Why Choose the ABB CM-MSS.33S Thermistor Motor Protection Relay?
The ABB CM-MSS.33S (1SVR730712R2200) is a high-performance thermistor motor protection relay designed to monitor electric motor winding temperatures and help protect industrial motors against overheating, thermal overload and insufficient cooling. Part of ABB's CM-MSS motor protection relay range, it works with compatible PTC thermistor temperature sensors embedded in motor windings to provide direct temperature-dependent protection.
Designed for 110–130 V AC or 220–240 V AC control supplies, the CM-MSS.33S provides flexible integration into industrial motor control systems. It features one PTC sensor measuring circuit, two change-over (SPDT) relay contacts and a closed-circuit operating principle that enables protective switching when excessive motor temperature or a monitored sensor fault is detected.
The ABB CM-MSS.33S combines automatic, manual and remote reset options with sensor short-circuit monitoring, dynamic interrupted-wire detection and integrated fault indication. Its compact 22.5 mm DIN rail-mounted housing, screw-terminal connections and front-mounted Test/Reset button make it suitable for industrial machinery, motor control centres and automated process installations.
Designed in accordance with IEC/EN 60947-8 and supported by relevant ATEX certification, the CM-MSS.33S provides a dependable solution for industrial motor temperature supervision where reliable detection of thermal faults is essential.
Key Advantages
- Reliable PTC thermistor motor protection for industrial electric motors.
- Directly monitors motor winding temperature through compatible embedded PTC sensors.
- Helps protect motors against overheating, thermal overload and insufficient cooling.
- Supports 110–130 V AC and 220–240 V AC control supplies.
- One PTC sensor measuring circuit for temperature-dependent motor protection.
- Two change-over (SPDT) output contacts for flexible motor control and alarm signalling.
- 250 V AC / 4 A contact rating for appropriately rated control circuits.
- Closed-circuit operating principle supports protective fault signalling.
- Automatic, manual and remote reset options suit different motor control requirements.
- Integrated Test/Reset button supports commissioning and maintenance.
- Sensor short-circuit monitoring helps identify faults in the thermistor circuit.
- Dynamic interrupted-wire detection provides additional sensor circuit supervision.
- LED indicators help distinguish operating conditions and fault causes.
- Overvoltage-protected supply and measuring inputs support reliable industrial operation.
- Compact 22.5 mm housing width saves control cabinet space.
- Double-chamber cage screw terminals provide secure electrical connections.
- Suitable for appropriately designed ATEX-related motor protection applications, subject to the applicable approval conditions.
- Designed in accordance with IEC/EN 60947-8 for thermistor motor protection devices.
Key Features
- ABB CM-MSS thermistor motor protection relay series.
- CM-MSS.33S model with screw-terminal connections.
- 110–130 V AC / 220–240 V AC rated control supply voltage.
- 50/60 Hz AC supply operation.
- Compatible with suitable PTC thermistor temperature sensors.
- One temperature sensor measuring circuit.
- Direct temperature-dependent motor winding protection.
- Closed-circuit operating principle.
- Two change-over (SPDT) relay contacts.
- 250 V AC / 4 A output contact rating.
- Automatic reset after the monitored fault clears.
- Manual reset for controlled fault acknowledgement.
- Remote reset capability for compatible external control circuits.
- Integrated Test/Reset pushbutton.
- Short-circuit detection in the PTC sensor circuit.
- Dynamic interrupted-wire detection in the sensor circuit.
- LED indication for operating status and fault diagnosis.
- Overvoltage-protected supply and measuring inputs.
- Double-chamber cage screw-terminal technology.
- DIN rail mounting for industrial electrical panels.
- 22.5 mm compact housing width.
- IP50 housing protection and IP20 terminal protection.
- Optional sealable transparent cover for protection against unauthorised adjustment.
- Designed to meet IEC/EN 60947-8 requirements.
- ATEX-certified product, with use subject to the applicable certificate and installation requirements.
