Section 7. Electrical equipment of special installations

Electrical installations in hazardous areas. Wiring, conductors and cable lines

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

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7.3.92. In hazardous areas of any class, the use of uninsulated conductors, including conductors for cranes, hoists, etc., is prohibited.

7.3.93. In explosive zones of classes B-I and B-Ia, wires and cables with copper conductors must be used. In explosive zones of classes B-Ib, B-Ig, B-II and B-IIa, the use of wires and cables with aluminum conductors is allowed.

7.3.94. Conductors of power, lighting and secondary circuits in networks up to 1 kV in explosive zones of classes B-I, B-Ia, B-II and B-IIa must be protected from overloads and short circuits, and their cross-sections must be selected in accordance with Ch. 3.1, but not less than the cross section adopted for the rated current.

In explosive zones of classes B-Ib and B-Ig, the protection of wires and cables and the choice of sections must be made as for non-explosive installations.

7.3.95. Wires and cables in networks above 1 kV, laid in explosive zones of any class, must be checked for heating by short-circuit current.

7.3.96. The protection of supply lines and power consumers connected to them above 1 kV must meet the requirements of Ch. 3.2 and 5.3. Overload protection must be carried out in all cases, regardless of the power of the electrical receiver.

In contrast to the requirements of 5.3.46 and 5.3.49, protection against multi-phase short circuits and against overload must be provided by two relays.

7.3.97. Branch conductors to electric motors with a squirrel-cage rotor up to 1 kV must in all cases (except those located in explosive zones of classes B-Ib and B-Ig) be protected from overloads, and their cross sections must allow a continuous load of at least 125% of the rated current of the electric motor.

7.3.98. For electric lighting in hazardous areas of class B-I, two-wire group lines must be used (see also 7.3.135).

7.3.99. In explosive zones of class B-I in two-wire lines with a zero working conductor, the phase and zero working conductors must be protected from short-circuit currents. To simultaneously disconnect the phase and zero working conductors, two-pole switches must be used.

7.3.100. Zero working and zero protective conductors must have insulation equivalent to that of the phase conductors.

7.3.101. Flexible current conduit up to 1 kV in hazardous areas of any class should be made with a portable flexible cable with copper conductors, with rubber insulation, in a rubber oil and gasoline-resistant sheath that does not spread combustion.

7.3.102. In hazardous areas of any class, the following can be used:

a) wires with rubber and PVC insulation;

b) cables with rubber, PVC and paper insulation in rubber, PVC and metal sheaths.

The use of cables with an aluminum sheath in explosive zones of classes B-I and B-Ia is prohibited.

The use of wires and cables with polyethylene insulation or sheath is prohibited in hazardous areas of all classes.

7.3.103. Junction, branch and feed-through boxes for electrical wiring must:

a) in an explosive zone of class B-I - have a level of "explosive-proof electrical equipment" and correspond to the category and group of an explosive mixture;

b) in the explosive zone of class B-II - be intended for explosive zones with mixtures of combustible dusts or fibers with air. It is allowed to use boxes with the level of "explosion-proof electrical equipment" with the type of protection "explosion-proof enclosure", intended for gas-vapor-air mixtures of any categories and groups;

c) in explosive zones of classes B-Ia and B-Ig - be explosion-proof for the corresponding categories and groups of explosive mixtures. For lighting networks, it is allowed to use boxes in a sheath with a degree of protection IP65;

d) in explosive zones of classes B-Ib and B-IIa - have a sheath with a degree of protection IP54. Until the industry adopts IP54 enclosure boxes, IP44 enclosure enclosures may be used.

7.3.104. The input of wires laid in the pipe into machines, devices, lamps, etc. must be carried out together with the pipe, while a separating seal must be installed in the pipe at the input, if there is no such seal in the input device of the machine, apparatus or lamp.

7.3.105. When passing pipes of electrical wiring from a room with an explosive zone of class B-I or B-Ia to a room with a normal environment, or to an explosive zone of another class, with a different category or group of explosive mixture, or outside, the pipe with wires in places of passage through the wall must have separating seal in a specially designed box.

In explosive zones of classes B-Ib, B-II and B-IIa, the installation of separating seals is not required.

Separating seals are installed:

a) in the immediate vicinity of the place where the pipe enters the explosive zone;

b) when a pipe passes from an explosive zone of one class to an explosive zone of another class - in a room of an explosive zone of a higher class;

c) when a pipe passes from one explosive zone to another of the same class - in an explosive zone with a higher category and explosive mixture group.

Separating seals can be installed on the side of the non-hazardous area or outside, if the installation of separating seals in the hazardous area is not possible.

7.3.106. The use of junction and branch boxes for making separating seals is not allowed.

7.3.107. Separating seals installed in electrical wiring pipes must be tested with an excess air pressure of 250 kPa (about 2,5 atm) for 3 minutes. In this case, a pressure drop of no more than 200 kPa (about 2 at.) is allowed.

