Magnetic Starter : Circuit, Working, Wiring, Vs Contactor, Advantages & Its Applications

A motor starter is an electrical device used to control an electric motor in various applications by controlling the electrical power to start, stop, protect, and reverse the electric motor. This device includes two essential components like contactor and an overload relay where the contactor helps to control the current flow to the motor by making or breaking the supply to the circuit. An overload relay is used to protect the motor from any damage. So the starter turns ON/OFF the motor and also provides the required overload protection for the circuit. There are different types of motor starters available like; manual and magnetic starters. This article provides brief information on a magnetic starter, their working, and their applications.

What is a Magnetic Starter?

An electromagnetically operated device that is used to start & stop a connected load is known as a magnetic starter. These starters include an electrical contractor & an overload that helps protect the motor in case of an unexpected power loss. This device provides a secure method to start an electric motor through a large load and also provides overload & under-voltage protection and an automatic cutoff power when a power failure occurs. This starter operates electromagnetically which means the load connected to the electric motor starter is started & stopped typically with lower & safer voltage than the voltage of the motor.

Features of Motor Starters

Motor starters are utilized on a large scale because of their number of features which are extremely useful for electrical devices like the following.

• These starters make possible of starting & stopping of the electric motor.
• These are rated by power in kilowatts or horsepower & current in amperes.
• This device allows you to make & break current supply rapidly.
• These provide the required overload protection for the electric motor.
• They have remote on or off control features.

Parts of Magnetic Starter

A magnetic starter includes a contactor & an overload relay. The contractor is not a significant part of the magnetic motor starter. It is simply made out of a coil whenever it is powered up then generates a magnetic field that opens or closes electrical connections. So these contacts control whether the electrical motor is connected or disconnected to or from the supply. To meet the exclusive specifications of the electric motor they regulate, these are available in different sizes & configurations.

The overload relays in magnetic motor starters help protect the electric motor from over-current conditions. These relays trip if the current flowing throughout the motor increases above a certain limit. So these relays help in avoiding damage to the electric motor cutting off the supply in the occurrence of an overload.

How Does a Magnetic Starter Work?

Magnetic starter simply works by depending on electromagnets. These starters have a set of contacts that are electromagnetically operated to control the connected motor load & also an overload relay. This relay detects an overload on an electric motor by simply opening the control voltage to the starter coil. A control circuit with momentary contact devices that are connected to the coil executes the start and stop function.

Magnetic Starter Circuit Diagram

Magnetic starter is the most commonly used type of motor starter that is used mostly for high-power AC electric motors. So these kinds of motor starters work electromagnetically similar to a relay that simply makes or breaks the contacts with magnetism. This starter provides a very secure and lower voltage to start the motor & it also has protection from overcurrent and low voltage. This magnetic starter breaks the circuit automatically when a power failure occurs. The magnetic starter circuit diagram is shown below.

This starter generally includes two circuits like; a power circuit and a control circuit. The power circuit is responsible for supplying power to the electric motor. It includes electrical contacts that turn ON or OFF the power to the motor through an overload relay that is supplied simply from the supply line. The control circuit simply controls the contacts by either making or breaking the supply to the electric motor. The electromagnetic coil simply energizes (or) de-energizes for pulling or pushing the electrical contacts and therefore provides a remote control mainly for the magnetic starter.

Magnetic motor starters are the most commonly used single-speed type starters. For these types of starters, a selector switch or a pushbutton is connected to a digital input of a programmable logic controller which is used for activating a digital output of PLC. The output of this PLC will pull within a coil that holds the contacts of the starter closed magnetically by allowing the flow of current to supply to the electric motor. These starters are utilized with full voltage nonreversible as well as

Magnetic Starter Wiring Diagram

An electrical circuit may have many control switches to make the operating coil work as specified. So these two control switches may be connected either in series (or) parallel when an operating coil is controlled.

Even though, a circuit can also contain several electrical loads, which decide the necessary wire size as well as the incoming power supply rating. The whole current improves when loads are connected to the circuit.

When the two control devices are connected in series for controlling a coil within a magnetic motor starter is shown below. In this circuit, the two control switches are; a temperature switch & a flow switch. These switches are connected in series to control a coil within a magnetic motor starter. These two switches should close to permit current supply from L1 to the control device, after that the magnetic starter coil & the overloads, to L2.

When the two control devices are connected in parallel for controlling a coil within a magnetic motor starter is shown above. Either any one of the switches is closed to allow the current supply to flow from L1 throughout the control switch, the magnetic starter & the OL to L2. Apart from how these switches are connected within a circuit, they have to be connected between L1 & the operating coil.

The control device contacts may be either NO or NC. Here, the contacts utilized & the manner the control devices are allied into a circuit will determine the circuit function.

Magnetic Starter Vs Contactor

The difference between a magnetic starter and a contactor includes the following.

Advantages

The advantages of magnetic starters include the following.

• These starters provide overload & under-voltage protection.
• These automatically cut off the motor connection when a power failure occurs.
• These can also be wired flexibly to achieve functions like; flicking & changing based on the control necessities
• These are easily operated, controlled, and very easy to maintain.
• These are completely economical.
• These starters are used commonly as operating switches mainly for remotely or locally controlled electric motors.
• These are available in irreversible & reversible versions.

The disadvantages of magnetic starters include the following.

• These starters are limited to 5 HP or below 5 HP.
• The motor’s lifespan can be reduced.
• High inrush current causes harm to the windings of electric motor & a voltage drop potentially within the power line.

Applications

The applications of magnetic starters include the following.

• These types of starters are found commonly on equipment drawing numerous horsepower (or) higher like woodworking machinery (cabinet saws (or) shapers), and different machines with minor loads like drill presses.
• Magnetic starters are essential devices to use in motor control applications.
• These devices are stock components mainly for numerous machines.
• These types of motor starters are utilized in across-the-line applications.
• These can be used as reduced voltage starters mainly for single-phase and three-phase electric motors.

Thus, this is an overview of magnetic starters, working, circuits, wiring, differences, advantages, disadvantages, and applications. This is a type of electromagnetically working switch, used to provide a very secure technique to start an electric motor through a large load. These starters can also protect from overload and also turn off when a power failure occurs. Here is a question for you, what is a motor starter?