Purpose and device of the magnetic starter. Magnetic starter device and principle of operation. Schematic diagram of MP connection

Switches are used to turn on the lighting, and buttons and switches are used for household electrical appliances. This electrical equipment has one thing in common: they consume little power. And also - they are not switched on remotely or by automation devices. These tasks are solved with the help of magnetic starters.

Magnetic starter circuit. Device

The starter consists of two parts located in one housing: a control solenoid and a contact system.

The control solenoid includes a coil with a magnetic core, which includes a movable and a fixed part, held in the open state by a spring. When voltage is applied to the coil, the moving part of the magnetic circuit is attracted to the stationary part. The moving part is mechanically connected to the contact system.

The contact system includes movable and fixed groups of contacts. When voltage is applied to the starter coil, the magnetic circuit attracts the moving contacts to the fixed ones and the power circuits are closed. When the voltage is removed from the coil, under the action of a spring, the movable part of the magnetic circuit, together with the contacts, are brought to their original position.

An additional contact group is added to the power contacts of the starter, designed for use in control circuits. Its contacts are normally open (denoted by the numbers "13" and "14") or normally closed ("23" and "24").

Electrical characteristics of magnetic starters

Rated starter current- this is the current that the power contacts can withstand for a long time. For some models of obsolete starters, for different current ranges, the overall dimensions or “value” change.

Rated voltage- supply voltage, which withstands the insulation between the power contacts.

Control coil voltage- operating voltage at which the starter control coil operates. Starters are available with coils operating from a DC or AC mains.

The starter control is not necessarily powered by the voltage of the power circuits; in some cases, the control circuits are independently powered. Therefore, control coils are available for a wide range of voltages.

Starter control coil voltages

Alternating current	12	36	48	110	220	380
D.C	12	36	48	110	220

Reversing magnetic starter, push-button station

The most common application of starters is motor control. Initially, the name of the device is derived from the word "start". The circuits use additional contacts built into the case: to pick up the command from the "Start" button. Normally closed contacts of the "Stop" button break the power supply circuit of the coil, and the starter disappears.

Issued reversible blocks incorporating two conventional starters connected electrically and mechanically. Mechanical interlock does not allow them to turn on at the same time. Electrical connections provide two-phase reversal when operating different starters, as well as the elimination of the possibility of supplying power to both control coils at the same time.

For ease of installation, starters produce in housings together with control buttons. To connect, just connect the power cable and the outgoing cable to them.

In other cases, to control the work are used pushbutton stations, switching the control coil circuit and connected to the starter by a control cable. For conventional starters, two buttons are used, combined in one housing - "Start" and "Stop", for reversing - three: "Forward", "Back" and "Stop". The "Stop" button for quick shutdown in the event of an accident or danger is mushroom-shaped.

Depending on the purpose, the starters are made with three or four poles. But there are also devices that have one or two poles.

Manufacturers complement the line of manufactured devices accessories expanding their capabilities. These include:

additional contact blocks that allow you to connect signal lamps to the control circuit and generate commands depending on the state of the starter for the operation of other devices;
time delay blocks that delay the operation or shutdown of the starter;
sets of accessories that turn two starters into a reversing assembly;
pads that allow you to connect larger cables to the starter.

To protect electric motors from overloads, together with starters, thermal relays. Manufacturers produce them for the corresponding models of devices. The thermal relay contains a contact that opens when triggered and breaks the power supply circuit of the starter coil. To re-enable the contact must be returned to its original position by pressing the button on the body. To protect against short circuits, a circuit breaker is installed in front of the starter, which is detuned from the starting currents of the electric motor.

It is a low-voltage switching device designed to remotely turn off and turn on an electrical load in a network with a voltage of up to 1000 volts. This device can be used both in industry and in everyday life, so it is important to know about the nuances of choosing its characteristics. In this article we will tell you how to choose a magnetic starter in terms of power, current and other parameters.

Functionality

The following are typical functions performed by magnetic starters, which are far from exhaustive of their scope:

Control of asynchronous electric motors in drives of mechanisms for industrial use.
Inclusion of outdoor (street) city lighting, outdoor and intrashop lighting of industrial facilities.
Switching of electric heaters (heaters or infrared heaters) of electric heating systems.
Use as triggers in industrial automation circuits.

