Why Choose the ABB CM-MSS.33P Thermistor Motor Protection Relay?
The ABB CM-MSS.33P (1SVR740712R2200) is an industrial thermistor motor protection relay designed to monitor electric motor winding temperatures using PTC thermistor sensors. Part of ABB's CM-MSS measuring and monitoring relay range, it helps protect motors against excessive temperatures caused by heavy starting, mechanical overload, inadequate cooling and demanding operating conditions.
The CM-MSS.33P operates from selectable 110–130 V AC or 220–240 V AC control supplies and features one PTC thermistor sensor circuit. Its two changeover (SPDT) output contacts, rated at 250 V / 4 A, provide flexible switching for motor control, fault indication and industrial automation systems.
For enhanced protection, the relay incorporates sensor short-circuit monitoring, dynamic interrupted-wire detection and selectable automatic, manual or remote reset. Its ATEX-certified motor protection function, combined reset/test button, ABB Easy Connect push-in terminals and compact 22.5 mm DIN rail housing make it a versatile choice for industrial motor control panels and suitable explosion-protection applications.
Key Advantages
- Direct motor winding temperature monitoring using compatible PTC thermistors.
- Helps protect motors against overheating caused by overload, frequent starting and insufficient cooling.
- Dual AC supply ranges: 110–130 V AC or 220–240 V AC.
- One PTC sensor measuring circuit for direct thermal supervision.
- Two changeover (SPDT) contacts rated at 250 V / 4 A.
- Sensor short-circuit detection helps identify defective sensor connections.
- Dynamic interrupted-wire detection supports diagnosis of disconnected or damaged sensor wiring.
- Automatic, manual or remote reset for flexible operating requirements.
- Closed-circuit operating principle supports fault-responsive switching.
- ATEX-certified thermistor protection function for applications meeting the relevant certification conditions.
- Combined reset/test button simplifies commissioning and maintenance.
- Easy Connect push-in terminals provide convenient, maintenance-free connections.
- 22.5 mm DIN rail housing conserves control cabinet space.
- Operating ambient temperature range of −25 to +60 °C.
- Suitable for motor control centres, OEM machinery and industrial automation.
- Optional sealable transparent cover helps prevent unauthorised adjustments.
Key Features
- ABB CM-MSS.33P thermistor motor protection relay.
- Manufacturer order code: 1SVR740712R2200.
- Rated control supply voltage: 110–130 V AC / 220–240 V AC.
- Monitoring function: Motor winding temperature protection.
- Sensor type: PTC thermistors.
- Number of sensor circuits: 1.
- Sensor short-circuit monitoring: Integrated.
- Interrupted-wire monitoring: Dynamic detection.
- Reset functions: 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: Motor thermistor protection function.
- Terminal technology: ABB Easy Connect push-in terminals.
- Connection method: Screwless spring-clamp connection.
- Housing protection rating: IP50.
- Terminal protection rating: IP20.
- Mounting: DIN rail.
- Housing width: 22.5 mm.
- Optional sealable transparent protective cover.
Technical Specifications
- Manufacturer: ABB
- Product series: CM-MSS
- Model: CM-MSS.33P
- ABB order code: 1SVR740712R2200
- ABB product group: 310921-Measuring & Monitoring Relays
- Product type: Thermistor motor protection relay
- Rated control supply voltage: 110–130 V AC / 220–240 V AC
- Supply type: AC
- Monitoring function: Motor winding temperature monitoring
- Sensor type: PTC thermistors
- Number of sensor circuits: 1
- Sensor short-circuit detection: Yes
- Dynamic interrupted-wire detection: Yes
- Reset modes: 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
- Rated insulation voltage, supply to measuring circuit: 300 V
- Rated insulation voltage, supply to output circuit: 300 V
- Rated insulation voltage, measuring to output circuit: 300 V
- Rated insulation voltage, between output circuits: 300 V
- ATEX approval: Yes, subject to certificate conditions
- ATEX certificate reference: TPS 18 ATEX 044254 0018 X
- Terminal type: Easy Connect push-in terminals
- Connection technology: Screwless spring-clamp connection
- Housing protection rating: IP50
- Terminal protection rating: IP20
- 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: 0.162 kg
- EAN: 4013614496530
- Customs tariff number: 85364900
Reliable PTC Thermistor Motor Temperature Protection
The ABB CM-MSS.33P monitors the resistance of PTC thermistor sensors installed in electric motor windings. When the motor temperature approaches the sensor's rated response temperature, the PTC thermistor resistance increases sharply. The relay detects this change and switches its output contacts to indicate an excessive temperature condition.
Unlike motor protection methods based solely on electrical current, PTC thermistor monitoring responds to the actual temperature of the motor windings. This makes it useful for identifying overheating caused by prolonged mechanical overload, repeated starting, blocked ventilation, insufficient cooling and elevated ambient temperature.
