Most of the mechanically held lighting contactors that I've seen are more like a solenoid that drives a linkage over center on a cam. The contactor is either forced closed by the cam or allowed to spring open. The cam also switches a form c contact set with the "a" contact going to the "Open" terminal and the "b" contact going to the "Close" terminal. The common goes to the hi side of the coil. The contacts just have to stay closed long enough to guarantee that there is enough inertia to get the linkage over center. Even a mechanically held contactor will chatter or buzz if it doesn't make it.
Joe
