Re: Defective Bulb Tripping Ckt Breaker: How Possible ?
- From: Yukio YANO <yano@xxxxxxx>
- Date: Tue, 31 Oct 2006 17:10:22 GMT
N Cook wrote:
Robert11 <rgsros@xxxxxxxxx> wrote in messageThis all sounds nice BUT the two strands of the broken filament limits the current to ~ current to less than 1 Amp. !
news:AaadnUKll9619trYnZ2dnUVZ_sednZ2d@xxxxxxxxxxxxxx
Hi,hall
Boy, this is a funny one.
Wife turned on a hall light switch last night, big flash by one of thelights, and the ckt breaker tripped.
Was about 2 days since putting in a new bulb there.
Was the el-cheapo brand picked up at CVS, and made in China.
Replaced the bulb with a GE one, and so far everything seems O.K.
Question: I can't imagine how anything, like e.g., a broken filament
perhaps, can short out the circuit.
But, perhaps ?
Can anyone think of a bulb failure mechanism that might trip the breaker ?
Or, might this be just a coincidence ?
Thanks,
Bob
I'm only going by memory and may have it a bit wrong.
A tiny part of the filament wears to the point it creates a hot-spot which
rapidly gets worse causing the first part of the intense flare. In that
super-heated process a plasma state is formed within the bulb. In a plasma
state the effective conductivity across the 2 filament suspension end points
becomes orders of magnitude less than the original filament resistance so
for very short duration , can pass tens or hundreds of amps.
It is the same mechanism whereby a lightning discharge through air can pass
millions of amps through a channel that is only about 1/2 inch in diameter
which no metal could pass. The same discharge passing into the right soil/
conditions leaves a yards long but same 1/2 inch wide hollow tube punched
through the ground, see keyword fulgurite.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
More likely the Light-bulb in question was mounted Socket-Down and a portion of the broken filament dropped down and shorted across base conductors. The short length of filament's Resistance would be much less than the nominal ~ 200 ohms of the intact filament. The resulting arc would vaporize in the Argon Gas of the light-bulb and create a miniature MIG (Metal Inert Gas)Welding condition at which time, the Circuit Breaker would Open due to the excessive current draw. A photographic Flash-bulb would be a good analogue. Source Impedance and Current Limiting of Household wiring were engineered to safely harness electrical energy!
Yukio YANO
.
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