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Problem with LED and Halogen GU10 Lamps Blowing

Discussion in 'Electrics UK' started by Echo the husky, 7 May 2016.

  1. Echo the husky

    Echo the husky

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    Hi guys, a colleague called me to ask about what could be causing 8 LED GU10 lamps to blow when they are switched off. It started last week, all 8 LED lamps dead. They were all replaced and worked fine. Switch on again the next morning and all were dead again. A couple of 50W halogen lamps were fitted as a test, they were both dead the next morning. Only these lights are affected. The supply to the building is standard 3ph 4wire the loads are very very poorly balanced across the phases. Approximate total lighting load for the building is going to be around 220A.

    Further information:
    The lamps are installed in a display cabinet in a shop, they have been there for more than a couple off years with no faults. I do not know how old the first LED lamps were, but they were not fitted recently. The lamps are not cheap Chinese tat, the first LEDs were Megaman, the second were purchased from a local wholesaler. The wiring to the lights was poor and they have now been rewired. They are plugged in to the lighting circuit.

    The shop has some key switches which allows a chunk of the lighting (and possibly other non essential loads) to be switched on/off at the start/end of the day. The majority of the lighting is 4' fluorescents with wound ballasts in the ceiling grid, along with a load of 70W metal halide spots.

    On inspection of the failed halogen lamps, the filaments had just broken, there were no signs of the filament vaporising from a large blast that you might get from connection across 2 phases.

    2 of us are going back Monday night to look again when we will be able to play with the lighting controls and trace the wiring as it is not clear where the supply is from.

    This is not a fault I am familiar with, or have even heard of. If anyone has any ideas please let me know.

    Echo
     
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  3. 333rocky333

    333rocky333

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    Only a quess but could it be a heat problem, i stopped using 50 wattts some time ago, 35watts tend to last longer.
    may be worth checking the voltage at the lamps whilst there
     
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  4. Echo the husky

    Echo the husky

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    The lights are open back downlights along the open top of a cabinet, there is free air all around and about 2' gap between the lights and the rooms ceiling. Voltage measured at lamps 239V. Whatever the wattage they should last more than 10 hours!
     
  5. flameport

    flameport

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    If a TPN contactor is used to switch the lighting, is may be worn/damaged causing the neutral contact to open before the phase contacts.

    This will result in excessive voltage on some of the lighting circuits as they will be briefly connected to the phases without a neutral. Unbalanced loads across the phases will make the problem worse.
     
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  6. Echo the husky

    Echo the husky

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    Good thinking! That will certainly be a good place to start. I'm embarrassed that I hadn't thought of that.:oops: I've not seen the switching arrangements so don't know if the neutral is switched as well. Much of the wiring has been very poorly installed.
     
  7. DetlefSchmitz

    DetlefSchmitz

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    I did once have a fluorescent light (under kitchen cabinet type), which when switched off used to put a sufficient voltage spike on the circuit that an electronic timeswitch in another room exploded. (I know it happened because I got a free replacement timeswitch, and the same happened again).

    May be worth a thought.
     
  8. Echo the husky

    Echo the husky

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    Well it looks like Flameport could well be right. (y) Will have to wait a week or so but no lamps failed after a couple of switchings. Neutral for that contactor is now permanently connected. The contactor was 4 pole and feeds a whole DB. There was lots of soot marks around all the terminal holes which would go with the contacts being worn. There is no indication of which terminal should be used for neutral, so I don't know if the 4th terminal makes first, breaks last, but it isn't likely. The last large 4 pole contactor I fitted had a specific neutral terminal with this feature.

    Echo
     
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