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Thread: Deck Light

  1. #1
    In the Trades mattbee24's Avatar
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    Default Deck Light

    Ok....this is weird. I was on the deck at a friends house. There are 2 gfi's and a switch running to a light. They are all connected with pvc conduit. When the center gfi is on, the light won't turn on. But if you trip the gfi, the light will work. I didn't take anything apart to see how it is wired. How is this even possible?Name:  Deck.JPG
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  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by mattbee24 View Post
    I didn't take anything apart to see how it is wired
    We need this information before we can answer

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    Retired Defense Industry Engineer jadnashua's Avatar
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    However it's wired, it's wrong, but I guess you knew that. It sort of sounds like when the gfci is on, when you try to turn the light on, there's power on both leads, and when the gfci gets turned off, somehow the neutral is switched to an actual neutral and then you have a complete circuit. You could check that by seeing if the neutral has 120vac when the switch is off. On the light, with the switch off, 120vac on the neutral, with it on, 120vac on both sides.
    Jim DeBruycker
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  4. #4

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    Sounds to me like its working normally and I think your just confused as to whether the GFI was on or off.

    -rick

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    Electrician ActionDave's Avatar
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    How old is the GFI. They have evloved from allowing power if miswired, to not. Also a broken GFI will do unpredictable things.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    The initial assumption would be that the light is connected to the center GFCI and that IT is wired improperly.
    Licensed residential and commercial plumber

  7. #7
    In the Trades mattbee24's Avatar
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    I understand that I will have to take it apart to see how it is wired. I was just trying to imagine a scenario that would make it work like this. And yes, I'm sure the GFI is Tripped when the light works. I even plugged something into the GFI to make sure. When there is power to the receptacle, the light will not work, and vice versa.

    In other words, If you were starting from scratch, could you even wire it to make it work like this?
    Last edited by mattbee24; 03-09-2012 at 09:44 AM.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    It all depends on what the internal bits in the GFCI do when it is tripped. If it ties the netural between line/load together, or some other weird thing.

    As I said, if when the GFCI is enabled, there's voltage on both the hot and neutral of the lamp, it won't light. Only when one lead is hot and the other is neutral will it light. My guess is tripping the GFCI is creating the neutral path. But, can't tell without some diagnostics - you'd have to be there.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades mattbee24's Avatar
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    Thanks Jim,

    I understand what you are saying. That would kind of work like the old hot 3-ways. I guess I just don't see a scenario where a tripped gfi could make a neutral path. I suppose it could be a faulty gfi, but then how is it working normally?

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    When you are wiring a switch leg, when the switch is on, both the white and black are connected together to make the light come on. If you mess up, and switch the neutral verses the hot, you can get some weird things happen, especially when a gfci is involved. It can get confusing, as often when wiring things up, you tend to try to tie all of the neutrals (white wires) together. If you did that on a switch leg, you'd create problems.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    Moderator & Master Plumber hj's Avatar
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    It would take some serious miswiring, because the hot would have to supply the GFCI and the light switch, but the "neutral" from GFCI would have to connect some other item. The light's "neutral connection" would also be fed from the GFCI "hot" lead. When the GFCI was "on" the light would not have a neutral, but when the GFCI was tripped, the other item would daisy chain to the light and supply its neutral. Both items would be at less the full power however. IF the GFCI did not interrupt the neutral wire, then the same thing could happen if something were plugged into the GFCI at the time.
    Licensed residential and commercial plumber

  12. #12
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by mattbee24 View Post
    Ok....this is weird. I was on the deck at a friends house. There are 2 gfi's and a switch running to a light. They are all connected with pvc conduit. When the center gfi is on, the light won't turn on. But if you trip the gfi, the light will work. I didn't take anything apart to see how it is wired. How is this even possible?Name:  Deck.JPG
Views: 103
Size:  7.4 KB
    Did it ever work properly ?

    Most GFIs that I have seen have a single throw switch. That makes it imposable for it to pass any Current if it is really OFF.

    It is possible that it is using the ground wire for the return path.

    Or it is a battery powered emergency light.
    Theory only works perfect in a vacuum.

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