Marking of wires and cables according to the standards of PUE

  1. Marking rules for current-carrying parts according to PUE
  2. Wire color marking
  3. Letter marking of wires
  4. Non-rated wire designations
  5. Conclusion

Proper wire marking

Proper labeling of wires and cords can greatly facilitate the installation and repair of any electrical networks. After all, the correct labeling will not only facilitate the installation process itself, but will also allow you or any other person to just look at the junction box, shield or wires, to determine their purpose.

For these purposes, the marking of wires must be carried out in accordance with the uniform rules that are given in the "Bible" of any electrician - PUE (Rules for electrical installations).

Marking rules for current-carrying parts according to PUE

To ensure clarity, simplicity and ease of recognition of individual parts of the electrical network in accordance with section 1.1.30 of electrical installation equipment, all electrical installations should have an alphanumeric and color designation. Moreover, the presence of one of these designations does not obviate the need for another.

And the only indulgence is the possibility of applying the marking not along the entire length of the conductor, but only in the connection points, as shown in the video.

Wire color marking

The marking of wires by color is the most obvious and allows you to quickly determine the purpose of any wire. Such marking can be done by selecting wires with the appropriate color of the insulation of the wires, by applying paint on the tires or by painting or using special colored electrical tape at the connection points of the wires.

Moreover, the paint on the tire can be applied not along the entire length, but only in the connection points or at the ends of the tires.

Designation of phase conductors


  • If we talk about the color designation of wires and cables, then we should start with phase conductors. According to p.1.1.30 of PUE in a three-phase network, phase conductors should be marked in yellow, green and red. So respectively, phase A, B and C are indicated.
  • The instruction for a single-phase electrical network implies the designation of the phase conductor in accordance with the color, the continuation of which it is. That is, if the phase conductor is connected to the phase “B” of the three-phase network, then it should have a green color.

Note! In a single-phase network of an apartment or house, you often don’t know to which phase your phase wire is connected. In order to comply with GOST, you do not need to find out. It is enough to designate the phase conductor in any of the proposed colors. After all, for a single-phase network of illumination it is completely unimportant to which phase your conductor is connected. The only exception is the lighting network in which two different phase conductors are used.

  • As for the neutral conductors, they must have a blue color. And the color of the zero core does not depend on the three-phase, two-phase and single-phase network in front of you. It is always indicated in blue.
  • Wire marking with a yellow-green strip indicates protective conductor. It connects to the body of electrical appliances and provides security from electric shock in case of damage to electrical insulation.

Designation of null and protective conductors

  • If the neutral conductor and the protective conductor are combined, then according to P.1.1.29 of the OSP, such a conductor should have a blue color with yellow-green stripes on its ends. In order to carry out such marking with your own hands, it is enough to simply take the blue wire and mark it with paint on its end seals or use colored electrical tape for this.
  • As for DC networks, the positive conductor of the wire or bus should be indicated in red, and the negative should be blue. In this case, the designation of the zero and the protective core corresponds to the marking in AC networks.

Letter marking of wires

But the marking of wires in color is not always convenient. In the switchboards, switchgears and on the schemes is much more convenient letter designation. It must be used in conjunction with color coding.


  • The letter marking of the phase conductors in a three-phase network corresponds to their colloquial designation - phase “A”, “B” and “C”. For a single-phase network, it should be the same, but this is not always convenient. Moreover, it is not always possible to accurately determine which phase. Therefore, often use the designation "L".

Note! Paragraph 1.1.31 of the OLC regulates not only the alphanumeric designation of conductors, but also their location. So for a three-phase network with a vertical arrangement of tires, phase "A" should be the top one, and phase "C" the bottom. And with a horizontal arrangement of conductors, the “C” phase nearest to you, and the most distant “A” phase should be.

  • If the marking of wires in the panel is carried out, then under the symbol "N" denote the zero wire.
  • For the designation of the protective wire used the letter designation "PE". In addition, a grounding sign is often used, but the fact is that it cannot always accurately indicate the network diagram.

The photo shows a ground sign.

  • The fact is that you can meet the designation "PEN". It denotes the combination of the neutral and protective conductor. This is possible in the TN-CS systems that we talked about in one of our previous articles.
  • But the labeling of wires of electric DC is performed by the symbolism "+" and "-". What respectively means positive and negative wire. For DC there is another difference. The zero conductor is denoted by the symbol "M", which is sometimes misleading.

DC labeling

Non-rated wire designations

But unfortunately the marking of wires is phase zero, grounding is not always carried out in accordance with the standards of ПУЭ. Often you can find other symbols. This is especially true of old circuits, electrical equipment, as well as some new devices from non-certified manufacturers.

And so that they do not mislead you, let's look at the most common options.

  • Quite often on the old Soviet schemes can be found the characters "F" or "F1", "F2" and "F3". The decoding of this designation is quite simple - it denotes a phase. Moreover, the symbol without the letter designation is used for a single-phase network, and with a letter one for a three-phase one.
  • On the new schemes you can find the designation “L” or “L1”, “L2” and “L3”, respectively. So foreign manufacturers often designate a phase. As for the digital symbols, the same rule applies here - without a digit for a single-phase network, with numbers for a three-phase one.

Note! For a single-phase network, the designation "F" or "L" denotes not the principle of strict adherence to the phases. That is, you can connect any phase. The same applies to the three-phase network with digital designation. If there is a designation "Fa", "Fv", "FS" or "" La "," Lv "," Lc ", then the observance of the alternation of phases is mandatory.

  • Marking of wires in shields may contain the symbol "0" . This designation of the neutral wire is often used to this day both in the diagrams and in the designation of conclusions on the equipment.

Example of non-standard designations on diagrams

  • To denote the protective wire is often used the symbol of grounding, which we have already mentioned above . It is usually used to designate the place where the protective conductor is connected, made according to a system other than TN-CS.
  • The labeling of the wires of the dc panel may contain the symbols “L +” and “L―”. These symbols represent the positive and negative conductor, respectively, and should not mislead you.


Proper marking of wires in color and designation can greatly facilitate not only installation, but also subsequent maintenance of electrical installations. Moreover, the cost of fulfilling the requirements for labeling is extremely low, and the requirements are not so difficult to implement. Therefore, if you want to do everything “according to your mind” and facilitate your further exploitation of your electrical network, we advise you to comply with these standards.