The choice of magnetic starters is made when designing control and automation circuits, or in the process of their repair, when it is necessary to choose its analogue to replace an outdated or missing device.

Criterias of choice

When choosing the necessary electrical apparatus, its technical characteristics and design features are considered. Let's dwell on the main ones.

Rated voltage of the switched circuit. Most often, magnetic starters are used to start asynchronous motors with a squirrel-cage rotor for an industrial voltage of 220/380 Volts. It is for this choice that most of the manufactured models of switching devices are designed. When using devices for 380/660 Volt electric motors, which are much less common, it is necessary to select a starter of the appropriate voltage.

Rated current of main contacts. Comparison of the current of the connected load with the rated current of the switching device is one of the first steps when choosing the latter. Magnetic starters manufactured in the Russian Federation according to Soviet GOSTs, for example, PML, are conventionally classified according to values \u200b\u200bcorresponding to the rated current of the device. Below is a table of ratios of values \u200b\u200band rated currents. According to it, you can correctly select a magnetic starter by current, or by power, by recalculating according to the formula.

Value	O	I	II	III	IV	V	VI
I nom	6.3 A	10 A	25 A	40 A	63 A	100 A	160 A

Products of foreign manufacturers are represented by a wide selection of contactors of various designs for various rated currents.

Switching durability. This characteristic displays the number of operations, which is guaranteed by the manufacturer. There are 3 wear resistance classes: A, B and C. Class A is the highest and guarantees from 1.5 to 4 million operation cycles of the magnetic starter. Class B models are guaranteed to work from 0.63 to 1.5 million cycles. Class B is the lowest and is characterized by 0.1 to 0.5 million operation cycles.

Mechanical durability. An equally important characteristic that displays the number of on / off cycles of the device without repair or replacement of its parts. In this case, switching on and off must be carried out without load (when there is no current in the circuit). Mechanical wear resistance can be from 3 to 20 million operation cycles.

To power three-phase electric motors, devices with three poles are used. This is the most common implementation. However, there are a number of situations when it is required to choose a device with a different number of poles. For example, when the load is lighting circuits or electric heaters. In this case, it is convenient to choose a switching device from the line of contactors of foreign manufacturers, represented by a wide variety of designs.

Rated coil voltage. Magnetic starters used in electrical equipment control circuits are most conveniently used with coils for the same voltage as the switched load. For this reason, the most common versions are with 220 or 380 Volt coils. When building various kinds of automatic circuits, for a number of reasons it may be necessary to use control coils to a different voltage level. This is due to the use in these circuits of relays, sensors or other components designed for a certain supply voltage. In this case, in the lines of domestic and foreign manufacturers, there is a choice of options for supplying coils with any voltage from the nominal range from 9 Volts and above (9, 12, 24, 36, 110, 220 or 380 V).

Number and characteristics of auxiliary contacts. In addition to the main power contacts that switch the main electrical circuits of the load, magnetic starters are equipped with auxiliary contacts that operate synchronously with the main one. These contacts are intended for switching control circuits, blocking, power supply of signal lamps, relay coils and other auxiliary devices. Auxiliary contacts can be of two types - normally open and normally closed. The first ones are open when the control coil is de-energized and close when the electromagnetic starter is triggered, for the second, everything happens the other way around. The need to select a certain number of additional contacts of one type or another is determined by the circuit in which the device is used.

For example, to organize the simplest control of a mechanism using a two-button post, it is enough to choose the option with one pair of normally open auxiliary contacts that pick up the control coil when the Start button is pressed. There are versions of closed-type magnetic starters equipped with start and stop buttons on the case. If it is necessary to signal the state of the mechanism, you need to select a starter that has two more pairs of contacts. Normally closed ones feed the “Disabled” signal lamp, normally open ones - the “On” lamp.

The presence of a reverse. If you need to choose a magnetic starter to control a reversible motor, give preference to a reversible model, in which there are two separate starters connected to each other.

Presence of protection. In the basic version, the magnetic starter is not equipped with protection of the connected electrical equipment. The thermal relay protection module is optional and can be selected according to the required characteristics. You can learn more about that from our article.

