there is a little more info that you could provide to nail this down. you said the pitch of the generators is close..that isn't good enough. typically cummins generators are 2/3 pitch and cat are optimum pitch. this causes circulating current problems if the neutrals/ grounds are connected to a common point. the last ditch effort would be to float the cat neutral/ground or put a reactor in the line isolating the neutral/ground, ps you didn't say if this was delta or wye. get the serial number of the generator, call your local cat dealer and have him verify the pitch. second, the load share lines cannot be connected because cat uses 0 to 3 vac as their load share signal. cummins uses a 0 to 1 ma signal on their governor. the simple way to do this hookup would be to make sure the voltage droop is the same % on each regulator. than set the largest generator in isoc and the other in droop (governors. this will allow the isoc unit to be the base load unit and the droop generator will float with the load. oh yah, make sure your sync lights are wired correctly (if you have any)if the cat is a power module, there will be sync lights on the panel I think you might be in a bind from the beginning if you manual parallel because i think the power command controller does not have a manual parallel feature so the cat unit will have to parallel to the cummins unit. the neat thing about the isoc /droop setup is not having to worry about a load share gov. there are methods of isoc parallel but as an earlier responder said, it is $$$$$$ you have to convert one or the other load share sig. probably 10,000 or more depending on how much protective relaying you want.
