Symbol in electrical circuits. Graphic and letter symbols

If you are engaged in electrical work, then you definitely need to know the conventions in the electrical circuits. The ability to read electrical circuits is an important quality of fitters, instrumentation technicians, circuit designers. And if you do not have special training, it’s unlikely that you can immediately understand all the subtleties. But you need to remember that the symbols on the schemes that are developed for Russian consumers differ from generally accepted standards abroad - in Europe, the USA, and Japan.

History of designations on diagrams

Back in the Soviet years, when electrical engineering developed rapidly, there was a need for the classification of devices and their designation. It was then that the Unified System for Design Documentation (ESKD) and state standards (GOST) appeared. Everything was standardized so that any engineer could read the legend on the drawings of his colleagues.

But in order to understand all the subtleties, you will need to listen to many lectures and study a lot of special literature. GOST is a huge document, and to fully study all the graphic symbols and their standard sizes, notes are almost impossible. Therefore, you must always have at hand a small "cheat sheet", which will help you navigate the whole variety of electrical components.

Electrical wiring in the drawings

Wiring is a general concept, it means conductors with very low resistance. With their help, the voltage is transmitted from the source of electricity to consumers. This is a general concept, since there are many types of wiring.

People who do not understand the wiring diagrams and features may decide that the conductor is an insulated cable that connects to switches and sockets. But in fact there are many types of conductors, and on the diagrams they are indicated differently.

Conductors on circuits

Even copper tracks on PCBs are a conductor, you can even say that this is an option for electrical wiring. It is indicated on the electrical diagrams in the form of a straight connecting line passing from one element to another. In the same way, the electric wires of the high-voltage line laid in the fields between the posts are also indicated on the diagram. And in apartments, connecting wires between lamps, switches and sockets are also indicated by direct connecting lines.

But can be divided into three subgroups designations of conductive elements:

1. Wires.
2. Cables.
3. Electrical connections.

The wiring plan is an incorrect definition, since wiring means both wiring and cables. But if you significantly expand the list of elements, as necessary in the detailed diagram, it turns out that it is necessary to include transformers, circuit breakers, residual current devices, grounding, insulators.

Sockets on the schemes

Sockets are plug connections intended for non-rigid connection (there is the possibility to manually disconnect the connection) of electrical circuits. Symbols in the drawings are strictly regulated by GOST. With its help, rules are established for designating on the drawings apparatuses and lighting devices and various other electrical consumers. Plug-type sockets can be divided into three categories:

1. Designed for outdoor installation.
2. Designed for hidden installation.
3. A unit that includes an outlet and a switch.

These three categories can be divided into several subgroups, depending on the connection options and the presence of protection:

1. Single pole sockets.
2. Bipolar.
3. Bipolar and protective contact.
4. Three-pole.
5. Three-pole and protective contact.

This is enough, there are no features at the sockets, there are many options for execution. All devices have a degree of protection, the choice must be made on the basis of the conditions to be used: humidity level, temperature, the presence of mechanical stress.

Circuit breakers

Switches are devices that break an electrical circuit. This can be done automatically or manually. The graphic designation by GOST is regulated, as with sockets. The designation depends on the conditions in which the element works, what design it has, and the degree of protection. There are several types of switch designs:

1. Unipolar (including double and triple).
2. Bipolar.
3. Three-pole.

The diagrams must indicate the parameters of the disconnecting device. And the graphic designation shows which type is used: a simple switch, a button with and without latching, an acoustic device (responding to cotton) or an optical one. If there is a condition for the lighting to turn on when dark and turn off in the morning, you can use an optical sensor and a small control circuit.

Fuses (fuse links)

There are many types of protection devices - fuses (disposable and self-healing), circuit breakers, UZO. Many types of design, areas of application, different response speeds, reliability, use under certain conditions characterize these devices. The symbol for the fuse is a rectangle; parallel to the long side, a conductor passes through the center . This is the simplest and cheapest element that can protect the circuit from short circuits. It should be noted that such components are rarely used in electrical circuit diagrams. Symbols of another type can be found - these are self-resetting fuses, which, after opening the circuit, return to their original state.

The wide name for fuses is fuse-link. It is used in many devices, in distribution switchboards. In disposable traffic jams you can meet them. But there are still devices used in high voltage switchboards. They are structurally made of metal tips and the main ceramic part. Inside is a section of the conductor (its cross section is selected depending on what maximum current should pass through the circuit). The ceramic body is filled with sand to exclude the possibility of ignition.

Circuit breakers

Symbols of devices of this type depend on the design, degree of protection. The reusable device can be used as a simple switch. In fact, it performs the functions of a fusible insert, but it is possible to transfer it to its original state - to close the circuit. The design consists of the following elements:

1. Plastic case.
2. Lever to turn on and off.
3. Bimetal plate - when heated, it is deformed.
4. Contact group - it is included in the electrical circuit.
5. Arcing chamber - allows you to get rid of the formation of sparks and arcs during connection breaks.

