What Is a Magnetic Switch?
A magnetic switch is a switch that combines an electromagnetic contactor, whose contact is switched open and closed by an electromagnet, and a thermal relay, which interrupts the circuit when overloaded.
In a circuit that supplies power to a load, it functions as a protective device for the load in the event of an overload (overcurrent).
A breaker is a similar protective device, but whereas a breaker protects wires and prevents short-circuit accidents, a magnet switch prevents overcurrents to the load.
Uses of Magnetic Switches
A magnet switch is a device that shuts off power in the event of an overcurrent and is capable of interrupting currents of about 10 or more times the rated output.
This function is mainly used to protect motors, quickly detecting and stopping the operation of a motor in a missing-phase state (a motor running in single-phase operation when it should be running in three-phase operation) due to a broken wire or poor contact, etc., thereby preventing motor failure due to overload.
Magnet normally switches have three main contacts, which are connected to a star-connected or delta-connected coil when used to protect a 3-phase motor.
Principle of Magnetic Switches
A magnet switch consists of an electromagnetic contactor and a thermal relay. The thermal relay thermally senses the current and trips in the event of an overcurrent. contact opens and shuts off the power supply in the event of an overcurrent. The a-contact output can also be used by connecting it to an abnormality display, etc.
Pressing the reset button after the thermal relay has cooled to air will restore power, but if the overload condition continues, power will be immediately shut off again.
Electromagnetic contacts require mirror contacts to reliably detect the welding of the contacts. Mirror contact is a feature that guarantees that if one of the main contacts (the normally used contact) is closed, the auxiliary contact, which is NC (normally closed), will be open. The mirror contact allows the detection of a welded main contact if the auxiliary contact is open when the coil is OFF (not attempting to close the contact).