In addition to the criteria listed above, it is necessary to choose the right climatic version and products. The procedure for such selection is the same as for any electrical equipment. For example, if the starter will be placed in a protected cabinet, you can choose the degree of protection IP20. If the conditions for placing the device are unfavorable (high dust content, humidity, etc.), we recommend choosing a magnetic starter in a housing with a degree of protection of IP54 or IP65.

Expert advice

These are all the most important criteria for choosing a magnetic starter. If you have any questions or you did not find the information you need, write in the comments below the entry, we, in turn, will try to help you find the right answer!

Usually we see this device in the form of a neat box with two buttons: “start” and “stop”. If you remove the top cover, inside you will find a switch of a rather complex design that can perform several tasks (both in turn and simultaneously).

This is an electromagnetic starter. The question arises: why create complex electrical devices if you just need to close two (or more) contacts? There are buttons with fixation, lever switches, circuit breakers, knife switches. Consider a typical application of a magnetic starter: turning on a powerful electrical installation (for example, an asynchronous electric motor).

A powerful contact group with arc extinguishers is required; accordingly, a large force will be required to close the contacts. A manual drive will be quite cumbersome (the use of a classic knife switch does not always fit into the aesthetics of the workplace).
Manual switches make it difficult to quickly change the operating mode (for example, change the direction of rotation of the motor). The magnetic starter device allows you to assemble such a connection scheme.
Defense organization. Any machine with an emergency shutdown is not designed to be switched on multiple times. The purpose (albeit not the main one) of the magnetic starter is not only to repeatedly switch, but also to turn off the power circuit in case of overloads and short circuits. At the same time, it has an undeniable advantage over other switches. The trip is irreversible: that is, after an emergency opening of the contacts, or a momentary power outage, the working contacts do not return to the "ON" position by default. The principle of operation of the magnetic starter implies only forced re-closing.

Device and principle of operation of the device

The main difference between the starter and any other switching device is that the power supply connected to it is also the control one. How it works?

Consider the general principle of operation of a magnetic starter using an illustration:

Power contacts (3) through which high current power flows to the consumer (electrical installation).
They are interconnected by means of contact bridges (2). The pressing force is provided by springs (1), which are a specially formed steel plate. The contact groups themselves are made of copper alloys for better electrical conductivity.
The plastic traverse (4), on which the bridges (2) are fixed, is connected to the movable anchor (5). The entire structure can be moved vertically with the help of an external force (button), and returns back after the pressure on it stops.
The electromagnet coil (6) creates a magnetic field that presses the movable armature (5) against the fixed part of the core (7). The force is sufficient to overcome the resistance of the return spring.
Power is supplied to the electromagnet using additional contacts (8). To ensure the correct operation of the circuit, the power to these contacts is connected in parallel with the power ones (3), from a single source. To open the entire contact group, a disconnect button is provided, which is installed in the chain of additional contacts.

Types of contactors

By equipping with protective equipment: almost all models include a thermal relay block that opens the circuit of additional contacts in case of overcurrent. In this sense, the principle of operation of a magnetic starter does not differ from a circuit breaker. After an emergency shutdown and cooling of the protective group (the power supply circuit of the electromagnet winding is restored), the power contacts do not close. It is assumed that the operator will eliminate the cause of the emergency and restart the electrical installation.

According to the method of closing contacts, there are the following types of magnetic starters:

Wiring diagrams

Why do you need a magnetic starter? Mainly for the organization of safe connection (and control) of asynchronous three-phase motors. Therefore, we consider the options for the operation of the circuit under various conditions. In all illustrations, there is a protective relay, marked with the letter "P". The bimetallic plates actuating the emergency disconnector (installed in the control circuit) are located on the power lines of the contact group. They can be placed on one or more phase conductors. In case of overheating (it occurs when the load is exceeded or a banal short circuit), the control line breaks, power is not supplied to the KM coil. Accordingly, the power contact groups "KM" open.

Classic scheme for direct connection of a three-phase electric motor

The control circuit uses voltage supply between two adjacent phase lines. When the "Start" button is pressed, with the help of its main contact, the circuit of the "KM" coil is closed. In this case, all contact groups, including additional contacts in the control circuit, are connected under the control of the coil electromagnet. There are two ways to open the circuit: when the alarm relay is triggered, or by pressing the "Stop" button. In this case, the magnetic starter returns to its original "all off" position (or in the case of two categories of contacts, normally closed groups will be connected).

