1、 STD-ITU-T RECMN K-27-ENGL L77b m Vb257L Ob21747 448 m INTERNATIONAL TELECOMMUN CATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU PROTECTION AGAINST INTERFERENCE K.27 (0519 6) BONDING CONFIGURATIONS AND EARTHING INSIDE A TELECOMMUNICATION BUILDING ITU-T Recommendation K.27 (Previou
2、sly “CCITT Recommendation”) FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to stan
3、dardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by
4、 the Members of the IT-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). 1T.U-T Recommendation K.27 was revised by ITU-T Study Group 5 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 8th of May 1996. NOTES 1. In this Recommen
5、dation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. 2. follows: The status of annexes and appendices attached to the Series K Recommendations should be interpreted as - - an annex to a Recommendation f
6、orms an integral part of the Recommendation; an appendix to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. O ITU 1996 All rights reserved. No part of this publication may be reproduced or util
7、ized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. . STD-ITU-T RECMN K-27-ENGL 177b 48b2591 Ob21749 210 CONTENTS Introduction Scope Definitions 3.1 IEC definitions 3.2 Definitions for telecommunication earthin
8、g installations Principles of bonding and earthing . 4.1 Summary of theory 4.2 Implementation principles . Protection against electric shock . 4.4 Protection against lightning . 4.3 4.5 Functional earthing . Power distribution 5.1 a.C. power distribution . 5.2 d.c. power distribution Comparison betw
9、een IBN and mesh-BN installations Maintenance of bonding networks Examples of connecting equipment configurations to the CBN . Annex A . Brief theory of bonding and earthing networks . A.l Overview . Annex B - Examples of bonding configurations . B.l Mesh-BN . B.2 Mesh-IBN with a bonding mat configu
10、ration B.3 Star or sparse mesh-IBN with isolation of d.c. power return References . Recommendation K.27 (05/96) Page 1 1 2 2 3 4 4 5 7 7 8 8 8 8 10 11 11 11 11 14 14 16 18 21 i Recommendation K.27 BONDING CONFIGURATIONS AND EARTHING INSIDE A TELECOMMUNICATION BUILDING (Geneva, 1991; revised in 1996)
11、 1 Introduction The main subject of the CCITT Handbook on “Earthing of telecommunication installations” i, comprises the potential rise of a telecommunication building and the reduction of the associated voltage drop by combined use of intentional and incidental earth electrodes. However, the transi
12、tion from analogue to complex digital telecommunication systems has indicated inadequacies with earthing techniques of the past and has therefore caused renewed interest in bonding and earthing techniques and their impact on electromagnetic compatibility (EMC). Consequently, there is a need for a CC
13、IT Recommendation on bonding configurations and earthing inside a telecommunication building. Within the field of EMC, regulations restricting electromagnetic emissions must be satisfied, and for acceptable perform- ance, equipment must possess a specific level of immunity. Electromagnetic compatibi
14、lity may be achieved by the construction of a common, earthed, conductive shielding network or structure (the Common Bonding Network: CBN). The CBN is the principal bonding and earthing network inside the building. The CBN may be augmented with nested shielding structures having “single-point” conne
15、ctions to the CBN. These single-point connected structures will be referred to as Isolated Bonding Networks (IBNs). In a telecommunication building, the bonding and earthing network takes the form of the CBN, to which equipment is attached by multiple connections (mesh-BN) or by a single point conne
16、ction (IBN). The selection of the bonding configuration has an important influence on the responsibility for achieving EMC. A defined bonding configuration permits clear, structured cable routing and earthing. It facilitates control of electromagnetic emissions and immunity, which is especially impo
17、rtant for buildings containing newly installed and existing equipment. A comparison of these approaches (IBN and mesh-BN), including their attributes as functions of frequency are discussed in clause 6 and Annex A. As part of its shielding function, the bonding and earthing network provides for pers
18、onnel safety and lightning protection, and helps control electrostatic discharge (ESD). Since the publication of the Earthing Handbook in 1976, several different bonding and earthing configurations have been introduced, and it is desirable to promote standardization by defining generic versions of t
19、hese configurations. Although there are differences among the configurations, there are many important common aspects. These are discussed in this Recommendation. In addition, three example configurations are described. 2 Scope Experience in the operation of telecommunication centres shows that the
