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Old 02 October 2009, 07:34   #11
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Maybe someone is trying to assassinate you!!!

The best way to make a nasty exploding light bulb is to dill a small hole in the base - inject something like easystart or petrol - then seal the hole back up with wax...............
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Old 02 October 2009, 17:07   #12
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Suffer the same sort of problem. Got one of those 6 lamp B&Q ceiling lights with exactly the same golf ball SES bulbs. They blow regularly and although they haven't exploded yet, they do trip the fuse every time. As you say, sometimes they last months, other times it's no more than a few days. A kind of built in obsolesence on a grand scale! We've swapped ours for the compact fluorescents, which aren't really compact at all, but certainly last longer. Take a good few minutes to warm up and reach reading brightness mind you.
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Old 03 October 2009, 13:50   #13
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You also need to check your lighting protection as this fuse should have blown before the main breaker to the whole board went out. This could also be down to your external loop impedance value.
And our survey said? Uh-huh XXXX !

I don't think it was the "main breaker" do you? More likely to be an RCD. If all the lights go out Ie upstairs and downstairs, it's probably worth going for a split board with one RCD protecting upstairs and one for downstairs..or switch () to them newfangled RCBO thingies....
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Old 03 October 2009, 14:00   #14
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I am a bit confused about this too as a low loop impedance value is a good thing as I seem to remember? It is all to do with getting a low enough value to ensure short disconnection times for faulty circuits. Values are usually fairly low to ensure current flow under a fault condition is high enough to operate the disconnection devices fast enough to avoid injury.

On another tack a short circuit with the lamp isn't even affected by the loop impedance value as this is through the earth path rather than via the neutral which is where this fault current goes in this case
(at least till it gets back to the incoming supply where neutral and earth are connected together in a large number of supply types but this is outside the internal circuitry of the house itself)

Also it is quite possible to bypass a fuse or breaker (more common with fuses) that theoretically should have protected a circuit. I have seen someone plug in a faulty table lamp with a 3 amp fuse in it and take out the main building pillar fuse rated at 250 amps with the 3 amp fuse surviving intact.......
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Old 03 October 2009, 16:46   #15
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The earth point on many distribution transformers is the star point on the transformer, which is also used for the neutral. Many supply cables actually combine the earth and neutral and only separate it at the distribution board, supply is then called TNC ( terra, neutral, combined)

I should have explained it better. When testing installations this term is referred to as fault current and should be measured between neutral and the live phases, but in practice most use the Ze value.

You can get very low on the resistance and the current rises to fast for the breaker or RCD to react, in order to minimize the current generated in a short circuit condition. This is normally when the distribution transformer is very close to your house/flat/factory.
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Old 04 October 2009, 09:55   #16
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Earth loop impedance is generally less than 1 ohm depending on application, 0.5ohm or even 0.1 ohm would be classed as even better although hardly achievable in practice.
There are no actual minimum values as disconnection times less than the maximum are a good thing.
The whole point of the fault current via earth is to disconnect as fast as possible so the larger the fault current that can flow the faster fuses or breakers operated and the less of a danger there is to any person holding whatever is faulty.
In the example of the bulb it is just the fault current via the neutral that is involved rather than the earth or its impedance within the installation. This again should be as high as possible to operate the relevant breaker within the disconnection time (0.4 secs if I remember correctly for this type of circuit) I am unaware of any mimimum limit of cable resistance that applies in this case as the whole idea is to minimise resistance in the supply and protective cabling.
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Old 04 October 2009, 13:28   #17
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Only me , Get a spark to check your external loop impedance, sounds like it could be a very low value, do you live near to the distribution transformer?

You also need to check your lighting protection as this fuse should have blown before the main breaker to the whole board went out. This could also be down to your external loop impedance value.

Any questions, please don't ask.
ARE YOU REALLY A QUALIFIED SPARK and to think i am not allowed to wire my house because i am a scientist therefore not competent

All thats happening is cheap bulbs dont have a fuse in the cap. they are also gas filled not vacuum lamps.
When the filament fails a gas and metal vapour(tungsten and molybdenum from the filament and supports) plasma is formed across the filament this plasma has a very low resistance (practically none) so a large current flows, this rapidly expands the gas fill in the lamp causing it to explode.
the only way to prevent this is to fit an individual fuse in each lamp cap(used to be std practice), or go back to vacuum lamps. they dont explode but still blow the fuses if no breaker is fitted.
unfortunately in compact lamps there either isnt room, or manufacturers in the far east dont bother fitting them.

theres a wealth of info on the net, even a slow mo video of the internals of a bulb as it happens!
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Old 04 October 2009, 17:09   #18
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Any questions, please don't ask.

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I don't think it was the "main breaker" do you? More likely to be an RCD.
Yes I'm sorry I should have been clearer it was one of those RCD jobbies ...

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The earth point on many distribution transformers is the star point on the transformer,...................................... ............................................. close to your house/flat/factory.


Erm no .. a mile from a sub station at least....

My technical conclusion doesnt need a PHD in electrophysics, and neither a critical masters in Ohms law .. the answer is that the lightbulbs were cheap european shite

As of now have been replaced with some natty flourescents with a supposed () 10 year life span

Anyway .. the point of the original post was people beware .. these are violent little buggers .......


*edit*

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Maybe someone is trying to assassinate you!!!
You watch too many movies codders .. your methods are close but very crude
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Old 04 October 2009, 17:34   #19
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Yes I'm sorry I should have been clearer it was one of those RCD jobbies ...



Erm no .. a mile from a sub station at least....

My technical conclusion doesnt need a PHD in electrophysics, and neither a critical masters in Ohms law .. the answer is that the lightbulbs were cheap european shite

As of now have been replaced with some natty flourescents with a supposed () 10 year life span

Anyway .. the point of the original post was people beware .. these are violent little buggers .......


*edit*



You watch too many movies codders .. your methods are close but very crude


That was my point! it dont take a rocket scientist to work out cheap bulbs with no internal fusing blow up when they burn out
its got F all to do with transformers, Earthing or RCDs ground loops I had some cheap bulbs too 240v halogen ones Christ they go with a bang
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Old 04 October 2009, 17:43   #20
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had a glut of these in the past. A bit of digging revealed that the big brand name manufacturer sent all the bits out to the far east to be assembled there and then shipped back. Bits of stray wire protruding from the solder stuff on the terminals of the bayonet cap ones was the usual cause. Crazy when they ship the bits around the world to be stuck together and then shipped back here cos its cheaper, so much for carbon footprints
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