> A changeover contactor is best ie one that is mechanically unable to 
 > close to both utility and generator at the same time. Unfortunately! these 
 > are uncommon and costly. Most designers use two separate contactors that 
If you're homebrewing a changeover contactor, look for a "reversing motor 
starter". These should be able to be scrounged from places that do salvage of 
industrial electrical equipment. They meet the requirements of being 
mechanically interlocked, plus usually have small contacts to provide 
electrical interlocking. Most of them have 120-volt coils (in the US) and are 
available in many sizes. Even a NEMA Size One would be large enough for many, 
and those will be quite common, being used for motors in the 10-15 HP range.
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