- 1 measure circuit
- Automatic reset
- Over voltage protected measure- and supply input
- Improved immunity according to EN 62061 with evaluation criterion "Fail-Safe"
- Housing material with maximum fire protection classification UL 94 V-0
- Installation and removing on/from DIN-rail without tools possible
- Screwed connection
- Overall width 22.5 mm (0.89 inch)
Thermistor Motor Protection Relays - Benefits and Pros, Applications
Thermistor motor protection relays series CM-MSx protect motors with PTC temperature sensors against high temperatures. The temperature sensors are installed in the motor coils and therefore measure the motor warming directly.
Direct temperature measuring
Generally engine damage caused by overload or overheating can be avoided in different ways. Compared with the indirect temperature measuring, which controls the motor current, the temperature in the motor can be controlled by direct temperature measuring. this allows the direct control and evaluation of the following operating conditions:
- Heavy-duty start-up
- Increased frequency of operation
- Single-phase operation
- Phase imbalance
- High ambient temperature
- Insufficient cooling
- Shutdown cycle
Therefore the implications of overheating like abrasion as well as electric failures can be avoided.
The direct measuring is realised by the Thermistor motor protection relay and 3 PTC sensors which are installed by the manufacturer directly into the motor coil.
The thermistor motor protection relay measures the resistance of the PTC sensors, which indicates the internal motor temperature. If the temperature in the motor coil increases and the rated response temperature (NAT) is reached, the thermistor motor protection relay detects this situation and the output relay shuts down. The motor protection gets triggered and the motor shuts down.
Application / Control function
The thermistor motor protection relay controls the motor coil temperatur and therefore protects the motor of overheating, overload and insufficient cooling according IEC 60947-8, control units for built-in thermal protection (PTC) for rotating electrical machines.
Mode of operation
The thermistor motor protection relays CM-MSS.12 and CM-MSS.13 are in use to control the temperature of motors and generators, which are equipped with PTC temperature sensors type A. The sensors are installed in the motor coil and measure the heating of the motor. When the motor temperature is raising the resistance of the PTC sensor raises as well. When the motor overheats (>2.7 kh) the output relay releases and the corresponding LED display the over temperature. A reset is only possible, after the motor cooled down (<1.2 kh).
As soon as the error is resolved and the measurement drops below the restart conditions an automatic reset is operated.