IEC Contactor Utilization Categories (IEC 947-4)
AC-1 This applies to all AC loads where the power factor is at least 0.95. These are primarily non-inductive or slightly inductive loads. Breaking remains easy.
AC-2 This applies to Slip-ring motors; starting, switching off.
AC-3 This applies to squirrel cage motors where the breaking of the power contacts would occur while the motor is running. On closing, the contactor experiences an inrush which is 5-8 times the nominal current, and at this instant, the voltage at the terminals is approximately 20% or the line voltage. Breaking remains easy.
AC-4 This applies to the starting and breaking of a squirrel cage motor during an inch or plug reverse operation. On energization, the contactor closes on an inrush current approx. 5-8 times the nominal current of the motor. On de-energization, the contactor breaks the same magnitude of nominal current at a voltage that can be equal to the supply voltage. Breaking is severe.
AC-5a Switching of electric discharge lamps
AC-5b Switching of incandescent lamps
AC-6a Switching of transformers
AC-6b Switching of capacitor banks
AC-7a Slightly inductive loads in household appliances and similar applications
AC-7b Motor-loads for household applications
AC-8a Hermetic refrigerant compressor-motor control w/ manual resetting of overload releases
AC-8b Hermetic refrigerant compressor-motor control w/ automatic resetting of overload releases
DC-1 This applies to all DC loads where the time constant (L/R) is less than or equal to one msec. These are primarily non-inductive or slightly inductive loads.
DC-3 This applies to starting and breaking of a shunt motor during inching or plugging. The time constant shall be less than or equal to 2 msec. On energization, the contactor sees current similar to that in Cat. DC-2. On de-energization, the contactor will break around 2.5 times the starting current at a voltage that may be higher than the line voltage. This would occur when the speed of the motor is low because the back e.m.f. is low. Breaking is severe.
DC-5 This applies to the starting and breaking of a series motor during inching or plugging. The time constant being less that or equal to 7.5 msec. On energization, the contactor sees about 2.5 times the nominal full load current. On de-energization, the contactor breaks the same amount of current at a voltage which can be equal to the line voltage. Breaking is severe.
DC-6 Switching or incandescent lamps