20、use of a bonding. and earthing network that is coordinated with equipment capability and with electrical protection devices, has the following attributes: - promotes personnel safety and reduces fire hazards; - enables signalling with earth return; - minimizes service interruptions and equipment dam
21、age; - minimizes radiated and conducted electromagnetic emissions; - reduces radiated and conducted electromagnetic susceptibility; - improves system tolerance to discharge of electrostatic energy, and lightning interference. Recommendation K.27 (05/96) 1 Within this framework, this Recommendation:
22、a) is a guide to bonding and earthing of telecommunication equipment in telephone exchanges and similar telecommunication switching centres; is intended to comply with safety requirements imposed by IEC 2 or national standardizing bodies on a.C. power installations; can be used for installation of n
23、ew telecommunication centres, and, if possible, for expansion and replacement of systems in existing centres; treats coordination with external lightning protection, but does not provide details of protective measures specific to telecommunication buildings; addresses the shielding contribution of t
24、he effective elements of the building; addresses shielding provided by cabinets, cable trays and cable shields; b) c) d) e) f) g) is intended to encourage EMC planning, which should include bonding and earthing arrangements that accommodate installation tests and routine diagnostics; h) does not inc
25、lude: - required values of surge current immunity and insulation withstand voltages; - - limits of radiated and conducted electromagnetic emission or immunity; techniques for verifying and maintaining bonding and earthing networks. 3 Definitions In this Recommendation, definitions with respect to ea
26、rthing already introduced by the IEC 3 are used to maintain conformity. For convenience, they are reproduced in 3.1. Definitions specific to telecommunication installations, and not covered by the IEC, are added in 3.2. 3.1 IEC definitions The following definitions are taken from IEC 50 3. The term
27、“earthing network” is defined in Chapter 604, all others are in Chapter 826. 3.1.1 to zero (in some countries the term “ground” is used instead of “earth”). earth: The conductive mass of the earth, whose electric potential at any point is conventionally taken as equal 3.1.2 electrical connection wit
28、h earth. earth electrode: A conductive part or a group of conductive parts in intimate contact with and providing an 3.1.3 interconnections. earthing network: The part of an earthing installation that is restricted to the earth electrodes and their 3.1.4 equipotential bonding conductors and conducto
29、rs for functional earthing, if any, to the means of earthing. main earthing terminal: A terminal or bar provided for the connection of protective conductors, including 3.1.5 electrode. earthing conductor: A protective conductor connecting the main earthing terminal or bar to the earth 3.1.6 conducti
30、ve parts at a substantially equal potential. equipotential bonding: Electrical connection putting various exposed conductive parts and extraneous 3.1.7 equipotential bonding conductor: A protective conductor for ensuring equipotential bonding. 3.1.8 the transmission of electrical energy. neutral con
31、ductor (N): A conductor connected to the neutral point of a system and capable of contributing to 2 Recommendation K.27 (05/96) STD-ITU-T RECMN K.27-ENGL 3.1.9 electrically connecting any of the following parts: protective conductor (PE): A conductor required by some measures for protection against
32、electric shock by - exposed conductive parts; - extraneous conductive parts; - main earthing terminal; - earth electrode; - earthed point of the source or artificial neutral. 3.1.10 conductor. PEN conductor: An earthed conductor combining the functions of both protective conductor and neutral 3.2 De
33、finitions for telecommunication earthing installations 3.2.1 bonding network (BN): A set of interconnected conductive structures that provides an electromagnetic shield for electronic systems and personnel at frequencies from d.c. to low rf. The term “electromagnetic shield”, denotes any structure u
34、sed to divert, block or impede the passage of electromagnetic energy. In general, a BN need not be connected to earth but all BNs considered in this Recommendation will have an earth connection. The following definitions of BN configurations are illustrated in Figures 1 and 2. 3.2.2 common bonding n
35、etwork (CBN): The CBN is the principal means for effecting bonding and earthing inside a telecommunication building. It is the set of metallic components that are intentionally or incidentally interconnected to form the principal BN in a building. These components include: structural steel or reinfo
36、rcing rods, metallic plumbing, a.C. power conduit, PE conductors, cable racks, and bonding conductors. The CBN always has a mesh topology and is connected to the earthing network. 3.2.3 mesh-BN (MBN): A bonding network in which all associated equipment frames, racks and cabinets, and usually, the d.
