I read in sci.engr.electrical.compliance that Jeff frontline_electronic
wrote (in
et.att.net) about 'Lamp ratings', on Wed, 2 Jul 2003:

Hi John, I was wondering if the higher voltages there
had any strange effects that we might not see here?

Some designs of lamp incorporate a fuse in the internal wires so that if
an arc occurs between the ends of a broken filament, the resulting high
current and temperature do not persist and cause the lamp to explode. I
should think arcing is much rarer with 120 V supplies.

I had one low voltage lamp filament break and weld
itself to a short internally.(very small 3.2mm lamp)
Now one lamp in a group of many was causing the
supply to shut down and the supply feeds other
systems.... in short (no pun) who starts by looking for
a shorted lamp, not me.

I do know of this as an extremely rare event with low-voltage lamps.
'AC/DC' tube radios had the tube heaters in series and there was
sometimes a dial lamp in the chain. If the lamp failed, a high voltage
would develop across the break and would occasionally weld the whole
internal metalwork into a solid blob. So the dial light would go out but
the radio would still work. In this case, the 'arc lamp' was fed via the
resistance of the tube heaters and any additional resistance, so the
current was limited to a less than catastrophic value.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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