To understand how to connect a magnetic starter, you should understand the principle of its operation. It is simple and completely identical to the way any relay works.
The main task of the magnetic starter is to remotely connect a powerful load, which can be done both manually and during the algorithmic work of an industrial automated installation.
The main components of the magnetic starter are an inductive coil that creates a magnetic field, an armature mechanically connected to one of the contact groups, and another pair of contacts.
The inductor is included in the control circuit, consisting of sequentially connected Stop buttons with normally closed contacts and Start with normally open. In parallel with the “Start” button, one more contact pair is turned on, which closes at the same time as the load is connected.
The magnetic starter operates as follows: when you press “Start”, the electric circuit closes , the current passes through the closed contacts of this button and the “Stop” button (because they are normally closed), which means that until the button is pressed, the circuit will not open. When an electric current passes through the coil, a magnetic field arises in it, attracting the armature, which, in turn, connects the contacts - there are only four of them. Three of them are basic and are designed to include a three-phase payload, such as a powerful electric motor. The fourth pair is connected in parallel with the start button, which can then be released, and the current in the circuit will pass through these contacts.
In order to disconnect the load, it is enough to open the solenoid circuit. For this purpose, the “Stop” button is intended, the contact group of which in the normal position is closed and opens when pressed. Now everything happens in the reverse order: the circuit is interrupted, the magnetic field of the coil disappears, all contacts open, both power and holding. The “Stop” button can be released - the current will not go through the control circuit anymore, because the contacts of the “Start” button are open when not pressed. That's it, the magnetic starter is off.
As a rule, the coil of a magnetic starter is designed for a voltage of 220 volts of alternating current with a frequency of 50-60 Hertz. It is better not to use devices that use magnetic coils or transformers designed exclusively for a frequency of 60 Hertz in our circuit - they may fail, but a domestic or European magnetic starter can be used in America without restrictions.
A typical installation error is the inclusion of a control circuit not between the neutral and the phase, but between the phases. In this case, 380 volts instead of 220 fall on the coil, and it burns out.
With all the simplicity of the device, the design of the magnetic starter is constantly being improved. Design bureaus creating new switching devices strive to reduce noise during operation and to reduce the electric arc formed at the moment of connection or disconnection of contacts. This is especially true for high-voltage starters, designed to work with a voltage of a thousand volts. So, the joint Swiss-Swedish company Asea Brown Boveri Ltd has been producing switching equipment for electrical circuits since the end of the nineteenth century, and it has gained vast experience in the production of this equipment. The ABB magnetic starter is the same as the Rolls-Royce among cars.