Why Choose the ABB CM-MSS.32P Thermistor Motor Protection Relay?
The ABB CM-MSS.32P (1SVR740712R0200) is an industrial thermistor motor protection relay designed to monitor motor winding temperatures using PTC thermistor sensors. Part of ABB's CM-MSS measuring and monitoring relay range, it helps protect electric motors against overheating caused by excessive loading, inadequate cooling and demanding operating conditions.
Operating from a 24 V AC/DC control supply, the CM-MSS.32P features one PTC thermistor measuring circuit and two changeover (SPDT) output contacts rated at 250 V / 4 A. It operates according to the closed-circuit principle and includes both sensor short-circuit detection and dynamic interrupted-wire monitoring, providing additional diagnostic capability beyond basic temperature supervision.
The CM-MSS.32P also supports automatic, manual or remote reset after a fault has cleared. Its ATEX-certified protection functionality, combined reset/test button, maintenance-free Easy Connect push-in terminals and compact 22.5 mm DIN rail housing make it a practical choice for industrial motor control centres, production machinery and suitable hazardous-area motor protection applications.
Key Advantages
- Direct motor winding temperature monitoring using compatible PTC thermistor sensors.
- Helps protect industrial motors against overheating caused by overload and insufficient cooling.
- 24 V AC/DC control supply for industrial automation circuits.
- One PTC sensor measuring circuit for motor temperature supervision.
- Two changeover (SPDT) output contacts rated at 250 V / 4 A.
- Sensor short-circuit detection helps identify faults in the measuring circuit.
- Dynamic interrupted-wire detection supports diagnosis of damaged or disconnected sensor wiring.
- Automatic, manual or remote reset provides flexibility for different operating requirements.
- Closed-circuit operating principle supports dependable motor fault signalling.
- ATEX-certified thermistor motor protection functionality for applications within the applicable certification conditions.
- Combined reset/test button simplifies local operation and functional checks.
- ABB Easy Connect push-in terminals support efficient, maintenance-free wiring.
- Compact 22.5 mm housing width helps conserve control cabinet space.
- Tool-free DIN rail mounting and removal.
- Operating temperature range of −25 to +60 °C.
- Optional sealable transparent cover helps prevent unauthorised changes.
Key Features
- ABB CM-MSS.32P thermistor motor protection relay.
- Manufacturer order code: 1SVR740712R0200.
- Rated control supply voltage: 24 V AC/DC.
- Monitoring function: Motor winding temperature protection.
- Sensor technology: PTC thermistors.
- Number of sensor circuits: 1.
- Sensor short-circuit monitoring: Integrated.
- Interrupted-wire monitoring: Dynamic detection.
- Reset options: Automatic, manual or remote.
- Local operation: Combined reset/test button.
- Operating principle: Closed-circuit principle.
- Output configuration: 2 changeover (SPDT) contacts.
- Contact rating: 250 V / 4 A.
- ATEX certification: Thermistor motor protection function.
- Terminal technology: ABB Easy Connect push-in terminals.
- Connection method: Screwless spring-clamp connection.
- Mounting: DIN rail.
- Housing dimensions: 85.6 × 22.5 × 103.7 mm.
- Product net weight: 0.120 kg.
- Optional sealable transparent protective cover.
Technical Specifications
- Manufacturer: ABB
- Product series: CM-MSS
- Model: CM-MSS.32P
- ABB order code: 1SVR740712R0200
- ABB product group: 310921-Measuring & Monitoring Relays
- Product type: Thermistor motor protection relay
- Rated control supply voltage: 24 V AC/DC
- Monitoring function: Motor winding temperature monitoring
- Temperature sensor type: PTC thermistors
- Number of sensor circuits: 1
- Sensor short-circuit detection: Yes
- Dynamic interrupted-wire detection: Yes
- Reset functions: Automatic, manual or remote
- Local reset/test: Combined front-mounted button
- Operating principle: Closed-circuit principle
- Output contacts: 2 changeover (SPDT)
- Output contact rating: 250 V / 4 A
- UL/CSA contact rating: B300
- Maximum UL/CSA output operating voltage: 300 V AC
- ATEX approval: Yes, subject to applicable certificate conditions
- ATEX certificate reference: TPS 18 ATEX 044254 0018 X
- Terminal type: Easy Connect push-in terminals
- Connection technology: Screwless spring-clamp
- Mounting type: DIN rail mounting
- Operating ambient temperature: −25 to +60 °C
- Storage temperature: −40 to +85 °C
- Dimensions (H × W × D): 85.6 × 22.5 × 103.7 mm
- Product net weight: 0.120 kg
- EAN: 4013614496578
- Customs tariff number: 85364900
Reliable PTC Thermistor Motor Temperature Protection
The ABB CM-MSS.32P monitors the resistance of PTC thermistor sensors installed within electric motor windings. When the motor temperature approaches the thermistor's specified response temperature, sensor resistance increases sharply. The relay detects this resistance change and switches its output contacts to indicate an excessive temperature condition.
