Why Choose the ABB CM-MSS.31S Thermistor Motor Protection Relay?
The ABB CM-MSS.31S (1SVR730712R1400) is a reliable thermistor motor protection relay designed to monitor electric motor winding temperatures and help protect motors against overheating, excessive thermal loading and insufficient cooling. Part of ABB's CM-MSS motor protection relay range, it works with compatible PTC thermistor temperature sensors installed in motor windings to provide temperature-dependent protection.
Operating from a wide 24–240 V AC/DC control supply, the CM-MSS.31S continuously evaluates its connected PTC sensor circuit. When the motor reaches the thermistor's specified response temperature, the relay changes its output state, allowing a connected motor starter, contactor or automation system to initiate a protective response.
The relay combines automatic, manual and remote reset options with sensor short-circuit detection, dynamic interrupted-wire detection and non-volatile fault storage. Its one normally open and one normally closed output contact, integrated Test/Reset button and compact 22.5 mm DIN rail-mounted housing make it a practical solution for industrial motor protection and electrical control panels.
Key Advantages
- Reliable PTC thermistor motor protection for industrial electric motors.
- Monitors motor winding temperature to detect thermal overload conditions.
- Helps protect motors against overheating and insufficient cooling.
- Wide 24–240 V AC/DC rated control supply supports different industrial control systems.
- One PTC sensor measuring circuit for temperature-dependent motor protection.
- Automatic, manual or remote reset provides flexible fault recovery options.
- Sensor short-circuit monitoring helps identify measuring circuit faults.
- Dynamic interrupted-wire detection supports reliable sensor circuit supervision.
- Non-volatile fault storage retains fault information through supply interruptions.
- One normally open and one normally closed contact supports control and alarm signalling.
- 250 V AC / 4 A output contact rating for compatible control loads.
- Closed-circuit operating principle supports protective switching behaviour.
- Integrated Test/Reset button simplifies commissioning and maintenance.
- LED indicators help distinguish operating conditions and fault causes.
- Compact 22.5 mm housing width saves space in motor control cabinets.
- Double-chamber cage screw terminals provide secure electrical connections.
- Designed in accordance with IEC/EN 60947-8 for thermistor motor protection devices.
- ATEX certification supports use in appropriately designed and approved motor protection installations, subject to certificate conditions.
Key Features
- ABB CM-MSS thermistor motor protection relay series.
- CM-MSS.31S model with screw-terminal connections.
- 24–240 V AC/DC rated control supply voltage.
- Designed for compatible PTC thermistor sensors.
- One temperature sensor measuring circuit.
- Temperature-dependent motor winding protection.
- Closed-circuit operating principle.
- One normally open (1 n/o) output contact.
- One normally closed (1 n/c) output contact.
- 250 V AC / 4 A output contact rating.
- Automatic reset option after the monitored fault clears.
- Manual reset option for controlled motor restart.
- Remote reset capability for compatible external control circuits.
- Integrated Test/Reset pushbutton.
- Short-circuit detection in the sensor circuit.
- Dynamic interrupted-wire detection in the sensor circuit.
- Non-volatile fault memory.
- LED status indication for operating and fault conditions.
- Overvoltage-protected supply and measuring inputs.
- Double-chamber cage screw-terminal technology.
- DIN rail mounting for industrial electrical panels.
- IP50 housing protection and IP20 terminal protection.
- Optional sealable transparent cover for protection of accessible settings.
