DOL Motor Starter Supply and Control Performance level e (PL e) example

This example shows the power supply and control of a direct-on-line (DOL) 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 three-phase supply is taken from the busbar -L1, -L2 and -L3 and connected to the motor circuit breaker -Q1. The motor circuit breaker provides protection for the motor circuit against short circuits and overloads.

The protected three-phase supply is then connected to two power contactors, -Q2 and -Q3, which are connected in series. Both contactors must be energized to supply power to the motor. Using two contactors provides redundant switching for the safety-related motor shutdown function.

The contactors -Q2 and -Q3 are controlled by the safety output Q320.0. The motor circuit breaker -Q1 also provides a feedback signal to the PLC, connected to input I301.7, allowing the control system to monitor the status of the motor circuit breaker.

The contactors -Q3 and -Q2 have an NC mirror contact used for feedback monitoring. This feedback signal is connected to PLC input I302.0, allowing the control system to monitor the actual state of the contactors and detect a failure of the contactor to open.

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.