Technical Specifications
- Manufacturer: ABB
- Series: CM-MSS Thermistor Motor Protection Relays
- Model: CM-MSS.33S
- ABB order code: 1SVR730712R2200
- 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: 110–130 V AC or 220–240 V AC
- Supply type: AC
- Supply frequency: 50/60 Hz
- Sensor type: PTC thermistor temperature sensors
- Sensor measuring circuits: 1
- Measuring principle: PTC thermistor resistance monitoring
- Operating principle: Closed-circuit principle
- Output contacts: 2 change-over contacts
- Contact configuration: 2 c/o (2 × SPDT)
- Output contact rating: 250 V AC / 4 A
- Reset options: Automatic, manual or remote
- Test/Reset control: Integrated front-mounted Test/Reset button
- Sensor short-circuit monitoring: Yes
- Dynamic interrupted-wire detection: 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: 0.172 kg
- EAN: 4013614496646
- Minimum order quantity: 1 piece
- Customs tariff number: 85364900
- Applicable product standard: IEC/EN 60947-8
- ATEX certification: EU Type Examination Certificate TPS 18 ATEX 044254 0018 X; application subject to certificate conditions
- RoHS status: Following EU Directive 2011/65/EU
Reliable PTC Thermistor Protection for Industrial Motors and Machinery
Industrial electric motors are exposed to thermal stresses caused by excessive mechanical loading, frequent starting, restricted ventilation, high ambient temperatures and abnormal operating conditions. If motor winding temperatures rise beyond their permitted limits, insulation damage and premature motor failure can occur. The ABB CM-MSS.33S thermistor motor protection relay helps reduce these risks by monitoring temperature-sensitive PTC thermistors installed in the motor windings.
Unlike conventional overload protection devices that estimate motor heating from electrical current, the CM-MSS.33S evaluates the resistance of the connected PTC sensor circuit. As the motor winding temperature approaches the sensor's rated response temperature, the thermistor resistance increases sharply. The relay detects this change and switches its output contacts to signal an overtemperature condition.
The closed-circuit operating principle supports protective monitoring. Under normal operating conditions, the relay output is energised when the supply and sensor circuit are healthy. When the monitored motor temperature exceeds the PTC response threshold, or a specified sensor fault occurs, the output relay releases. This switching signal can be used to operate a suitable motor contactor, activate an alarm or notify an industrial controller.
The relay provides two change-over output contacts, allowing flexible integration into motor control and alarm circuits. One contact may be used for a motor starter control circuit while the other provides a separate indication to a programmable logic controller or alarm system, subject to the installation design and contact ratings.
The CM-MSS.33S also supervises the integrity of its thermistor measuring circuit. Short-circuit monitoring and dynamic interrupted-wire detection help identify sensor wiring faults that could otherwise compromise temperature monitoring. Its LED indicators assist maintenance personnel in distinguishing different operating and fault conditions.
The automatic, manual and remote reset functions allow the relay to be configured for different motor control requirements. Automatic reset is suitable only where the overall system prevents hazardous unexpected restarting. Manual or remote reset provides an additional acknowledgement step after the monitored fault has cleared, supporting controlled restart procedures.
With a choice of 110–130 V AC or 220–240 V AC control supply operation, the CM-MSS.33S can be integrated into compatible industrial control voltage arrangements. Its compact DIN rail housing, double-chamber cage screw terminals and front-mounted Test/Reset button simplify installation and maintenance.
The relay is designed in accordance with IEC/EN 60947-8 and has relevant ATEX certification. Where it is used as part of an explosion-protection-related motor installation, the complete protective arrangement must comply with the applicable certificate, motor and installation requirements. The CM-MSS.33S is a monitoring and control device rather than a direct motor power switching or short-circuit protection device.
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 equipment.
- Manufacturing and production machinery.
- Automated machinery incorporating embedded motor PTC sensors.
- Motor protection systems requiring manual or remote reset.
- Industrial equipment requiring sensor short-circuit and interrupted-wire detection.
- Applications using 110–130 V AC or 220–240 V AC control circuits.
- Appropriately designed ATEX-related motor protection installations, subject to relevant certification requirements.