Technical Specifications
- Manufacturer: ABB
- Series: CM-MSS Thermistor Motor Protection Relays
- Model: CM-MSS.31S
- ABB order code: 1SVR730712R1400
- ABB product group: 310921-Measuring & Monitoring Relays
- Product type: Thermistor motor protection relay
- Primary function: Motor winding temperature monitoring and thermal protection
- Rated control supply voltage: 24–240 V AC/DC
- Supply type: AC/DC
- Sensor type: PTC thermistor temperature sensors
- Sensor circuits: 1
- Measuring principle: PTC thermistor resistance monitoring
- Operating principle: Closed-circuit principle
- Output contacts: 1 normally open + 1 normally closed
- Contact configuration: 1 n/o + 1 n/c
- Output contact rating: 250 V AC / 4 A
- Reset options: Automatic, manual or remote
- Reset/Test control: Integrated Test/Reset button
- Sensor short-circuit detection: Yes
- Dynamic interrupted-wire detection: Yes
- Non-volatile fault storage: Yes
- Status indication: LED indicators for operating and fault conditions
- Supply and measuring input protection: Overvoltage protected
- Operating ambient temperature: -25 to +60 °C
- Storage temperature: -40 to +85 °C
- Housing protection rating: IP50
- Terminal protection rating: IP20
- Terminal type: Screw terminals
- Connection technology: Double-chamber cage screw terminals
- Mounting type: DIN rail mounting
- Product height: 85.6 mm
- Product width: 22.5 mm
- Product depth: 103.7 mm
- Dimensions (H × W × D): 85.6 × 22.5 × 103.7 mm
- Net weight: 0.128 kg
- EAN: 4013614496653
- Minimum order quantity: 1 piece
- Customs tariff number: 85364900
- Applicable product standard: IEC/EN 60947-8
- ATEX certification: Certified; application subject to relevant certificate conditions
- RoHS compliance: Following EU Directive 2011/65/EU
Reliable PTC Thermistor Protection for Industrial Motors
Industrial electric motors can experience excessive winding temperatures because of mechanical overload, frequent starting, inadequate ventilation, high ambient temperatures or abnormal operating conditions. These thermal stresses may damage motor insulation, shorten equipment service life and cause unexpected production downtime. The ABB CM-MSS.31S thermistor motor protection relay helps protect against these risks by monitoring temperature-sensitive PTC thermistors installed in the motor windings.
Unlike a conventional motor overload relay that estimates thermal conditions from electrical current, the CM-MSS.31S evaluates the resistance of the connected PTC thermistor sensor circuit. As the motor winding temperature approaches the thermistor's rated response temperature, sensor resistance increases sharply. The monitoring relay detects this change and switches its output contacts to signal a thermal fault.
The relay operates according to the closed-circuit principle. During normal operation, its output relay is energised when the supply and monitored sensor conditions are acceptable. When an overtemperature fault or specified sensor circuit fault occurs, the output relay releases, enabling a compatible motor contactor or control system to stop the motor or activate an alarm.
The CM-MSS.31S also monitors the integrity of its sensor circuit. Its short-circuit detection and dynamic interrupted-wire detection help identify faults that could compromise temperature monitoring. Non-volatile fault storage preserves fault information, supporting diagnosis after a supply interruption.
For fault recovery, the relay offers automatic, manual and remote reset modes. Automatic reset can be used where restart behaviour is controlled safely by the overall installation. Manual or remote reset provides an additional intervention step after the monitored fault has cleared. The appropriate reset mode should be selected according to the machine's safety requirements, particularly where unexpected motor restart could create a hazard.
The 24–240 V AC/DC supply range supports integration into a wide variety of motor control systems. With its compact DIN rail-mounted housing, screw terminals and integrated Test/Reset button, the CM-MSS.31S is suitable for motor control centres, machine control cabinets and industrial automation installations. It provides temperature monitoring and control signals rather than directly interrupting the motor's main power circuit.
Typical Applications
- PTC thermistor protection for industrial electric motors.
- Motor winding overtemperature monitoring.
- Industrial motor starter and contactor control circuits.
- Motor control centres and electrical control cabinets.
- Industrial pumps and pumping systems.
- Compressors and refrigeration machinery.
- Fans, blowers and industrial ventilation equipment.
- Conveyor systems and material handling machinery.
- Industrial mixers, agitators and process machinery.
- Manufacturing and production equipment.
- Automated machinery with embedded motor PTC sensors.
- Motor protection systems requiring manual or remote reset.
- Motor protection applications requiring sensor circuit fault detection.
- Suitable ATEX-related motor protection installations where the complete system meets the relevant approval conditions.
