Siemens SIRIUS 3RN1 Thermistor Motor Protection Relay

Siemens SIRIUS 3RN1 Thermistor Motor Protection Relay Suppliers,Exporters in India

ARP IMPEX is a supplier and exporter of Siemens SIRIUS 3RN1 Thermistor Motor Protection Relays in India. We handle enquiries for existing motor control panels, industrial maintenance, replacement requirements and projects where the installed equipment still uses a Siemens 3RN1 relay.

The Siemens 3RN1 protects motors by monitoring temperature through PTC sensors fitted inside the motor winding. When the winding reaches the sensor’s rated response temperature, the sensor resistance rises sharply, and the relay changes the state of its output contacts. The control circuit can then stop the motor before continued heating damages the insulation or winding.

This type of protection is useful where motor temperature may rise without a matching increase in operating current. Long starting periods, frequent switching, low-speed operation with a frequency converter, high ambient temperature and poor ventilation are typical examples. A normal overload relay remains important for current-based protection, while the 3RN1 gives direct temperature-based protection from inside the motor.

The Siemens 3RN1 series includes different versions for basic motor temperature protection, manual or automatic reset, sensor-circuit fault monitoring, warning and tripping, and multi-motor monitoring. The exact control voltage, contact arrangement, reset method and terminal type depend on the complete part number.

Important Product Status

Siemens announced the phase-out of the SIRIUS 3RN1 range in 2017. The preferred successor is the Siemens SIRIUS 3RN2 series. Buyers looking for an exact 3RN1 replacement should therefore share the full old part number before ordering, as the matching 3RN2 model must have the correct supply voltage, reset method, output contacts and sensor-circuit functions.

ARP IMPEX handles enquiries for remaining Siemens 3RN1 requirements as well as suitable 3RN2 replacement models, subject to part-number verification and availability.

How the Siemens 3RN1 Is Used in a Motor Panel

PTC sensors are normally installed in the motor winding by the motor manufacturer. The sensor leads connect to the thermistor relay inside the control panel.

During normal operation, the sensor resistance remains below the relay’s trip level. If the winding temperature becomes too high, the resistance rises, and the 3RN1 operates its output contact. This contact is generally wired into the contactor or motor shutdown circuit.

The relay does not measure the motor load current. It responds to the actual temperature detected by the PTC sensors. For this reason, it can detect overheating caused by restricted cooling, repeated starts or high ambient temperature even when the motor current alone does not clearly indicate the problem.

Technical Specifications

• Brand: Siemens
• Product range: SIRIUS
• Series: 3RN1
• Product type: Thermistor motor protection relay
• Monitoring method: Direct temperature monitoring
• Sensor type: Type A PTC thermistor sensors
• Main function: Protection against excessive motor winding temperature
• Control supply: 24 V AC/DC to 240 V AC/DC, depending on the model
• Rated frequency: 50/60 Hz
• Reset options: Automatic, manual or remote, depending on the version
• Sensor circuits: One, two or multiple circuits, depending on the model
• Outputs: The relay contact arrangement depends on the complete part number
• Sensor fault monitoring: Wire-break and short-circuit detection on applicable versions
• Test facility: Test/reset button on manual-reset models
• Mounting: 35 mm DIN rail
• Alternative mounting: Screw mounting with an adapter
• Installation position: Any mounting position
• Degree of protection: IP20
• Operating temperature: Approximately –25°C to +60°C
• Storage temperature: Approximately –40°C to +80°C
• Standards: IEC 60947-8 and applicable industrial-control standards
• Approvals: Model-dependent; selected versions carried PTB, CSA, UL and marine approvals

These values cover the wider 3RN1 family. They should not be used to select a relay without checking the complete Siemens article number.

