Not so much electronics, more electrics

All incandescent light bulbs use a tungsten filament. When the filament fails, this is because it eventually melted away to be an opened circuit. Over the lifetime of a light bulb, as the filament is heated to near white hot temperatures to generate light, it starts to slowly break down.

When the filament in a lamp burns out, it sometimes has a bit of a meltdown. Sometimes pieces of it can short out the metal support contacts feeding itself. If there is a short, it can cause a fuse to blow, or a circuit breaker to go to the open mode.

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JANA
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"hooch"  wrote in message 
news:a50b49d2-a8f3-4a2b-8d3b-e45a2a48bff9@w28g2000hsf.googlegroups.com...
I have two halogen bulbs on the same lighting circuit (240V - UK)
controlled by the same two switches, i.e, either switch will turn on
or turn off both lights.   Recently one of the two bulbs died (open
circuit, as expected), causing the fuse / circuit breaker to trip.
Can anyone offer an explanation?

Ah, thanks. That's OK, then. I thought it may have been something to do with the wiring.

I have read that filament-type bulbs will sometimes arc when the filament opens, and that the arc can draw a whole lot more current than one would expect.

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                 Angry American flags attack Hillary Clinton!

Pretty common. There are many theories why, but bulbs often short out on failure. Many incorporate a fuse to try and prevent it taking out the circuit. In the UK 'C' type circuit breakers are available which stand an overload for longer before tripping. Might be useful if the light in question is in a hallway where others will give at least some light if it blows.

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*7up is good for you, signed snow white*

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Geez, this again??? :)

While the scenario of the bits of the filament shorting is possible with some lamps (usually with long thin filaments, though unlikely with the short filaments of halogen lamps), the more likely cause is the arc resulting when the filament opens. This results in the arc moving towards the filament supports, with a lower resistance than the filament had originally, leading to a high current.

See:

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What I never figured out is how the arc is maintained for more than 1/120 of a second when there's no air around the arc to ionize.

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                 Angry American flags attack Hillary Clinton!

There's argon or other inert gas in there, it ionizes just like the arc in a discharge lamp.

clifto wrote:

Tiny bulbs are often evacuated--but larger bulbs are filled with gas. The gas pressure helps prevent the filament from evaporating (which would not only thin it prematurely but would lead to metal deposition on the inside of the glass, dimming the light output).

Look at the light bulb aisle next time you go out. Standard bulbs are filled with Argon. "Super" bulbs are filled with Krypton or Xenon.

There's an inert gas.

Only the smallest incandescent lamps have a vacuum inside.

--- sam | Sci.Electronics.Repair FAQ:

Repair | Main Table of Contents:

+Lasers | Sam's Laser FAQ: | Mirror Sites:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

As, I think, do TV picture tubes. I like your TV Repair FAQ, by the way.

And any other vacuum tube, but this discussion was specific to lightbulbs.