Wiring a lamp in this manner is illegal in some countries. One of the off positions delivers line voltage to the lamp, making it less than idiot-proof.
I voted you up because you cite such a good source, but please note that the diagram in the article shows one wire between just the lamp and the switches, i.e. the Carter system. The common system would have an unswitched wire to neutral, as shown and described in the wikipedia article you cited.
The way I see it is that the article simplifies by just saying "lamp" for the lamp and mains, because the only relevant part to the article is the switching part. For it to be the Carter system, the mains live (hot) and neutral have to be connected to a pair of wires in the switching part.
I think the article does not mention the mains details because the neutral wiring never even enters the switch, as in the switch on the wall which he unscrewed as a child. Perhaps the diagrams would have been a bit better if the bottom part was
The line in the diagram connects the lamp to both switches. You can't say it's the common system with parts omitted for simplicity. It has a part included that only exists in the Carter system.
Looking at the diagrams again, I suppose such an interpretation is possible. I still maintain that the diagram is ambiguous due to the mains connections being left out entirely.
Really? In North America, black is hot and white is neutral, and you always switch (and fuse, and breaker) the black wire.
"A neutral wire is the return leg of a circuit; in building wiring systems the neutral wire is connected to earth ground at least at one point. North American standards state that the neutral is neither switched nor fused. The neutral is connected to the center tap of the power company transformer of a split-phase system, or the center of the wye connection of a polyphase power system. American electrical codes require that the neutral be connected to earth at the "service panel" only and at no other point within the building wiring system. Formally the neutral is called the "grounded conductor"; as of the 2008 NEC, the terms "neutral conductor" and "neutral point" have been defined in the Code to record what had been common usage. [1]
Hot is any conductor (wire or otherwise) connected with an electrical system that has electric potential to electrical ground or neutral."
I think they meant it is not uncommon for someone to mistakenly rewire a switch so that the neutral line is switched.
In high school I worked in a hardware store (where I first learned how a 3-way light worked) and you would be surprised at how often someone would want to return a light switch as faulty after they incorrectly wired it. The symptoms were always the same. They turn the breaker back on after replacing the switch and either the breaker trips immediately, or the light is on and when they flip the switch the breaker trips. Inside the switch box they would connect white to white and black to black (because that is always the way to hook-up wires, right?) and then hook white to one side of the switch and black to the other. God only knows how many switched the white wire and were happy they "fixed" the switch -- until they try to unscrew a broken light bulb.
