Section 1 General Rules

Grounding and electrical safety protective measures. Protective conductors (PE conductors)

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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1.7.121. The following can be used as PE conductors in electrical installations with voltages up to 1 kV:

1) specially provided conductors:

• conductors of multicore cables;
• insulated or uninsulated wires in a common sheath with phase wires;
• permanently laid insulated or bare conductors;

2) open conductive parts of electrical installations:

• aluminum cable sheaths;
• steel pipes for electrical wiring;
• metal shells and supporting structures of busbars and complete prefabricated devices.

Metal boxes and trays of electrical wiring can be used as protective conductors, provided that the design of the boxes and trays provides for such use, as indicated in the manufacturer's documentation, and their location excludes the possibility of mechanical damage;

3) some third party conductive parts:

• metal building structures of buildings and structures (trusses, columns, etc.);
• reinforcement of reinforced concrete building structures, subject to the requirements of 1.7.122;
• metal structures for industrial purposes (crane rails, galleries, platforms, elevator shafts, lifts, elevators, channel frames, etc.).

1.7.122. The use of exposed and third-party conductive parts as PE conductors is permitted if they meet the conductivity and continuity requirements of this chapter.

Third-party conductive parts can be used as PE conductors if they also simultaneously meet the following requirements:

1) the continuity of the electrical circuit is ensured either by their design or by appropriate connections protected from mechanical, chemical and other damage;

2) their dismantling is impossible unless measures are taken to maintain the continuity of the circuit and its conductivity.

1.7.123. It is not allowed to use as PE conductors:

• metal shells of insulating tubes and tubular wires, supporting cables for cable wiring, metal hoses, as well as lead sheaths of wires and cables;
• gas supply pipelines and other pipelines of flammable and explosive substances and mixtures, sewerage and central heating pipes;
• water pipes with insulating inserts in them.

1.7.124. Neutral protective conductors of circuits are not allowed to be used as neutral protective conductors of electrical equipment powered by other circuits, and also to use open conductive parts of electrical equipment as neutral protective conductors for other electrical equipment, with the exception of shells and supporting structures of busbars and complete factory-made devices that provide the possibility connecting protective conductors to them in the right place.

1.7.125. The use of specially designed protective conductors for other purposes is not permitted.

1.7.126. The smallest cross-sectional areas of protective conductors must comply with table. 1.7.5.

The cross-sectional areas are given for the case when the protective conductors are made of the same material as the phase conductors. The cross-sections of protective conductors made of other materials must be equivalent in conductivity to those given.

It is allowed, if necessary, to take the cross-section of the protective conductor less than required if it is calculated according to the formula (only for shutdown time ≤ 5 s):

where S is the cross-sectional area of ​​the protective conductor, mm2;

I is the short circuit current, which ensures the shutdown time of the damaged circuit by the protective device in accordance with Table. 1.7.1 and 1.7.2 or in a time of no more than 5 s in accordance with 1.7.79, A;

t is the response time of the protective device, s;

k is a coefficient, the value of which depends on the material of the protective conductor, its insulation, initial and final temperatures. The values ​​of k for protective conductors under various conditions are given in table. 1.7.6-1.7.9.

If the calculation results in a cross section different from that given in table. 1.7.5, then you should choose the nearest larger value, and when obtaining a non-standard cross-section, use conductors of the nearest larger standard cross-section.

The maximum temperature values ​​when determining the cross-section of the protective conductor should not exceed the maximum permissible heating temperatures of conductors during a short circuit in accordance with Chapter. 1.4, and for electrical installations in explosive areas must comply with GOST 22782.0 "Explosion-proof electrical equipment. General technical requirements and test methods."

Table 1.7.5. Smallest cross-sections of protective conductors

1.7.127. In all cases, the cross-section of copper protective conductors that are not part of the cable or laid not in a common shell (pipe, box, on the same tray) with phase conductors must be no less than:

• 2,5 mm2 - in the presence of mechanical protection;
• 4 mm2 - in the absence of mechanical protection.

The cross-section of separately laid protective aluminum conductors must be at least 16 mm2.

1.7.128. In the TN system, in order to meet the requirements of 1.7.88, it is recommended to lay neutral protective conductors together or in close proximity to the phase conductors.

Table 1.7.6. The value of the coefficient k for insulated protective conductors not included in the cable, and for non-insulated conductors touching the cable sheath (the initial temperature of the conductor is assumed to be 30 ºC).

Table 1.7.7. The value of the k coefficient for a protective conductor included in a multi-core cable

Table 1.7.8. The value of the k coefficient when using an aluminum cable sheath as a protective conductor

Table 1.7.9. The value of the coefficient k for bare conductors, when the indicated temperatures do not create a danger of damage to nearby materials (the initial temperature of the conductor is assumed to be 30 ºС)

* The indicated temperatures are permissible if they do not degrade the quality of the connections.

1.7.129. In places where damage to the insulation of phase conductors is possible as a result of sparking between an uninsulated neutral protective conductor and a metal shell or structure (for example, when laying wires in pipes, boxes, trays), the neutral protective conductors must have insulation equivalent to the insulation of phase conductors.

1.7.130. Bare PE conductors must be protected against corrosion. At the intersection of PE conductors with cables, pipelines, railway tracks, at places where they are introduced into buildings and in other places where mechanical damage to PE conductors is possible, these conductors must be protected.

At the intersection of temperature and sedimentation seams, compensation for the length of PE conductors must be provided.

See other articles Section Rules for the installation of electrical installations (PUE).

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