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3-way switch illuminated when off??

Discussion in 'Electronic Basics' started by js5895, Apr 17, 2005.

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  1. js5895

    js5895 Guest

    Hi,

    I have a 3-way wall switch that lights when the load is off.
    It somehow seems to work with one wire or in series with the load.
    how does that work? I understand basic electrical but, this is weird.

    Thank you.
     
  2. Chris

    Chris Guest

    It's most likely a neon in series with the line/active/hot and the load and
    neutral to complete the circuit. When the switch is in the on position it
    shorts this out.
    If it isn't lit, it means the globe is blown.

    Cheers.
     
  3. js5895

    js5895 Guest

    a single AC phase by it's self can't power anything, may it be an AC or
    DC circuit, right?
     
  4. John G

    John G Guest

    Chris's reply was correct . There is a neon (and resisitor) across the
    switch contact.
    When the switch is OFF the neon is fed from the hot side thru the load
    to neutral.
    When the switch is ON the neon is shorted and the load works.
     
  5. js5895

    js5895 Guest

    I find that strange, because, won't the load's resistance dim or
    brighten the switches neon lamp. Or would if the load was a receptacle.
     
  6. John G

    John G Guest

    In the case of a lamp the current used by a neon is so small as to be
    insignificant compared to the lamp so will not be dimmed by a change in
    lamp power.

    If there was no lamp or no load on a receptical then this approach would
    not work correctly and it would be better to have the neon on the load
    side of the switch withits other end conected to neutral thereby
    lighting when the switch is on, not off, regardless of the load.

    Having it light when the lamp is off allows you to find the switch in
    the dark.
     
  7. Lord Garth

    Lord Garth Guest

    Neon lamps need a series resistance and the draw extremely little power.

    O---------------------------traveler------o--------------------O
    | |
    (NE2 shorted) |
    Hot O---^^^^---neon--- ---neon---^^^^---O---O
    incandescent lamp O---O neutral
    (NE2 open) |
    On
    O--------------------o------traveler------o--------------------O

    OR

    O---------------------------traveler------o--------------------O
    |
    (NE2 open)
    Hot O---^^^^---neon--- ---neon---^^^^---O---O
    incandescent lamp O---O neutral
    | (NE2 shorted) |
    | On
    O--------------------o------traveler------o-------------------O





    O---------------------------traveler------o--------------------O
    | |
    Hot O---^^^^---neon--- ---neon---^^^^---O---O
    incandescent lamp O---O neutral
    |
    | Off
    O--------------------o------traveler------o--------------------O

    OR

    O---------------------------traveler------o--------------------O
    |
    |
    Hot O---^^^^---neon--- ---neon---^^^^---O---O
    incandescent lamp O---O neutral
    | |
    Off
    O--------------------o------traveler------o-------------------O
     
  8. Lord Garth

    Lord Garth Guest

    Neon lamps need a series resistance and the draw extremely little power.




    O--o-----------------traveler------------------o---O
    | | (NE2 on) |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent lamp O---O neutral
    (NE2 on) | | | Off
    O----------------o---traveler---o------------------O

    OR

    O--o-----------------traveler------------------o---O
    | (NE2 on) | |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent lamp O---O neutral
    | (NE2 on) | | Off
    O----------------o---traveler---o------------------O





    O--o-----------------traveler------------------o---O
    | | (NE2 off) | |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent lamp O---O neutral
    (NE2 off) | | On
    O----------------o---traveler---o------------------O

    OR

    O--o-----------------traveler------------------o---O
    | (NE2 off) |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent lamp O---O neutral
    | (NE2 off) | | | On
    O----------------o---traveler---o------------------O


    Looks better in Courier
     
  9. js5895

    js5895 Guest

  10. Lord Garth

    Lord Garth Guest

    Just unscrew the bulb and see if they go out.....
     
  11. Bob Monsen

    Bob Monsen Guest

    Are you saying that the switch itself is illuminated, or that the lamp
    plugged into the switch is illuminated? I have a wall switch that is
    lighted, in which the light is on when the switch is off.

