What type of switch is this?

I have one light switch in a bathroom that is different from every other light switch in my home. I would like to replace it with a Z-wave light switch. It seems to have a black and a white wire coming into the box, and a black and white wire leaving the box. My best guess is that this is a DPST switch, being used to switch both the neutral and the Load wires. Though I have no idea why it would be done this way.

Can someone please tell me what I've got here? If my description, above, is correct, can't I just directly connect the 2 white wires on the Common input of a Z-Wave switch, and put the black wires onto the Line and Load inputs of that switch?

Your help is very much appreciated.


I have never seen a DPST switch... But it could be...

My guess would be that this is a 3 or 4-way switch, though typically one of the wires is red in a 3 or 4-way setup...

If you have a volt meter, you might be able to figure out based on what happens when the switch is toggled. A diagram of those switch found online might help with this.


I am 90% sure it's a double pole switch and they are not as common in home but do have it's purpose. They are rated much higher amp and 2 isolated loads so it's common to control appliances such as pump or 2 line wires.. etc. You can easily check with a meter.


It is a 2 pole Double throw switch. It is used in "4 way" switches. aka when you have 3 switches for the same light you will need one of these.

It is the middle switch in this diagram....

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Well, I am a bit confused, now. This is a small bathroom with a light over the sink, and also a ceiling light/fan. There is only this single switch, and it only activates the lights in this bathroom.

Does my though about it being a DPST used to switch both Line and Neutral not make sense?

So. I think I'll remove it and check the voltage at each wire.

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Make sense unless you have more wires in the box and 2 hidden 3 ways switches somewhere and you are not telling us.

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Well, as best I can verify, the switch is a DPST switch. I had forgotten, but this used to be a double switch that turned on/off the 2 separate lights in the bathroom. It was replaced long ago with this switch, which turns on/off both lights in the bathroom at the same time. A Contractor looked at this switch many years ago and said something about the wiring being this way to save the installer having to run a wire. ???

I took the wires off of the switch and the diagram, below shows what I found. The black and white wires on top seem to be Line and Neutral wires. When you connect the 2 black wires, one of the lights goes on. When you connect the 2 white wires, the other light goes on.

Does anyone know what this is? How do I get a Smart Switch working here?

This is very odd and unusual. I am not an electrician, but I don’t think having 2 live wires in the same power box is a good idea, as there is a risk that they are not on the same phase, so something connected to the two would give you 220V (That is how 220V baseboard heater works).

A good approach might be to disconnect the white wire at the breaker box if possible and condemn it. That would leave the Black live wire. The two light cables can probably be combined together to power on both lights at the same time.

As for automation, Lutron and Inovelli have dimmers that don’t require a white cable. That would work.