Contactor AC-1, AC-3 and AC-4 Utilization Categories
Compare contactor load duties, read operational current at the stated voltage and utilization category, and separate coil, thermal and motor switching ratings.
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Compare common switching duties
A contactor can carry several current ratings because carrying current and interrupting a motor duty place different demands on its contacts. Read the utilization category together with operational voltage and current. The coil supply rating answers a different question.
| Category | Duty described | Rating-reading consequence |
|---|---|---|
| AC-1 | Non-inductive or slightly inductive loads, including resistance heating. | Do not transfer the AC-1 current directly to motor starting duty. |
| AC-3 | Starting squirrel-cage motors and switching off while running. | Use the operational voltage, current and applicable motor rating together. |
| AC-4 | Starting, plugging and inching squirrel-cage motors. | Repeated interruption during demanding motor conditions needs the stated AC-4 duty data. |
| Other categories | Lighting, transformer and capacitor switching have separate categories. | A similar running current does not establish equivalent switching duty. |
Read a rating block
Find Ie (rated operational current), Ue (rated operational voltage), the category and any motor power table. Keep Ith or a thermal current rating separate. Read the coil voltage, AC/DC supply and frequency from the coil identification rather than from the power-contact rating.
Illustrative reading exercise: a label offers a larger AC-1 current and a smaller AC-3 current at one voltage. These are two qualified ratings for the same device. The larger number is not a general-purpose motor rating. This illustration intentionally supplies no selection current or replacement model.
Document the actual duty
- Record load type and operating sequence, including jogging, reversing or plugging.
- Record supply voltage, motor data, operations per hour and expected endurance.
- Retrieve the exact contactor rating table, environmental derating and coordination information.
- Check the associated overload and short-circuit protective arrangement separately.
Category names do not establish coil compatibility, SCCR or suitability as an isolation device. Compare terminal labels with contactor terminal markings, and read the command sequence in motor control diagrams.
For supported conductor and protection lookups, continue to the motor circuit reference tool. Keep those circuit calculations separate from the contactor manufacturer’s duty ratings and coordination requirements.