Thermistor motor protection relay, Standard evaluation unit, 22,5mm enclosure, screw-type terminal, Control supply voltage: AC/DC 24-240 V, 2-change-over contact, 2 LEDs (Ready/Tripped), Reset: Manual/Auto/Remote, Safe galvanic isolation, Test/reset button, Wire break monitoring, Short circuit monitoring, non-volatile, with ATEX approval
Thermistor motor protection devices are used for direct monitoring of the motor winding temperature. For this purpose, the motors are equipped with temperature-dependent resistors (PTC) that are directly installed in the motor winding and abruptly change their resistance at their limit temperature.
SIRIUS 3RN2 thermistor motor protection relays are available in the following versions:
They comply with
The 3RN2 thermistor motor protection relays with ATEX approval fulfill SIL1 in compliance with EN 50495.
The terminals of the auxiliary contacts are designated in accordance with EN 60947-1.
3RN2 evaluation units are suitable for snap-on mounting onto TH 35 standard mounting rails according to IEC 60715 or for screw fixing using an adapter (accessory).
Direct motor protection through temperature monitoring of the motor winding offers 100% motor protection even under the most difficult ambient conditions, without the need to make adjustments on the device. Versions with hard gold-plated contacts ensure, in addition, a high switching reliability that is even higher than an electronic control.
The SIRIUS thermistor motor protection relays 3RN2011, 3RN2012-...30, 3RN2013 and 3RN2023 for PTC sensors are certified according to ATEX Ex II (2) G and D for environments with explosive gas or dust loads.
IEC 60204 stipulates that motors must be protected from overheating at a rating of 0.5 kW and higher. The protection can take the form of overload protection, overtemperature protection or current limiting.
For motors with frequent starting and braking and in environments where cooling may be impaired (e. g. by dust), it is recommended to use the overtemperature protection option in the form of a protective device coordinated with this mode of operation. A good choice in this case is the use of 3RN2 thermistor motor protection devices.
On rotor-critical motors, overtemperature detection in the stator windings can lead to delayed and hence inadequate protection. In this case the standards stipulate additional protection, e. g. by means of an overload relay.
This combination of thermistor motor protection and an overload relay is recommended for full motor protection in case of frequent starting and braking of motors, irregular intermittent duty or excessive switching frequency. To prevent premature tripping of the overload relay in such operating conditions, a higher setting than that normally required for the operational current is chosen. The overload relay then performs the stall protection, and the 3RN2 thermistor motor protection relay monitors the temperature of the motor windings.