Note, I don't think this belongs in DIY; it's a bit more complicated than that.
I bought a Lutron Maestro occupancy sensor switch, and was perplexed to learn that it doesn't need a neutral in the switch box (they brag about this as a feature, and the instructions don't mention it).
Note that in addition to the line and load (black) wires, the switch has both a bare wire and a green wire (drawing on top of 2nd page). I'm thinking maybe the bare wire (which is connected to the yoke) is the "real" ground and the green one carries the return current from the sensor and logic circuitry. But the instructions say to tie both to the switch box's ground
This seems most odd to me. I thought the whole point of NEC rule 404.2C, which requires a neutral in every switch box (with a few exceptions), is that when "smart" devices such as this are installed, that no currents are introduced into the grounding system.
I wonder what's going on. Is it:
Does the switch somehow not return any current to ground ? I'm not sure this is possible, unless there's some sort of charge pump or something working off the hot wire(s).
Does the switch's logic sensor and logic circuitry use so little current that it is deemed (by UL and/or NEC) acceptable for those currents to flow through the EGC ? I did not know there was a threshold.
This is only meant for retrofits into older construction not compliant with 404.2(C) ? Would this even be legal ? And if so, why don't the instructions say to tie one of the wires (presumably the green one) to a neutral if it is present ?