The standard utilization categories defines the current making and breaking values for contactors.
They depend on the following:
- The type of load to be controlled (squirrel cage or slip ring motor, resistors)
- The operating cycle conditions (motor running, stalled or starting, reverse operation, counter-current braking)
This applies to all AC devices (loads) with a power factor of at least 0.95 (cos phi greater than or equal to 0.95).
Example of use: resistive load, heating, distribution.
This applies to squirrel cage motors where breaking occurs while the motor is running.
Example of use: all squirrel cage motors, lifts, escalators, conveyors, bucket elevators, compressors, pumps, mixers, air conditioning units, etc.
Note concerning contactor part numbers
The most common application of contactors is controlling squirrel cage asynchronous motors.
Hence, Schneider Electric contactor part numbers are based on the AC-3 rating.
For example, the LC1D18xx contactor is designed to control motors with a nominal current rating of 18 A (AC-3).
This contactor is capable of withstanding current peaks (~ 100 A) on starting, such as are typical on inductive machines like motors, without sustaining any damage.
It can also control resistance heaters for current ratings up to 32 A (AC-1). This load is resistive, hence there are no current peaks.