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Fuse keeps blowing in string of lights, please help!!

Discussion in 'Electrics UK' started by samuelvictor, 5 Oct 2007.

  1. samuelvictor

    samuelvictor

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    Hi there, firstly, I'm new to the forums, and incredibly un-knowledgeable about electrics, please excuse my ignorance, I'm trying to learn! :oops:

    I'm trying to build a string of 7 40Watt light bulbs, each a metre and a half apart. By this I mean I bought 7 light bulb fittings (standard cheap bayonet style, unearthed), 7 lightbulbs, a plug and 3A fuse and some 2way wire (as recommended by the DIY shop I bought it in for making light fittings) and wired it all together.

    I thought nothing could go wrong or be wired incorrectly, a simply enough job, just the 2 wires coming out of the plug, into the first fitting, out of that, into the second and so on.

    I appear to have wired it correctly, in the sense that plugging it in means that all 7 lightbulbs light up.

    However, they won't all stay on for log, before the fuse goes pop. Replacing the fuse means they all light up again, however its not long before it goes once more.

    I'll be honest, I've NO idea why. It could simply be that 7 light bulbs from one plug is too much of a load on the 3A fuse?

    Would a 5A or 13A be better for the job? Or would thew wrong ampage blow the bulbs? (I'm afraid I have no idea what the ampage on a fuse means in real terms to me, I've tried reading the articles on Wikipedia etc and still can't quite work out what it all means in this context.)

    If there's no particular reason why a 3A plug can't run 7 40watt light bulbs, what other reasons could there be? I'm afraid I'm really in the dark here (literally lol)

    Any suggestions or help would be very much appreciated. Thanks in advance!
     
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  3. Lectrician

    Lectrician

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    The load of the lights is not more than around one and half amps I guess.....

    I would think you have maybe constructed this poorly, and have left the terminations to long at the terminals?

    Could you take a photo of the insides of the plug and insides of a couple lamp holders?
     
  4. electronicsuk

    electronicsuk

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    You have a total load of 280w, divide this by the supply voltage (let's assume 230v) and you have a load of 1.22 Amps. Either the bulbs you were sold aren't 40w, or you've made a mistake somewhere - perhaps you stripped back the insulation too far or left a couple of whiskers or wire out of the terminals that are causing a short on one of the fittings? It's a longshot, as I would expect this to be noticable (noise or sparks) but it can't hurt to check.
     
  5. Lectrician

    Lectrician

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    180w? - 280 ;)
     
  6. breezer

    breezer

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    i think its the lamp, if it were a short it would go strait away

    simple anser take all but 1 lamp out and switch on, wait for say 10 mins, add another lamp................
     
  7. rjb

    rjb

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    Are the lights all bright when they are lit up or are they getting dimmer the more you add on. They may have been wired up in series rather than in parallel so there could be a voltage drop problem. (ie the voltage is not 230V (or close to it) across all the lights).

    Got a picture for us?
     
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  9. Lectrician

    Lectrician

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    I personally think that he would have really struggled to wire them in series! He would also notice as he removed lamps.

    If there was a short, it would not necessarily blow the fuse - the short may come and go as he moves the lights around.....

    Could very well be a dodgy lamp though - rare if it carries on working though...
     
  10. electronicsuk

    electronicsuk

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    Ok, typo :p Have edited my post to avoid confusion.
     
  11. Softus

    Softus

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    Not necessarily.

    We're all gambling with sparse information, but my money is on some damaged insulation. An IR test would home in this in a trice.
     
  12. breezer

    breezer

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    agreed, but not a diy thing to have an IR tester sitting around
     
  13. Softus

    Softus

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    :rolleyes:

    Indeed not, but if he has a pair of eyes and a torch he could easily inspect every termination and spot where he's been over-enthusiastic with the knife/cutters/strippers.
     
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