A few days ago, i bought this remote-conrolled light switch. When installing it, i wondered why i had only two lines to connect (the one going to AC power and the one to the lamp); i thought i needed a ground connection as well to provide power to the electronics.
However, the switch works after connecting only two lines (L to AC and L2 to the lamp); it has some electronics inside, and does not seem to contain a battery. Where does it get the power from it needs for the electronics?
There actually is a complete circuit; hot side of the line through the switch then through the lamp and back to the ground side of the line.
When the lamp is supposed to be "off", the electronics "steals" just enough current to power itself, but not enough to light the lamp. When the lamp is on, again the switch steals just enough power to run itself.
This technique has been around a long time, it used to be used to provided illuminated light switches (typically using a NE-2 neon lamp), which would glow when the lamp is off.
This only works if current can be drawn through the lamp when the lamp s off. Obviously this works fine for conventional incandescent lamps. I would guess it doesn't work for CFL's. There is probably a list on the instructions.
