That is even easier then what I had proposed-- no contactor necessary. Problem is it would not be legal when two switches were on. The contactors would avoid that.
I see what you are saying: If both switches are on , the wire are in parallel, which probably would not be allowed.
That's true if we are talking about a premisis wiring system, and the loads are something other than a control relay or some type of insturmentation. And you would be right - the contactors would always be a legit install.
But if it just so happens that the source, the switches and the loads are all together in some kind of black box, then the NEC might not apply, and the swtiches just might be OK. I guess since the detail showed a DC power supply, I was thinking of something more along these lines.