Requirements of PUE and other regulatory documents for electrical wiring in civil buildings

Electrical wiring is characterized by the method of laying, the minimum permissible cross-section, the permissible current load. Wiring methods are regulated by the Rules for Electrical Installation (PUE) and GOST R 50571.15-97 (IEC 364-5-52-93) "Electrical installations of buildings. Part 5. Selection and installation of electrical equipment. Chapter 52. Wiring «.

The standard contains a number of requirements and provisions that differ significantly from the PUE requirements in effect at the time of publication of the standard.

The requirements of the standard relating to the characteristics of cabling in office buildings are given below.

1. Insulated wires are allowed to be laid only in pipes, ducts and on insulators. It is not allowed to lay insulated wires hidden under plaster, in concrete, brickwork, in cavities of building structures, as well as openly on the surface of walls and ceilings, on trays, on cables and other structures. In this case, insulated wires or sheathed cables should be used.

2.In single-phase or three-phase networks, the cross-section of the zero working conductor and the PEN-conductor (combined zero working and protective conductors) must be equal to the cross-section of the phase conductor with its cross-section of 16 mm2 and less for conductors with a copper core.

With large cross-sections of phase wires, it is allowed to reduce the cross-section of the neutral working wire under the following conditions:

• the expected maximum operating current in the neutral conductor does not exceed its continuous allowable current;

• the protective neutral conductor is protected against overcurrent.

At the same time, the standard made a special note about the current in the neutral wire: the neutral wire may have a smaller cross-section compared to the cross-section of the phase wires if the expected maximum current, including harmonics, if any, is expected in the neutral wire by time of normal operation does not exceed the permissible current load for a reduced cross-section of the neutral conductor.

This requirement must be related to the fact of the flow of the 3rd harmonic of the current in the neutral conductor of three-phase networks with pulsed power supplies (computers, telecommunications equipment, etc.) as part of the loads.

The magnitude of the effective value of the current in the neutral working conductor under such loads can reach 1.7 of the effective value of the current in the phase conductors.

From 06.10.1999, new editions of section No. 6 «Electrical lighting» and 7 «Electrical equipment of special installations» of the seventh edition of PUE. The content of these sections is aligned with the IEC set of standards for electrical installations in buildings.

In a number of separate clauses of the new edition of Sec.6 and 7 PUE impose even more stringent requirements than in the standard based on IEC materials. These sections are issued as a separate booklet "Rules for electrical installation" (7th edition — M.: NT ENAS, 1999).

The seventh section of the PUE contains ch. 7.1 deserves special attention. The chapter is called "Electrical installations of residential, public, administrative and household buildings" and applies to electrical installations:

• residential buildings listed in SNiP 2.08.01-89 «Residential buildings»;

• public buildings listed in SNiP 2.08.02-89 "Public buildings and facilities" (except for buildings and premises listed in chapter 7.2);

• administrative and auxiliary buildings listed in SNiP 2.09.04-87 «Administrative and auxiliary buildings».

For electrical installations of unique and other special buildings not included in the above list, additional requirements may be imposed.

Chapter 7.1 contains requirements for wiring and cable lines. When choosing the method of laying and sections of electrical wiring, guided by both the requirements of GOST R 50571.15-97 and PUE, it should be borne in mind that the new edition of PUE in part of clause 7.1.37 is formulated as follows : "... electrical wiring in the premises must be carried out replaceably: hidden - in the channels of building structures, monolithic pipes; outdoors — in electrical skirting boards, boxes, etc.

In technical floors, underground ... electrical wiring is recommended to be carried out openly ... In buildings with building structures made of non-combustible materials, it is allowed to permanently install monolithic group networks in the channels of walls, partitions, ceilings, under plaster, in the floor preparatory layer or in the cavities of building structures filled with cable or insulated conductors in a protective sheath.

The use of permanent, monolithic laying of wires in panels of walls, partitions and ceilings, made during their production in the plants of the construction industry or made in the assembly joints of panels during the assembly of buildings, is not allowed. »

In addition (point 7.1.38 of PUE) electrical networks placed behind impenetrable suspended ceilings and in partitions are considered hidden electrical wires and they must be fulfilled:

• behind ceilings and in cavities of partitions of combustible materials in metal pipes with the possibility of localization and in closed boxes;

• behind ceilings and in partitions of non-combustible materials, in pipes and boxes of non-combustible materials, as well as fireproof cables. In this case, the possibility of replacing wires and cables must be provided. Non-combustible suspended ceilings are those that are made of non-combustible materials, while other building structures located above the suspended ceilings, including intermediate floors, are also made of non-combustible materials.

Annex 3 provides a sample of GOST R 50571.15-97 with examples of electrical wiring in relation to office buildings. These illustrations do not accurately describe the product or installation practice, but rather describe the installation method.

To carry out the wiring of the uninterruptible power supply network, it is necessary to use wires and cables with copper conductors only. The use of solid cables and wires is recommended.

The use of flexible multiwire cables is possible on network sections that are subject to reconstruction during operation or to connect individual energy consumers.

All connections must be made with splitters or spring terminals, while stranded wires must be crimped with special equipment.

Due to the fact that the cross-section of the neutral working wire must be designed for a current that can exceed the phase current by 1.7 times, and the existing nomenclature of wires and cables does not always allow to unambiguously solve this problem, it is possible to perform three-phase electrical wiring in the following ways:

1. When laying with wires, the section of the phase and protective conductor is made with one section, and the zero working (neutral) conductor is made with a section designed for a current that is 1.7 times greater than the phase one.

2. When laying with cables, there are three options:

• when three-core cables are used, the cable cores are used as phase conductors, the neutral working conductor is made with a wire (or several conductors) with a section designed for a current that is 1.7 times greater than phase 1, zero protection

• wire with a cross-section in accordance with point 7.1.45 of PUE, but not less than 50% of the cross-section of the phase wires; instead of wires, it is possible to use cables with an appropriate number of cores and cross-section;

• when using four-core cables: three cores are phase conductors, the zero working conductor is also one of the cable cores, and the neutral protective conductor is a separate conductor. At which cross section of the cable it is determined by the working current in the neutral working wire, and the cross-section of the phase wires is overestimated (this solution is the best from a technical point of view, but more expensive than others and is not always possible at high currents);

• when using five-core cables with cores of the same cross-section: three cores are phase conductors, two combined cable cores are used as a neutral working conductor and a separate conductor for the neutral protective conductor. In this case, the cross-section of the cable is determined by the phase current (such a solution is also the best from a technical point of view, but quite expensive; there are also difficulties in fulfilling the government order, as well as with the supply of cables).

At high powers, it is possible to lay phase, neutral working and protective conductors with two or more parallel cables or conductors. All cables and wires belonging to the same line must be laid along the same route.

The laying of a neutral protective conductor for information and computer technology and electrical equipment must meet the requirements of GOST R 50571.10-96 «Grounding devices and protective conductors», GOST R 50571.21-2000 «Grounding devices and potential equalization systems in electrical installations, containing information processing equipment «and GOST R 50571.22-2000» Grounding of information processing equipment «.