Siemens SIRIUS 3RN2 Thermistor Motor Protection Relays
Siemens SIRIUS 3RN2 Thermistor Motor Protection Relays Suppliers, Exporters in India
Siemens SIRIUS 3RN2 Thermistor Motor Protection Relays monitor the actual temperature inside a motor winding. They work with PTC thermistor sensors fitted in the motor and trip the control circuit when the winding temperature reaches the sensor’s rated response point.
This direct temperature monitoring is useful in operating conditions where a standard overload relay alone may not provide complete protection. A motor can overheat because of frequent starting, heavy starting duty, high ambient temperature, blocked ventilation, reduced cooling or operation through a frequency converter. In such cases, the motor current may not always show the full heating condition.
The PTC sensors are normally installed in the motor winding by the motor manufacturer. When the temperature rises above the permitted level, the sensor resistance increases sharply. The 3RN2 relay detects this change and operates its output contacts so that the contactor or motor starter can disconnect the motor.
The Siemens 3RN2 range includes compact and standard evaluation units with automatic, manual or remote reset options. Selected models also provide sensor wire-break monitoring, short-circuit monitoring, fault memory and ATEX approval for motors used in hazardous areas.
ARP IMPEX supplies and exports Siemens SIRIUS 3RN2 Thermistor Motor Protection Relays for industrial motors, machine panels, pump systems, compressors and replacement requirements. Share the complete Siemens article number, control voltage, reset type and required quantity for price and availability.
Technical Specifications
- Brand: Siemens
- Product range: SIRIUS
- Series: 3RN2
- Product type: Thermistor motor protection relay
- Operating principle: Direct monitoring of motor winding temperature
- Sensor type: PTC thermistor sensors; selected versions also work with bimetallic temperature switches
- Available designs: Compact and standard evaluation units
- Housing width: 17.5 mm or 22.5 mm, depending on the model
- Control supply options: 24 V AC/DC or 24–240 V AC/DC, depending on the article number
- Output options: One changeover contact, one NO plus one NC contact, or two changeover contacts
- Reset options: Automatic, manual and remote reset, depending on the model
- Status indication: LED indication for ready and tripped conditions on applicable versions
- Sensor circuit monitoring: Wire-break and short-circuit monitoring on selected models
- Fault memory: Available on selected non-volatile versions
- Terminal options: Screw terminals or spring-loaded push-in terminals
- Mounting: DIN rail mounting
- ATEX approval: Available on selected models
- Electrical isolation: Standard or safe galvanic isolation, depending on the version
- Special versions: Models with two sensor circuits for warning and shutdown
- Applications: Motors, transformers and other equipment with built-in temperature sensors
The electrical arrangement and protection functions vary across the 3RN2 range. The complete Siemens article number should be checked before selecting a relay for a new motor or replacing an existing unit.
Features
- Measures temperature directly through sensors inside the motor winding
- Trips the motor control circuit when the permitted winding temperature is reached
- Protects motors during heavy starting and frequent start-stop operation
- Helps protect motors where cooling may be reduced or interrupted
- Works independently of the motor operating current
- Compact construction saves space inside the control panel
- Wide-range supply models reduce the need to stock several voltage variants
- Automatic, manual and remote reset versions are available
- LED indication shows the relay and trip condition
- Selected models detect broken or shorted sensor wiring
- Non-volatile versions retain the trip condition after a supply interruption
- Test and reset button available on applicable models
- Screw and push-in terminal versions suit different panel wiring practices
- Removable terminals simplify replacement without disturbing the complete wiring
- ATEX-approved models are available for explosion-protected motors
- Selected models provide separate warning and shutdown outputs
- Siemens offers models with permanent sensor-circuit monitoring and approved versions for
- motors used in areas exposed to gas or dust explosion risks.
- Why Use a Thermistor Protection Relay with an Overload Relay?
- A conventional overload relay mainly responds to the current drawn by the motor. The Siemens
- 3RN2 responds to the winding temperature measured by the built-in thermistor sensors.
Using both devices gives protection against different motor problems. The overload relay handles overload and stalled-motor conditions, while the 3RN2 monitors temperature caused by poor cooling, high ambient heat, frequent starting or other difficult operating conditions.
The 3RN2 should therefore not automatically be treated as a replacement for the motor overload relay. The protection arrangement should follow the motor manufacturer’s recommendation and the control-panel design. Siemens also describes the overload relay and 3RN2 as performing separate protection duties.
Applications
- Siemens SIRIUS 3RN2 Thermistor Motor Protection Relays are commonly used for:
- Pumps and pumping stations
- Air compressors
- Industrial fans and blowers
- Conveyor motors
- Crushers and material-handling equipment
- Machine tool motors
- HVAC motors
- Refrigeration compressors
- Mixers and agitators
- Centrifuges
- Hoists and cranes
- Motors with frequent starting duty
- Motors operating through variable-frequency drives
- Motors installed in high ambient temperatures
- Motors with restricted or external cooling
- Explosion-protected motors
- Process plant machinery
- Transformer winding temperature monitoring
- Industrial maintenance and replacement work
Siemens 3RN2 Thermistor Motor Protection Relay Supplier and Exporter
ARP IMPEX supplies Siemens SIRIUS 3RN2 Thermistor Motor Protection Relays for panel builders, OEM machine manufacturers, EPC contractors and industrial maintenance teams.
The 3RN2 range includes basic automatic-reset relays as well as models with manual reset, remote reset, sensor-circuit fault monitoring, trip memory and ATEX approval. Buyers should not select the relay only by its supply voltage. The sensor type, output contacts, reset arrangement and hazardous-area requirement must also match the application.
Siemens introduced the 3RN2 range as the successor to the older 3RN1 thermistor motor protection relays. For a replacement enquiry, share the complete 3RN1 or 3RN2 part number printed on the existing relay.
