Operating principle
Control relay is used in combination with PTC thermistor probes (not supplied) for thermal protection of machines (motors, alternators, transformers, etc). The probes are placed at critical points on
the equipment to be protected (normally inserted into the stator windings of motors). The resistance of the PTC probe has a positive temperature coefficient. As soon as the nominal trip temperature
of the probe is exceeded, the resistance of the probe increases rapidly. Protection relay detects this and opens the power supply circuit of the protected equipment (eg motor) and the yellow fault
indicator LED lights up (version ETM2/ETM22).
Test button
The ETM2/ETM22 has a TEST button which can be used to simulate a thermal overload in order to test the service condition of the relay.
Tripping
The relay drops out as soon as the protected equipment is subjected to a thermal overload, short-circuit or break in the probe measuring circuit.
Early warning of tripping
If the equipment being protected has another PTC proble with a lower nominal trip temperature, a second ETM/ETM2/ETM22 relay can be used to give early warning of tripping and thus prevent
breaks in operation.
Control relay ETM/ETM2/ETM22 is automatically reset as soon as the temperature drops below the trip threshod (the yellow fault indicator LED goes out).
The relay is reset either using the RESET pushbutton on the front face or by opening the external contact S2 (remote reset), or by cutting the auxiliary power supply (terminals A1 - A2).
If the auxiliary power is cut for a period of time greater than the reset time (500 ms), the relay is reactivated if the proble detects a normal temperature when the power supply voltage is restored.
Unless otherwise specified, the characteristics given are applicable to all or part of the product range selected
