Table of Contents
What is Contactor?
A contactor is an electrical switch designed to control an electric circuit by making and breaking the electrical connections. It is typically used in high-power applications where a standard switch may not be suitable due to the current and voltage requirements.
Contactor construction includes a set of contacts, usually made of high-conductivity materials such as copper, designed to handle the electrical load without excessive heating or arcing. The contacts are enclosed within a housing, which is often made of an insulating material to prevent electric shock and protect against environmental factors.
Contactors are widely used in various industrial and commercial applications to control electric motors, lighting systems, heating elements, and other electrical loads. They are commonly employed in motor control centers (MCCs), electrical panels, and machinery where the current and voltage levels may be too high for conventional switches.
In simple terms, a contactor acts as an electrically operated remote switch that allows or interrupts the flow of electricity to control the operation of electrical devices and equipment. It is typically controlled by a separate low-power circuit, such as a control relay or a programmable logic controller (PLC). When the control circuit is energized, the contactor’s contacts close, allowing the current to flow through the main electrical circuit. When the control circuit is de-energized, the contacts open, interrupting the current flow and turning off the connected electrical load.
Construction of Contactor
The construction of a contactor involves several key components that work together to make and break electrical connections. While contactor designs may vary slightly based on their application and manufacturer, the fundamental components are generally as follows:
Contacts
The primary component of a contactor is its contacts. These are conductive materials, often made of high-quality copper, capable of handling the electrical current without excessive heating or arcing. Contacts come in pairs: the main contacts, responsible for carrying the load current, and the auxiliary contacts, used for control and signaling purposes.
Coil
The coil is an electromagnet that acts as the control element for the contactor. It is typically wound around an iron core and is responsible for generating the magnetic field when current flows through it. When energized, the magnetic field attracts the movable part of the contactor (armature), causing the contacts to close. When the coil is de-energized, the magnetic field weakens, allowing springs or other mechanisms to move the contacts back to their open position.
Armature and Plunger
The armature is a movable part, often attached to the contacts. When the coil is energized, the armature is pulled toward the electromagnet’s core (plunger) due to the magnetic attraction. This movement causes the main contacts to close, allowing the electrical current to flow.
Enclosure
The contacts and coil are enclosed within a housing made of insulating materials, such as plastic or bakelite, to protect against electrical shocks and provide environmental protection. The enclosure also helps prevent the risk of accidental contact with live components.
Mechanical Interlock (optional)
Some contactors feature a mechanical interlock mechanism that prevents the simultaneous closure of multiple contactors. This is important to avoid short-circuits and other hazardous situations when dealing with multiple contactors in a control panel.
Auxiliary Contacts (optional)
Apart from the main contacts, contactors may have auxiliary contacts. These contacts are used for control purposes, such as indicating the status of the contactor (e.g., open or closed) or providing feedback to a control circuit.
Arc Suppressors
To minimize arcing and its detrimental effects on the contacts, some contactors are equipped with arc suppressors or arc chutes. These devices help dissipate the energy from arcing and prolong the contactor’s life.
Contactors are available in various sizes and ratings, depending on the application’s voltage, current, and switching requirements. They play a crucial role in controlling electrical circuits in a wide range of industrial and commercial applications.
Operating principle of contactor
The operating principle of a contactor involves the use of an electromagnetic coil to control the opening and closing of electrical contacts. When the coil is energized, it generates a magnetic field that attracts a movable part (armature) connected to the contacts. This attraction causes the contacts to close, allowing current to flow through the main electrical circuit. When the coil is de-energized, the magnetic field weakens, and springs or other mechanisms move the contacts back to their open position, interrupting the current flow.
Here’s a step-by-step explanation of the operating principle of a contactor
De-energized State (Contacts Open)
When the coil of the contactor is not energized (no current flowing through it), the electromagnetic field is not active. In this state, the movable part (armature) is held away from the electromagnetic coil by springs or other mechanisms. As a result, the main contacts remain open, and no current can flow through the contactor.
Energization of the Coil
When a control signal is applied to the coil, current flows through it, creating an electromagnetic field around the coil’s core. This electromagnetic field generates a magnetic force that attracts the movable armature towards the coil.
Closing of the Contacts
As the armature is pulled toward the electromagnetic coil, it moves the main contacts along with it. This movement causes the main contacts to come into contact with each other, effectively closing the electrical circuit. Now, current can flow through the contactor and onward to the electrical load or equipment connected to it.