Unlike protection methods that rely exclusively on motor current, PTC thermistor monitoring responds to the actual thermal condition of the motor windings. This helps identify overheating associated with mechanical overload, repeated starting, inadequate ventilation, elevated ambient temperature or other demanding operating conditions.
The relay operates according to the closed-circuit principle. During healthy operation, its output relay is energised; when a relevant fault occurs, the relay changes state. This arrangement supports fault-responsive control circuits when correctly connected to suitable external switching equipment.
With two changeover contacts, the CM-MSS.32P can provide suitable signals for motor contactor control, PLC monitoring and alarm indication. The contacts are intended for control functions and do not replace appropriately rated motor power switching or short-circuit protection devices.
Advanced Sensor Circuit Diagnostics
In addition to monitoring motor winding temperature, the CM-MSS.32P supervises the condition of its PTC sensor circuit. This helps identify faults that could otherwise interfere with reliable thermal monitoring.
Sensor short-circuit detection identifies an abnormally low-resistance condition in the measuring circuit. Such a condition may indicate damaged sensor wiring or another fault requiring investigation.
Dynamic interrupted-wire detection provides additional supervision for disconnected or damaged PTC sensor connections. By detecting interruptions in the measuring circuit, the relay helps maintenance personnel distinguish sensor circuit faults from genuine motor overheating conditions.
These diagnostic functions are particularly valuable in industrial machinery where sensor wiring may be exposed to vibration, movement, heat or other demanding environmental conditions.
ATEX-Certified Motor Protection Functionality
The ABB CM-MSS.32P has an ATEX-certified thermistor motor protection function, making it suitable for consideration in motor protection arrangements where the relevant explosion-protection requirements apply.
The ATEX certification relates to the relay's specified protective function and must be interpreted together with the applicable certificate, installation instructions and conditions of use. The certificate reference associated with this model is TPS 18 ATEX 044254 0018 X.
ATEX certification does not mean that the relay itself may automatically be installed inside a hazardous area. Its installation location, connected motor, sensor arrangement and overall protective system must comply with the applicable certificate conditions and electrical installation requirements.
For applications involving potentially explosive atmospheres, the complete motor protection design should be assessed by suitably qualified personnel against the current ABB certification documentation and applicable standards.
Flexible Reset Functions and Operational Control
The CM-MSS.32P supports automatic, manual and remote reset after the monitored fault condition has cleared. These options allow the device to be configured for different industrial operating and maintenance requirements.
With automatic reset, the relay can return to its normal state once the motor temperature and sensor circuit conditions are acceptable. Manual reset requires deliberate operator intervention, while remote reset supports integration with an external control arrangement.
The combined reset/test button provides convenient local access for commissioning and maintenance checks. Its operation must follow ABB's instructions and the selected reset configuration.
Where unexpected motor restarting could create a hazard, the complete control system must include appropriate restart prevention and interlocking. The reset function of the thermistor relay alone does not constitute a complete machinery safety system.
Easy Connect Push-In Terminals and Compact DIN Rail Installation
The ABB CM-MSS.32P features Easy Connect Technology, using screwless push-in terminals to provide secure, maintenance-free electrical connections when correctly installed.
The push-in connection system simplifies wiring and reduces the need for conventional screw terminal tightening. It is particularly useful in OEM machinery, industrial control panels and production equipment where consistent wiring quality and efficient installation are important.
Its compact 22.5 mm DIN rail housing allows efficient use of control cabinet space. With dimensions of 85.6 × 22.5 × 103.7 mm and a net weight of approximately 0.120 kg, the relay is suitable for densely populated electrical panels.
An optional sealable transparent cover is available to help protect against unauthorised changes to the device's settings or controls.
Typical Applications
- Motor winding temperature protection in industrial machinery.
- Thermal monitoring of motors equipped with PTC thermistors.
- Industrial motor control centres and automation cabinets.
- Pump motor overheating protection.
- Fan and ventilation motor thermal supervision.
- Compressor motor temperature monitoring.
- Conveyor and material handling machinery.
- Manufacturing and processing equipment.
- Industrial motors subject to frequent starting and stopping.
- Motor protection systems requiring sensor short-circuit diagnostics.
- Applications requiring interrupted-wire detection.
- PLC-based motor fault monitoring and alarm signalling.
- Suitable ATEX motor protection arrangements, subject to certification conditions.
- OEM machinery using 24 V AC/DC control supplies.
- Industrial installations requiring local or remote reset.
- Compact DIN rail control panels with push-in wiring.