The same connection option, only the control circuit is connected to phase and neutral. From the point of view of the starter, there is no difference. Buttons and a protective thermal relay work exactly the same way.

Reversible connection of a three-phase electric motor

As a rule, two electromagnetic starters are used for this, in which the outputs of the phase contacts are combined with a shift. The devices are combined into one switch, so it can be considered as a single element.

Depending on which contact group is connected to the electric motor, its rotor rotates in one direction or the other. This option is indispensable when used on conveyors, machine tools, and other electrical installations, which provide 2 directions of rotation (movement).

How does this scheme work in practice? See illustration:

A single control scheme with two groups of start buttons: "Forward" and "Back". Each of them includes a corresponding electromagnet coil. Why is the scheme general? The “Stop” button, according to safety conditions, should be the same. Otherwise, in the event of an emergency, the operator will lose precious seconds in search of the necessary button (for “Forward” or for “Back”).

Checking the performance of the magnetic starter and its repair

The device is checked by supplying power to the control (additional, or block contacts). If the working group closes, its contacts are dialed using a multimeter. A short circuit is then provoked to test the protective relay.

Any switching device consists of elements similar in design. Therefore, the repair of the magnetic starter is carried out according to the general principle: search for a faulty node, repair or replacement.

Mechanical parts (bridge, clamping or return spring) change, contacts can be cleaned. The control coil is rewound, or a burnt coil is restored by soldering.

Related videos

The name of this electrical device for 0.4 kV electrical installations contains two fundamental actions at once:

1. operation as an electromagnet from the passage of electric current through the coil winding;

2. start-up of the electric motor by power contacts.

Structurally, any magnetic starter consists of a permanently fixed part and a movable anchor moving along the skids. It is highlighted in blue in the picture.

How the electromagnetic system works

In a very simplified way, the starter can be represented as one button, on the body of which there are terminals with connected power circuits and stationary contacts. A contact bridge is mounted on the moving part. Its purpose:

1. providing a double break in the power circuit to turn off the power to the electric motor;

2. reliable electrical connection of the incoming and outgoing wires when the circuit is turned on.

With manual pressure on the anchor, the compression force of the built-in springs is well felt, which must be overcome by magnetic forces. When the armature is released, these springs push the contacts back to the off position.

This method of manual control of the starter during the operation of the circuit is not used, it is used during checks. During operation, starters are controlled only remotely due to the action of electromagnetic fields.

For this purpose, a coil winding with turns wound on it is placed inside the housing. It connects to a voltage source. When current is passed through the coils around the coil, a magnetic flux is created. To improve its passage, a laminated steel magnetic circuit was created, cut into two parts:

the lower half permanently fixed in the device body;

mobile, which is part of the anchor.

In a de-energized state, there is no magnetic field winding around the coil, the armature is thrown by the energy of the springs from the stationary part upwards. Under the influence of magnetic forces arising after the passage of electric current through the winding, the armature moves down.

Attracted to the fixed part of the magnetic circuit, its movable half creates in the complex a single structure with a minimum magnetic resistance. Its value during operation is affected by:

adjustment violations;

corrosion of steel parts of the magnetic circuit and its fastening;

surface wear;

technical condition of springs, their fatigue;

defects of the short-circuited coil of the magnetic circuit.

The movement of the anchor inside the hull is limited by two boundary values. In the lower tightened position, a reliable clamping of the contact system must be created. Its weakening leads to burning of the contacts, an increase in the value of the transient electrical resistance, excessive heating and subsequent burnout of the wires.

An increase in the magnetic resistance of the magnetic circuit for any reason is manifested by an increase in noise due to the appearance of vibrations, which lead to a weakening of the contact system pressure and, as a result, to failures in the operation of the magnetic starter.

How the power contact system works

Structurally, power contacts are designed for reliable and long-term operation. For this they:

made of technical silver alloys deposited by special methods on copper jumpers;

created with a margin of safety;

made in a shape that provides maximum electrical contact when turned on and well withstand the electric arc that occurs when the load is broken.