7.3.108. Cables laid openly in explosive zones of any class (on structures, walls, in channels, tunnels, etc.) must not have external covers and coatings made of combustible materials (jute, bitumen, cotton braid, etc.).

7.3.109. The length of cables above 1 kV, laid in hazardous areas of any class, should be limited as far as possible.

7.3.110. When laying cables in explosive zones of classes B-I and B-Ia with heavy or liquefied combustible gases, cable ducts should, as a rule, be avoided. If necessary, the installation of channels, they must be covered with sand.

Permissible continuous currents for cables covered with sand should be taken from the relevant tables of Ch. 1.3, as for cables laid in the air, taking into account correction factors for the number of operating cables according to table. 1.3.26.

7.3.111. In hazardous areas of any class, it is forbidden to install connecting and branch cable glands, with the exception of intrinsically safe circuits.

7.3.112. Cable entry into electrical machines and apparatus must be carried out using input devices. The entry points must be sealed.

It is prohibited to enter pipe wiring into machines and devices that have entries for cables only.

In explosive zones of classes B-Ia and B-IIa for high-power machines that do not have inlet couplings, it is allowed to install all types of terminations in cabinets with a degree of protection IP54 located in places accessible only to service personnel and isolated from the explosive zone ( for example, in foundation pits that meet the requirements of 7.3.61).

7.3.113. If in an explosive zone the cable is laid in a steel pipe, then when the pipe passes from this zone to a non-explosive zone or to a room with an explosive zone of another class or with another category or group of explosive mixture, the pipe with the cable at the point of passage through the wall must have a separating seal and meet requirements of 7.3.105 and 7.3.107.

A separating seal is not installed if:

a) the pipe with the cable comes out, and the cables are laid further openly;

b) the pipe serves to protect the cable in places of possible mechanical impacts and both ends of it are within the same explosive zone.

7.3.114. Openings in the walls and in the floor for the passage of cables and electrical wiring pipes must be tightly sealed with fireproof materials.

7.3.115. Through explosive zones of any class, as well as at distances of less than 5 m horizontally and vertically from the explosive zone, it is forbidden to lay transit electrical wiring and cable lines of all voltages that are not related to this technological process (production). It is allowed to lay them at a distance of less than 5 m horizontally and vertically from the explosive zone when performing additional protective measures, for example, laying in pipes, in closed boxes, in floors.

7.3.116. In lighting networks in rooms with an explosive zone of class B-I, laying group lines is prohibited. It is allowed to lay only branches from group lines.

In rooms with explosive zones of classes B-Ia, B-Ib, B-II and B-IIa, group lighting lines are also recommended to be laid outside explosive zones. If it is difficult to comply with this recommendation (for example, in large industrial premises), the number of junction and branch boxes installed in hazardous areas on these lines should be as small as possible.

7.3.117. Electrical wiring connected to electrical equipment with the type of protection "intrinsically safe electrical circuit" must meet the following requirements:

1) intrinsically safe circuits must be separated from other circuits in compliance with the requirements of GOST 22782.5-78*;

2) the use of one cable for intrinsically safe and non-intrinsically safe circuits is not allowed;

3) wires of intrinsically safe circuits of high frequency should not have loops;

4) the insulation of the wires of intrinsically safe circuits must have a distinctive blue color. It is allowed to mark in blue only the ends of the wires;

5) wires of intrinsically safe circuits must be protected from pickups that violate their intrinsic safety.

7.3.118. Permissible methods of laying cables and wires in hazardous areas are given in Table. 7.3.14.

7.3.119. The use of bus ducts in explosive zones of classes B-I, B-Ig, B-II and B-IIa is prohibited.

In explosive zones of classes B-Ia and B-Ib, the use of busbars is allowed under the following conditions:

a) tires must be insulated;

b) in explosive zones of class B-Ia, the tires must be copper;

c) permanent connections of tires must be made by welding or crimping;

d) bolted connections (for example, at the points of connection of tires to devices and between sections) must have devices that do not allow self-unscrewing;

e) bus ducts must be protected by metal casings providing a degree of protection of at least IP31. Covers must only be opened with special (socket) keys.

Table 7.3.14. Permissible ways of laying cables and wires in hazardous areas¹⁾

1. For intrinsically safe circuits in hazardous areas of any class, all methods of laying wires and cables listed in the table are allowed.

7.3.120. External laying of cables between explosive zones is recommended to be carried out openly: on overpasses, cables, along the walls of buildings, etc., avoiding, if possible, laying in underground cable structures (channels, blocks, tunnels) and trenches.

7.3.121. On overpasses with pipelines with combustible gases and flammable liquids, in addition to cables intended for own needs (for controlling pipeline valves, signaling, dispatching, etc.), it is allowed to lay up to 30 armored and unarmored power and control cables, steel water and gas pipes with insulated wires .

Unarmored cables should be laid in steel water and gas pipes or in steel boxes.

