01-08-2025
What is Magnetic starter? Distinguishing between magnetic and contactor starters
- News
- Dec 31, 2024
- 1366 views
Magnetic starter is a combination of electromagnetic switches, which works to start electric motors with large loads safely. Magnetic motor starters appear a lot in the way 3-phase electrical systems use motors. In fact, this set of equipment is easily confused with a contactor. A compilation of knowledge about magnetic starters including components, operating principles, how to distinguish them from contactors and applications will be in the following article from BTB Electric.
What is Magnetic Starter?
A magnetic starter or motor starter is an electromagnetic switch that starts and stops the engine. This device ensures the motor runs within a safe threshold, protecting the motor from overloading. When energized through the motor starter, the current passes through the contacts to reach the motor. When there is a problem, the internal contact separates to cut off the current.
The magnetic start is usually installed and controlled via buttons and knobs on the surface. In modern electrical systems, the start can be controlled remotely or automatically via a PLC.
Structure of the magnetic starter
The magnetic starter consists of contactor and overload relay as the two main components, the sub-components are the control circuit and the self-sustaining circuit.
Contactor
The contactor is the most important component of the magnetic starter and is often confused with this kit. The contactor works according to the electromagnetic principle, with a coil located inside. When there is an electric current flowing through the coil, a magnetic field is generated and attracts the contacts inside the contactor together to allow the current to flow through. When there is no current, the suction coil releases the contact.
The contactor does not directly protect the motor, but needs to be combined with a thermal relay to cut off the power when an overload is detected. The function of the contactor is to switch off high-power circuits with a continuous switching frequency.
Overload relay
The overload relay is the protective component of the magnetic starter. The main function of the overload relay is to monitor the current of the motor, detect the electrical overload, and break the circuit. There are 2 types of relays used for magnetic start: thermal relays and electronic relays:
- Thermal relay: Interacts with the overload current through the thermal mechanism to interrupt the circuit.
- Electronic Relay: Interact with overload current using a state-of-the-art microprocessor, which has a faster reaction time than a thermal relay.
Control Circuit
The magnetic starter uses a control circuit with two push buttons – the engine start button and the engine stop button. These buttons connect to the control voltage to activate the coil in the contactor.
The start button is a temporary switch that only closes the circuit to start the motor when pressed. The stop button is a type of switch that is normally closed, when pressed, will stop the motor.
Self-sustaining circuit
When the start button is pressed for the starter, the motor does not receive direct power. Instead, the contactor is energized and energizes the motor, creating a self-sustaining circuit. This mechanism keeps the engine running after the start button is released. Contactor continued to work after that.
Working principle of magnetic starter
The starter has a relatively simple operating principle. When the start button is pressed on the circuit, the electrical signal is transmitted to the contactor's coil. The coil coil draws contacts to allow current to flow to the motor.
During motor control, the relay monitors the operating current. If the motor power exceeds the rating, the relay will trip, opening the circuit and stopping the motor. This mechanism helps protect the motor from damage caused by heat-generating overload currents. In many complex systems, a PLC controller can be added to control the motor through pressure, humidity or timing.
Comparison of starter and contactor
Contactors are often confused with magnetic starters. In fact, the contactor is the main component of the magnetic starter with the task of switching off the electrical circuit. The mechanism that allows the current to flow through the contactor is the mechanism that closes and breaks the circuit of the magnetic starter.
Contactors have the main application of switching off electrical circuits, but do not have a protection function when overload or short circuit occurs. On the contrary, starting from because there is an additional component, the overload relay will have this function. Therefore, the word starter has more functions, higher applicability than contactor.
Benefits of using magnetic starters
The biggest benefit of using magnetic starters for motors is that they protect the motor against overloads and short circuits. The unit will shut off power to the motor when the current exceeds the limit. This helps the motor to operate stably, prolong its life, and limit damage.
The magnetic starter can be controlled remotely, allowing for flexible and systemically focused operation. Therefore, magnetic starters are very suitable for complex, high-capacity industrial power systems. Besides, automatic control systems can be integrated for this set of equipment.
The use of magnetic starters adds an extra layer of safety in motor control and, more broadly, the entire system. The engine starter prevents the engine from restarting itself after a power failure, preventing unexpected dangerous problems.
Application of Industrial Magnetic Starter
Magnetic starters are typically used for industrial machinery with a capacity of 5HP (3.7kW) or more. Some of the applications of the word startup today are:
- Control of industrial electrical equipment such as cutters, lathes, robotic arms, conveyors, pumps, motors,...
- Control saws, milling machines, grinding machines,.. in woodworking.
- Use for HVAC systems to manage compressors and ventilation fans.
A magnetic starter is a combination of motor control devices, which includes a contactor and an overload relay. Using a magnetic starter allows the motor to operate within safe thresholds against circuit risks.
BTB Electric offers devices for magnetic starters, including contactors and thermal relays with high compatibility. Refer to the two product ranges at:
