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From: Kevin McMurtrie
Subject: Re: TRIAC "wears out" on dimmer circuit
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Tue, 29 Oct 2002 04:16:06 GMT
NNTP-Posting-Date: Mon, 28 Oct 2002 20:16:06 PST
In article ,
Terry King wrote:
>> > > ** An arc across the remaining ends
> will never be anything like 60 amps
>I have also read about this and seen the effect. It is most pronounced
>when short tungsten-halogen lamps fail open while powered on. The
>physically open filament creates a METAL arc for a short period of time,
>and the dynamic lamp resistance is far LOWER than the connected filament
>was. The current does not just flow from the broken ends of the
>filament; the metal arc flows all around the attaching metal rods
>that go thru the seals, as well. Good theatrical dimmers have special
>fuses (Silver conductor in a sand-filled ceramic tube) that "blows"
>fast under high currents to protect the TRIACS / SCR's .
I had a 75W 120V halogen floodlamp arc like this but it, unlike good
bulbs, didn't have an internal fuse. It buzzed and flashed wildly for
about 5 seconds before tripping a 15A breaker.
I think the original poster was talking about series string lights.
There's no problem with a few of them shorting out.
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