Contactors switch motors on and off, motor protection breakers protect them against overload and short circuit. Both are wear parts whose contacts age with every operation.
The main ratings
Contactors are rated to IEC 60947-4-1 with a utilisation category. AC-3 stands for starting and switching off squirrel-cage motors, AC-1 for almost resistive loads. High-efficiency motors of classes IE3 and IE4 have their own category AC-3e. The rated current always applies to a given category and voltage. Coil voltage and auxiliary contacts are added.
For the motor protection breaker, the setting range is chosen so that the rated motor current lies within it. For short-circuit protection, the breaking capacity at the installation point matters. Matching link modules often combine contactor and breaker into a starter.
What a request for contactors should contain
- type designation of the existing device
- motor power or rated current at AC-3, for IE3/IE4 motors AC-3e
- coil voltage and type of current
- number and type of auxiliary contacts
- for motor protection breakers: setting range
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