Here is an example of a potential relay rating specification. The continuous coil voltage is 300; pick-up voltage is 285 minimum and 305 maximum; and the dropout voltage is 77 maximum. The pick-up voltage for a specific potential relay will be listed as a minimum and a maximum. The actual pick-up voltage must stay within its range for proper operation. The pick-up is the back electro-magnetic field (EMF) voltage generated across the start winding by the motor's rotor when it is up to about ¼ speed.
If the pick-up voltage generated by back EMF is under the minimum, the contacts between terminals one and two will never open. The start capacitor will then stay in the circuit. This will cause high amp draws and open motor protective devices.