Aux, I don’t think. I THINK you can do the same with a 4-way Line/Load in separate boxes, but I’d have to stare at it a bit more to be sure.

Here is generally look at when I evaluate these. This is for neutral, Line to a box installation. I look at the wires “involved” at each switch location. “Involved” means either partially connected to the switch or to a 3-wire likely going to the other switch(es).

One 2-wire and one 3-wire at the 3-way switches = Line and Load in separate boxes

Two 2-wires and a 3-wire at one 3-way switch; One 3-wire at the other = Line and Load in the same box

One 2-wire and one 3-wire at one 3-way switch; One 3-wire at the other = Line in one box with the light in the middle.

The above is generally true for 4-way and up legs. The problem however is that you can start with power to the 4-way in the middle as well. If that’s the case, then the above won’t apply.


Thank you! I’m going to try and take some photos tonight or tomorrow! I’ll post what I find.

Thank you for the detailed reply! Really helpful. If I’m understanding correctly, I can figure out the basic set up (line/load in same box or separate box), but I can’t figure out where the line is without a meter?

You need a meter or a non contact voltage tester

NO, you do not want a contact voltage tester!!! You want a meter that has two probes so that you can test the voltage between two conductors.

Non-contact testers are designed to test to make sure voltage isn’t present before you work on something. They are not designed to measure voltage.

Well, by looking at the wiring configurations you can get a good sense of what is going on. But then you need to test to confirm. For example, in your case, one of the 2-wires is likely going to be a Line and neutral. You need to use a meter to determine which of these it is. If you do the trial and error method, you may smoke the switch in the process. And to be honest, that’s not a safe way to proceed.

If you’re not comfortable with using a meter to test for voltage, you might wish to consult with a licensed electrician.