RDOL Motor Starter Supply and Control – Performance Level e (PL e)
This example shows the power supply and control of a reversing direct-on-line (RDOL) motor starter. The motor is supplied from a three-phase busbar, with the motor circuit protected and controlled by the components shown in the drawing. The circuit allows the motor to operate in both clockwise and counterclockwise directions.
The three-phase supply is taken from the busbar -L1, -L2 and -L3 and connected to the motor circuit breaker -Q7. The motor circuit breaker provides protection for the motor circuit against short circuits and overloads.
The protected three-phase supply is then connected to the reversing contactor assembly -Q9. This assembly contains two contactors that change the phase sequence supplied to the motor, allowing its direction of rotation to be reversed. The contactors are interlocked to prevent both directions from being activated simultaneously.
The reversing contactor assembly is controlled by two safety outputs:
Q320.2 – Motor start clockwise.
Q320.3 – Motor start counterclockwise.
A separate main contactor -Q8 is used to switch the motor power supply. It is controlled by safety output Q320.0. This provides an additional switching element for the safety-related motor shutdown function.
The circuit also includes feedback signals to the PLC, allowing the control system to monitor the status of the motor protection and switching devices:
I302.4 – Motor circuit breaker -Q7 feedback.
I302.5 – Clockwise contactor -Q9 feedback.
I302.6 – Counterclockwise contactor -Q9 feedback.
I302.7 – Main contactor -Q8 feedback.
These feedback signals allow the control system to monitor the actual switching states and detect discrepancies between the commanded and actual states of the motor starter.
Safety Note
This redundant contactor arrangement is designed to achieve Performance Level e (PL e) for the motor safety function in accordance with EN ISO 13849-1, as part of the machinery safety requirements of the Machinery Directive 2006/42/EC.
The achieved Performance Level must be confirmed through the complete safety-system design, including the required calculations, component characteristics, diagnostics, and validation. The contactor wiring alone does not establish PL e independently of the complete safety function.