I've worked on a few of these systems.
They were billed as a low cost way to get fancy switching configurations in a residential system. P&S still offers a selection of hardware. Look at
[i]Low Voltage Switching Copmponents[/i] .
The switches mount in standard Despard plates. The relays may be mounted in a cabinet in a mechanical area, or, more commonly, are mounted through the sidewall of the metal ceiling box that the controlled light fixture is mounted to.
Al
