Electrical installations of buildings--Part 4:Protection for safety--Chapter 44:Protection against overvoltages--Section 443:Protection against overvoltages of atmospheric origin or due to switching
443.1 General
443.1.1 Scope and object
This standard specifies protection of electrical installations against transient overvoltages of atmospheric origin transmitted by the supply distribution system and against switching overvoltages generated by the equipment within the installation, in Electrical Installations of Buildings - Part 4: Protection for Safety.
Consideration shall be given to the overvoltages which can appear at the origin of an installation, to the expected ceraunic level and to the location and characteristics of overvoltage protective devices, so that the probability of incidents due to overvoltage stresses is reduced to an acceptable level for the safety of persons and property, as well as for the continuity of service desired.
The values of transient overvoltages depend on the nature of the supply distribution system(underground or overhead) and the possible existence of a low-voltage protective device upstream of the origin of the installation and the level of the supply system.
This standard provides guidance where protection against overvoltages is covered by inherent control or assured by protective control. If the protection according to this standard is not provided, insulation coordination is not assured and the risk due to overvoltages shall be evaluated.
Notes:
1 Where, in this standard, the term "transient overvoltage" is used, it is intended to mean statistical lightning overvoltage as defined:
The statistical level of overvoltages is defined as the overvoltage applied to equipment as a result of an event of one specific type in the system (line energization, reclosing, fault occurrence, lightning discharge, etc.), the peak value of which has a probability of being exceeded which is equal to a specified reference probability.
2 As regards transient atmospheric overvoltages, no distinction is made between earthed and unearthed systems.
3 Switching overvoltages generated outside the installation and transmitted by the supply network are under consideration.
4 The rules of this standard do not apply to telecommunication systems.
443.1.2 Normative References
The following standards contain provisions which, through reference in this standard, constitute provisions of this standard. At time of publication, the editions indicated were valid. All the standards will be modified, however, parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below.
GB 16895.11-2001 Electrical Installations of Buildings - Part 4: Protection for Safety - Chapter 44: Protection against Overvoltages - Section 442 - Protection of Low-voltage Installations against Temporary Overvoltages and Faults between High-voltage Systems and Earth (idt IEC 60364-4-442: 1993)
GB/T 16935.1-1997 Insulation Coordination for Equipment within Low-voltage Systems - Part 1: Principles, Requirements and Tests(idt IEC 60664-1: 1992)
IEC 60038:1983 Standard Voltages
IEC 60050(826): 1990 International Electrotechnical Vocabulary (IEV) - Chapter 826: Electrical Installations of Buildings
IEC 60364-5-534: 1997 Electrical Installations of Buildings - Part 5: Selection and Erection of Electrical Equipment - Chapter 53: Switchgear and Controlgear - Section 534: Devices for Protection against Overvoltages
IEC 61024-1:1990 Protection of Structures against Lightning - Part 1: General Principles
Foreword i
IEC Forward ii
IEC Introduction iii
443.1 General
443.2 Classification of Impulse Withstand Categories (Overvoltage Categories)
443.3 Arrangements for Overvoltage Control
443.4 Selection of Equipment in the Installation
Annex A (Informative) Guidance for Protective Control Applied in the Overhead Lines according to Note 1 of 443.3.2.1