These are the elements that make up any circuit breaker. But you need to remember that after tripping it will not be able to return immediately to its original position, time must pass before the bimetallic plate cools down. The service life of the machines is measured in the number of operations and ranges from 30000-60000.

Grounding on the diagrams

Grounding is the connection of the current conductors of an electric machine or device to ground. In this case, both the earth and part of the circuit of the device has a negative potential. Thanks to grounding during the breakdown of the case, no destruction of the device or electric shock will follow, all the charge will go to the ground. Grounding is of the following types according to GOST:

1. The general concept of grounding.
2. Pure ground (noiseless).
3. Protective grounding type.
4. Connection to the mass (housing) of the device.

Depending on which grounding is used in the circuit, the symbol will be different. An important role in drawing up the diagrams is played by the drawing of the element, it depends both on the specific section of the circuit and on the type of device.

If we are talking about automotive technology, then there will be "mass" - a common conductor connected to the body. In the case of wiring at home - conductors driven into the ground, connected to sockets. In logic circuits, you should not confuse “digital” grounding with ordinary grounding - these are different things and they work differently.

Electric motors

On the electrical circuits of cars, workshops, devices, you can often find electric motors. Moreover, in industry more than 95% of all used motors are asynchronous with squirrel-cage rotor. They are indicated in the form of a circle, to which three wires (phases) fit. Such electric machines are used in conjunction with magnetic starters and buttons ("Start", "Stop", "Reverse" if necessary).

DC motors are used in automotive technology, control systems. They have two windings - working and excitation. Instead of the latter, some types of motors use permanent magnets. By means of the field winding, a magnetic field is created. It pushes the rotor of the engine, which has an anti-directional field - it is created by a winding.

Wire color coding

In the case of single-phase power, the conductor with the phase is black, gray, purple, pink, red, orange, turquoise, white. Most often you can find brown. This marking is generally accepted and is used in the preparation of diagrams, installation. The neutral conductor is marked:

1. Blue color indicates zero working (N).
2. Yellow with a green stripe - ground wire, protection (PE).
3. Yellow with green and blue marks on the edges - protective and neutral conductors are combined.

It should be noted that blue marks must be applied during installation. The symbol in the electrical circuits should also have a link to the fact that there are labels. The conductor must be indicated by the PEN index.

By functional purpose, all conductors are separated as follows:

1. Black wires - for switching power circuits.
2. Red wires - for connecting control elements, measuring, signaling.
3. Blue conductors - control, measurement and alarm when working on direct current.
4. Blue color marking is made of zero working conductors.
5. Yellow and green are wires for grounding and protection.

Alphanumeric Designations

The clamps are conventionally marked in the following electrical circuits:

• U, V, W - wiring phases;
• N is a neutral conductor;
• E - grounding;
• PE - protective circuit wire;
• TE - conductor for silent connection;
• MM - conductor connected to the body (mass);
• SS is an equipotential conductor.

Designation on the wire diagrams:

• L - letter designation (general) of any phase;
• L1, L2, L3 - 1st, 2nd and 3rd phases, respectively;
• N - neutral wire.

In DC circuits:

• L + and L- are the positive and negative poles;
• M is the middle conductor.

These are the signs most often used in diagrams and drawings. They can be found in descriptions of simple devices. If you need to read the diagram of a complex device, you will need a lot of knowledge. After all, there are still active elements, passive ones, logic devices, semiconductor components, and many others. And each has its own designation in the diagrams.

UGO winding elements

There are many devices that convert electric current. These are inductors, transformers, chokes. The symbol of the transformer in the diagrams is two coils (shown in the form of three semicircles) and a core (usually in a straight line). The straight line indicates the core made of transformer steel. But there may be designs of transformers that do not have a core, in this case there is nothing on the circuit between the coils. Such a symbol designation of the elements can be found in circuits of radio reception equipment, for example.

In recent years, transformer steel has been increasingly used in technology for the manufacture of transformers. It is very heavy, it is difficult to collect the plates into the core, a buzz appears when loosening. The use of ferromagnetic cores is much more effective. They are integral, have the same permeability in all areas. But they have one drawback - the complexity of the repair, since disassembling and assembling is problematic. The symbol of a transformer with such a core is practically no different from that in which steel is used.

Conclusion

This is not all the conventions of electrical circuits, the dimensions of the components are also regulated by GOST. Even simple arrows, connection points have requirements, their drawing is carried out strictly according to the rules. It is necessary to pay attention to one feature - differences in the schemes made according to domestic standards and imported. The intersection of conductors in foreign circuits is indicated by a semicircle. And there is such a thing as a sketch - this is an image of something without observing the requirements of GOST for the elements. Separate requirements are presented to the sketch itself. Such images can be performed to visually represent the future design, wiring. Subsequently, a drawing is drawn up on it, on which even the symbols for conventional cables and connections comply with the standards.