What Is a Magnetic Starter? Components, Working Principle and Benefits

An electromechanical device called a magnetic starter controls whether a motor is on or off and protects it from damage. The typical application for a magnetic starter is in industrial equipment such as machinery, pumps, compressors, conveyor systems, heating and cooling systems, etc., that operate using electric motors. The combination of a contactor with overload protection allows for better operational safety and reliable automation by preventing damage to motors.

To properly choose motor control equipment for each of your motors, whether in an industrial facility, a shop, a water treatment plant, or anything else, you need to understand how a magnetic starter works. This article will explain the key elements of the design and operation of magnetic starters, as well as potential applications, and types of starters with advantages and important selection factors.

What Is a Magnetic Starter?

magnetic starters are a type of motor control equipment that operates based on the principles of magnetism. They use a magnetic field created by an electromagnet to operate power contacts. When the coil within the starter is energized (turned on), it creates a magnetic field that pulls the contacts closed, allowing electrical current to flow from the power source to the motor. Conversely, when the coil is de-energized (turned off), the contacts will open and stop supplying power to the motor.

magnetic starters give you advantages over just using a simple manual switch, including the ability to remotely control your motor, automatically start and stop your motor, protect it from overloads, and start it more safely than if you were turning it on and off manually. This is especially beneficial when using an automatic control system or anytime you have a motor that requires frequent on/off operations (starting/stopping).

Why Is a Magnetic Starter Important?

Electric motors can start drawing high currents and getting damaged if they are overloaded, jammed, or subjected to other abnormal conditions. magnetic starters will limit these risks because they operate in a controlled manner for switching and provide protection functions.

In many industrial and commercial applications, magnetic starters are used because they offer:

• Safe motor control for starting and stopping motors
• Overload protection to prevent overheating and motor failure
• Remote operation through push buttons, sensors, PLCs, or control panels
• automatic restart prevention after a power failure in many control circuits
• Long service life for equipment that requires frequent switching

Main Components of a Magnetic Starter

A magnetic starter has various components that work together to start and protect the motor. While the actual construction will be determined by many factors such as the manufacturer’s design, voltage rating, motor size or type, and how it's used, most magnetic starters have the following basic parts.

1. Contactor

The key part of a magnetic starter that switches the electrical supply to a motor is the contactor. A contactor normally has four basic components: main contacts, auxiliary contacts, an electrical coil for electromagnetism, and a mechanical framework.

When current is applied to the coil, the main contact closes, letting the motor receive power from the supply. When power is removed from the coil, the main contacts open and disconnect power to the motor.

2. Electromagnetic Coil

The contactor is powered by a magnetic field produced by the coil in the contactor. The coil may be constructed to operate at various control voltage levels, including 24V, 110V, 120V, 220V, and 240V, depending on the control circuit.

Coil voltage must correspond to the voltage of the control power supply. Using an incorrect coil voltage can cause the starter to malfunction and to either overheats or to fail completely.

3. Overload Relay

The overload relay reduces the chance of the electric motor overheating due to too high a voltage. If the electric motor draws more voltage than is rated for too long, it will shut down. The overload relay will stop the motor before serious harm occurs because it trips by opening the electrical circuit to the electric motor when it sees excessive current draw.

Depending on the use case, overload relays come in various types, including thermal, electronic and adjustable overload relays. The proper setting of an overload relay is critical for dependable protection of motors.

4. Main Contacts

The motor current is carried by the primary contacts. They are designed to carry the rated voltage and current of the motor. The contacts must be rated appropriately for application use due to the higher starting current than running currents of the motor.

5. Auxiliary Contacts

Auxiliary switches are used in many control circuits for interlocking, signaling, self-holding, and connecting to other devices (e.g., indicator lights, PLC inputs, and alarms).

A starter can be energized by an auxiliary contact that maintains the current state when the start button has been released; in addition, all auxiliary contacts that are part of two contactors will prevent these two contactors from operating simultaneously when used as a reversing motor starter.

6. Start and Stop Push Buttons

The electrical control of several magnetic motor starters consists of push buttons; a start button which will apply energize the coil, and a stop button which will de-energize the control circuit and therefore stop the motor.

They can be mounted either on their corresponding starter enclosure, at a hydraulic station or controller wired separately from the starters themselves, or obviously on an operator panel.

7. Enclosure

A magnetic starter is protected from dust, moisture, contact with other objects, and external damage by an enclosure. An enclosure can be specified for the particular environment where it will be placed, such as either indoors or out; with protection against dust or water; or for preventing rust.

How Does a Magnetic Starter Work?

Electromagnetism causes a magnetic starter to work. When you press the "Start" button, an electromagnet is generated by the coil, which then closes the internal contacts and starts the motor. The motor will continue to run even after you let off the start button because of an auxiliary circuit that provides power while you are not pressing the button. By pressing the "Stop" button, you break power to the motor, stopping it. If the motor is overloaded, the device will automatically disconnect from the power supply to prevent damage.

