This part of IEC 60947 specifies rules for control units, which perform the switching functions in response to the thermal detectors incorporated in rotating electrical machines according to IEC 60034-11, and the industrial application. It specifies rules for that type of system comprising a positive temperature coefficient (PTC) thermistor detector having particular characteristics, and its associated control unit. The PT100 detectors are covered by IEC 60751, where the resistor values are given according to the temperatures of the detector. The present rules lay down the characteristics of association of this particular positive temperature coefficient th