Switch Wiring - 3 way?

[MK_Chicago]

Sorry for the poor quality video but hopefully it helps. I am trying to change out a switch (for more modern one) that I thought was a 3 way but am noticing some unusual wiring.

The existing switch has three screws with two black wires and one white wire connecting to them. One of the black wires is the hot wire. When the switch is off, neither the second black nor the white has power to it. However, when I flip it to on, power is now running to BOTH the other black and the white.

Maybe I am missing something but I didn't think this was correct. Can anyone clarify for me so I can swap out this switch?

Thanks!

 

[WorthFlorida]

Look on the faceplate of the switch and their might be a stamp that it is a three way switch and it sure looks like one and there be no on/off labeled on the toggle. Is there another switch that controls the same light? Where is the red wire? Is this original when the home was built or maybe an add on after the fact? You're in Chicago so you most likely have conduit? It might explain the two black wires, the electrician might have been out of red wire that day.

Depending which end this switch is of the three way and where the power source is the wiring does change a little so it is hard to say. There are thousands of three way switch wiring diagrams on the net so you can compare. Just a note that the white wire here is not a neutral but one of the travelers and it will have power to it in one position or the other.

If you disconnect all three wires, one of them should have power. Check that please.

 

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[Kreemoweet]

Those non-contact voltage sensors are simply not a reliable means of detecting "power". Their
indications are merely suggestive, and require the use of an actual electrical meter to get information worthy of the name.