Contactor main structure

An AC contactor is an electrical device that uses its main contacts to open and close a circuit, while its auxiliary contacts are used in the control circuit to manage the operation of the contactor.

The main contacts are typically normally open (NO), meaning they remain open until activated. In contrast, the auxiliary contacts often consist of two pairs—some normally open and some normally closed (NC)—allowing for more complex control functions. Smaller contactors are frequently used as intermediate relays to interface with the main circuit.

The contacts themselves are made from silver-tungsten alloy, which offers excellent conductivity and resistance to high temperatures caused by arcing. This material ensures reliable performance even under heavy load conditions.

The power of the AC contactor is generated through the magnetic field created by an AC coil wrapped around a soft iron core. The core is constructed using stacked silicon steel laminations shaped like a "mountain," with one of the fixed cores housing the coil. The operating voltage can be selected based on the application. To reduce vibration and stabilize the magnetic force, a short-circuit ring is added to the core’s surface. When power is lost, the contactor resets via a spring mechanism.

The other half of the core is a movable iron core, designed similarly to the fixed one. It moves when the coil is energized, driving the motion of both the main and auxiliary contacts.

Contactors rated at 20 amps or higher are equipped with an arc suppression cover. This component helps to quickly extinguish the arc that forms when the circuit is broken, protecting the contacts from damage.

These devices are capable of operating at high frequencies, making them ideal for applications requiring frequent on/off cycles. They can handle up to 1,200 operations per hour, depending on the model.

Contactors are known for their long lifespan. Mechanically, they can last between several million to tens of millions of operations, while their electrical life ranges from hundreds of thousands to millions of cycles, depending on the load and usage conditions.

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