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if the butchered lamp doesn't have the same resistance as a good one,
then the others will have to carry more voltage across them,
so they won't last long !
 

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Slave to the grind
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High voltage might be able to bridge a small gap but...that dude's Uni-Brow could bridge the San Francisco Bay.:brows:
 

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Donuts > Fried Eggs
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Outta "Thanks" but thanks:
...The shunt wire contains a coating that gives it fairly high resistance until the filament fails. At that point, heat caused by current flowing through the shunt burns off the coating and reduces the shunt's resistance...
That's the part I was curious about.
 

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Fond of three phase
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It's called a shunt.
Most of the time, those shunts don't work, as intended. The shunt has some kind of a dielectric coating that doesn't always break down at full line voltage.
There is a gadget that is sold for $19.95, that's supposed to do the spark thing to locate open lamps.
They showed it on a Fox affiliate channel. The inventor couldn't get it to work either. He told the lady, she had too many bad lamps. :laughing:
 

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Donuts > Fried Eggs
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More on the shunt, apparently it's dead simple:
...It consists merely of a piece of OXIDIZED aluminum wire, wrapped around the lead-in wires, just above the bead in the lamp. At normal operating voltage the oxide coating acts as an insulator, and the current goes through the filament. But when a lamp burns out, There is an OPEN CIRCUIT, and, in all series wiring, that puts the FULL LINE VOLTAGE across the defective lamp, and the 120 volts will "BURN" through the extremely thin oxide coating on the shunt, causing the shunt to actually short the lamp out....

...This very same principal was applied to the old series incandescent street lights. The open circuit volts here though was typically either 2400 volts, or 4160 volts, and the shunt was in the socket, between two prongs. It was called a "FILM-DISC CUTOUT" and was a pair of metal discs about the size of a dime, or a little smaller, separated by a thin piece of silk cloth. When a lamp burned out, the high voltage would puncture through the silk, shorting the lamp socket out, and completeing the circuit. A voltage/current regulator compensated for blown lamps, so the others would not get more voltage! The mini-lights have no regulator, so as they fail and short, the remaining ones get more voltage.
Retiredspark, isn't the tester they sell just a little tic-tester? Seems like on old series strings without the shunt, you'd just be looking for the last place you had voltage. Not sure how it would work with a shunt, I guess it doesn't?
 

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this will save me a lot of trouble with a bad lamp.all i will have to do when they come back on is find the bad one & replace!:thumbup:
 

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Electric Al
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I used to try repairing my Christmas lights .

Very frustrating !

Now I just toss them out , they are not worth the frustration ! :mad:
 

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Keep in mind the shunt is a short circuit rather than a filament, when its activated the remaining bulbs will see a higher voltage. If enough bulbs are shorted "shunted" the remaining filaments begin to burn open triggering a chain reaction until the fuse burns out in the plug. By then nearly all bulbs are trshed so often one cant just replace the bulbs. Key is replacing burnt bulbs before they continue to add up.
 
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