In three-phase circuits, magnetic starters are used with three power and several additional contacts that repeat the position of the armature and are used in motor control circuits. All of them are drawn on the diagrams in a position corresponding to the absence of current in the coil and the unclenched state of the springs.

The control contacts, when the starter is activated, close (called "make") or, conversely, open the circuit. They in the attracted position create a platform in the form of a point. To do this, the stationary part is made by a plane or a sphere (in critical nodes), and the movable part is made by a sphere.

Power contacts are more responsible, they must withstand increased loads. They are made to create a contact line consisting of many points. To this end, the stationary part is made by a plane or a cylinder, and the movable part is made only by a cylinder.

Magnetic starters manufactured by domestic manufacturers are classified according to their ability to work with loads of different capacities into 7 groups and are designated by increasing value from zero with a switching current up to 6.3 amperes inclusive and up to the sixth - (160 A).

Starters produced by foreign manufacturers are classified according to other criteria.

Electricians involved in the maintenance of magnetic starters and supervising their work are required to control the quality of the fit of the contact pads and their cleanliness. The current opinion is that “for modern starters, the contacts are made reliably and you don’t need to inspect them” not entirely correct.

Contact cleanliness depends on many factors, including:

load mode;

switching frequency;

environmental conditions.

All of them manifest differently on each specific device. Therefore, they must be periodically monitored and, at the first sign of contamination, washed with alcohol. When it is not available to perform such work, they use an ordinary school eraser, which, while cleaning the metal, leaves its crumbs with dielectric properties on the outer surface.

They are removed by rubbing surfaces with thin, dried wooden sticks from non-resinous tree varieties. Best suited for these purposes:

When wiping the contacts, hard wood species additionally polish the treated surfaces.

Minor burnouts of the contact surfaces are removed with homemade "crows". So in the language of electricians they call flat segments of strong metal plates (usually they are made from broken hacksaw blades for metal), the surface of which is slightly treated with the finest emery.

Such a tool allows you to remove a very thin layer of burnt metal and bring the contacts into working condition, preserving their original shape. It is impossible to use fine sandpaper and needle files for such purposes. You can quickly break the formed contact line. “Sandpaper” also clogs the treated surface with abrasive crumbs.

Schemes for switching on electric motors with magnetic starters

The easiest control

Such a motor connection can be made according to the picture below.

Three-phase power supply ≈380 through the power contacts K1-s is supplied to the electric motor, the temperature of the windings of which is controlled by a thermal relay kt. The control system is powered by any phase and zero. It is perfectly acceptable to replace the working zero with a ground loop.

In order to increase electrical safety, an isolation or step-down transformer TP1 is used. Its secondary winding must not be grounded.

The simplest fuse FU protects the control circuit from possible short circuits. When the operator presses the "Start" button, a circuit is created in the control circuit for the flow of current through the winding of the starter K1, which simultaneously closes its power contacts K1-s. How long the worker presses the button, so much the engine works. For the convenience of a person, such buttons are mounted with a trigger mechanism.

A running electric motor can be turned off when the button is pressed:

removing power from the power distribution board;

by pressing the "Stop" button;

operation of the thermal relay kt in case of motor overheating;

blown fuse.

Such schemes are used where, according to the conditions of technology, it is required to keep hands constantly on the equipment and not be distracted from the production process. An example would be working with the press.

Scheme with holding the button by the contact of the starter

Adding only one make contact of the K1-y starter to the considered circuit allows you to set the "Start" button to be blocked by this addition and eliminates its constant pressing. Otherwise, the scheme completely repeats the previous algorithm.

Scheme with reverse

Many machine tool drives require changing the direction of rotation of the motor rotor during operation. This is done by changing the phases of the alternation of the power circuit - switching the connection points of any two windings on the switched off engine. In the picture below, the windings of phases "B" and "C" are reversed. Phase "A" does not change.

Two magnetic starters No. 1 and No. 2 are already included in the circuit. The engine can rotate only from one of them clockwise or in the opposite direction. To do this, an opening contact for controlling the reverse rotation starter is introduced into the control circuit of each winding K1 and K2. It blocks both starters from being connected at the same time.

