Re: Again power is not measured in AMP, but in WATT you stupid american jerks, Give it up now suckers.

Yeah about 25 pct of the time. Good idea, poorly executed.

You must be very young. I remember, oh, about a half-century ago, laying the Xmas tree lights out on the floor, and if the string didn't light, we'd take a known good bulb and go down the string swapping out bulbs, one at a time; if the string didn't light, we'd take the bulb we just removed from its socket and swap it out with the next one, and so on. When the string lights up, you'd throw away the bulb that you just removed/replaced.

Nowadays, they apparently do have low-V bulbs that are designed to fail short; I'm danged if I know how they accomplish it. :-)

I can guess - one of the filament supports is springy - when the filament opens, that support springs back, contacting another electrode, shorting the bulb - but wouldn't that be kinda expensive?

Thanks, Rich

That's not how they work. It's generally a wire-wound shunt across the filament supports that has enough oxide that it breaks down well below line voltage (when the lamp fails) but not at the operating voltage of the lamp (a few volts). Costs next to nothing to wind a few turns of wire around the filament supports.

Except a fillament virtually can NOT fail shorted. The bulb has to besigned to be "failsafe", so if the filament does not heat the bulb shorts

Except that I was referring to arc lamps.

Also, there is no 'virtually' about it. Short of an impact that jams both input leads together, an incandescent lamp can NEVER "fail" shorted.

In fact, a good way to 'fix' one is with a swift thud while under power. If it hits the lead, it will re-weld itself back on, and that usually (certainly) will not last as long as a properly cinched filament. It will usually get you a few more hours out of the bulb, but I have seen them go on for years after a re-attachment.

It has nothing to do with design. The ONLY failure mode IS an open filament, and that is the only place such a bulb ever fails short of the encapsulation being breached. That is just the physics of it by default.

You're nuts.

A light bulb is, by default, a very low resistance device. Any shorting of its internals or the device which it is mounted in would trip the branch circuit protection. If not, the mount is suspect of total non-compliance.

The bulb is specifically designed to couple as little heat as possible to the base it sits in. That is why you never see a dense epoxy holding the base on the bulb. It is always "airy" baked material of very low density and therefore low thermal conductivity.

IF the filament feeder leads were to be shorted (broken bulb under power)(happens a lot with old style garage shop lights), they would NOT heat the base, the short would cause a breaker to trip immediately.

We are talking SERIES STRING lighting and they do in fact exist - not only that they are very common. And they work as described.

It's time you read the thread, and thought it out before you answer.

The answer was in response to this : And, like the series Xmas lights of yore, when one goes out, they all go out.

YES, ditz, and THAT very remark was made in reference to our discussion about carbon arc lamps in series!

And my response to that remark was ALSO about carbon arc lamps in series, and anyone that actually lived back then knows it.

Have a look at this image:

Just above the bead of glass that stabilizes the electrodes/filament supports you will see a few turns of silver wire wrapped around the supports. This is the wire that causes the bulb to fail shorted. Under normal operation only the bulb's nominal operating voltage is present (2.5V-12V AC depending on the number of bulbs in the string) which is not enough to burn through the oxide layer. Once the filament breaks the full line/mains voltage is suddenly put across the bulb and the oxide layer is penetrated causing the silver wire to short to the supports which makes the bulb unit itself a short circuit. The result is that the rest of the bulbs in the string stay on and get slightly brighter because of the slightly increased voltage across each of them. The raised voltage also shortens the life of the rest so they end up burning out in a cascade effect until either A: they all burn out and short which blows the 3 amp fuse in the plug, or B: the set gets jarred or shaken which knocks loose some of the shorts which then don't reshort because the line voltage is distributed across all of the opens and is not high enough across any given one to cause the bulb to reshort.

Both outcomes result in a dead string of lights so it is best to change a burned out bulb as quickly as possible to extend the life of the set.

You are talking Brockie Pel style arclamps from the late 1800s - I know they were common particularly on the right side of the pond into the 1900s. They were 50 volt units run 10 or 12 in a string on 500 or

And if a carbon arc lamp did not light it also was designed to "fail shorted"

Not ALSO, you ditz. THAT is what I was referring to, and NO, they do NOT fail shorted, also or otherwise, by design.

The one I had had a fixed rod positioner, and if the lamp extinguished, they did not spring together!

Well the Brockie Pel's which WERE series connected DID fail shorted. In the Brockie Pell system that is the way they worked, and I was only speeking of the Brockie Pell - which was used in Bristol among other places.

Also the quite common Thomson-Houston system had an auxiliary solenoid directly across the arc, slamming the electrodes together if the arc was estinguished and also provided continuity to the current loop.

Paul

No, I said, "like the Xmas lights of yore," i.e., about fifty years ago. (which I also wrote quite clearly.)

Ergo, I took you at your word from your response to it.

So go take your nap, and quit being so bitchy.

Thanks, Rich