They depend on:
    - The nature of the load to be switched (resistive, squirrel cage motor, etc.),
    - The conditions under which the making and breaking occurs (motor started or stalled, reversing direction of operation, etc.).

Utilisation categories AC-1 to AC-4, which are already included in the IEC 158 standard, have been incorporated into the IEC 947 standard:
    - AC-1: this applies to all loads supplied by alternating current at cos > 0.95,
    - AC-2: staring, plugging and inching of slip-ring motors,
    - AC-3: starting squirrel cage motors, and breaking with motor running,
    - AC-4: starting, plugging, and inching of squirrel cage motors.

The new standard defines additional utilization categories concerning the rating of contactors for the following loads: discharge lamps (AC-5a, incandescent lamps (AC-5b), transformers (AC, capacitors (AC-6b), refrigeration compressors (AC-8).

The standard also takes into account categories AC-7a and AC-7b for domestic applications.

Category AC-11 (IEC 337) for switching electromagnets loads by auxiliary contacts or by control relays is replaced by the following two categories: AC- 14 for electromagnets drawing less than 72 VA in closed position (steady state current 10le). The application most frequently encountered is the switching on contactor coils.