Q.How long is the interconnect from the uC to the motor ?
A. The motor connections are routed to the controller via contactors which are switched from relays which in turn are switched using darlington config transistors.controlled through optocouplers the wiring is approximately 2mts in length.

Q.Is the uC powered from a separate power line ?
A. the uC is powered through a 5V, 5A rated SMPS the connections do not in any physical form mix with the other voltages used in the power circuits (i.e. 12V DC, 24V DC, 220VAC)

Q.How do you power the side of the optocouplers that face the motor ?
A. The opto is powered by a 12V 5A rated SMPS
the opto drives a darlington config transistor which energizes the relays.

EDGAR-- What do you mean by "Real Earth"?