Lanterns/Fixtures > Antique

Rupture Disc for Series Light Bulbs

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rjluna2:
It is my understanding that they used rupture disc insert in between the lamp and the socket.  I never seen one.  Does anyone has one in their collection?

Medved:
I know about bypass shunt (break down and short the lamp when the filament interrupt) and as i understood, they were simple piece of paper clamped between spring loaded contacts...

Nevada Willis:
The most common names for these were film disc cutouts or "dimes" (because they were about the size and shape of a dime.)  I don't have any more or I'd post a photo of one.  They were a kind of shunt, passing extremely low current across them until the bulb they were shunting failed. Then the high voltage in the series circuit would arc through them fusing the sides together and completing a relatively resistance free circuit.

To understand how these cutouts fit into the design of series lamps, here's a feature on an old Line Material series street light that shows the components.  

http://www.kbrhorse.net/signals/l-m01.html

Here's a technical page that has a pretty good illustration.

http://www.tpub.com/content/construction/14026/css/14026_204.htm



BTW, what they mean by open loop and closed loop is that in an open loop only one conductor is on each pole and the circuit makes a big open loop around town.  A closed loop has both conductors on each utility pole.

icefoglights:
I've seen photos of the socket with the prongs on the top that the cutout fits into (there's even one on eBay).  My question is what holds the socket in the light?  I couldn't see any method of holding the socket into the head or making electrical the connection to it.

Medved:
There are side contacts, that fit to the disc area, so when the socket is removed, thes contact short out, so keep the rest of the string working.

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