Current Flow through the Contactor
Once the main contacts are closed, the contactor allows the electrical current to pass through from the power source to the connected load, such as an electric motor or a lighting circuit.
De-energization and Opening of Contacts
When the control signal to the coil is removed, the coil is de-energized. As a result, the magnetic force holding the armature is reduced, allowing the springs or other mechanisms to move the armature back to its original position. This movement separates the main contacts, opening the electrical circuit and interrupting the current flow.
End of Current Flow
With the main contacts open, the current flow to the electrical load is cut off, turning off the connected equipment or load.
The contactor operates as a remote-controlled switch, allowing for the safe and efficient control of high-power electrical circuits. It finds extensive use in various industrial applications, especially for motor control, lighting systems, heating elements, and other high-current applications where conventional switches may not be suitable.
How does a feedback contact work in contactor
A feedback contact in a contactor (also known as an auxiliary contact or an interlock contact) is an additional set of contacts that provides feedback or signaling to the control circuit about the status of the main contacts. These auxiliary contacts are mechanically linked to the main contacts in the contactor, so their state changes whenever the main contacts open or close.
The feedback contact operates based on the following principle
Mechanical Linkage
In a contactor, the main contacts and the feedback (auxiliary) contacts are mechanically linked together. This means that when the main contacts open or close due to energization or de-energization of the coil, the feedback contacts will mirror this action.
Status Indication
The main purpose of feedback contacts is to provide feedback to the control circuit about the status of the contactor. For instance, if the contactor is used to control a motor, the feedback contacts can indicate whether the motor is running (main contacts closed) or stopped (main contacts open).
Interlocking and Control Logic
Feedback contacts are often used in control circuits to interlock various devices and implement specific control logic. For example, they can be used in combination with other control elements to prevent the simultaneous closure of multiple contactors, thus avoiding short-circuits and potential damage.
Signaling and Alarming
In some cases, the feedback contacts can be used to trigger alarms or indicate specific conditions. For instance, a contactor controlling a pump may have a feedback contact connected to a control panel that signals low oil pressure or overheating when the main contacts are closed.
Feedback contacts come in various configurations, such as normally open (NO) or normally closed (NC). In a normally open configuration, the feedback contacts are open when the main contacts are open and close when the main contacts close. In a normally closed configuration, the feedback contacts are closed when the main contacts are open and open when the main contacts close. The choice of the feedback contact configuration depends on the specific application and control requirements.
Different Types of Contactor
Contactors come in various types and configurations to suit different applications and operating conditions. Here are some of the different types of contactors:
AC Contactor
AC contactors are designed specifically for alternating current (AC) applications. They are commonly used for controlling motors, lighting systems, heating elements, and other electrical loads in AC power systems.
DC Contactor
DC contactors are designed to handle direct current (DC) applications. They are used in DC motor control, battery charging systems, and other DC power applications.
Definite Purpose Contactor
Definite purpose contactors are specialized contactors designed for specific applications, such as HVAC systems, refrigeration, air compressors, and other industrial equipment.
Reversing Contactor
Reversing contactors have multiple sets of main contacts and are used to reverse the direction of rotation of three-phase motors. They can switch the motor’s phase sequence to change its rotation direction.
Mini Contactor
Mini contactors are compact-sized contactors used in space-constrained applications, where standard-sized contactors may not fit.
Power Contactor
Power contactors are heavy-duty contactors designed to handle high-power loads and have higher current and voltage ratings. They are used in industrial applications, such as large motors and machinery.
Lighting Contactor
Lighting contactors are designed specifically for controlling lighting circuits, especially in commercial and industrial buildings. They can handle the high inrush currents associated with lighting loads.
Vacuum Contactor
Vacuum contactors use a vacuum as the arc-quenching medium instead of air. They are used in applications where high switching frequency, low maintenance, and high reliability are required.
Magnetic Contactor
Magnetic contactors are contactors that use electromagnetic coils to control the opening and closing of contacts.
Solid-State Contactor
Solid-state contactors use semiconductor devices, such as thyristors or triacs, to switch electrical loads. They are used in applications where silent operation and high switching speed are essential.
Defrost Contactor
Defrost contactors are used in refrigeration systems to control the defrost cycle of evaporator coils, preventing frost buildup.
Motor Starter Contactor
Motor starter contactors are part of motor starter assemblies that provide overload protection and control for electric motors.