    However is there is a short through the switch, you should replace it.
    Sadly, I had trouble interpreting your picture.

    For a three way switch, you have this situation:
    {view with fixed-point font)

    S1
    line --[lamp]--o o---------------------oo
    \ \
    \ \
    oo---------------------o o---- neutral
    S2

    Thus, either of the switches can light the lamp.

    If one of the switches has failed such that it is closed on both paths,
    or if the wiring is broken in this way, it'll light in either
    position. So, for example, if S2 has a path like this:

    S1
    line --[lamp]--o o---------------------oo
    \ \
    \ \
    oo---------------------oxxxxxxo---- neutral
    S2

    Then even if the xxxxx path is fairly high resistance, the lamp may
    act like you are describing. You can test this by disconnecting
    neutral from S2, and line from S1 and testing the resistance between
    the two throws of S1. If it is less than 10MEG, you have trouble.

    Note that the lamp may be in a different place; thus, I wouldn't trust
    that pulling the lamp will disconnect you from line.
     
  12. Lord Garth

    Lord Garth Guest

    I learned to never switch the neutral line, only the hot (black) wire.
    Be careful, you set up a situation where you are the ground link.

    Use courier font to view the diagram, it is a fixed width font.
    I drew all four possible switch positions. The three O at each end
    are the three terminals on the SPDT switches, center is the toggle.
    The resistor and series neon are within the switch & connected across
    the throws...that's the top and bottom O at the ends. The lines labeled
    'traveler' is the interconnect between the switch throws at each end
    of the room.

    The neons in the switches should go out when the bulb is removed
    from the socket. This is because they loose their connection to neutral
    through the incandescent bulb.



    O--o-----------------traveler------------------o---O
    | | (NE2 on) |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent
    lamp O---O neutral
    (NE2 on) | | | Off
    O----------------o---traveler---o------------------O

    OR

    O--o-----------------traveler------------------o---O
    | (NE2 on) | |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent
    lamp O---O neutral
    | (NE2 on) | | Off
    O----------------o---traveler---o------------------O





    O--o-----------------traveler------------------o---O
    | | (NE2 off) | |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent
    lamp O---O neutral
    (NE2 off) | | On
    O----------------o---traveler---o------------------O

    OR

    O--o-----------------traveler------------------o---O
    | (NE2 off) |
    Hot O --^^^^---neon-- --neon---^^^^--o O---O incandescent
    lamp O---O neutral
    | (NE2 off) | | | On
    O----------------o---traveler---o------------------O
     
  13. js5895

    js5895 Guest

    There is no bulb, the switch isn't wired up, it's in my hand right now.
    I did a test on my desk with a digital clock, by wiring it normally,
    hooked up the travelers and tested it with the load connected to
    the common, then the line conected to the common and then the
    neon stayed lit, when the switch was off, BTW, I'm setting it up
    with one neon switch in my dark hall way, and one non-neon, 3-way
    switch in the house. I just wanted to know how a switch can light
    up inside, with no neutral connection, because it's a switch, and light
    up and be off at the same time, FYI, I changed the picture:
    http://home.nycap.rr.com/joshs­/threewaywire.bmp

    Thanks.
     
  14. Lord Garth

    Lord Garth Guest

    There is no bulb, the switch isn't wired up, it's in my hand right now.
    I did a test on my desk with a digital clock, by wiring it normally,
    hooked up the travelers and tested it with the load connected to
    the common, then the line conected to the common and then the
    neon stayed lit, when the switch was off, BTW, I'm setting it up
    with one neon switch in my dark hall way, and one non-neon, 3-way
    switch in the house. I just wanted to know how a switch can light
    up inside, with no neutral connection, because it's a switch, and light
    up and be off at the same time, FYI, I changed the picture:
    http://home.nycap.rr.com/joshs­/threewaywire.bmp

    Thanks.
     
