Residential electric - 3 & 4-way switch wiring?

I have some existing wiring for 3- and 4-way light switches. The wiring was done at some point in the past, but never connected.

I'm just now attempting to get the light fixtures installed, so I pulled out my multimeter to make sure I the circuit was dead, and noticed I measured 30vac at the light. I checked the switches, removed them from the circuit and confirmed operation, then reinstalled.

I'm measuring 112v into the switch. With the other black, and red wire disconnected, I have 0v on both. As soon as I connect either wire to the switch and confirm it has 112v, I measure the 3rd wire - which is disconnected at both ends - and I measure 30v.

Ok, so I disconnect the power again, pull the switches out of the circuit and check continuity. There is none between the red/black wires(which is good). So how am I getting 30v on it?

Broken wire or someone put a nail/screw/staple through it.

Shawn

When measuring the voltage on the 3rd wire, what are you measuring against? Did you try measuring between the hot lead and 3rd wire to see what the reading is using that as a reference?

If the third wire is left floating it could give funny readings since it doesn't have a ground reference.

jstand wrote: When measuring the voltage on the 3rd wire, what are you measuring against? Did you try measuring between the hot lead and 3rd wire to see what the reading is using that as a reference? If the third wire is left floating it could give funny readings since it doesn't have a ground reference.

This is a possibility. Funny voltage readings can mean an open neutral (ground) on the fixture.

I was measuring using the ground wire as a reference.

I confirmed everything was connected correctly at the switches, installed the fixture, and it works fine. We have three 3-way circuits and a 4-way, and all of them read around 30v. I'm going to check the panel and make sure we have a good ground reference there.

Assuming you're using an digital multimeter, you may be seeing a phantom or ghost voltage - the circuit may be in fact dead but the high impedance of the meter can cause a false reading. Here's an explanation: http://www.fluke.com/Fluke/usen/community/fluke-news-plus/ArticleCategories/DMMs/Stray+Voltage.htm

Wonder if you might be getting a weak inductive reading from a wire parallel in the wall somewhere? AC can be weird stuff sometimes.

Using the ground as a reference will not confirm that the neutral is bonded at the panel .