37、c. power return conductor, are bonded together as well as at multiple points to the CBN. Consequently, the mesh-BN augments the CBN. 3.2.4 isolated bonding network (IBN): A bonding network that has a single point of connection (“SPC”) to either the common bonding network or another isolated bonding
38、network. All IBNs considered here will have a connection to earth via the SPC. 3.2.5 single point connection (SPC): The unique location in an IBN where a connection is made to the CBN. In reality, the SPC is not a “point” but, of necessity, has sufficient size to accommodate the connection of conduc
39、tors. Usually, the SPC takes the form of a copper bus-bar. If cable shields or coaxial outer conductors are to be connected to the SPC, the SPC could be a frame with a grid or sheet metal structure. 3.2.6 SPC window (SPCW): The interface or transition region between an IBN and the CBN. Its maximum d
40、imension is typically 2 metres. The SPC bus-bar (SPCB), or frame, lies within this region and provides the interface between IBN and CBN. Conductors (e.g. cable shields or d.c. return conductors) that enter a system block and connect to its IBN must enter via the SPCW and connect to the SPC bus-bar
41、or frame. 3.2.7 mesh-IBN: A type of IBN in which the components of the IBN (e.g. equipment frames) are interconnected to form a mesh-like structure. This may, for example, be achieved by multiple interconnections between cabinet rows, or by connecting all equipment frames to a metallic grid (a “bond
42、ing mat”) extending beneath the equipment. The bonding mat is, of course, insulated from the adjacent CBN. If necessary the bonding mat could include vertical extensions, resulting in an approximation to a Faraday-cage. The spacing of the grid is chosen according to the frequency range of the electr
43、omagnetic environment. 3.2.8 star IBN: A type of IBN comprising clustered or nested IBNs sharing a common SPC. 3.2.9 system block: All the equipment whose frames and associated conductive parts form a defined BN. Recommendation K.27 (05/96) 3 - STDmITU-T RECMN K.27-ENGL 177b 9Bb2571 Ob21753 741 3.2.
44、10 to a BN. More complex configurations are possible, see 5.2. isolated d.c. return (d.c.-I): A d.c. power system in which the return conductor has a single point connection 3.2.11 common d.c. return (a.C.-C): A d.c. power system in which the return conductor is connected to the surrounding BN at ma
45、ny locations. This BN could be either a mesh-BN (resulting in a d.c.-C-MBN system) or an IBN (resulting in a d.c.-C-IBN system). More complex configurations are possible (see 5.2). star topology lD5067609Yd01 Mesh topology Rack, equipment, modde o - Bmdng conductor FIGURE 11K.27 Bonding network conf
46、igurations forming a system block 4 Principles of bonding and earthing 4.1 Summary of theory Bonding and earthing refer to the construction and maintenance of Bonding Networks (BNs) and their connection to earth. In this Recommendation the acronym BN implies that a connection to earth exists. Also,
47、BN is used to refer to CBNs and IBNs collectively. The primary purpose of a BN is to help shield people and equipment from the adverse effects of electromagnetic energy in the d.c. to low rf range. Typical energy sources of concern are lightning, and a.C. and d.c. power faults. Of generally lesser c
48、oncern are quasi steady-state sources such as a.C. power harmonics, and “function sources” such as clock signals from digital equipment. All of these sources will be referred to generically as “emitters”. People and equipment that suffer adversely from the energy from the emitters will be referred t
49、o as “susceptors”. The coupling between a particular emitter and a particular susceptor may be characterized by a transfer function. The purpose of a BN is to reduce the magnitude of the transfer function to an acceptable level. This may be achieved by appropriate design of the CBN, and the MBNs and IBNs attached to that CBN. Theoretical and quantitative aspects are discussed in Annex A. Practical aspects are discussed below. Other purposes of a BN are to function as a “return” conductor in some signalling applications, and as a path for power fault currents, The capability of
