Electrical Contactors AC1, AC2, AC3, AC4

Electrical Contactors Utilization Categories: AC1, AC2, AC3, AC4, and More

Electrical contactors are one of the most important components in electrical power and control circuits. They are widely used for switching, controlling, and protecting loads such as motors, heaters, lighting, and capacitor banks.

To ensure reliability and safety, contactors are classified into utilization categories based on their current making and breaking capacity. These categories are defined in IEC 60947-4-1 and depend on:

• Type of load (resistive, inductive, capacitive, motor, lighting)
• Operating duty (normal switching, frequent switching, inching, plugging, etc.)
• Current & voltage rating (AC or DC supply conditions)

Understanding these utilization categories is essential for electrical engineers, designers, and maintenance teams while selecting the right contactor for an application.

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Common AC Utilization Categories for Contactors

AC-1

• Application: Non-inductive or slightly inductive loads.
• Typical Loads: Resistive heating elements, electric ovens, furnaces, heaters.
• Example: Switching a 20 kW electric heater.

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AC-2

• Application: Starting of slip-ring motors.
• Function: Handles high inrush current during motor starting.
• Example: Slip-ring induction motors used in cranes, hoists, or large mills.

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AC-3

• Application: Starting and stopping of squirrel cage induction motors (switching off only after motor reaches speed).
• Function: Makes high inrush current (6–8 × rated current) and breaks rated running current.
• Examples of Use:
• Pumps
• Compressors
• Lifts and escalators
• Conveyors and bucket elevators
• Air-conditioning units and mixers

💡 Note: AC-3 is the most widely used category in industrial applications.

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AC-4

• Application: Frequent inching, jogging, reversing, and plugging duty of squirrel cage motors.
• Function: Must withstand making and breaking high starting currents repeatedly.
• Examples:
• Rolling mills
• Paper machines
• Crushers
• Heavy-duty hoists requiring rapid start/stop cycles

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AC-6a

• Application: Switching of transformers.
• Function: Handles magnetizing inrush current when energizing transformers.

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AC-6b

• Application: Switching of capacitor banks.
• Function: Designed to withstand very high inrush currents (20–30 × rated current) when capacitors are energized.

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AC-11

• Application: Auxiliary control circuits (not power circuits).
• Examples: Control relays, pilot signals, low-power command contacts.

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Difference Between AC-1 and AC-3 Contactors

This is one of the most frequently asked questions among engineers:

Parameter	AC-1 Contactor	AC-3 Contactor
Load Type	Resistive or slightly inductive loads	Induction motors (squirrel cage)
Application	Heaters, ovens, resistive loads	Pumps, lifts, compressors, conveyors
Current Breaking	Breaks small or no inductive current	Breaks motor full-load current
Inrush Current Handling	Low	High (6–8 × motor rated current)

👉 In short:

• Use AC-1 for resistive heating applications.
• Use AC-3 for induction motor control and industrial machinery.

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Key Takeaways

• Always match the utilization category with the load type. Wrong selection can cause overheating, contact welding, or premature failure.
• AC-3 is the most common in motor applications.
• AC-4 is used when motors need rapid switching or reversing.
• AC-6a & AC-6b handle transformer and capacitor switching, respectively.

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✅ Pro Tip for Engineers:
When selecting a contactor, never rely on only kW or current ratings. Always check the utilization category on the nameplate to ensure safe and reliable operation.