The electrical protections that are found  on the power supply line of the motor can not be enough to ensure the protection of overloads. In fact, if the ventilation conditions worsen, the motor will overheat but the electrical conditions will not be modified, thus blocking the protection on the line. Special protections must be assembled on the windings to get round this problem.

Bimetal device A normally closed electromechanical device that opens electrically once the release temperature has been achieved; it will be automatically reset when the temperature falls below the release limit. Bimetal devices are available with various intervention temperatures and without automatic resetting, according to EN 60204-1. PTC Thermistor device This device has a resistance changing in a sudden and positive way once the intervention temperature has been achieved. PT100 device This device has a resistance that varies continuosuly and increasingly depending on the temperature. Electronic equipments are supplied to perform the continuous detection of the winding temperature.