I am designing a contactor for both DC and AC mainly for polarity independent circuit-breaker. It has a contactor unit, actuating solenoid, arc chute, Electromagnetic arc blow out coil Auxiliary contacts and base plate. Basically i got stuck in the Time constant measurement, ie the Bracking and Closing time. What does parallel connected diode to coil signify? The time constant measurement without protective device, with parallel connected varistor to coil, with parallel connected diode to coil all are coming the same. Attaching the drawing of the same for better understanding.