To change the direction of rotation of the motor, the operator must:

press the "Stop" button. The gap formed by it opens the control circuit and interrupts the flow of current through a working starter. In this case, the springs recline the armature, and the power contacts turn off the power supply from the electric motor;

wait for the rotor to stop rotating and press the "Start" button of the next starter. The current will flow through its coil, the button will be held by the closing contact, and the winding circuit of the reverse rotation starter will be broken by the opening contact.

Design features of various models

If earlier magnetic starters were supplied with power contacts and one or two of their repeaters of the position for closing or opening, then modern models are given additional structural elements, due to which they have more possibilities.

For example, complete products from leading manufacturers allow you to perform various control functions for three-phase electric motors, including reversing by integrating additional equipment into the starter. The consumer only needs to connect the electric motor and power wires to the purchased module, and the circuit itself has already been mounted and adjusted for certain loads.

A promising technical solution is a scheme that allows:

spin the motor rotor up to the rated speed by connecting its windings according to the "star" scheme;

turn on under load when switching to the "triangle".

Cases of magnetic starters can be open or protected from dust and / or moisture penetration by a special shell with seals.

Separate modern models of small capacities.

Powerful magnetic starters can be equipped with an arc extinguishing system that occurs when the current is turned off by power contacts.

For a person who is far from electrical engineering, a household appliance seems to be some kind of black box in which something is spinning. Everyone knows about the electric motor, but few know how it is connected with the buttons on the panel. Meanwhile, any circuit in which there is an electric motor also contains a device that closes the circuit and connects the engine to the same power button. This device is called a magnetic starter, although its correct name is an electromagnetic starter.

Principle of operation

In order for the appliance to work, it is necessary to ensure the circuit is closed. This is ensured not by the button, but by the switching device behind it. There are many types of such devices, for example:

contactor;
knife switch;
fuse;
relay.

Moreover, there can be several of them in one chain. So, the fuse opens the circuit during overload, although after it there are simple switches in the circuit. Emergency opening can also be provided by thermal relays. But to find out why you need a magnetic starter, you should understand its device.

Internal organization

Such a switch consists of two parts - movable and fixed. The fixed part is a coil on the armature, the stationary half of the core, and also contains fixed contacts. The moving part is the second half of the core and the moving contacts.

When you press the button, you close the circuit and current flows through the coil. It attracts the moving part to itself and the button can be released: while the coil is energized, the contacts will be closed. If the circuit is opened with the off button, then the movable part of the starter will return to its original position due to the built-in spring. In a word, the principle of operation of a magnetic starter is simple.

Wiring diagrams

The simplest connection diagram for a three-phase electric motor according to the “on and off” principle looks like this:

This diagram shows:

Start - power button.
KM-1 - magnetic starter.
R - thermal relay.
C - off button.
PR - fuse.

It can be seen from the figure that something in the place under which two letters are written - "BK" - will remain closed after you release the button. Pay attention to the fact that the engine is being protected: a fuse and a thermal relay are included in the circuit. In case of overheating or short circuit, the circuit will open.

In practice, those schemes are more common that provide rotation of the engine in different directions - that is, with reverse. Such a circuit can be equipped with both different switching devices and one reversing starter. The reverse diagram looks like this:

If you look closely, you will notice that when the engine rotates in one direction, the second circuit is blocked - this can be seen by the designation KM-1 on the circuit where KM-2 stands, and vice versa. In electrician jargon, this is called foolproofing.

If the engine is connected to a simple single-phase circuit, which is in any apartment, then the switching devices are put on the phase, and resistance is added to them.

Range and marking of devices

On the market of such switches, you can find their various modifications. This is due to both the variety of devices in which there are electric motors and the parameters of the circuits where they operate. There are magnetic starters almost everywhere: in forced ventilation systems and air conditioners, washing machines and electric stoves with a grill, elevators, and recently some electricity consumers have begun to put them in shields - they are much more convenient than simple knife switches.

To choose the right starter, you should pay attention to the following:

what are the maximum currents in your circuit;
do you need a reverse;
where you put your switching device.

The latter matters if you are going to install the starter in a shield near the house. Now on sale there are products suitable for installation on DIN rails.

