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Motor protecting switch units with 1, 2 or 3 switching steps are suitable for speed control of voltage-controlled 1-(MSE) or 3-(MSD) phase fans and offer optimal protection for motors with built-in thermal contacts or PTCs. The devices are available in various ratings and formats. Speed selection is done manually through the built-in step switch or through an external thermostat for automatic switch units. When using 3-speed motor switch units, their combination with the proper motor drive must be considered. Normally, motor protection is provided by thermal contacts. Motor protecting switch units for PTC connection are marked with a K in the type designation.