In communications, Jeff
Wisnia wrote:

Just what is in the "shunt" built into series string decorative lamp
bulbs which takes over when the filament opens?

Is it something like a PTC thermistor which heats up and melts some
powdered metal into a permanent short?

My curious mind wants to know.

As it turns out, I don't really know what those things are made of.

I would guess the whole string needs some sort of fuse - eventually all
of the shorting devices will do so.

- Don Klipstein )