1SVR730722R1400 ABB CM-MSS.21S Thermistor Motor Protection Relay 24–240 V AC/DC

Why Choose the ABB CM-MSS.21S Thermistor Motor Protection Relay?

The ABB CM-MSS.21S 1SVR730722R1400 is a compact thermistor motor protection relay designed to monitor PTC temperature sensors installed in electric motor windings. As part of the ABB CM-MSS range, it helps protect motors against excessive winding temperatures caused by conditions such as overload, heavy-duty starting or insufficient cooling.

The CM-MSS.21S features one PTC sensor circuit with both short-circuit detection and dynamic interrupted-wire detection. These functions allow the relay to supervise the integrity of the temperature sensor circuit as well as the thermal condition of the motor, while non-volatile fault storage supports reliable fault indication.

A wide 24–240 V AC/DC control supply provides flexibility for industrial control systems. The relay has one normally open and one normally closed output contact rated at up to 250 V / 4 A, automatic reset after a fault has cleared, ATEX approval and screw terminals in a compact 22.5 mm wide DIN-rail housing.

Key Advantages

• Dedicated PTC thermistor motor protection for winding temperature supervision.
• Wide 24–240 V AC/DC control supply simplifies integration.
• One PTC sensor circuit for direct motor temperature monitoring.
• Short-circuit detection supervises the PTC sensor circuit.
• Dynamic interrupted-wire detection helps identify sensor wiring faults.
• Non-volatile fault storage supports dependable fault monitoring.
• Automatic reset after the monitored fault has been removed.
• 1 N/O + 1 N/C output contacts for control and signalling functions.
• ATEX approved for applicable motor protection installations.
• Compact 22.5 mm width conserves DIN-rail space.

Key Features

• ABB CM-MSS.21S thermistor motor protection relay.
• 1 PTC sensor circuit.
• 24–240 V AC/DC rated control supply voltage.
• 1 normally open + 1 normally closed output contact.
• Output contacts rated at 250 V / 4 A.
• Short-circuit monitoring of the sensor circuit.
• Dynamic interrupted-wire monitoring.
• Non-volatile fault storage.
• Automatic reset after fault removal.
• Closed-circuit operating principle.
• ATEX approved.
• Screw terminals with double-chamber cage connection technology.
• DIN-rail mounting for industrial control cabinets.

Comprehensive PTC Sensor Circuit Monitoring

PTC thermistors installed in motor windings respond directly to increasing winding temperature, with their resistance rising sharply when the specified response temperature is reached. The ABB CM-MSS.21S continuously evaluates the connected PTC sensor circuit and changes its output state when an excessive temperature condition occurs, enabling the associated motor-control system to initiate a protective response.

In addition to thermal monitoring, the CM-MSS.21S provides short-circuit and dynamic interrupted-wire detection for the sensor circuit. Combined with non-volatile fault storage, automatic reset and a wide 24–240 V AC/DC supply range, these functions provide comprehensive supervision for industrial motor protection applications.

Typical Applications

• PTC-equipped electric motor thermal protection.
• Motor winding temperature monitoring.
• Pumps, fans and ventilation equipment.
• Compressors and refrigeration machinery.
• Conveyors and material handling equipment.
• Industrial production and process machinery.
• Motor control centres and electrical control panels.
• OEM machinery and industrial automation systems.