Magnetic Starter vs. Contactor: What Is the Difference?

One question frequently asked is "Is a contactor just another name for a magnetic starter?" The two devices are related to each other but they cannot be described as being the same thing.

Contactor is a device that is used to switch electrical circuits. A magnetic starter is a contactor that provides overload protection; it may also have a control button, additional mechanical contacts for controlling loads or for controlling other control devices, plus a physically enclosed shape for protection from accidental contact with the live circuits.

In simple terms:

• Contactor: Switches the motor on and off
• Magnetic starter: Switches the motor on and off while also protecting it from overload

For motor drives, magnetic starters are seen as advantageous because motors require both control and safe operational limits.

Types of Magnetic Starters

Different varieties of magnetic starters can be found to suit various types of motor control. The type of starter chosen will depend on the motor, load, power supply, and also the operating conditions.

1. Direct-On-Line Magnetic Starter

A Direct-On-Line (DOL) Starter is an electrical device that connects the motor directly with power supply at time of start. This type of starter is easy to use, inexpensive and has been used for many applications of smaller and medium Sized Motors.

Starting a motor using DOL isn't a good option for large motors or machinery that requires a lot of torque, because when the motor is first started, the starting current will be very high.

2. Reversing Magnetic Starter

A reversing magnetic starter can enable a motor to reverse both ways. Two contactors are utilized for each direction, and both types of interlocks prevent the two directions from being energized at once.

Hoists, conveyors, machine tools and equipment that need directional control, often use this type of machine.

3. Star-Delta Starter

To reduce inrush current at startup, A star-delta starter initially connects motor windings in a star configuration before ultimately connecting motor windings together in a progressive transition from star to delta configuration for normal operation.

It is often used for larger three-phase motors where reducing starting current is important.

4. Manual Reset Magnetic Starter

Using a manual-reset magnetic starter requires the operator to clear an overload trip, in order to help keep an unexpected restart from occurring while troubleshooting and increase your safety.

5. Automatic Reset Magnetic Starter

If an automatic reset magnetic starter has an overload condition, it will reset itself when the overload condition clears. An automatic reset magnetic starter is used in applications that might be unattended. If using an automatic reset magnetic starter, care must be taken because the automatic restart may create safety hazards.

Key Benefits of Using a Magnetic Starter

Magnetic starters are used extensively because of both their benefits for equipment safety and operating efficiency.

1. Motor Overload Protection

An overload protection is a significant advantage of a magnetic starter. Motors can be overheated by operating under excessive loads, experiencing phase failure, or being mechanically blocked. The overload relay disconnects from the motor before any irreparable harm to it.

2. Improved Operator Safety

Operators are provided with a safe method for controlling motors through low-voltage controlled circuits and remote push buttons via magnetic starters; therefore, there is no longer a need for an operator to come in direct contact with high power circuits.

3. Remote and Automatic Control

By using push buttons, float switches, pressure switches, limit switches, timers, sensors or PLC systems, you can remotely control the operation of your magnetic starter. This ability to control the magnetic starter remotely makes it particularly well-suited for use in process control and automation applications.

4. Protection After Power Failure

A lot of magnetic starter circuits, when power has failed, will cause the contactor to drop out and stop the motor from working. When power comes back on, unless the start button has been pressed again, the motor will not automatically restart. This helps to prevent equipment from unexpectedly starting.

5. Longer Motor Life

A magnetic starter will also help increase the lifespan of the motor and reduce the overall cost of maintenance by using overload protection and controlling how motors start and stop.

6. Suitable for Frequent Switching

Magnetic starters are designed for various types of machinery to be switched on and off repeatedly. This makes them great for equipment that starts and stops throughout the day.

Common Applications of Magnetic Starters

Magnetic starters have many uses in commercial and industrial motor applications. Examples include these common uses:

• Pumps and water supply systems
• Air compressors
• Fans and blowers
• Conveyors and material handling systems
• HVAC equipment
• Industrial mixers and agitators
• Machine tools
• Packaging machinery
• Agricultural equipment
• Hoists, cranes, and lifts

How to Choose the Right Magnetic Starter

Choosing the proper magnetic starter is vital to ensure safe and reliable operation of your equipment. Prior to buying or installing a magnetic starter, there are a few important factors to take into consideration.

1. Motor Voltage

Verify the motor plate and confirm that the supply voltage, both single and three-phase power, agrees with the starter. The starter must also match the configuration of the motor system.

2. Motor Full Load Current

One of the select parameters that are significant in regard to selecting a motor is FLA of the motor nameplate, or full load current. The contactor and overload relay must have an appropriate rating for the motor current.

