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Faulty lights

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  1. #1
    ab1
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    Default Faulty lights

    This is for all the electricians.

    Was at a townhouse in Melbourne a while ago. When i turned on the hot tap in the kitchen some of the lights turned on in the place.

    When I turned the tap off, the same lights turned off.

    What do you think was wrong??

  2. #2
    Golden Member nev25's Avatar
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    Quote Originally Posted by ab1 View Post

    What do you think was wrong??
    You had too much to drink

  3. #3
    ab1
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    Come on Nev, I'm being serious here.

  4. #4
    Retired Marine Engineer 1K Club Member Ashore's Avatar
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    Gremlins
    Ashore




    The trouble with life is there's no background music.

  5. #5
    Slow but rough Uncle Bob's Avatar
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    Did the joint have an instantaneous (edit: electric) hot water heater?

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    Retired Marine Engineer 1K Club Member Ashore's Avatar
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    Good reasoning bob if there was a fault or an induced current , maybe
    Ashore




    The trouble with life is there's no background music.

  7. #7
    ab1
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    That's pretty good Bob.

    3 phase HWS. Supply auth connected the power earlier that day.

    2 phases were working, not the blue service fuse.

    From memory, the HWS was connected in delta. When the light switch's were left on on the third phase and hot (warm) water flowed, the blue phase was energised, all be it in series, and on came the lights.

    Now that's a trick for young players, Nev.

  8. #8
    2K Club Member chrisp's Avatar
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    I like it - good one ab1

  9. #9
    Golden Member nev25's Avatar
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    Quote Originally Posted by ab1 View Post

    From memory, the HWS was connected in delta. When the light switch's were left on on the third phase and hot (warm) water flowed, the blue phase was energised, all be it in series, and on came the lights.
    Interesting Theory
    So the water would be carrying current IE Alive

    Lights in Series?????

  10. #10
    2K Club Member chrisp's Avatar
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    Nev,

    Remember ab1 stated the blue phase was missing the supply fuse and, by implication, the lights were on the blue phase. The lights would have been switched on but wouldn't have actually come on.

    What happened is that when the water is turned on, the 3-phase water heater switched on (its an instantaneous unit). One element works as intended (red-white element), and the other two elements (red-blue & white-blue) get half the normal voltage as they now appear to be in series and connected between red-white phases (i.e. they get 207V each instead of 415). The floating blue phase gets pulled to the mid point between the red and white phases (about 120V from neutral and 180 degrees from its normal phase angle) as the two elements act as a resistive divider. The light circuit sees this (almost) 120V and the lights come on (the light switch(s) were on) - but somewhat dimly.

    This wouldn't happen if it was a star arrangement with a neutral connection - the lights would have stayed off, but two elements in the HWS would have worked as normal.

    It is an interesting problem - thanks for sharing ab1.
    Last edited by chrisp; 22nd Aug 2008 at 10:27 AM. Reason: minor typo

  11. #11
    Golden Member nev25's Avatar
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    Sorry missed the instantaneous bit

  12. #12
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    So, the lighting circuit in question was connected to the "load" side of
    [the/a] [contactor/switching] circuit, which supplied the HWS?

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    I think that Chrisp is correct, given that no other 3 phase appliances exist within the abode. It's strange that the OP didn't mention a reduced brightness of the lights affected by this scenario. From his/her original post, the brightness of lights is not mentioned. 230v lights that are supplied with 200v to 210v will be a little dimmer than usual, given that the supply voltage is somewhere between 230v to 260v. Usually, a 5% reduction in voltage is noticeable with light brightness. So, in actual fact, the lights didn't "come on", they came "half on".

  14. #14
    Slow but rough Uncle Bob's Avatar
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    Quote Originally Posted by chrisp View Post
    as the two elements act as a resistive divider.
    Good work Chrisp, I was thinking that it was just induction in the light circuit from the heavy current in water heater circuit

  15. #15
    Slow but rough Uncle Bob's Avatar
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    Quote Originally Posted by elkangorito View Post
    I think that Chrisp is correct, given that no other 3 phase appliances exist within the abode. It's strange that the OP didn't mention a reduced brightness of the lights affected by this scenario.
    Possibly they're a multi-voltage switch mode auto sensing transformer-less type (if they exist, though I can't see any reason why not).

  16. #16
    ab1
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    Crisp is spot on.

    At the time I didn't notice the lights to be dim but it was pretty bright in the room from the sun. Lots of windows.

    The downlights were just standard ones, probably the old black atco looking at the age of the building.

    The lights must have been a bit dim as they would have been in series.


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