Beatrice Lang
An electrical contactor is a type of switch for opening and closing an electric circuit. Its operation can be mechanical, electromagnetic, or pneumatic. Synonyms for an electrical contactor include 'switch', 'starter', 'interruptor', 'connector', 'switcher', and 'breaker'. Devices switching more than 15 amperes or circuits rated more than a few kilowatts are usually called contactors. They are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.
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What You'll Learn
Electromagnetic contactors
An electrical contactor is a type of switch used to repeatedly open and close an electrical circuit. It is a special type of relay used for switching an electrical circuit on or off. A basic contactor has a coil input, which may be driven by an AC or DC supply. The coil may be energised at the same voltage as a motor the contactor is controlling, or it may be separately controlled with a lower coil voltage.
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Controlling electrical circuits
Electrical contactors are a type of relay or switch used to control electrical circuits. They are designed for remote control and automation, making them ideal for industrial and commercial applications where safety and convenience are paramount. Contactors enable operators or automated systems to control the flow of electricity to various loads without physical interaction with the circuit. This capability is essential for handling heavy machinery, industrial equipment, and large electrical loads, where contactors ensure that power can be safely switched on and off.
Contactor design plays a critical role in minimizing arcing, ensuring the longevity and safety of electrical circuits. Arcing occurs when electrical contacts open or close, creating sparks that can damage the contacts and potentially lead to hazardous conditions. Contactors are specifically engineered to reduce arcing during operation. The contacts, which are the current-carrying part of the contactor, are made of high-quality conductive materials like silver or copper alloys, chosen for their high electrical conductivity, mechanical strength, and stability under arcing and oxidation.
The coil, or electromagnet, is at the heart of an electrical contactor. It generates a magnetic field when energized, attracting the contactor's armature and, in turn, opening or closing the electrical contacts. The coil operates on the principle of electromagnetic induction, creating a magnetic field as current flows through it. The coil's input can be driven by either an AC or DC supply, depending on the contactor design. Universal coils, compatible with both AC and DC, are also available.
In addition to remote control and arcing reduction, contactors provide overload protection and enable interlocking in electrical circuits. Some contactors are equipped with overload relays, which monitor the current passing through the contactor. If the current exceeds safe levels for an extended period, the overload relay trips, de-energizing the contactor and preventing potential damage to the circuit or equipment. Interlocking ensures that specific operations occur in a particular sequence or under certain conditions. For example, in a motor control circuit, contactors can be interlocked to prevent the motor from starting in the reverse direction or while another operation is in progress.
Contactor applications include controlling electric motors, thermal evaporators, lighting, capacitor banks, heating, and other electrical loads. They range in size from small devices that can be picked up with one hand to large units measuring about a meter on each side. Contactors are indispensable components in modern electrical systems, contributing to the efficient, safe, and convenient operation of machinery and equipment.
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Higher current capacity
A contactor is a type of switch used for repeatedly opening and closing an electrical circuit. It is used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.
Contactors are most commonly used with electric motors and lighting applications. They are helpful in large industrial applications to turn on, start, and prevent large motors necessary for machinery, conveyors, pumps, and compressors. They help to make the motors run by checking on them to avoid electrical failures such as overloading and short-circuiting.
Contactors are also used to regulate lighting circuits, allowing for automation of lighting schedules, cutting energy costs, and enhancing light utilization. They are usually interfaced with building management systems to offer flexible and effective lighting control.
Contactors differ from relays in terms of their capacity to handle higher current and voltage levels. They are designed to be directly connected to high-current load devices and are typically built for and used in 3-phase applications.
The contacts are the current-carrying part of the contactor and are made of materials with high electrical conductivity, mechanical strength, and stability under arcing and oxidation. Commonly used metals include alloys of tungsten, molybdenum, copper, and silver with cadmium oxide added to improve durability and arc resistance.
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Coil input
A contactor is a type of switch for opening and closing an electric circuit. It is used to control high-power electrical devices such as motors, fans, pumps, lighting installations, heating, capacitor banks, and thermal evaporators.
The three core components of an electrical contactor are the coil (or electromagnet), the contacts, and the device enclosure. The coil input is the connection of power to the coil, which energizes it and creates an electromagnetic field. This field causes the contacts to close, completing the circuit and allowing power to flow. The coil may be energized at the same voltage as the device being controlled, or it may be controlled separately with a lower coil voltage.
When the coil is energized, a magnetic field is created, which attracts the moving core of the contactor. The electromagnet coil draws more current initially until its inductance increases when the metal core enters the coil. This movement of the core propels the moving contact, and the force developed by the electromagnet holds the moving and fixed contacts together.
In some contactors, an economizer circuit may be installed to reduce the power required to keep the contactor closed. This allows the energized coil to stay cooler and saves a substantial amount of power.
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Electric motors
An electrical contactor is a type of switch that controls electric motors, lighting, heating, capacitor banks, and other electrical loads. Electric motors are used in a variety of applications, from residential to commercial settings. In a residential setting, 2 and 3-pole contactors are commonly found in HVAC equipment, sewage pumps, and outdoor lighting units.
The basic unit of a contactor consists of 3 power poles, L1, L2, and L3, which are normally open. When the coil is energized, it creates a magnetic field that pulls the contactor's armature together, allowing power to flow to the equipment. This process involves three main components: an electromagnetic system, a contact system, and an arc extinguishing device.
To accommodate different electrical applications, there are several types of contactors available, including definite-purpose contactors, safety contactors, and non-reversing (FLNR) contactors. For example, safety contactors mechanically link the contacts, ensuring that all three poles close simultaneously and that the contactor fails in an open state.
Motor starters are also important in motor load applications as they combine the ability to start a motor with branch circuit protection and overcurrent protection for the motor. Overall, contactors play a crucial role in the safe and efficient operation of electric motors by providing a means of control and protection for high-load devices.
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Frequently asked questions
A contactor is a type of electrical relay or switch.
A relay is similar to a contactor but designed for lower current or low-voltage switching.
A switch is a device that opens and closes an electric circuit.
A contactor uses an electromagnet (or coil) to generate a magnetic field, which pulls contacts together and closes the circuit.
Contactors are commonly used to control electric motors, lighting, heating, capacitor banks, and other electrical loads. They are helpful in large industrial applications and provide a safe and efficient means of starting and stopping motors.
