A contactor is an electrically-controlled switch used for switching an electrical power circuit. A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch.
Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low-current contacts, contactors are almost exclusively fitted with normally open (“form A”) cont
Contactors are rated by designed load current per contact (pole), maximum fault withstand current, duty cycle, design life expectancy, voltage, and coil voltage. A general purpose motor control contactor may be suitable for heavy starting duty on large motors; so-called “definite purpose” contactors are carefully adapted to such applications as air-conditioning compressor motor starting.
North American and European ratings for contactors follow different philosophies, with North American general purpose machine tool contactors generally emphasizing simplicity of application while definite purpose and European rating philosophy emphasizes design for the intended life cycle of the application.
- Magnetic Contactors – These are the most common types available and for good reason as they are more efficient than the previously mentioned types. These contactors operate electromechanically and do not require human intervention. With their advanced technologies, they can be operated remotely, and this makes them safer and more efficient since they will not required to be operated manually.
- Knife Blade Switch – The knife blade switch contactors were introduced in the late 1800s. It is safe to assume that they were probably the first types of contactors that were used. Their applications were mostly to control electric motors.
- Manual Controller – After discovering the dangers involved with the use of the knife switchblade, engineers and researchers came up with another contactor device which offered better safety and a number of features that were not available in the knife blade switch.
- NEMA (National Electrical Manufacturers Association) is the largest trade association of electrical equipment manufacturers in the United States. NEMA encouraged manufacturers to standardize on frame sizes to allow users to confidently specify, purchase, and install electrical components from different manufacturers without a lot of hassle and cross-referencing. NEMA contactors also are designed with safety factors that go beyond design ratings (oversized), up to as much as 25%. NEMA is primarily a North American Standard.
- IEC (International Electrotechnical Commission) is a global standard. IEC contactors are not oversized. They are smaller than NEMA contactors and less expensive. The range of sizes offered by manufacturers is more numerous than the ten NEMA standards. As such, they are more specific to a given application and are specified when the operating conditions are well understood. Whereas, NEMA may be chosen when operating conditions, such as load are not well defined.
- Lighting Control Contactors are often used to provide central control of large lighting installations, such as an office building or retail building. To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils. One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts.
- Electric Motor Starter Contactors can be used as a magnetic starter. A magnetic starter is a device designed to provide power to electric motors. It includes a contactor as an essential component, while also providing power-cutoff, under-voltage, and overload protection.
Source : Wikipedi, Electgo, c3controls
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