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Comment by LeoPanthera | Hacker News Reader

Huh? Why not just use two wires and connect one wire to the other with each bulb.

Like this: http://www.planetchristmas.com/Images/MinisA.gif

I think the real answer is that if you did it this way (in traditional pre-transformer light sets), each bulb would have to be rated for 120v, or whatever your local line voltage is, which would make them both more expensive, and more dangerous.

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Interesting: That would suggest that if you let enough bulbs on a strand go out, you reach a cascading-failure threshold at some point, where the voltage across the remaining filaments is higher than their rating. And then I guess the breaker trips.

Yes, if you shunted enough of the bulbs in the strand you would get a cascading overvoltage down the line. It wouldn't trip a conventional breaker, though. Those bulbs can't pull enough power, even in over-voltage conditions. Might trip an Arc Fault Circuit Interrupter, though.

Higher voltage on the remaining filaments really just shortens their life. So yes it's a type of cascading failure, but it's not catastrophic (each set has a fuse in the plug anyway, otherwise that 28AWG wire would function as the filament of last resort, if you get my drift).

This means you want to replace burnt out bulbs when you notice them, rather than waiting for the whole segment to go dark.

That's not how parallel circuits work. The voltage is independent of how many devices are connected. That's how your wall plugs always provide 110V.

Edit: Sorry, I misread, I thought this subthread was about parallel circuits.

It's not a parallel circuit. It's a series circuit. If you have 100 bulbs in series, each is getting 1.1V across it.

If half of them burn out (and, as the article explains, become a short-circuit), then you have 50 bulbs, and each is getting 2.2V across it.

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The parent comment claimed that's not the case.

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