Okay, so it's like this: my workshop has surface mount metal electrical boxes linked with metal conduit throughout. The switches (a single 2-gang box that housed two single pole switches side by side) that controlled the overhead lights were located in an asinine location (in the MIDDLE of the pitch-dark room filled with sharp stuff).
I decided I'd like to use the snazzy smart switch (with timer and occupancy sensor with built in override, et al) to manage the lot of em, so I figured I'd cut out both switches, join em together into one. It was only after I'd cut and spliced everything to right next to the main door I realized: there are two CIRCUITS running into that box. Two separate breakers, each controlling half the lights.
How CAN I wire things up such that the single smart switch acts as the power on/off for ALL the lights?
I have to assume there's some kind of switch that draws power from neutral (or, in this case, the load wire from the smart switch) that functionally is in an "on" stare when energized and off when not. I don't want to screw with trying to rewire the whole ceiling, nor do I want a sub panel. I acknowledge it's safer to keep the load shared across two 15A breakers, too.
But, because this fancy schmancy switch does all this sensor-driven hoopla, simply stitching in another fancy one won't work (there'll be edge case inconsistencies), and stitching a vanilla single-pole alongside it defeats the POINT of said schmanciness.
Really, what I need is some means to complete Circuit B when this switch governing Circuit A has Circuit A energized. Are there 15A relay switches rated for home electrical system use? Everything on both circuits is done on 12/2 (1971).
What kind of switch do I seek?