Letter designations of quantities used in electrical engineering

Regulations

Taking into account the large number of electrical elements, a number of normative documents have been developed for their alphanumeric (hereinafter referred to as BO) and conventional graphic designations (UGO) to eliminate discrepancies. Below is a table showing the main standards.

Table 1. Standards for graphic designation of individual elements in installation and circuit diagrams.

It should be taken into account that the element base changes over time, and accordingly changes are made to regulatory documents, although this process is more inert. Let's give a simple example: RCDs and automatic circuit breakers have been widely used in Russia for more than a decade, but there is still no single standard according to GOST 2.755-87 for these devices, unlike circuit breakers. It is quite possible that this issue will be resolved in the near future. To keep abreast of such innovations, professionals monitor changes in regulatory documents; amateurs do not have to do this; it is enough to know the decoding of the main symbols.

Types of electrical circuits

In accordance with ESKD standards, diagrams mean graphic documents on which, using accepted notations, the main elements or components of a structure, as well as the connections connecting them, are displayed. According to the accepted classification, there are ten types of circuits, of which three are most often used in electrical engineering:

• Functional, it shows the node elements (depicted as rectangles), as well as the communication lines connecting them. A characteristic feature of this scheme is minimal detail. To describe the main functions of nodes, the rectangles displaying them are signed with standard letter designations. These can be various parts of the product that differ in functionality, for example, an automatic dimmer with a photo relay as a sensor or a regular TV. An example of such a scheme is presented below.

  
  Example of a functional diagram of a television receiver

• Fundamental. This type of graphic document displays in detail both the elements used in the design and their connections and contacts. The electrical parameters of some elements can be displayed directly in the document, or presented separately in the form of a table.

  
  Example of a circuit diagram of a milling machine

If the diagram shows only the power part of the installation, then it is called single-line; if all elements are shown, then it is called complete.

Single Line Diagram Example

• Electrical wiring diagrams. These documents use positional designations of elements, that is, their location on the board, method and order of installation are indicated.

  
  Installation diagram of a stationary flammable gas detector

If the drawing shows the wiring of the apartment, then the locations of lighting fixtures, sockets and other equipment are indicated on the plan. Sometimes you can hear such a document called a power supply diagram; this is incorrect, since the latter shows how consumers are connected to a substation or other power source.

Zero designation (N)

To mark the neutral or zero working core of the network, use the letter “N”. This is an abbreviation of the term neutral (translated as neutral). This is what is commonly called the neutral conductor all over the world. In our country, the word “Zero” is mostly used.

Most likely, the word NULL is taken as a basis here. The letter “N” in the diagram indicates contacts or terminals intended for switching the neutral core. A similar designation is accepted for both single-phase and three-phase circuits. Blue or white-blue (white-blue) insulation is used as a color designation for the neutral wire.

Graphic symbols

Each type of graphic document has its own designations, regulated by relevant regulatory documents. Let us give as an example the basic graphic symbols for different types of electrical circuits.

Examples of UGO in functional diagrams

Below is a picture depicting the main components of automation systems.

Examples of symbols for electrical appliances and automation equipment in accordance with GOST 21.404-85

Description of symbols:

• A – Basic (1) and acceptable (2) images of devices that are installed outside the electrical panel or junction box.
• B - The same as point A, except that the elements are located on the remote control or electrical panel.
• C – Display of actuators (AM).
• D – Influence of MI on the regulating body (hereinafter referred to as RO) when the power is turned off:

1. RO opening occurs
2. Closing RO
3. The position of the RO remains unchanged.

• E - IM, on which a manual drive is additionally installed. This symbol may be used for any RO provisions specified in paragraph D.
• F- Accepted mappings of communication lines:

1. General.
2. There is no connection at the intersection.
3. The presence of a connection at the intersection.

UGO in single-line and complete electrical circuits

There are several groups of symbols for these schemes; we present the most common of them. To obtain complete information, you must refer to the regulatory documents; the numbers of state standards will be given for each group.

Power supplies.

To designate them, the symbols shown in the figure below are used.

