The paint‑shop conveyor control unit integrates an alternating‑current relay to manage the start‑stop sequencing of the belt motor. By receiving a low‑level command from the line controller, the relay switches the main power to the motor, creating a clear separation between the control electronics and the high‑current drive circuit. This arrangement protects the programmable logic controller from voltage spikes generated during sudden load changes, while allowing precise timing of belt acceleration and braking as vehicles move through the coating tunnel. In the body‑shop welding cell, the same type of relay is employed to energise the welding robot’s spindle motor only when the safety gate is closed, ensuring that the robot cannot start inadvertently. The relay’s mechanical contacts also serve as a visual indicator for maintenance staff, who can verify that the circuit is open during routine inspections. Across the assembly line, the device enables quick reconfiguration of motor feeds when a production line is adapted for a new model, reducing downtime and simplifying the change‑over process.