low voltage feedback from switch

[rangerric]

I got great information from Rewired on my last post. I need help again on another project. This time I have to make up 2 wire without ground lead wire and 2 wire without ground switch wire in wall behind medicine cabinet for light above cabinet. Switch wire goes to conventional wall switch. I connected black wire from lead to black from switch and white from lead to one side of light and white from switch to one side of light. I get good voltage when switch is on, but still get low voltage when switch is off. What have I done wrong?

[Rewired]

Hey!!
first off, tape the white from the switch BLACK so there is no mistake later on of it being a neutral.. Could save a BIG headache later on
Anyway what voltages were you getting with the switch off? and was the light fixture connected at the time you were testing?
Oh ya, did the light work properly with the switch???
please let me know and I will figure it out from there!!

A.D

[kactuskid]

It sounds like what you are describing is a switch loop configuration. If there is a white wire going to the switch on one side and a black on the other side, then the white wire is not a neutral wire and is actually a hot wire. If this is what you have then the wireing for this is different than you would think. Here's a link that'll show you how to connect the wires in this case, be sure as Rewired mentioned to remark the white wire on both ends as a black wire by coloring it with a permanent black majic marker, tape can fall off over time.

http://www.estevancomp.ca/tesla/switchloopdiagram.htm

[jks55]

i just did this... i am having the same problem.

i used the switch loop configuration described and when the switch is off, I still get 5 volts at the light terminals with the light unscrewed. When I screw a bulb in, the voltage drops to mv. I tried this with other lights in my home and when I measured the voltage at other "unscrewed sockets," (and the switch off), I get millivolts.

I have tested for conductivity between all wires involved in the circuit and there are no apparent shorts. Brand new breaker, all brand new wiring...

What is wrong?

thanks

jeff

[kactuskid]

If you are using a digital meter to take your measurements with then you are probably reading phantom voltage, which means you're not really reading voltage at all. Try using an analog meter instead and I bet you will read nothing. Here's a link that explains more in detail.

http://www.nema.org/engineering/papers/PhanBull88.html

[jks55]

so phantom voltage is only associated with the capacitance of the NM style cable (what i used)... this would explain why the older cloth covered wires supplying power to the other "unscrewed sockets" in another room registered mv on my digital meter and the new NM wire Im using for the new switch gives me 5V.

Ive got some 1K resistors lying around... Ill try what NEMA says...

thanks

jeff

[Rewired]

You may also be showing a high voltage across the socket (bulb unscrewed) if the switch you are using is one of those "illuminated" ones.. illuminated as in they have a neon light across the contacts that lights when the switch is off. The voltage you see is nothing to worry about.

A.D