5-speed transformer fan speed controller for single-phase motors with thermal contacts. The (combined) maximum motor current is 7,5 A. The fan speed can be set via the rotary switch with OFF position. The motor can remotely be enabled or disabled via the digital inputs. The TK monitoring function deactivates the motor in case of overheating. After a power failure, the motor will automatically restart. The alarm output and the unregulated output can control external devices to generate alerts or to confirm normal operation. The enclosure can be surface mounted and offers an IP54 protection against ingress of dirt, dust and moisture. The fan speed is regulated by reducing the motor voltage via autotransformers in 5 steps. This technology generates an output voltage with perfect sinusoidal shape, guaranteeing quiet motor operation.