Resistor

Resistors, also known as PTC thermistors, are temperature-dependent semiconductor resistors whose main task is to change their electrical resistance significantly when their body temperature changes in the response range. PTC thermistors are mainly used to protect windings in electric motors or transformers from overheating. Other areas of application are machines and machine tools, especially machine bearings and the temperature monitoring of power semiconductors.

During installation, particular attention must be paid to good thermal contact between the sensors and the winding. The PTC thermistors should be embedded in the middle of the winding heads so that they are surrounded by the winding copper on all sides (at the warmest point). To install the PTC thermistor, the finished winding heads are to be spread open in the middle with a winding wood. The PTC thermistors must be inserted at least 40 mm parallel to the winding wires and, if necessary, additionally bandaged so that the winding wires are firmly in contact with the PTC thermistors.

PTC thermistors have an exact response range combined with small dimensions and low thermal inertia. The sensor leads consist of silver-plated copper strands with Teflon insulation.

Installing the PTC thermistor:

The PTC thermistor must be installed before the winding is impregnated.
Subsequent installation is not possible.

Each winding strand has a PTC thermistor. This means that 3 PTC thermistors must be installed in single-speed motors and 6 in pole-changing motors.

The sensors are arranged in series and routed to separate terminals in the terminal box.