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Fluorescent fitting blowing fuses?

Discussion in 'General Electronics Discussion' started by gijoe50000, Jun 21, 2016.

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  1. gijoe50000

    gijoe50000

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    Oct 6, 2015
    So I'm trying to figure out why a fluorescent light keeps blowing the same fuse immediately in my house.
    The other lights on the same fuse work ok until I switch on the fluorescent light. so I assume that's the problem, diagnosing is getting expensive at €1 a fuse!

    The fuse (in the main fusebox) is a 10A 500V and it blows immediately once I switch this light on, even with no tube in the fitting. It's a 58w Fluorescent with a 65w starter.
    I opened up the fitting, and the light switch, and everything looks ok, no crossed wires or anything. I don't know much about the ballast in a fluorescent fitting.. can a dodgy ballast blow a fuse?
    If not I assume it must be a fault inside the wall somewhere..
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    A typical fluorescent lamp is ste up as in this image. Without the lamp, neither a short circuited starter nor a short circuited ballast will be able to produce a short circuit in the main power circuit. Therefore the short is most likely within the lamp fixture itself or the wires leading to it.
    If the failure persists when you completely disconnect the fitting, the fault is in the wiring leading up to the lamp.
    If the failure disappears when removing the fixture, it is the fixture itself which is defect - or a defect in the connection between the mains wires and the fixture.
     
    shrtrnd likes this.
  3. gijoe50000

    gijoe50000

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    Oct 6, 2015
    Ah right.. Thanks.
    I'll go and double check the wiring again..
     
  4. gijoe50000

    gijoe50000

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    Oct 6, 2015
    So I disconnected the fitting from the mains and the problem went away. So at least it's not a problem with the wire in the walls.

    All the wiring in the fitting is fine too, no damaged, crossed, shorted wires etc. The started isn't shorted either so I suppose that just leaves the ballast and the PFC cap..
     
  5. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Sounds like you're doing a good job of isolating the problem. The most common failure in the situation you're describing is the ballast. But you've narrowed the possibilities pretty well.
     
  6. Minder

    Minder

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    Apr 24, 2015
    +1 on the ballast, that is the main cause I have found for blowing fuses.
    M.
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Only thing I wonder is how the ballast would trigger the fuse when no lamp is inserted:confused:
     
  8. gijoe50000

    gijoe50000

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    Oct 6, 2015
    Yea I think it must be the ballast alright. The only other thing is the cap, and the guy in a 'light shop' told me I can remove that without it having any effect anyway, I assume it's just there to keep the flow constant\steady. Guy in another shop said a failed ballast is the most common cause of blown fuses. The ballast seems to be a bit complicated, I've heard of them leaking oil..
     
  9. Minder

    Minder

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    Apr 24, 2015
    One way is a burnt winding with a short to ground.
    M.
     
    gijoe50000 likes this.
  10. shrtrnd

    shrtrnd

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    Jan 15, 2010
    +1 on the shorted ballast.
    I've seen them blow the end-caps off the old fixtures with metal plates.
     
    gijoe50000 likes this.
  11. gijoe50000

    gijoe50000

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    Oct 6, 2015
    Thanks for the replies.
    Think I'll pick up a ballast in the local hardware shop tomorrow and see how it goes..
     
  12. gijoe50000

    gijoe50000

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    Oct 6, 2015
    So I replaced the ballast and it was still blowing the fuse. What the hell?

    Turns out it was the PFC cap that was shorting it out!

    For some reason my brain didn't register that the capacitor was connected to the live AND the neutral.. I was convinced that it was in parallel with the circuit, even though I was staring at it! Duh like..
     
  13. shrtrnd

    shrtrnd

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    Jan 15, 2010
    So now I imagine you're ire is up, as we sent you on a wild-goose-chase?
    (Hey, I just noticed your flag. The Ire in Ireland, ... I'm a poet and don't know it).
    Anyway, I wouldn't have replaced a bad ballast without the cap, ... and to tell you
    the truth, I don't think that cap blew by it's lonesome. You can save your old ballast,
    but I wouldn't re-install it if I were you.
    Nice work in repairing your lamp.
     
  14. gijoe50000

    gijoe50000

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    Oct 6, 2015
    Haha, na, no ire.. Just happy to get it sorted and to get a little extra knowledge in the back pocket! I already brought the old ballast (€10) back to the hardware store and they exchanged it for the new cap (€9) +€1.
    I'll see how it goes anyway..
     
  15. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Glad you're happy. And that you can see again when night-time rolls around.
     
    gijoe50000 likes this.
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