Three way switch install - why am i getting voltage ?

[Gregory of Sherwood Forest]

Remodeling the garage and installing new light fixtures on a 3 way switch.

Two switches to be installed, but I'm getting a weird reading from switch #1, which is by the kitchen door. Switch #2 isn't even connected yet, nor are any other fixtures (although Sw#1 is sharing power from a switch that powers another light inside the kitchen).

This is pre-existing wiring with 12/3 with ground (black,red,white,ground wires)

So, I'm measuring the voltage across the wires from Sw#1 and here's what I'm getting:

** Sw#1 to ON position-
Red-white = 125v
Black-white = 38v
Black-red =0v


** Sw#1 to OFF position-
Red-white = 40v
Black-white = 125v
Black-red = 0v

Again, the fixtures are not yet connected and neither is the 2nd switch.

Why am i getting these readings? Does this mean there's something else connected that I haven't found?

Thanks in advance.

[TDKPE]

If you're measuring with a typical digital multimeter (DMM), you're reading so-called 'phantom' voltage, which is from capacitive coupling between conductors.  The DMM has such a high input impedance that there is real voltage with virtually no current behind it.  Put a wiggy or other solenoid type voltage tester on it, and it'll read nothing.  In other words, even a very tiny load would be enough to reduce the measured voltage to zero, but the DMM doesn't even do that since the impedence is extremely high (for this kind of work).

Edit: Oh, and I haven't sketched out what you did, as I assume you're asking about the 40V you're reading, and I'm further assuming you've connected the switch correctly.

[Gregory of Sherwood Forest]

Yup, just using a cheapo voltmeter. Phantom voltage at 40v? Okay, your explanation is good enough for me. I'll just continue install as if it were reading 0v.

Thanks!

[EricU]

that freaked me out the first time I saw it too.  Figured that the electrician had done something wrong

[Gregory of Sherwood Forest]

Another question- I was thinking that the Red wire was my "traveler", but based on these readings, it appears the White wire is. Is that correct?

[AnHonestOpinion]

There are actually 2 travelers, the red and the black that go between the two switches.  The white should be your neutral conductor.

[EricU]

all three conductors attached to a 3-way switch are going to be hot at one time or another.  Either as one of the two travelers, the supply in, or the hot out.  White should be re-marked to reflect this.  If there is a standard way of using the 3 colors, I don't know what it is.

[Mr_Mike]

The white isn't switched and doesn't get remarked. The black and red are the travelers between switches. The light is either before or after the switches, but not in between. Generally it after the switches.

[Gregory of Sherwood Forest]

   

Is this correct??

[Bob10]

there are 3 configurations to wire a three way switch.  Lowes used to have it on their website probably still do