Dave Plowman (News) wrote:
In article ,
Sam Goldwasser wrote:

This can't be done unless you have a neutral at the switch position.
When the switch is on there is no potential difference between the
terminals therefore no power source.


It could be battery or supercap powered.


Might be difficult to fit all this inside a switch backing box?


Or, if the box is grounded, there will be line voltage between the load
side and the box in a correctly wired normal (not 3-way) circuit.


I hope you're not recommending this? In the UK it would be forbidden - not
least because it unbalances the line and neutral.



UK electrical boxes are incredibly tiny compared to those in the
US/Canada. Our standard boxes are 2.5" deep but you can get them up to
4" deep in the standard 3.5"x2" size used for single switches and
receptacles.


Connecting between line and ground would not be legal by code, but if
the circuit is designed carefully it would not be a danger either. I'd
lean towards powering it with a battery personally, much safer for the
novice.