Models Covered Under the Siemens 3RN1 Range

The 3RN1 family was supplied in several versions, including:

• Siemens 3RN1000 compact thermistor protection units
• Siemens 3RN1010 standard evaluation units
• Siemens 3RN1011 thermistor motor protection relays
• Siemens 3RN1012 multifunction protection units
• Siemens 3RN1013 units with additional sensor-circuit monitoring
• Siemens 3RN1022 relays with separate warning and trip stages
• Siemens 3RN1062 units for monitoring several motors

The 3RN1022 uses two measuring circuits so that one stage can provide a warning before the second stage stops the motor. The 3RN1062 was designed for multi-motor protection and includes six measuring circuits with a common fault indication.

Part numbers within the same series can still differ considerably. For example, two 3RN1011 relays may have different control voltages, reset arrangements, terminals or output contacts.

Features

• Monitors the temperature directly inside the motor winding
• Works with PTC sensors selected according to the motor temperature limit
• Protects against overheating that may not be detected from current alone
• Useful during long and heavy motor starting
• Helps protect motors operating with frequent starts and stops
• Suitable for motors running at low speed with frequency converters
• Detects heating caused by blocked or insufficient motor cooling
• Manual, automatic and remote reset versions were available
• Applicable versions monitor sensor wiring for open circuit and short circuit
• Warning and shutdown stages were available within the range
• Multi-motor monitoring versions were also supplied
• DIN-rail construction suits motor control panels and MCCs
• Manual-reset models provide a test function through the front button
• Selected versions were suitable for motor-protection schemes involving explosive atmospheres
• Different contact and supply-voltage options suit various control circuits
• Can work alongside a thermal or electronic overload relay

The relay should generally form part of the complete motor-protection circuit rather than replace every other protective device. Current overload, phase failure, short circuit and temperature protection may require separate or combined devices according to the motor application.

Applications

Siemens SIRIUS 3RN1 Thermistor Motor Protection Relays were widely used for:

• Three-phase induction motors
• Motors with built-in PTC sensors
• Pumps and pumping stations
• Compressors
• Industrial fans and blowers
• Cooling-tower motors
• Conveyors
• Mixers and agitators
• Centrifuges
• Crushers and mills
• Motors with long starting times
• Motors with frequent switching cycles
• Variable-frequency drive applications
• Motors operating at reduced speed
• Equipment installed in high ambient temperatures
• Motors exposed to dust or restricted cooling
• Process-plant motor control panels
• Motor control centres
• Machine control panels
• Water and wastewater treatment plants
• Cement, steel and mining plants
• Chemical and petrochemical facilities
• Replacement of discontinued Siemens 3RN1 relays

The 3RN1 was also used for monitoring temperatures in transformer windings, bearings, oils and other equipment where compatible PTC sensors were installed.

Siemens 3RN1 Replacement with 3RN2

A Siemens 3RN2 should not be selected only because the first four characters are similar. The replacement must match the functions of the installed 3RN1.

The following points need to be checked:

• Existing 3RN1 article number
• Control supply voltage
• Number and type of output contacts
• Manual, automatic or remote reset
• Number of sensor circuits
• Requirement for wire-break or short-circuit detection
• Screw or spring-type terminals
• ATEX or other approval requirement
• Available panel width and terminal arrangement

Siemens states that the 3RN2 range succeeded the 3RN1 series and is functionally compatible with its predecessors, but the exact successor still depends on the old ordering code.

Siemens 3RN1 Supplier and Exporter in India

ARP IMPEX handles Siemens 3RN1 Thermistor Motor Protection Relay requirements for industrial users, panel builders, maintenance contractors, machine manufacturers and export buyers.

We handle enquiries for discontinued Siemens 3RN1 relay replacement, Siemens 3RN1011 price and availability, PTC motor winding protection relays, 3RN1-to-3RN2 replacement and thermistor relays for existing motor control panels.

For an accurate quotation, send the complete Siemens part number, required quantity and destination country. For replacement requirements, also share a clear photograph of the relay label and front terminal markings.