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- posted
18 years ago
RCD tripping when a bulb blows
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18 years ago
I've had a 25W oven lamp take out a 32A MCB. The lamp was in an enclosure with a screw-on thick glass cover. The 'explosion' had blown the glass cover half off, cross-threading it so there was no way it could be unscrewed. I had to take the whole fitting out and carefully prise the front glass so it would pop back into the threads, and could then be unscrewed. Interestingly, the bulb inside appeared to be intact at a first glance. On touching it, I found that the glass was shattered, but held together with the stretched filament which was now welded all round the inside of the glass. It was most strange - you could touch it and the glass 'bent' showing lots of tiny fractures, but when you let go, the filament pulled it all back into shape. Unfortunately, there was no way to get it out of the lampholder without completely breaking it.
The lamp had come from Maplin about a week before, and probably done about 3 hours service when it blew. It took out the 10A BS1362 oven fuse, and the 32A circuit MCB.
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18 years ago
Also, a flame conducts electricity, as it's hot enough to ionise the air. Boiler flame detectors rely on this.
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18 years ago
Several reasons, the hot combustion gasses rise and deposit carbon on fittings, fittings are affected by heat and become partially conductive, plastic pipes melt and spray water over fittings.
The first two are usually the most significant. Some trials I did many moons ago we could get a 30mA RCD to trip in a house fire about
1 minute after the smoke alarm went off. In a fire at night (when most fatal ones are) you really don't want the lights going out while you are trying to find your way to the door.- Vote on answer
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18 years ago
ISTR deaths from electrocution from lighting circuit are apx 0 per year.
NT
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18 years ago
High speed spikes may be out of phase to some extent. There may be the same system capacitance L-E as N-E, but the Vs across the 2 are quite different, so there may be different phase shift. And that implies real earth leakage too.
NT