Announcement

Collapse
No announcement yet.

3-way switch off and still some power?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • 3-way switch off and still some power?

    I was relocating ceiling light fixture box (hallway) and found something very odd (though I'm not a pro). The fixture box runs off of two 3-way switches on either end of a stairwell. I tested the power to the fixture box with the breaker on and both switches off, and there seems to be a very, very slight charge at the fixture box, even though the switch is turned off. It barely (and dimly) flickered my circuit tester. But what I dont understand is why, with the switch turned off, there is any power (however little) at all to the fixture (or is this normal for 3-way switch configuration)? With the switch turned on, the line tests correctly.

    I replaced both wall switches after I noticed the issue (which probably doesnt matter), but it seems that there is still some power at the fixture with them turned off. It probably wont affect the operation of a light fixture, but my head hurts from scratching it and Im tired of running down the basement to turn on and off the breaker. I would appreciate any insight.

  • #2
    Re: 3-way switch off and still some power?

    With the switch off there should be no voltage present. Is the voltage on the hot wire or the neutral? Does your 'tester' show similar problems at other fixtures. Is your tester broke? - Check friends house.
    Get a voltmeter and check for voltage
    My favorite would be have an electrician check your panel

    Comment


    • #3
      Re: 3-way switch off and still some power?

      Out of curiosity... what sort of switches are you using? Just plain jane switches, or something fancy like motion sensors or something?

      Comment


      • #4
        Re: 3-way switch off and still some power?

        Bobby,
        I hate to burst your bubble here, but continue to run down to the basement and switch off that breaker. Wall switches, especially if they are the cheapy ones, not the spec grades, will leak small amounts of voltage. If you use a volt meter on them, you may even find that they will leak up to about 90 volts. Not enough to light a lightbulb, but certainly enough to wake you up if you happen to go arm to arm on the circuit. Electricians are taught to never ever trust a light switch when they are working on a lighting circuit just for this reason. This can be especially critical when working in a location with a bare concrete floor be it a garage, shop or basement. Lighting circuits are normally not GFCI protected and getting your bell rung while standing on a concrete floor will be an experience you will not want to repeat. And yes, you can trust me on this, it is the voice of experience talking. (Yes, we often violate the very safety rules we are taught to obey."Be safe out there we want to continue having you as a member.
        Jim Don

        Comment


        • #5
          Re: 3-way switch off and still some power?

          Thanks for all you replys. I had the breaker off when I moved the fixture and it was only in testing the line that I had the breaker on. What is happening is, with the breaker on, and the wall switch off, there is still some power at the positive line after the switch. Is that normal for a 3-way configuration? I changed both switches (40 year old levitons) with new levitions, and there still seams to be a very little power coming through. I have a cheap $3 type circuit tester that lights up when a current passes through it, so I dont believe that the tester could light up on its own.

          Comment


          • #6
            Re: 3-way switch off and still some power?

            If your using a digital volt meter (high input impedance), you can some times read power where there is actually not actual live power there,

            jsut for an example some times you if touch a hot lead with a digital meter and not any thing on the other lead jsut in the AIR you will see a power reading if the humidity is up some, jsut into the air. (yes in this instance there is power there but there should not be a reading if there is not flow).

            on dead lines you sometimes will also get readings,

            I have called it phantom voltage or stray voltage, (my assumption is it is actual voltage potential in some way, but because the meter is so sensitive it will read it, and analog meter will not read it. fluke has a kit for there meters to get truer reading when one runs in to that type of situation. "The Fluke TL225, Stray Voltage Adapter Test Lead Set"

            There can also be induced voltages by live circuits that are running near the circuit that is shut down,

            ~~~~~~~~~~~~~~~~~

            http://support.fluke.com/find-sales/...01_ENG_B_W.PDF

            If the above url doesn't work try below,

            http://us.fluke.com/usen/Home/Search...note&x=11&y=5#
            Look under:
            1. Stray voltage affects multimeter measurements
            or
            2. Stray voltage and multimeter measurements

            The problem is to make sure that the power is really off,

            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

            You must have posted while I was typing ,

            there is a way of wiring a three way switch (not to code any more) that uses two different live circuits, on the same side of the 120, normally it was used from building to building, but any thing is possible, so it is possible to have the light off and both switches "off" and have a full 120 volt potential on a three way circuit,
            Last edited by BHD; 12-03-2007, 10:37 AM.
            Push sticks/blocks Save Fingers
            ~~~~~~~~~~~~~~~~~~~
            "The true measure of a man is how he treats someone who can do him absolutely no good."
            attributed to Samuel Johnson
            ~~~~~~~~~~~~~~~~~~~
            PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

            Comment


            • #7
              Re: 3-way switch off and still some power?