UGO power supplies on schematic diagrams (GOST 2.742-68 and GOST 2.750.68)

Description of symbols:

• A is a constant voltage source, its polarity is indicated by the symbols “+” and “-”.
• B – electricity icon indicating alternating voltage.
• C is a symbol of alternating and direct voltage, used in cases where the device can be powered from any of these sources.
• D – Display of battery or galvanic power supply.
• E- Symbol of a battery consisting of several batteries.

Communication lines

The basic elements of electrical connectors are presented below.

Designation of communication lines on circuit diagrams (GOST 2.721-74 and GOST 2.751.73)

Description of symbols:

• A – General display adopted for various types of electrical connections.
• B – Current-carrying or grounding bus.
• C – Designation of shielding, can be electrostatic (marked with the symbol “E”) or electromagnetic (“M”).
• D - Grounding symbol.
• E – Electrical connection with the device body.
• F - On complex diagrams, consisting of several components, a broken connection is thus indicated; in such cases, “X” is information about where the line will be continued (as a rule, the element number is indicated).
• G – Intersection with no connection.
• H – Joint at intersection.
• I – Branches.

Designations of electromechanical devices and contact connections

Examples of the designation of magnetic starters, relays, as well as contacts of communication devices can be seen below.

UGO adopted for electromechanical devices and contactors (GOSTs 2.756-76, 2.755-74, 2.755-87)

Description of symbols:

• A – symbol of the coil of an electromechanical device (relay, magnetic starter, etc.).
• B – UGO of the receiving part of the electrothermal protection.
• C – display of the coil of a device with mechanical interlock.
• D – contacts of switching devices:

1. Closing.
2. Disconnecting.
3. Switching.

• E – Symbol for designating manual switches (buttons).
• F – Group switch (switch).

UGO of electric machines

Let us give several examples of displaying electrical machines (hereinafter referred to as EM) in accordance with the current standard.

Designation of electric motors and generators on circuit diagrams (GOST 2.722-68)

Description of symbols:

• A – three-phase EM:

1. Asynchronous (squirrel-cage rotor).
2. The same as point 1, only in a two-speed version.
3. Asynchronous electric motors with phase-phase rotor design.
4. Synchronous motors and generators.

• B – Collector, DC powered:

1. EM with permanent magnet excitation.
2. EM with excitation coil.

Designation of electric motors on diagrams

UGO transformers and chokes

Examples of graphic symbols for these devices can be found in the figure below.

Correct designations of transformers, inductors and chokes (GOST 2.723-78)

Description of symbols:

• A – This graphic symbol can indicate inductors or windings of transformers.
• B – Choke, which has a ferrimagnetic core (magnetic core).
• C – Display of a two-coil transformer.
• D – Device with three coils.
• E - Autotransformer symbol.
• F – Graphic display of CT (current transformer).

Designation of measuring instruments and radio components

A brief overview of the UGO of these electronic components is shown below. For those who want to become more familiar with this information, we recommend viewing GOSTs 2.729 68 and 2.730 73.

Letter designations

In electrical diagrams, in addition to graphic symbols, alphabetic symbols are also used, since without the latter, reading the drawings will be quite problematic. Alphanumeric marking, just like UGO, is regulated by regulatory documents, for electrical this is GOST 7624 55. Below is a table with BO for the main components of electrical circuits.

Letter designations of main elements

Unfortunately, the size of this article does not allow us to provide all the correct graphic and letter symbols, but we have indicated regulatory documents from which all the missing information can be obtained. It should be taken into account that current standards may change depending on the modernization of the technical base, therefore, we recommend monitoring the release of new additions to regulations.

Designation of wires in electrics by letter

Electrical communications in the domestic and industrial spheres are organized through insulated cables, inside of which there are conductive cores. They differ from each other in insulation color and markings. The designation l and n in electrical engineering makes it possible to speed up the implementation of installation and repair activities by an order of magnitude.

The application of this marking is regulated by a special GOST R 50462 : this applies to those electrical installations that use voltages up to 1000 V.

As a rule, they are equipped with a solidly grounded neutral. Often residential, administrative and business facilities have electrical equipment of this type. When installing electrical networks in buildings of this type, it is necessary to have a good understanding of color and letter instructions.

Graphic

As for the graphic designation of all elements used in the diagram, we will provide this overview in the form of tables in which the products will be grouped by purpose.