3. Horsepower or Kilowatt Rating

A magnetic starter can be rated based on either the motor horse power or on the kilowatt value of the motor being started. When selecting a magnetic starter, ensure that it is compatible with the motor size and application duty rating.

4. Coil Voltage

A coil needs to match the control circuit voltage; a coil with 275V coil would need to have 275V in the control circuit. For example, if your control circuit uses a 220V coil; Therefore you would require 24V for the coil.

5. Application Type

When reviewing the motor, you need to identify if it requires simple start-stop control, reverse operation, reduced voltage startup, or should be integrated with other automation equipment.

6. Enclosure Rating

An enclosure must be selected based on the environment in which it will be installed. Locations that are wet, dusty, outdoor, or corrosive all require the appropriate enclosure for protection.

7. Overload Relay Range

The motor full load current should be used to define the overload relay set point; inappropriate relay adjustment can cause false tripping or an insufficiently protected motor.

Magnetic Starter Installation Considerations

Qualified electrical professionals must perform installations according to local electrical codes and manufacturer instructions. Incorrectly wiring or sizing the product(s) can create numerous hazards and expose the installer to dangerous situations.

Important installation considerations include:

• Verify power supply voltage before wiring
• Use proper wire size based on motor current
• Confirm correct coil voltage and control circuit design
• Set the overload relay according to the motor nameplate current
• Ensure proper grounding
• Install the starter in a suitable enclosure
• Test start, stop, and overload functions before normal operation

Common Problems and Troubleshooting Tips

A magnetic starter that has been properly selected and installed can also suffer from malfunction if operated in severe operating conditions. Some common types of problems and possible reasons for these problems associated with magnetic starters include the following:

Starter Does Not Energize

• No control voltage available
• Faulty start button or control switch
• Open stop circuit
• Damaged contactor coil
• Tripped overload relay

Motor Starts but Stops Quickly

• Overload relay setting is too low
• Motor is overloaded
• Mechanical load is jammed
• Voltage drop during startup
• Loose wiring connection

Contactor Chatters or Hums

• Low control voltage
• Dirty or damaged contactor core
• Loose coil connection
• Incorrect coil voltage

Overload Relay Trips Frequently

• Motor load is too high
• Overload setting is incorrect
• Motor bearings or driven equipment are faulty
• Phase loss in a three-phase system
• Poor ventilation causing motor overheating

Magnetic Starter Maintenance Tips

If you have a magnetic starter and a motor being controlled, regular maintenance will increase their reliability and lifespan.

• Inspect contacts for wear, pitting, or burning
• Check terminal screws and wiring connections
• Remove dust and debris from the enclosure
• Verify overload relay settings
• Test start and stop functions regularly
• Listen for unusual humming or vibration
• Replace worn or damaged components promptly

Frequently Asked Questions About Magnetic Starters

Does every motor need a magnetic starter?

While not all motors will need a magnetic starter, many commercial and industrial motors will receive a benefit from being controlled by one. Motors requiring overload protection (thermal overload capable), remote control capability, automation capability, or are often switched are all good cases to use magnetic starters to control them.

Can a magnetic starter be used for a single-phase motor?

For both single-phase and three-phase motors, you can use magnetic starters. To select the right starter, consider the motor's voltage, current, and application needs.

What happens when an overload relay trips?

In an overload relay, once an overload relay trips, the control circuit is opened, which causes the contactor's coil to lose energy. In doing this, the contactor will cut off all power supplying the motor and help to prevent overheating or damage.

Is a magnetic starter the same as a motor starter?

Magnetic starters are one of several different types of motor starters. A motor starter may be any number of devices to start an electric motor, such as a manual starter, magnetic starter, soft starter, or variable frequency drive.

Can a magnetic starter reduce starting current?

Conventional direct-on-line (D.O.L.) magnetic starters do not provide a significant drop in motor starting current; however, certain types of motor (e.g., star/delta or reduced-voltage) starters are capable of reducing starting current for larger motors.

Final Thoughts

A magnetic starter provides reliable motor control plus expanded functionality (such as overload protection). By integrating electromagnetic switching with overload protection, a magnetic starter can help prevent damage to your equipment from being accidentally started or stopped.

It can be used in applications ranging from pumps and compressors to conveyors and HVAC systems. A magnetic starter helps keep your motors running smoothly and safely, while also helping you to automate part of your processes.

There are several considerations when selecting a magnetic starter, such as motor voltage, current rating, horsepower, coil voltage, overload relay range, enclosure type, and application requirements, among others. A correctly selected and properly installed magnetic starter can minimize downtime and give longer life to the motor, as well as help the electrical system perform better. We provide a complete line of rugged magnetic starters for many different types of motors. Please do not hesitate to reach out to us with product selection or technical questions.