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I have a stairway light in my house. There are two switches, one upstairs and one downstairs. When both switches are in the "off" position, the light is off. When one switch is in the "on" position, the light is on. When both switches are in the "on" position, the light is off. This means that by flicking only one of the switches, the light will change from on to off or from off to on.

I understand how parallel circuits and series circuits work, but this circuit doesn't seem to be any one of them. Could someone explain how this circuit works?

Thanks

Peter Ye
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    Probably like this: https://commons.wikimedia.org/wiki/File:3-way_switches_position_1.svg –  Mar 07 '18 at 22:34
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    This reminds me of a line from Horowitz's and Hill's Art of Electronics, something along the lines of "The rare electrical engineer, and every electrician, knows how to wire up a circuit so that any one of N switches can turn a light on or off." See here for the general solution: just keep adding 4-way switches. – Chemomechanics Mar 07 '18 at 23:37
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    It reminds me of the puzzle - how do you wire up a single light in a lighthouse with 30 or more floors and on/off switching required on every floor.............................. a single switch at the top with a very long string.... – tom Mar 08 '18 at 01:12
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    I'm voting to close this question as off-topic because it's not a physics question. [diy.se] might be more appropriate for this question. – Kyle Kanos Mar 08 '18 at 11:28

1 Answers1

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There are two lines between the two switches.

enter image description here

Hope the circuit makes sense.

consider what happens when either switch is switched....

tom
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