categories cover the main areas for alternating current contactors AC -
categories) and direct current (DC- categories). For normal operation of
contactors they define the making and breaking conditions at rated
operational current (le) and at rated voltage (Ue).
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.).
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.
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.
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.