In the starting solenoied valve of the Arriel 1 is the "start inhibitor" switch. At 45% N1 round about pending atmospheric conditions, the centrifugal compressor air pressure closes the switch thus inhibiting the starting cycle and bleed the injectors. Due to this action the generator will come online if selected on once it's voltage is o.5V above the batteries/ground power.
When you do the maintenance check referred to, you are actually checking the working of the switch in the starting solenoid valve.
Hope it helps and enjoy your 350!