Voltimetric Relay

Usually used in medium-sized commercial applications where start and run capacitors are present in the motor connection scheme. The voltmeter relay has normally closed contacts. The relay coil is connected in parallel with the starting coil of the compressor.
The starting coil voltage increases as the motor speed increases until the specific pick-up value is reached, at which point the relay armature is attracted by opening its contacts and disconnecting the starting capacitor from the circuit. After opening, there is enough induced voltage on the starter coil to continue attracting the armature and keeping the relay contacts open.