It’s important to select the appropriate type of contactor based on the specific requirements of the application, such as voltage and current ratings, environmental conditions, switching frequency, and load characteristics. Proper selection ensures safe and efficient operation while extending the contactor’s lifespan.
Contactor – Working, Type, Construction, Application and More
How to wire a contactor
Wiring a contactor involves connecting the necessary control circuit and power circuit to the contactor terminals. The specific wiring process may vary slightly depending on the contactor model and the application, so always refer to the manufacturer’s documentation and follow safety guidelines when wiring electrical components. Below are general steps to help guide you through the process of wiring a contactor:
Note: Before proceeding with any electrical work, ensure that the power source is turned off and take appropriate safety precautions to prevent electrical shocks or hazards. If you are not familiar with electrical work, consider consulting a qualified electrician.
Tools and materials you may need
Contactors (main and auxiliary/feedback contacts if applicable)
Control power source (e.g., low-voltage control circuit)
Power supply or line voltage source
Control switches or relays (if needed for control logic)
Wire strippers
Wire connectors (wire nuts)
Electrical wires (appropriate gauge for the current requirements)
Protective gear (safety glasses, insulated gloves, etc.)
Steps for wiring a contactor:
Read the Manual
Familiarize yourself with the contactor’s specifications and wiring requirements by reading the manufacturer’s documentation.
Select the Proper Contactor
Ensure that the contactor is suitable for the specific application and has the appropriate voltage and current ratings.
Prepare the Control Circuit
Identify the control circuit that will energize the contactor’s coil. This circuit typically uses low voltage (e.g., 24V) and is controlled by switches, relays, or a programmable logic controller (PLC).
Identify the Main Power Circuit
This circuit will carry the higher voltage and current that powers the electrical load connected to the contactor.
Disconnect the Power Source
Turn off the power source to the contactor and ensure it is de-energized before proceeding.
Connect the Control Circuit Wires
Connect the wires from the control circuit to the appropriate control terminals on the contactor. Typically, contactors have two coil terminals: one for the control voltage (e.g., A1 or A) and one for the control common (e.g., A2 or B).
Connect the Power Circuit Wires
Connect the wires from the power source to the main power terminals on the contactor. Usually, these terminals are labeled L1, L2, and L3 for three-phase systems or L1 and L2 for single-phase systems.
Connect the Load Wires
Connect the wires from the electrical load (e.g., motor, lighting system) to the load terminals on the contactor. These terminals are often labeled T1, T2, and T3 for three-phase loads or T1 and T2 for single-phase loads.
Optional
Connect Feedback Contacts: If your contactor has feedback contacts (auxiliary contacts), connect them to the control circuit to provide status feedback or signaling.
Check Wiring Connections
Double-check all wiring connections to ensure they are secure and correctly connected.
Test the Wiring
After confirming that all wiring connections are correct, you can power up the contactor and control circuit. Test the contactor’s operation by energizing and de-energizing the coil using the control circuit.
Enclose and Secure Wiring
Once everything is working correctly, enclose the contactor and wiring in an appropriate electrical enclosure or control panel, ensuring proper cable management and secure connections.
Contactor Ratings
Contactors are rated based on several important parameters, which indicate their suitability for specific applications and the maximum electrical load they can handle. The key contactor ratings include:
Voltage Rating
This indicates the maximum voltage the contactor can safely handle. Contactors are available for various voltage levels, such as low-voltage (e.g., 24V, 110V) and high-voltage (e.g., 230V, 400V, 690V). It is crucial to select a contactor with a voltage rating that matches the voltage of the electrical circuit it will be controlling.
Current Rating
This indicates the maximum current-carrying capacity of the contactor. It is expressed in amperes (A) and represents the highest current the contactor can safely switch without overheating or damaging the contacts. The current rating should be suitable for the connected load’s maximum current requirements.
Pole Configuration
The pole configuration refers to the number of main contacts in the contactor. Common configurations include 3-pole and 4-pole contactors. A 3-pole contactor is used in three-phase applications, while a 4-pole contactor may be used for special purposes or specific control schemes.
Motor Power Rating
For contactors used in motor control applications, the motor power rating indicates the maximum power (in kilowatts or horsepower) the contactor can handle. It depends on the rated voltage and current.
Switching Frequency
The contactor’s switching frequency refers to how many times it can safely open and close its contacts in a given time period. The switching frequency can affect the contactor’s lifespan and suitability for specific applications, especially in high-frequency switching operations.
Short-Circuit Withstand Rating
This rating indicates the contactor’s ability to withstand the forces generated during a short-circuit event. It ensures the contactor can handle the high fault currents without damage.