Armored cables should be used in rubber, polyvinylchloride and metal sheaths that do not spread combustion. It is recommended to choose these cables without cushion. At the same time, steel pipes for electrical wiring, steel pipes and boxes with unarmored cables and armored cables should be laid at a distance of at least 0,5 m from pipelines, if possible from the side of pipelines with non-combustible substances.

The building structures of overpasses and galleries must comply with the requirements of Ch. 2.3.

With more than 30 cables, they should be laid along cable racks and galleries (see Chap. 2.3). It is allowed to build cable racks and galleries on common building structures with pipelines with combustible gases and flammable liquids when performing fire prevention measures. Laying of unarmored cables is allowed.

7.3.122. Cable racks can cross racks with pipelines with combustible gases and flammable liquids both from above and from below, regardless of the density of the transported gases relative to air.

With the number of cables up to 15 at the intersection, it is allowed not to build cable racks; cables can be laid in a tube block or in a tight-fitting steel box with a box wall thickness of at least 1,5 mm.

7.3.123. Cable racks and their intersections with racks of pipelines with combustible gases and flammable liquids must meet the following requirements:

1. All structural elements of cable racks (racks, flooring, fences, roof, etc.) must be constructed from fireproof materials.

2. At the intersection plus up to 1,5 m on both sides of the external dimensions of the overpass with pipelines with combustible gases and flammable liquids, the cable overpass should be made in the form of a closed gallery. The floor of the cable rack, when passing below the rack with pipelines with combustible gases and flammable liquids, must have openings for the release of heavy gases that have got inside it.

The enclosing structures of cable racks intersecting with racks with pipelines with combustible gases and flammable liquids must be fireproof and comply with the requirements of Ch. 2.3.

3. At the intersection of the overpass with pipelines with combustible gases and flammable liquids, they should not have repair sites and the pipelines should not have flange connections, compensators, valves, etc.

4. Cable sleeves should not be installed at the intersections on the cables.

5. The clear distance between pipelines with combustible gases and flammable liquids and a cable rack or a pipe block with cables or electrical communications must be at least 0,5 m.

7.3.124. External cable ducts may be constructed at a distance of at least 1,5 m from the walls of rooms with explosive zones of all classes. At the entrance to the explosive zones of these rooms, the channels must be covered with sand along a length of at least 1,5 m.

7.3.125. In cable ducts passing in the explosive zone of class B-Ig or across the territory from one explosive zone to another, sand jumpers with a length of at least 100 m along the top must be installed every 1,5 m.

7.3.126. In hazardous areas of any class, it is allowed to lay cables in blocks. Cable outlets from blocks and joints of blocks must be tightly sealed with non-combustible materials.

7.3.127. The construction of cable tunnels in enterprises with explosive zones is not recommended. If necessary, cable tunnels can be constructed under the following conditions:

1. Cable tunnels should be laid, as a rule, outside hazardous areas.

2. When approaching explosive zones, cable tunnels must be separated from them by a fireproof partition with a fire resistance limit of 0,75 hours.

3. Openings for cables and pipes of electrical wiring introduced into the hazardous area must be tightly sealed with non-combustible materials.

4. In cable tunnels, fire prevention measures must be taken (see 2.3.122).

5. The exits from the tunnel, as well as the exits of the ventilation shafts of the tunnel, must be located outside the explosive zones.

7.3.128. Open conductors up to 1 kV and above of flexible and rigid structures may be laid across the territory of the enterprise with explosive zones on specially designed racks or supports.

It is prohibited to lay open conductors on racks with pipelines with combustible gases and flammable liquids and instrumentation racks.

7.3.129. Conductors up to 10 kV in a sheath with a degree of protection IP54 can be laid across the territory of the enterprise with explosive zones on special racks, racks with pipelines with combustible gases and flammable liquids and instrumentation racks, if there is no possibility of harmful pickups on the instrumentation circuits from current conductors. Conductors should be laid at a distance of at least 0,5 m from pipelines, if possible from the side of pipelines with non-combustible substances.

7.3.130. The minimum allowable distances from current conductors to rooms with explosive zones and to outdoor explosive installations are given in Table. 7.3.15.

7.3.131. Permissible distances from cable racks to rooms with explosive zones and to outdoor explosive installations:

a) with transit cables - see table. 7.3.15;

b) with cables intended only for a given production (building) - not standardized.

The ends of branches from cable racks for supplying cables to rooms with explosive zones or to outdoor explosive installations can be adjacent directly to the walls of rooms with explosive zones and to outdoor explosive installations.

Table 7.3.15. The minimum allowable distance from current conductors (flexible and rigid) and from cable racks with transit cables to rooms with explosive zones and to outdoor explosive installations^{1), 2), 3)}

1. The passage of fire trucks to the cable overpass is allowed from one side of the overpass.

2. The minimum allowable distances of 6 m are applied to buildings and structures of I and II degrees of fire resistance with explosive industries, subject to the conditions specified in the SNiP for the design of master plans for industrial enterprises.

3. The distances indicated in the table are calculated from the walls of rooms with explosive zones, from the walls of tanks or from the most protruding parts of outdoor installations.

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

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