Voltage monitor Relay connection
Learn how to wire a voltage monitor relay in a DOL starter to protect 3-phase motors from phase loss, phase reversal, and voltage faults with easy connection steps.
voltage monitor relay wiring diagram
A voltage monitor relay may be applied in a DOL starter by connecting the three-phase supply to the sensing terminals on the relay, via its NO contact in series with the start button and contactor coil, and the relay output to the overload relay. That is, this provides automatic motor trip upon phase faults.
Formula & Table Summary:
Motor Start Condition: Voltage Healthy + Correct Phase Sequence + Overload NC = Contactor Energized
dol starter control circuit with relay
A voltage monitor relay (phase failure relay) within a DOL starter protects a motor against damage under conditions of phase loss, phase sequence improper, or abnormal voltage. This type of wiring has the relay sense all three phases (l1, l2 and l3) and as such will only enable the contactor to energize when correct conditions are met. Its normally open (NO) output contact has been connected in series with the starter control circuit so that only healthy voltage and phase conditions will cause the motor to start. Provided there is a fault, then the relay will break open the circuit immediately, shutting off the motor and creating no damage. Four -wire connection is a necessitated approach to safety and reliability of industrial 3-phase motors.
motor protection relay connection
| Condition | Relay Output | Motor Status |
|---|---|---|
| All phases OK | Closed | Running |
| Phase loss | Open | Stopped |
| Phase reversal | Open | Stopped |