              Thanks again. It may be just "induced voltages" because there is power going "through" the box, from which the switch line taps into. It is weird in that, depending upon where I touch the exposed tip of the positive line, the tester will dimly flicker on and off, almost like I'm catching a certain frequency by trolling down the exposed copper. It may just be something it is "picking up" from the current travelling "through" the box into another room.

              Comment


              • #8
                Re: 3-way switch off and still some power?

                On additional item to check would be that the threeway switches all have a black, a red and a white wire connected. It is possible, although unsafe and illegal to wire one up using 2 conductor instead of 3 conductor cable.

                Comment


                • #9
                  Re: 3-way switch off and still some power?

                  sorry bacon4life,but you can do a three way with 2 conductor as long as you have a neutral at both ends.Make sure that the hot is switched and not the neutral.In the old days they switched the neutral.Also if there is a lighted switch on either end it will cause feedback.This is normal.

                  Comment


                  • #10
                    Re: 3-way switch off and still some power?

                    There are actually several different ways to configure a 3-way switch:
                    source - switch - switch - light
                    source - switch - light - switch
                    source - light - switch - switch

                    If you get the wiring wrong on any of them, it can cause problems. Here are a couple of clear three-way switch diagrams for the various configurations:

                    http://www.indepthinfo.com/3-way-switch/

                    Comment


                    • #11
                      Re: 3-way switch off and still some power?

                      The question I would ask is:
                      Is the wiring the old knob and tube system? During those days, it was common practice to switch the neutral, while leaving the hot wire to the fixture constantly live. (On the belief that switching the neutral doesn't create a spark, thus extending the life of the switch). Also, is the feed going to the fixture box first? Plus, if you have enough residual voltage to induce a small amount of power through your little tester, it may indicate a grounding issue.

                      I have come accross a house that had undergone numerous remodels, and get belted off the grounding wire a few times. Course every switch had a built-in nightlight, so that may have added to the problem.

                      Comment


                      • #12
                        Re: 3-way switch off and still some power?

                        Originally posted by tailgunner View Post
                        The question I would ask is:
                        Is the wiring the old knob and tube system? During those days, it was common practice to switch the neutral, while leaving the hot wire to the fixture constantly live. (On the belief that switching the neutral doesn't create a spark, thus extending the life of the switch). Also, is the feed going to the fixture box first? Plus, if you have enough residual voltage to induce a small amount of power through your little tester, it may indicate a grounding issue.

                        I have come accross a house that had undergone numerous remodels, and get belted off the grounding wire a few times. Course every switch had a built-in nightlight, so that may have added to the problem.
                        I was going to say something about switched neutrals as well... I'm fairly certain that a switched neutral isn't the case here, but everyone should be aware of it or you may find yourself flat on your back next to a toppled ladder with wire nuts, screwdrivers and a pair of dykes strewn all about, wondering "what the F___ just happened???" I would also advise that I found switched neutrals with old black-sheathed romex. That's interesting about sparking. I always wondering what problem a switched neutral could possibly address or why that would ever be deemed to make life easier.

                        Also, I'm able to get a false reading out of my tester sometimes by taking a length of scrap wire and quickly running the tester along the length of it. A chirp isn't necessarily indicative of voltage at the fixture.

                        If the run is parallel to and adjacent to a seperate feed, I think you can pick that up with some circuit testers as well.

                        If you have a multimeter you could be more positive about your chances of getting a shock or you could just flip the breaker.
                        Last edited by jimboburnsy; 09-14-2009, 04:11 PM.

                        Comment

                        Working...
                        X