Home>Discussions>ELECTRICAL & LIGHTING>3-Way Switches Leaking Voltage?
12 posts / 0 new
JLMCDANIEL

I hate to disagree with the poster but 90 volts will light a bulb if it's actually there. Switches are mechanical. A set of contacts that are either open or closed. A small feed through may be posible if there is excess lubricant in the switch. When you say you are seeing 90 volts what are you connected to, from common to hot, from ground to hot, or from ground to neutral?

Jack

HomebrewerDan

Depending on the setting of the switches --

If the switches are in the 'on' position, I measure 120VAC from common to ground at the switch connected to the ceiling fixture as I'd expect. The travelers to ground measures 90VAC.

If the switches are in the 'off' position,l I measure 90VAC from common to ground and 120VAC from the travelers to ground.

I was skeptical that an incandescent wouldn't light up myself -- I haven't hooked anything to the fixture yet but was thinking of trying it tomorrow.

So do you think it's just a bad set of switches?

JLMCDANIEL
HomebrewerDan wrote:

Depending on the setting of the switches --

If the switches are in the 'on' position, I measure 120VAC from common to ground at the switch connected to the ceiling fixture as I'd expect. The travelers to ground measures 90VAC.

If the switches are in the 'off' position,l I measure 90VAC from common to ground and 120VAC from the travelers to ground.

I was skeptical that an incandescent wouldn't light up myself -- I haven't hooked anything to the fixture yet but was thinking of trying it tomorrow.

So do you think it's just a bad set of switches?

Well you definitely have something wrong. Common to ground should always be zero volts. My guess is you have a floating common (not bonded to ground) or your wiring is wrong.
You might want to take a look at this http://www.wfu.edu/~matthews/courses/p230/switches/3way/variations.html and see if any of these compare to what you have.
Basically on one of the three way switches the hot connection should always be 120 vac, there should always be 120 vac on one traveler but never both, if both switches are up or both switches are down the hot screw on the second switch should be 120 vac, if one switch is up and one is down the the hot screw on the second switch should be 0 vac.
Jack

kentvw

First I think we need to define “common”.

Common can be defined as a neutral as Jack mentioned but it can also be referred as common on a three way switch and would be connected to either the hot on one switch or the switch leg to the fixture on the other switch.

Leviton, Decora switches are quality switches and though I learn new things about the electrical trade every day I have never heard of switches leaking voltage.

Here is what I think is going on. Are you using a digital meter? Are the travelers running in the same cable or with the switch leg you are seeing the voltage on? If that is the case digital meters can show an induced voltage on the conductor. 90 seems a little high but that could be the meter. Even though you see the 90 volts there is no available current and what you are seeing is normal. An analog meter will not show the "phantom" voltage.

One thing you might do is set your meter on its highest Ohm setting (20meg?) and check between the switch common and travelers........... With the power off of course.

JLMCDANIEL

After thinking about the use of "common" I edited my post with some references and description to clarify the wiring of a 3-way switch and the readings one should get.
Jack

Ernie_Fergler
kentvw wrote:

First I think we need to define “common”.

Common can be defined as a neutral as Jack mentioned but it can also be referred as common on a three way switch and would be connected to either the hot on one switch or the switch leg to the fixture on the other switch.

Leviton, Decora switches are quality switches and though I learn new things about the electrical trade every day I have never heard of switches leaking voltage.

Here is what I think is going on. Are you using a digital meter? Are the travelers running in the same cable or with the switch leg you are seeing the voltage on? If that is the case digital meters can show an induced voltage on the conductor. 90 seems a little high but that could be the meter. Even though you see the 90 volts there is no available current and what you are seeing is normal. An analog meter will not show the "phantom" voltage.

One thing you might do is set your meter on its highest Ohm setting (20meg?) and check between the switch common and travelers........... With the power off of course.

A leaking switch is new to me as well.
But have you ever heard of an old outlet leaking voltage to trip an AFCI?

djohns

" Common " and " leaking voltage " . I hate those terms! :D

HomebrewerDan

Heh ;) I know the feeling from terms in my field (telecomms). Anyhow, I needed some other work done that is beyond my level of comfort (working at the breaker box), I called an electrician to finish the work and check out the switch while he's at it. I'll be sure to post what the assessment is when the work is done.

Thanks for the lively discussion!
Dan

kentvw
Ernie_Fergler wrote:

A leaking switch is new to me as well.
But have you ever heard of an old outlet leaking voltage to trip an AFCI?

Nope, that's a new one to me but I have read some conflicting info on AFCI breakers. The 08 NEC requires them on just about any circuit in a residence that is not GFCI protected.

Ernie_Fergler
kentvw wrote:

Nope, that's a new one to me but I have read some conflicting info on AFCI breakers. The 08 NEC requires them on just about any circuit in a residence that is not GFCI protected.

Literature packed with AFCI breakers mentions upgrading old outlets to prevent false trips....

## Pages

#### TV Listings

Find TV listings for This Old House and Ask This Old House in your area.