The control circuit is derived directly from the ship power circuit. The control circuit provides power to the timers, relays, switches and other components: necessary to control the operating contacts of the main component in the power circuit.
The ‘control circuit’ controls the normally open contacts (and in some cases normally closed contacts too) in die power circuit that for example turn on or turn off the main component.
It is almost always a single-phase derivative from a three-phase power circuit: The control circuit generally consists of cables intended to carry lower currents or will be applied with lower voltages than the power circuit.
In short, the control circuit provides the logic behind the operation of the main component in the power circuit.
Control circuit is clearly separated from the power circuit with the help of a step-down transformer. Here the main focus is on controlling the main contactor coil KM which in turn has its normally open contacts in the power circuit of the 3-phase direct-on-line-started motor.