In the first table you can see how electrical boxes, panels, cabinets and consoles are marked on electrical circuits:

The next thing you should know is the symbol for power sockets and switches (including walk-through ones) on single-line diagrams of apartments and private houses:

As for lighting elements, lamps and fixtures according to GOST are indicated as follows:

In more complex circuits where electric motors are used, elements such as:

It is also useful to know how transformers and chokes are graphically indicated on circuit diagrams:

Electrical measuring instruments according to GOST have the following graphic designation on the drawings:

By the way, here is a table useful for novice electricians, which shows what the ground loop looks like on a wiring plan, as well as the power line itself:

In addition, in the diagrams you can see a wavy or straight line, “+” and “-”, which indicate the type of current, voltage and pulse shape:

In more complex automation schemes, you may encounter incomprehensible graphic symbols, such as contact connections. Remember how these devices are designated on electrical diagrams:

In addition, you should be aware of what radio elements look like on projects (diodes, resistors, transistors, etc.):

That's all the conventional graphic symbols in the electrical circuits of power circuits and lighting. As you have already seen for yourself, there are quite a lot of components and remembering how each is designated is possible only with experience. Therefore, we recommend that you save all these tables so that when reading the wiring plan for a house or apartment, you can immediately determine what kind of circuit element is located in a certain place.

Interesting video on the topic:

Grounding symbol (PE)

In addition to the designation of phase and zero, electricians also use a special letter indication PE (Protective Earthing) for the ground wire. As a rule, they are always included in the cable, along with the neutral and phase conductors. Contacts and clamps intended for switching with the grounding neutral wire are also marked in a similar way.

For ease of installation, the grounding conductors are placed in yellow-green insulation. The DIYer should understand that these colors always indicate the ground wires only. Yellow and green are never used to indicate phase and zero in electrical engineering.

As practice shows, when organizing electrical networks in residential buildings, violations of generally accepted standards for the use of insulation color and corresponding alphanumeric markings are sometimes allowed. In this case, it is not always enough to have the ability to decipher the designations L, N or PE.

In order for the connection of electrical equipment to be truly safe, it is necessary to check whether the markings correspond to the actual state of things. To do this, use special devices (testers) or improvised devices. If you have no experience in such work, for your own safety it is better to invite an experienced electrician with the appropriate permit.

Designation l and n in electrics

The designation of phase and zero in electrics was introduced to ensure that electrical networks are safe and easy to use. For this purpose, special letter markings (l and n) and insulation of the corresponding color are used. There may also be conductors marked PE in yellow-green color: this is how grounding wires are designated.

In addition, the same letter designations are used on connecting contacts and terminals. All that needs to be done when installing an electrical appliance is to connect each of the wires to the terminal. To be on the safe side, it is advisable to check each of the wires with a tester.

Letter

We have already told you how to decipher the markings of wires and cables. Single-line electrical circuits also have their own letters, which make it clear what is included in the network. So, according to GOST 7624-55, the letter designation of elements on electrical circuits is as follows:

1. Relays for current, voltage, power, resistance, time, intermediate, indicating, gas and time-delayed, respectively - RT, RN, RM, RS, RV, RP, RU, RG, RTV.
2. KU – control button.
3. KV – limit switch.
4. CC – command controller.
5. PV – travel switch.
6. DG is the main engine.
7. DO – cooling pump motor.
8. DBH is a high-speed engine.
9. DP – feed motor.
10. DS – spindle motor.

In addition, in the domestic marking of elements of radio engineering and electrical circuits, the following letter designations are distinguished:

This completes a brief overview of symbols in electrical circuits. We hope that now you know how sockets, switches, lamps and other circuit elements are indicated on drawings and plans of residential premises.

Also read:

Phase designation (L)

The AC network includes live wires. Their correct name is “phase”. This word has English roots, and is translated as “line” or “active wire”. Phase conductors pose a particular danger to human health and property. For safe operation they are covered with reliable insulation.

The use of exposed live wires is fraught with the following consequences:

1. 1. Electric shock to people. This can result in burns, injuries and even death.
2. 2. The occurrence of fires.
3. 3. Damage to equipment.