Page 154 - EPR Catalog 2015

Thermistor motor protection relays
Benefits and advantages, Applications

The thermistor motor protection relays of the CM-MSx range protect motors with
PTC sensors against high temperature. These sensors are incorporated in the
motor windings thus measuring the motor heat directly.

2

Direct temperature measuring Monitoring the motor
Generally, motor damages caused by overload or overheating The thermistor motor protection relay measures the resistance
situations can be prevented in different ways. Compared to of the PTC sensors which reflects the internal motor tempera-
the indirect temperature measuring which monitors the motor ture permanently.
current, the temperature inside the motor can be measured by If the temperature in the motor windings rises excessively and
direct temperature measuring. reaches the nominal response temperature (NRT), the therm-
This enables direct control and evaluation of the following istor motor protection relay detects this situation and the
operating conditions like: output relay switches off.
– Heavy duty starting By doing so the motor contactor gets triggered and switches
– Increased switching frequency off the motor.
– Single phase operation
– Phase unbalance CM-MSS functionality video
– High ambient temperature
– Insufficient cooling
– Breaking operation
Therefore the consequences from overheating like abrasion as
well as electrical failures can be prevented.
The direct measuring principle is carried out by a combination
of the thermistor motor protection relay and 3 PTC sensors
which are installed directly in the motor by the manufac-
turer. Those 3 PTC sensors are placed directly at the thermal
hotspots, the motor windings.

Characteristics CM-MSS1) Features 1)
– Different types of contacts available – Additional functions:

– 1 x 2 c/o (SPDT) contacts – Dynamic interrupted wire detection
– 2 x 1 c/o (SPDT) contact – Short-circuit monitoring of the sensor circuit
– 1 n/o and 1 n/c contact – Non-volatile fault storage
– 1 or 2 measuring circuits – Single or sum evaluation
– Different types of reset functions – Easy configuration via DIP switches
– Automatic – LEDs to distinguish between different failure causes
– Manual – Screw connection technology or Easy Connect Technology
– Remote available
– Rated control supply voltages – Test/Reset button available
– 24 V AC/DC
– 24-240 V AC/DC 1) Depending on device the characteristics vary, for detailled overview see „Selection
– 110-130 V AC, 220-240 V AC table CM-MSx range“ on page 89.
– Approvals / Marks

A C R K E I1) / a b

Characteristics CM-MSE
– Auto reset
– Connection of several sensors (max. 6 sensors

connected in series)
– Monitoring of bimetals
– 1 n/o contact
– Excellenct cost / performance ratio

2/87 ABB | Catalog Electronic Products and Relays 2015 | 2CDC 110 004 C0210