I agree with Ben (sort of). I don't think the problem is transients and brownouts coming from outside as much as I think the transient and brownouts are generated by the system and back-feeding the 975. I'm concerned that the number of amps on the one circuit are causing high inrush currents (transients) and POSSIBLY low power factor (a potential source of brownouts) although I need to think about this some more. Adding protection to the input power is unlikely to solve the problem UNLESS it also isolates the individual loads from each other

BTW, It does makes sense to me that a floating neutral on a 240 volt feed to a dryer would cause a lot of problems with voltage levels on individual circuits as the input to your house is a center tapped transformer. Doesn't explain the third unit failure though.