What is AC1, AC2, AC3 Contactor?

Contactors are essential components in electrical systems, used to control the flow of high currents in various applications such as motor control. The designations AC1, AC2, and AC3 refer to different types of contactor duties as categorized by the International Electrotechnical Commission (IEC), which are based on the nature of the electrical loads they are designed to handle and their duty cycles. Here's a detailed explanation of each:

AC1 Contactor

• Application: AC1 duty contactors are used for resistive loads, such as heaters and electric furnaces. These are non-inductive or slightly inductive loads with a power factor between 0.95 to 1. The contactor's rated current is equal to the发热电流 (heating current), which means it can handle the continuous current without overheating.

AC2 Contactor

• Application: AC2 contactors are designed for slip-ring motors starters, which involve switching on and off the motor. They are preferred for high torque current applications where the starting current is high.

AC3 Contactor

• Application: AC3 contactors are generally used for starting squirrel-cage motors and switching off the motor during running time. This means the contactor can withstand high current continuously. Examples of applications include lifts, elevators, fans, etc. The rated current for AC3 contactors is lower than for AC1 because they are designed to handle the inrush current during motor startup, which can be 5 to 7 times the motor's rated full load current.

The difference between AC1 and AC3 contactors lies in the type of loads they handle. AC1 contactors are used for less inductive loads such as resistive loads (the power factor of the load is near about 1), but AC3 duty contactors are used for high inductive, squirrel cage motors which will be off during the motor is running condition.

In summary, AC1, AC2, and AC3 contactors are categorized based on their ability to handle different types of loads and operating conditions. Understanding these classifications is crucial for selecting the appropriate contactor for a specific application, ensuring the safety, reliability, and efficiency of the electrical system.