Magnetic starter - why it is needed and how to connect it

To understand how to connect a magnetic starter, you need to understand the principle of its operation. It is simple and completely identical to the one on which any relay works.

The main task of the magnetic starter is the remote connection of a powerful load, which can be performed both in manual mode and during the algorithmic operation of an industrial automated installation.

The main components of the magnetic starter are an inductive coil creating a magnetic field, an armature connected mechanically to one of the contact groups, and another pair of contacts.

The inductance coil is included in the control circuit, consisting of a series of "Stop" buttons with normally closed contacts and "Start" with normally open. Parallel to the "Start" button, another contact pair is switched on, which closes at the same time as the load connection.

The magnetic starter works as follows: when the "Start" button is pressed , the electric circuit closes , the current passes through the closed contacts of this button and the "Stop" buttons (they are normally closed), which means - until they press this button, the circuit will not open. When an electric current passes through a coil, a magnetic field appears in it, attracting the anchor, which, in turn, connects the contacts - there are only four pairs of them. Three of them are basic and are intended to include a three-phase payload, for example 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 sufficient to open the solenoid circuit. To do this, the "Stop" button is designed, 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, both power and holding, are opened. The "Stop" button can be released - the current will not go any more through the control circuit, because the contacts of the "Start" button in the unpressed position are open. Everything, the magnetic starter is off.

As a rule, the coil of the magnetic starter is designed for 220 volts AC voltage with a frequency of 50-60 hertz. Devices that use magnetic coils or transformers designed exclusively for the frequency of 60 hertz are better not to use - they can fail, but a domestic or European magnetic starter can be used in America without restrictions.

A typical installation error is that the control circuit is not connected between neutral and phase, but between phases. In this case, the coil gets 380 volts instead of 220, and it burns out.

Despite the simplicity of the device, the design of the magnetic starter is constantly being improved. The design bureaus that create new switching devices tend to reduce noise when triggered and reduce the arc generated when the contacts are connected or disconnected . Especially this applies to high-voltage starters, designed to work with a voltage of one thousand volts. Thus, the joint Swiss-Swedish enterprise Asea Brown Boveri Ltd has been producing switching equipment for electrical circuits since the late nineteenth century, and has accumulated vast experience in the production of this equipment. The magnetic starter ABB is the same as the Rolls-Royce among cars.