crash, I think most of us are uneasy about mixing systems in a conduit or control box, but sometimes it is unavoidable. I will add that when I open a box with multiple circuits and find installation notes written on the cover in jiffy marker, I don't care if the entire building is wired in extension cord, I still think the person who left the notes is the greatest electrician in the world.
As to circuits interfering with each other, the only time I saw a problem was where a contactor was mounted beside a circuit board. It was a system that counted pulses and the contactor would interfere with the count.
Hopefully, someone with more experience will stop by.