The CM-MSS.33P provides one PTC sensor measuring circuit and operates according to the closed-circuit principle. During normal operation, the output relay is energised; when a relevant fault occurs, its contacts change state to provide a fault signal.
Its two changeover contacts allow the monitoring output to be incorporated into suitable motor contactor circuits, PLC inputs and industrial alarm systems. The relay is intended for control and fault signalling rather than direct interruption of the motor's main power conductors.
Sensor Short-Circuit and Interrupted-Wire Diagnostics
The CM-MSS.33P incorporates diagnostic functions that supervise the condition of its PTC thermistor measuring circuit as well as the temperature-dependent sensor resistance.
Sensor short-circuit detection helps identify an abnormally low-resistance condition in the measuring circuit. This may indicate damaged wiring, incorrect connections or a sensor circuit fault that requires investigation.
Dynamic interrupted-wire detection helps identify an open circuit or disconnected sensor wiring. This additional supervision is particularly useful in machinery where cables may be exposed to vibration, mechanical movement or demanding operating environments.
By monitoring both overheating and sensor circuit faults, the CM-MSS.33P supports more dependable motor thermal protection and can help maintenance personnel identify the source of a detected fault.
Automatic, Manual and Remote Reset Functions
The ABB CM-MSS.33P supports automatic, manual and remote reset after the relevant fault condition has cleared. These options provide flexibility when integrating the relay into different motor control and automation systems.
Automatic reset allows the monitoring relay to return to its normal state once the motor has cooled sufficiently and the sensor circuit condition is acceptable. This can be appropriate in installations where automatic restoration of the monitoring signal is permitted.
Manual reset requires deliberate operator intervention following a fault. Remote reset enables reset control through a suitable external circuit, supporting centralised operation or integration into machinery control arrangements.
A combined reset/test button provides convenient local access for commissioning and functional checks. Reset operation depends on the selected mode and the condition of the connected PTC sensor circuit.
Important: Resetting the monitoring relay must not cause an unsafe or unexpected motor restart. Suitable interlocks and restart-prevention measures must be provided wherever required by the machinery risk assessment.
ATEX-Certified Thermistor Motor Protection Function
The CM-MSS.33P has an ATEX-certified thermistor motor protection function, making it suitable for consideration in protective arrangements involving motors used in potentially explosive atmospheres, subject to the applicable certification requirements.
The relevant certificate reference is TPS 18 ATEX 044254 0018 X. The certificate conditions, permitted sensor arrangement, motor protection requirements and installation instructions must be reviewed before the relay is used in an explosion-protection application.
ATEX certification of the protective function does not automatically authorise installation of the relay itself inside a hazardous area. The permitted installation location and complete protective arrangement must be determined from the current certification documents and applicable electrical standards.
For installations involving potentially explosive atmospheres, equipment selection and commissioning should be undertaken by suitably qualified personnel.
Dual AC Supply Ranges for Industrial Control Systems
The CM-MSS.33P is designed for 110–130 V AC or 220–240 V AC control supplies, providing flexibility for industrial installations that use common AC control voltages.
This supply specification is important when selecting a replacement thermistor motor protection relay. The CM-MSS.33P is not a 24 V AC/DC model and should not be substituted for one without checking the available control supply.
Its two changeover contacts support flexible integration into control circuits, enabling the monitoring system to provide switching signals to compatible motor contactors, alarms and PLC inputs.
Easy Connect Push-In Terminals and Compact DIN Rail Installation
The ABB CM-MSS.33P uses Easy Connect Technology, featuring screwless push-in terminals that simplify electrical installation and provide secure, maintenance-free connections when correctly wired.
The push-in connection system reduces the need for conventional screw terminal tightening and supports efficient panel assembly. This makes the relay particularly suitable for OEM machinery, industrial motor control centres and automation cabinets.
With dimensions of 85.6 × 22.5 × 103.7 mm, the CM-MSS.33P occupies just 22.5 mm of DIN rail width. Its compact construction allows efficient use of cabinet space alongside other monitoring and control components.
The housing has an IP50 protection rating, while the terminals are rated IP20. An optional sealable transparent cover is available to help prevent unauthorised changes to the relay's settings and controls.
Typical Applications
- Motor winding temperature protection in industrial machinery.
- Thermal monitoring of motors equipped with PTC thermistors.
- Industrial motor control centres and electrical control panels.
- Pump motor overheating protection.
- Fan and ventilation motor thermal supervision.
- Compressor motor temperature monitoring.
- Conveyor and material handling machinery.
- Manufacturing and processing equipment.
- Motors subject to frequent starting or demanding duty cycles.
- 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 110–130 V AC control supplies.
- Industrial installations using 220–240 V AC control supplies.
- Motor control systems requiring automatic, manual or remote reset.
- Compact DIN rail control cabinets with push-in wiring.