Starters are completed differently. So, most of them connect the motor according to the "triangle" scheme, so you can reduce the starting current. A number of products also contain thermal relays. You should pay attention to them when your electric motor will work for a long time and overheat. To avoid breakage, they put exactly a thermal relay. This is a simple bimetallic plate that bends to the side when heated: metals, when heated, expand in different ways, and the circuit opens.

Since the wiring is heated by current, the relay is selected so that the current in its marking is 10% more than the nominal one. In the passport of the latter, the value of this denomination must be indicated, and sometimes affixed to the case. The value of the current on the magnetic starter is also indicated.

As a rule, starters are packed in a case. It can be different and this determines the degree of its protection. When the starter is operating in a sealed housing of the main device, this parameter is not so important, but if it is in a shield where dust or precipitation enters, you should take care of good protection. Pollution can lead to an unpleasant situation - the device will buzz, or even completely fail.

Some starters are equipped with varistors that do not allow power surges in the network. It is advisable to put them in chains when you live in a private house and during a thunderstorm all your equipment can fail, especially your computer.

Marking

Electromagnetic starters of domestic production are marked according to GOST 50030-4 -1-2002. First of all, you need to pay attention to his contacts. The designations L1, L2, L3, etc. are connected to the control circuit, and T1, T2, T3 and the following - to the load. The number of contacts can be different, and their connection diagram is contained in the passport and sometimes on the case. Contacts A1 and A2 come from the coil, and NO are auxiliary, which they put in the device, which is called just in case. Some products can even be built up: a number of manufacturers produce contact attachments.

Most often, the starter marking begins with the abbreviation PML and four digits.

If the device can operate in a 380 V circuit, then the value of the load current is set on it. This is the first digit after PML, although the value of the current in direct form can also be set on the case.

0 - 6.3 Amps;
1 - 10 Amps;
2 - 25;
3 - 40;
4 - 63;
5 - 100;
6 - 160;
7 - 250.

The presence of a reverse and a thermal relay is also indicated by a number, it is the second:

1 - without reverse and without TL;
2 - without reverse with TL;
3 - with reverse without TL;
4 - with reverse from TL;

The device has four degrees of protection: IP00, IP20, IP40, IP54, while the first of them involves an open design, and the last one is a dust and splash proof design. Depending on the degree of protection, the presence of buttons and indication, the product is marked with the third digit as follows:

0 - IP00 without buttons;
1 - IP54 with "relay" button for resetting after operation;
2 - IP54, "start" and "stop";
3 - the same as 2, but with an indicator light;
4 - IP40 without buttons;
5 - IP40 with "start" and "stop" buttons;
6 - IP20.

Finally, the fourth digit indicates the number of contacts:

0 - 1 closing and 1 breaking;
1 - 2 closing and 2 breaking;
2 - 3 and 1;
3 - 4 and 1;
4 - 5 and 1.

The numbers 5 and 6 mark devices for DC circuits as 1 closing and 1 opening, respectively.

Some factories indicate the possibility of mounting on a rail, placement category and wear resistance, but more often you can find exactly four numbers.

For PM type starters, the first two digits are the series number, and the next three are the current rating in volts. The sixth digit indicates the presence of a reverse and a thermal relay: 1, 2, 5, 6 mean the same as 1, 2, 3, 4 for PML, and the value of the seventh is completely the same.

PMEs are marked with three numbers: current value, degree of protection and the presence of a reverse with a relay. The designations on the PMA are approximately the same as those on the PML.

Such a variety of markings is explained by the fact that magnetic starters are long-used devices and some factories use the old markings, while others use a new one, while the order of numbers may vary. Therefore, it is worth focusing not so much on it as on various tables and instructions on the case, as well as look at the product passport. This is especially true for foreign-made products.

Contactors and starters

These devices are fundamentally no different from starters. Purpose, device, principle of operation they have the same. The difference lies in the fact that the contactors are designed to operate in circuits with high currents and voltages, so their dimensions are appropriate.

They do not have a protective case, so they are placed in enclosed spaces, protected from external influences.

Contactors are equipped with more powerful power contacts and arc extinguishers; launchers don't have them.

Electric locomotives, trams, trolleybuses and industrial enterprises are equipped with these devices, where they close and open power circuits.