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What is the meaning of the utilisation categories AC1 and AC3 for the Tesys contactors?

The standard utilisation 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 etc.)
The operating cycle conditions (motor running, stalled or starting, reverse operation, counter-current braking etc.)

AC-1 category

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).
Examples of use: resistive load, heating, distribution

AC-3 category

This applies to squirrel cage motors where breaking occurs while the motor is running.
Examples of use: all squirrel cage motors, lifts, escalators, conveyors, bucket elevators, compressors, pumps, mixers, air conditioning units

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.

Utilization categories are defined in full in regulation IEC 60947-1