Electrical installations in hazardous areas. Zeroing and grounding

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 7. Electrical equipment of special installations

Electrical installations in hazardous areas. Zeroing and grounding

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

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7.3.132. Explosive zones of any class in rooms and outdoor explosive installations are subject to the requirements given in 1.7.38 on the admissibility of using a dead-earthed or isolated neutral in electrical installations up to 1 kV. With an isolated neutral, automatic control of the network isolation with an effect on the signal and control of the breakdown fuse must be provided.

7.3.133. In hazardous areas of classes BI, B-Ia and B-II, it is recommended to use a protective shutdown (see chapter 1.7). In hazardous areas of any class, potential equalization must be performed in accordance with 1.7.47.

7.3.134. In explosive zones of any class, the following are also subject to zeroing (grounding):

a) in change 1.7.33 - electrical installations at all voltages of alternating and direct current;

b) electrical equipment installed on zeroed (grounded) metal structures, which, in accordance with 1.7.48, clause 1, in non-explosive areas, may not be neutralized (not grounded). This requirement does not apply to electrical equipment installed inside zeroed (grounded) enclosures of cabinets and consoles.

As zero protective (grounding) conductors, conductors specially designed for this purpose should be used.

7.3.135. In electrical installations up to 1 kV with a solidly grounded neutral, the electrical equipment must be grounded:

a) in power networks in explosive zones of any class - a separate residential cable or wire;

b) in lighting networks in explosive zones of any class, except for class BI, - in the area from the luminaire to the nearest junction box - with a separate conductor connected to the zero working conductor in the junction box;

c) in lighting networks in an explosive zone of class BI - a separate conductor laid from the lamp to the nearest group shield;

d) in the network section from the switchgear and transformer substations located outside the explosive zone, to the shield, assembly, distribution point, etc., also located outside the explosive zone, from which electrical receivers located in explosive zones of any class are powered, is allowed as neutral protective conductor use the aluminum sheath of the supply cables.

7.3.136. Zero protective conductors in all links of the network must be laid in common shells, pipes, ducts, bundles with phase conductors.

7.3.137. In electrical installations up to 1 kV and higher with an insulated neutral, grounding conductors can be laid both in a common sheath with phase conductors and separately from them.

Grounding mains must be connected to grounding conductors in two or more different places and, if possible, from opposite ends of the room.

7.3.138. The use of metal structures of buildings, structures for industrial purposes, steel pipes for electrical wiring, metal sheaths of cables, etc. as zero protective (grounding) conductors is only allowed as an additional measure.

7.3.139. In electrical installations up to 1 kV with a solidly grounded neutral, in order to ensure automatic shutdown of the emergency section, the conductivity of the zero protective conductors must be chosen such that when a short circuit occurs on the case or the neutral protective conductor, a short-circuit current occurs that exceeds at least 4 times the rated current of the fuse-link of the nearest fuse and not less than 6 times the current of the release of the circuit breaker, which has a characteristic inversely dependent on the current.

When protecting networks with automatic switches that have only an electromagnetic release (without time delay), one should be guided by the requirements regarding the multiplicity of the short-circuit current and given in 1.7.79.

7.3.140. Calculation check of the impedance of the phase-zero loop in electrical installations with voltage up to 1 kV with a solidly grounded neutral should be provided for all electrical receivers located in explosive zones of classes BI and B-II, and selectively (but not less than 10% of the total) for electrical receivers located in explosive zones of classes B-Ia, B-Ib, B-Ig and BIIa and having the highest loop resistance phase - zero.

7.3.141. The passages of specially laid zero protective (grounding) conductors through the walls of rooms with explosive zones must be made in pipe sections or in openings. Openings of pipes and openings must be sealed with non-combustible materials. Connection of zero protective (grounding) conductors in the places of passages is not allowed.

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

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