Operating Temperature Range
The operating temperature range specifies the temperature limits within which the contactor can safely function. It is essential to consider the ambient temperature conditions in the installation area.
Coil Voltage Rating
The coil voltage rating indicates the voltage required to energize the contactor’s coil and activate the contacts. This rating must match the control voltage used in the control circuit.
Environmental Protection
Some contactors may have specific ratings related to environmental protection, such as ingress protection (IP) ratings. These ratings indicate the contactor’s resistance to dust and moisture.
When selecting a contactor, it is essential to choose one that meets or exceeds the requirements of the specific application in terms of voltage, current, motor power, switching frequency, and environmental conditions. It is also crucial to follow the contactor manufacturer’s guidelines and recommendations to ensure safe and reliable operation.
How to wire a contactor to the PLC and motor
Wiring a contactor to a programmable logic controller (PLC) and a motor involves connecting the control circuit from the PLC to the contactor’s coil and connecting the power circuit from the motor to the contactor’s main contacts. Below are the general steps to wire a contactor to a PLC and a motor:
Note: Before proceeding with any electrical work, ensure that the power source is turned off and take appropriate safety precautions to prevent electrical shocks or hazards. If you are not familiar with electrical work, consider consulting a qualified electrician or an experienced PLC technician.
Tools and materials you may need
PLC and PLC programming software
Contactors (main and auxiliary/feedback contacts if applicable)
Motor
Control power source (e.g., low-voltage control circuit)
Power supply or line voltage source
Control switches or relays (if needed for PLC control logic)
Wire strippers
Wire connectors (wire nuts)
Electrical wires (appropriate gauge for the current requirements)
Protective gear (safety glasses, insulated gloves, etc.)
Steps for wiring a contactor to a PLC and a motor:
PLC Control Circuit
a. Identify the PLC output that will control the contactor’s coil. In the PLC programming software, assign the desired control logic to this output.
b. Connect one terminal of the PLC output to one terminal of the contactor’s coil (e.g., A1 or A).
c. Connect the other terminal of the PLC output to one terminal of the contactor’s coil common (e.g., A2 or B).
d. If the PLC output requires external power to energize the contactor’s coil, connect a suitable voltage source (e.g., 24V DC) to the PLC output and to the contactor coil terminals.
Main Power Circuit
a. Identify the power source (line voltage) that will supply power to the motor.
b. Connect one phase (e.g., L1) of the power source to one of the main power terminals on the contactor (e.g., L1).
c. Connect the corresponding phase of the motor to the other main power terminal on the contactor (e.g., T1).
d. Connect the other phases (e.g., L2 and L3) of the power source to the remaining main power terminals on the contactor (e.g., L2 and L3).
e. Connect the corresponding phases of the motor to the remaining motor terminals on the contactor (e.g., T2 and T3).
Motor Protection (Optional)
If required, connect motor protection devices, such as overload relays, to protect the motor from excessive current draw. These devices may be connected in series with the motor phases and wired accordingly.
Optional: Feedback Contacts (Auxiliary Contacts)
If your contactor has feedback contacts, connect them to the PLC input(s) to provide status feedback or signaling. For example, you can use these contacts to monitor whether the motor is running or stopped.
Check Wiring Connections
Double-check all wiring connections to ensure they are secure and correctly connected.
Testing and Commissioning
a. After confirming that all wiring connections are correct, commission the PLC and test the contactor’s operation by energizing and de-energizing the coil using the PLC control logic.
b. Verify that the motor operates as expected when the contactor is energized.
Enclose and Secure Wiring
Once everything is working correctly, enclose the contactor, motor, PLC, and wiring in an appropriate electrical enclosure or control panel, ensuring proper cable management and secure connections.
Remember to follow the manufacturer’s guidelines for the PLC, contactor, and motor, and adhere to relevant electrical codes and safety practices. If you have any doubts or concerns, it’s best to seek assistance from a qualified electrician or PLC technician.
Contactor Applications
Contactors are widely used in various industrial, commercial, and residential applications for controlling electrical circuits and equipment. Their robustness, reliability, and ability to handle high current and voltage levels make them suitable for a wide range of applications. Some common applications of contactors include:
Motor Control
One of the primary applications of contactors is in motor control. They are used to start, stop, and control the speed and direction of electric motors in industrial machinery, pumps, fans, compressors, conveyor systems, and elevators.
