• Controls temperature of machines using built-in PTC probes
  • Line break or probe short-circuit detection
  • Fault latching function
  • Pushbutton for local reset
  • Remote reset via external contact
  • Pushbutton test facility
  • 2 LEDs to indicate relay and power supply status
OutputSupply voltageCode
2 changeovers24 V ∿/⎓84874035 Obsolete
2 changeovers120 V ∿84874033 Obsolete
2 changeovers230 V ∿84874034 Obsolete


Supply voltage Un 230, 120 and 24 VAC 50 / 60 Hz Galvanic isolation by transformer 24 VDC no galvanic isolation
Operating range 0.85 to 1.10 Un
Nominal power 3 VA
Maximal power 5 VA
Immunity from micro power cuts 10 ms
Delay on pick-up 500 ms
Insulation coordination Category III, degree of pollution 2 conforming to IEC/EN 60664-1 / VDE 0110 : 4 KV/2

Max. resistance of cold probes 1500 Ω
Trip threshold 3100 Ω ± 10 %
Reset threshold 1650 Ω ± 10 %
Short-circuit detection 0 - 10 Ω
Measurement voltage as per IEC/EN 60034-11 ≤ 2,5 V
Repetition accuracy with constant parameters ± 0.5 %
Temperature drift ± 0.05 % / oC
Voltage-dependent drift -2 %

Output AgNi 90/10
Breaking capacity 2000 VA / 80 W
Max. breaking current 8 A ∿
Max. breaking voltage 440 V ∿
Min. breaking current 100 mA
Maximum rate 360 operations / hour at full load
Mechanical life (operations) 5 x 106
Electrical life AC12 : 2000 VA - 105 operations AC15 : Cos φ = 0,3 - 6000 operations DC13 : L/R = 300 ms - 6000 operations

Reset time ≤ 500 ms
Response time ≤ 500 ms
Display on ETM2/ETM22 - power supply green LED
Display on ETM2/ETM22 - Relay yellow LED
Class of protection (IEC EN/60529) - Term. block IP 20
Protection class (IEC EN/60529) - Casing IP 50
Housing material Self-extinguishing
Weight (g) 145
Terminal capacity 2 x 1.5 mm2 with ferrule 2 x 2.5 mm2 without ferrule
Temperature limit operation (IEC 68.1.14) (°C) -20 →+60 °C
Temperature limits stored (IEC 68.1.1/2) (°C) -30 →+70 °C
Relative humidity (no condensation) 95 % (+2 % ; -3 %)

Technical sketches

Reset WITHOUT fault latching (Y1 and Y2 not connected for ETM2/ETM22)

Reset  WITHOUT fault latching (Y1 and Y2 not connected for ETM2/ETM22)
Unit power-up
Resistance between terminals T1 and T2
Output relay
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). 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. 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. 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).

Reset WITH fault latching (only for ETM2/ETM22) (Y1 and Y2 connected)

Reset WITH fault latching (only for ETM2/ETM22)  (Y1 and Y2 connected)
Unit power-up
Latching contact
Resistance between terminals T1 and T2
Output relay
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.

PTC probe specification According to standard IEC/EN 60034-11

PTC probe specification

According to standard IEC/EN 60034-11
Resistance R (Ω)
Nominal temprerature Tripping (°C)

ETM / ETM2 / ETM22

ETM / ETM2 / ETM22


A1 - A2 : supply voltage-
11 - 12 -14 : low treshold output relay (R1)-
21 - 22 -24 : high treshold output relay (R2)-
T1 -T2 : external PTC probe-
Y1 - Y2 : remote reset contact-



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