Rev4 G540 manual shows you connect one side of the DC relay coil to pin 6 and the other side of the coil to positive of the relay power supply. Negative from that PS goes to the negative motor power supply.
So you can power the step drives (in G540) and motors up to 50 volts. But relays are normally 12 or 24 volts. That’s why there are two PS.
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