Motor Generators

For the 4th MG set?

You are quite right that three contactors are enough, even for a closed-transition (Korndorfer) starter. Maybe he wants to use a contactor as the isolator also? Not a good idea.

I can't think what the 4^th contactor could be for. But at least you're doing away with the oil switches. They are a death trap! If they convert the starters it would be best if they go for a Korndorffer set up the transition is much smoother.

Sorry for my earlier comment. If we are talking about a group of contactors for each MG, what does the proposed schematic show that would use four?

This is just an outline proposal at the moment, no real details given. I went through the preamble which mentioned the vacuum contactors and changing from open transition to Korndorffer. I for one won't be sorry to lose the open transition oil switches.

Like most things this is all going to come down to the bean counters decision, what has engineering got to do with it!