  15. Lord Garth

    Lord Garth Guest

    There is no bulb, the switch isn't wired up, it's in my hand right now.
    I did a test on my desk with a digital clock, by wiring it normally,
    hooked up the travelers and tested it with the load connected to
    the common, then the line conected to the common and then the
    neon stayed lit, when the switch was off, BTW, I'm setting it up
    with one neon switch in my dark hall way, and one non-neon, 3-way
    switch in the house. I just wanted to know how a switch can light
    up inside, with no neutral connection, because it's a switch, and light
    up and be off at the same time, FYI, I changed the picture:
    http://home.nycap.rr.com/joshs­/threewaywire.bmp

    Thanks.


    Yes, it should have a resistive load connected, like an incandescent lamp.
    I suspect a fluorescent lamp wouldn't be right either but since the
    neon is all that's affected, no big deal. I wonder about folded fluorescent
    screw-in replacement lamps.

    Were you able to see my diagram using courier font?

    Your AOL / RoadRunner link isn't working here. :-|
     
  16. Lord Garth

    Lord Garth Guest

    Hmm, You know, you're going to make me go buy a switch just to cut it
    open! The setup should have been equivalent with the line & neutral
    either way though it needs an incandescent load. I hope you weren't
    reading voltage since you have your meter is in series. Reading current
    can lead to some bright flashes that you won't want to see when the
    source is the mains, usually current is read with a clamp on current probe
    for your own safety and the life of your meter.

    Your picture makes it hard to tell what is the pole and which are the
    throws. I'm going with top being the pole and the bottom two being
    the throws. If so, then I don't know how the neon lit at all. My though
    was that the neon was across the throws.
     
  17. js5895

    js5895 Guest

    I have the meter in voltage reading mode, not current mode, ouch!, lol.
    I was testing it the night I got it, and forgot the load, and it was
    lights out. When I have it in voltage mode it's in a complete circuit.
    I had it in current mode, line to each screw on the switch but,
    making sure it's wasn't a complete circuit, that's when it dimly lit,
    which was weird, since it wasn't a complete circuit, but it only did
    this once, I tried it again and nothing happened, it could of been
    some anomaly from the no load incident or, because it's new.
    I updated the image to show the common point, and where the switch
    is sending power, here:
    http://home.nycap.rr.com/joshs/threewaywire.bmp

    Thanks.
     
  18. Lord Garth

    Lord Garth Guest

    Hey thanks, that little arrow help a bunch. No, I can't tell you why it
    lit the neon at all, I'll just have to waste one! Have Dremel, will travel.
    Remember that voltage is read across a circuit or device, not in series.
    Please don't read current when your testing mains unless you get a clamp
    on probe. I'm glad you and the meter are okay!

    I have accidentally probed an outlet with my meter set to Ohms.
    Fortunately,
    I have a (generation one 1982) Fluke DMM. It shrugs off this sort of abuse.

    Once, while using a friends cheap DMM, I didn't see that his probes were in
    common and 10A. When he activated the light switch, the resulting bang
    blew me off the ladder! My friend caught me and I was uninjured but I was
    seeing spots for a while. Get this, the meter fuse was INTACT after
    that!!!!
    The rotary switch was welded though.
     
  19. spudnuty

    spudnuty Guest

    3 way switches have 3 terminals: a common and two non common. The
    common is wired to the load or to the hot. The two non commons are
    wired between the 2 switches via two wires, usually black and red. When
    the load is activated there is no potential between the common and non
    common 1 (shorted) or non common 2 (no connection), nor between the two
    non commons 1&2 (one is active the other no connection) When the load
    is off a potential appears between the two non commons 1&2 since one
    will carry the hot and the other will be connected to neutral through
    the load.
    The neon and series resistor will be connected between non common 1&2.
    Typically they draw .5 to 3 ma so when you connected your meter it
    caused the neon to light but dimly. The resistor is usually 19k to
    220k.
    Richard
     
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