Everything You Need to Know About Contactors and How They Work

What is a Contactor and What is it Used For?

A contactor is an electrically controlled switch used for switching an electrical circuit, similar to a relay. However, unlike a relay, a contactor is used in applications with higher current-carrying capacity.

As someone deeply involved in industrial automation and industrial control products, I’ve seen firsthand how contactors play a critical role in managing high-power circuits. They are designed to be connected directly to high-current load devices.

When energized, the coil within the contactor creates a magnetic field, which causes the core of the contactor to move, and close the contacts, allowing current to flow to the load.

Contactors are most commonly used with electric motors and are designed and built to handle the heavy loads and frequent switching that these applications require.

For example, in our manufacturing plants, we utilize contactors to control large motors that power our conveyor belts and other heavy machinery. Their ability to handle large amounts of electrical power makes them an essential component in our electrical systems. A contactor is used to control power to motors, lighting, heating, and other electrical loads.

What are the Different Types of Contactors?

There are various types of contactors available, each designed for specific applications. Some common types include AC contactors and DC contactors, definite purpose contactors, single-phase, and three-phase contactors.

Each type of contactor has its own set of features and is used in different scenarios based on the requirements of the electrical circuit and the load it is controlling. I remember a case where we had to switch from an AC contactor to a DC contactor when we upgraded our power supply system, which significantly improved the efficiency of our motor control.

How Does a Contactor Work? The Operating Principle

The operating principle of a contactor involves an electromagnetic coil and a set of contacts. When electrical current flows through the coil, it generates a magnetic field that attracts a movable core, also called an armature.

This movement causes the contacts to close, allowing current to flow through the circuit to the load. When the coil is de-energized, the magnetic field disappears, and a spring returns the contacts to their normally open position, interrupting the current flow.

In our engineering cases, we use contactors to control large motors. When the start button is pressed, the contactor coil is energized, creating a magnetic field that closes the contacts and starts the motor.

When the stop button is pressed, the coil is de-energized, and the contacts open, stopping the motor. This process allows for safe and efficient remote operation of high-power devices.

What is the Difference Between Contactors and Relays?

While both contactors and relays are used to switch electrical circuits, there are key differences between them. Contactors are designed to handle much higher currents and voltages than relays.

They are typically used in applications where large motors or other high-power devices need to be controlled. Relays are generally used for lower-power applications and signaling. Additionally, contactors often have features like arc suppression to handle the high currents and prevent damage. A great example of this is in our HMI Mitsubishi.

In our operations, we use relays for control signals and contactors for power switching. For instance, a relay might be used to activate a sensor, while a contactor is used to start a large motor based on that sensor’s input. This division of labor ensures the reliability and safety of our electrical systems.

How to Select the Right Contactor: A Contactors Selection Guide

Selecting the right contactor for your application is crucial to ensure proper operation and longevity of your equipment. Factors to consider include the voltage and current ratings, the type of load (e.g., motor, lighting, heating), the number of poles, and the operating environment. 

Ensure the contactor can handle the maximum operating voltage and current of the circuit. It’s also important to consider the duty cycle and the expected number of switching operations.

When we were designing a new production line, we had to carefully select contactors that could handle the high starting currents of our motors.

We consulted manufacturer specifications and chose contactors with appropriate electrical ratings and features like auxiliary contacts for control circuits.

AC Contactor vs. DC Contactor: Which One Do You Need?

AC contactors are designed for use in alternating current circuits, while DC contactors are designed for direct current circuits. The main difference lies in how they handle the arc that is generated when the contacts open and close. 

AC contactors use the zero-crossing of the AC waveform to help extinguish the arc, while DC contactors require additional arc suppression mechanisms.

In our engineering cases, we use AC contactors for most of our equipment since our power supply is AC.

However, we have some specialized equipment that uses DC power, and for those, we use DC contactors with arc chutes to manage the arc. You can find many PLC Mitsubishi types are sold online on our site.

Understanding Contactor Wiring Diagrams

A contactor wiring diagram shows how the contactor is connected within an electrical circuit. It typically includes the coil, the main contacts, and any auxiliary contacts. Understanding these diagrams is essential for properly installing and troubleshooting contactors.

This knowledge has been invaluable in quickly diagnosing and fixing issues with our equipment. Omron HMI devices provide detailed diagrams that have helped our team immensely.

Electrical Ratings and Specifications of Contactors

Contactors have various electrical ratings that specify their operating limits. These include the rated voltage, rated current, switching capacity, and mechanical and electrical endurance.

It’s crucial to select a contactor with ratings that meet or exceed the requirements of your application. You can find detailed information about electrical ratings in our Proface HMI manuals.

For example, when we installed new motors in our factory, we had to ensure the contactor we selected had a higher rated current than the motor’s full-load current to handle inrush currents during startup. We also considered the ambient temperature and chose contactors with appropriate derating factors.

Applications of Contactors in Industrial Automation

Contactors are widely used in industrial automation for controlling motors, lighting systems, heating elements, and other high-power devices.

They are an integral part of motor starters, control panels, and other automation equipment. Their ability to handle high currents and frequent switching makes them ideal for these applications.

We use contactors in various applications, from controlling the motors on our conveyor belts to managing the lighting in our production areas. Their reliability and durability are essential to maintaining our production efficiency.

Maintenance and Troubleshooting of Contactors

Regular maintenance of contactors is important to ensure their proper operation and prevent failures. This includes inspecting the contacts for wear and damage, checking the coil resistance, and ensuring that the contactor is properly mounted and wired.

Troubleshooting common issues with contactors involves checking for loose connections, burnt-out coils, and worn or damaged contacts. In our experience, regular inspections and timely replacement of worn components have helped us minimize downtime and keep our production running smoothly.