I suppose that I ought to expand a little on the "stuff that uses the ground path as a 'neutral' for the electronics."
I first saw this with some cheap timers. I later saw ti with soemphotocells.
There are a few clues that warn you this is the case. The most obvious is the lack of a neutral wire, along with a strong caution that the device will work properly only if installed wit a well-grounded circuit.
Another clue is a caution that the device may not work properly if there are other sensors or switches on the circuit.
Usually these are the cheaper controls.
The current flow in these cases is in the milli- or micro- amp range. In fairness, I have no idea as to just how much current is allowed. Also, there might be other electronic issues here besides operating current- I personally lack the patience to sit at a tech bench!
