(And why BCH Electric is India’s most trusted name in contactors)
TL;DR
Contactors are not “one size fits all.” Their AC duty ratings (AC1, AC2, AC3, AC4, etc.) define how they perform under different load conditions like resistive heating, squirrel-cage motors, or frequent inching/jogging. Choosing the wrong duty cycle shortens contactor life and risks system downtime. BCH Electric, with decades of engineering expertise, delivers internationally certified, India-ready contactors built to perform across all duty classes.
Why Do Contactor Ratings Matter?
A contactor may look like a simple switch, but in industrial systems, it must:
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Switch large electrical currents repeatedly
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Withstand arcs, surges, and heat cycles
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Handle very different loads (resistive heaters, motors, welders, compressors, etc.)
IEC 60947 (the international standard) classifies contactors into utilization categories like AC1, AC2, AC3, AC4 to specify exactly what duty they are suitable for.
Choosing by only current rating (A) is risky. For example, a 100 A contactor rated AC1 is not automatically suitable for a 55 kW motor in AC3 duty.
Key Contactor Duty Categories
🔹 AC1 – Non-Inductive or Slightly Inductive Loads
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Definition: For resistive or low-inductive loads (power factor ≈ 0.95).
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Typical Loads:
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Electric heaters
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Resistive ovens
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Lighting (incandescent, halogen)
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Characteristics:
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Current at making = Rated current
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Current at breaking = Rated current
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Example: A 100 A contactor in AC1 can switch 100 A of heater load continuously.
👉 Takeaway: AC1 is the least demanding duty, used mainly where switching does not involve motor inrush currents.
🔹 AC2 – Slip-Ring Motors (Starting, Plugging, Inching)
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Definition: For slip-ring (wound rotor) induction motors.
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Typical Loads:
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Large cranes
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Hoists
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Slip-ring compressors
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Characteristics:
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Current at making = 2.5 × rated motor current
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Current at breaking = 2.5 × rated motor current
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Example: A 50 A AC2 contactor handles the heavy starting conditions of wound rotor motors.
👉 Takeaway: AC2 is less common today as slip-ring motors are declining, but still critical in heavy industries.
🔹 AC3 – Squirrel-Cage Motors (Starting & Running)
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Definition: For squirrel-cage induction motors, the most common motor type.
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Typical Loads:
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Pumps
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Fans & blowers
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Compressors
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Conveyors
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Characteristics:
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Current at making = 6–7 × rated motor current (motor starting inrush)
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Current at breaking = Rated motor current (during normal running)
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Example: A 100 A AC3 contactor can reliably start and stop a 55 kW motor at 400 V.
👉 Takeaway: AC3 is the most widely used category in industrial applications.
🔹 AC4 – Squirrel-Cage Motors (Inching, Plugging, Reversing)
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Definition: For applications involving frequent starting, stopping, reversing, or plugging.
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Typical Loads:
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Press machines
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Elevators
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Crushers
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Rolling mills
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Welding equipment
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Characteristics:
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Current at making = 6–7 × rated motor current
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Current at breaking = 6–7 × rated motor current
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Example: A 40 A AC4 contactor is required for a crane hoist with constant inching and plugging operations.
👉 Takeaway: AC4 is the most demanding duty because the contactor must break motor inrush repeatedly, causing higher stress and arc erosion.
Why This Matters to Engineers & Buyers
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Incorrect selection = premature failure, downtime, and higher maintenance costs.
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Correct duty classification = longer service life, fewer breakdowns, and reliable plant operations.
Quick Rule of Thumb
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Heaters/Resistive Loads → AC1
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Slip-Ring Motors → AC2
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General Motors (Start/Stop) → AC3
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Frequent Jogging/Reversing → AC4
How BCH Electric Adds Value
As India’s leading contactor manufacturer, BCH Electric ensures:
✅ Full IEC & IS compliance – Products certified for AC1 through AC4 utilization categories.
✅ Wide Range – From 9 A to 1200 A, covering everything from small HVAC panels to heavy industry MCCs.
✅ Rugged Design – Built for Indian operating conditions: heat, dust, humidity, voltage fluctuations.
✅ Longer Life – Silver alloy contacts, arc-chutes, and advanced insulation for high endurance.
✅ Energy Efficiency – Low coil consumption contactors reduce panel energy use.
✅ Support & Customization – Application engineers guide you in selecting the right duty contactor for your load profile.
Whether you’re designing HVAC panels, automotive production lines, or heavy-duty cranes, BCH Electric contactors deliver unmatched reliability.
FAQs
Q1. Can I use an AC1 contactor for a motor load?
No. Motor loads require AC2/AC3/AC4 ratings depending on the type and duty. Using AC1 will cause premature failure.
Q2. Why is AC3 most common in industry?
Because squirrel-cage motors dominate industrial applications (fans, pumps, conveyors), and AC3 is rated for starting and breaking these loads.
Q3. What’s the difference between AC3 and AC4?
AC3 assumes motors are disconnected while running. AC4 assumes motors are disconnected during inrush—much harsher on contacts.
Q4. Does BCH Electric manufacture AC4-rated contactors?
Yes. BCH offers contactors designed for inching, plugging, and reversing duties, ensuring long service life even in harsh environments.
Q5. How do I size a contactor correctly?
Refer to the IEC utilization category tables and match to your load type. BCH application engineers can help you select the correct duty cycle contactor.
