Re: Insteon Observations

[G. Morgan <alarmpro@xxxxxxxxxxx>]

On Sat, 16 Dec 2006 01:53:22 GMT, nobody@xxxxxxxxxxxx (Dave Houston)
wrote:

>G. Morgan <alarmpro@xxxxxxxxxxx> wrote:
>
>>On Fri, 15 Dec 2006 18:04:57 -0500, Marc_F_Hult
>><MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>>When a tungsten filament fails, a "tungsten arc" can occur through vaporized
>>>tungsten connecting the ends of the foreshortened filament. There is a
>>>positive feedback in this effect, so as more tungsten is consumed to support
>>>the arc, the current path through the remaining filament becomes shorter, and
>>>the current increases causes more vaporization. This can result in the bright
>>>flash that is sometimes seen when a filaments fails.
>>>
>>>This is a well-known phenomenon. Some lamps have fuses built into the base to
>>>provide some measure of protection. One of the functions of the RC snubber
>>>circuit across a TRIAC is to protect the TRIAC gates from inductive spike
>>>during filament failure that can damage the TRIAC. This is also a problem with
>>>IGBT and MOSFETs used in reverse phase dimmers.
>>
>>Marc,
>>
>>So the net effect is indeed a current surge while the light bulb
>>filament is breaking apart?
>>
>>(x-posted to sci.engr.lighting,alt.engineering.electrical,sci.physics)
>
>The "tungsten arc" is indeed well-known and most household light bulbs have
>the built-in fuse to prevent it from blowing mains fuses or tripping circuit
>breakers (or even destroying triacs). How many people have had a circuit
>breaker pop when a bulb blows?
>
>I've recently had a spate of bulb failures that I attribute to ultra-cheap
>imported bulbs. They blew "not with a bang but a whimper" (actually, more
>like a "poof") and they did not harm the lamp modules (LM14A & LampLinc V2).
>Most (all but one) of my lamp modules are plugged into power strips with 15A
>breakers since I cannot get to the basement to replace fuses - none of the
>breakers have tripped.
>
>Given that the folks behind Insteon have been designing triac dimmers for
>several years, why would they have not taken this into account?


Please fix your sig line delimiter--- ;-)
http://en.wikipedia.org/wiki/Signature_block



Anyway,  I have never experienced what you describe (a circuit breaker
trip) on failure of a bulb.  My common sense tells me the arc (air gap
resistor) would be a great, sudden, resistance that would indeed draw
a large current spike.  Part of me thinks the opposite is true - for
which I have no basis!

I was not aware that common bulbs had a fuse either, I thought the
filament IS the fuse.

My interest in this has nothing to do with Insteon devices, it has
more to do with what I can do to protect the circuit for devices I
install, if the theory is true.  It may explain some anomalies I've
experienced with security devices.



--

-Graham

(delete the double e's to email)