Lighting Control
Contactors are employed in lighting control systems to switch large banks of lights, especially in commercial and industrial settings. Lighting contactors are used to control streetlights, stadium lights, and lighting in warehouses and factories.
Heating and Cooling Systems
Contactors are utilized in heating and cooling systems, such as air conditioners, HVAC units, and electric heaters, to control the flow of electricity to heating elements or compressor motors.
Electric Power Distribution
In electrical power distribution systems, contactors are used in motor control centers (MCCs) and switchgear panels to control and protect electrical loads, such as motors, transformers, and capacitor banks.
Industrial Machinery and Equipment
Contactors find applications in various types of industrial machinery, including manufacturing equipment, presses, pumps, conveyors, CNC machines, and packaging machines.
Electrical Panels and Distribution Boards
Contactors are used within electrical panels and distribution boards to control the flow of power to different electrical loads and equipment.
Automotive Applications
In electric vehicles (EVs) and hybrid electric vehicles (HEVs), contactors are used to control the high-voltage battery packs and the electric drivetrain.
Renewable Energy Systems
In solar power systems and wind turbines, contactors are used to control and switch the electrical output from solar panels and wind generators to inverters or grid connections.
Process Automation
Contactors are employed in various process automation applications, such as in industrial control systems and programmable logic controllers (PLCs) to control the operation of manufacturing processes.
Power Factor Correction
Contactors are used in power factor correction systems to switch capacitor banks to maintain a balanced power factor and improve the overall energy efficiency of electrical systems.
Water Treatment and Pumping Stations
Contactors are utilized in water treatment facilities and pumping stations to control the operation of pumps, valves, and other equipment.
Emergency Shutdown Systems
In critical applications, contactors may be used in emergency shutdown systems to quickly disconnect power to certain equipment in hazardous situations.
The versatility and wide range of contactor applications make them essential components in modern electrical systems, allowing for efficient and reliable control of various electrical loads and equipment.
Differences between a relay and a contactor
Relays and contactors are both electrical switches designed to control the flow of electricity in electrical circuits. While they share some similarities, there are several key differences between them, including their design, application, and electrical ratings. Here are the main differences between a relay and a contactor:
Current Rating and Load Capacity
Relays: Relays are typically used for low-power applications with relatively low current ratings, often in the range of milliamperes (mA) to a few amperes (A). They are suitable for controlling small electrical loads such as control signals, solenoids, and small motors.
Contactors: Contactors, on the other hand, are designed for high-power applications and have much higher current ratings, typically ranging from several amperes to hundreds or thousands of amperes. They are used to control heavy electrical loads, such as large motors, lighting systems, and industrial machinery.
Size and Construction
Relays: Relays are generally smaller and more compact in size, designed to fit within control panels and tight spaces. They often have a smaller number of contacts, typically single or a few pairs of contacts.
Contactors: Contactors are larger and more robust in construction to handle the higher currents and voltage levels associated with heavy loads. They usually have multiple sets of main contacts and may include auxiliary contacts for feedback and control signaling.
Application and Usage
Relays: Relays are commonly used in control and automation applications to switch signals, control components, and activate various electrical devices.
Contactors: Contactors are used in applications where switching high-power loads is required, such as motor control, lighting control, and industrial equipment control.
Coil Voltage
Relays: Relays typically have lower coil voltage requirements, often operating on low voltage levels, such as 5V, 12V, or 24V.
Contactors: Contactors usually require higher coil voltages, such as 110V, 220V, or 240V, to energize their coils and close the main contacts.
Control Circuits
Relays: Relays are commonly controlled by low-power control circuits, such as those found in programmable logic controllers (PLCs) or microcontrollers.
Contactors: Contactors are controlled by separate low-power control circuits or directly by control switches, relays, or PLCs, depending on the application.
In summary, relays are used for low-power control applications, while contactors are used for high-power switching applications. Contactors are designed to handle heavy loads, such as large motors and industrial equipment, while relays are used for switching smaller electrical loads and control signals.
FAQ’s
What is the working principle of the contactor?
Principle of operation of a contactor: the current passing through the contactor excites the electromagnet. The excited electromagnet produces a magnetic field that causes the contactor core to move the armature.
What types of contactors work and their applications?
Applications of a contactor include the control of electric motors, thermal evaporators, lighting, capacitor banks, heating and other electrical loads. Contactors vary in size and capacity. You have those that you can easily lift with your hand and other huge ones that measure around a meter on each side.
You may also like