1、 International Telecommunication Union ITU-T K.73TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2008) SERIES K: PROTECTION AGAINST INTERFERENCE Shielding and bonding for cables between buildings Recommendation ITU-T K.73 Rec. ITU-T K.73 (04/2008) i Recommendation ITU-T K.73 Shielding and bondin
2、g for cables between buildings Summary Bonding and earthing of telecommunication installations is done for reliability and personnel safety reasons. The evolution of the power architecture of telecommunication systems has created new installation conditions for equipment. To cover these situations,
3、bonding and earthing configurations need to be defined to ensure that adequate reliability and safety are maintained. Recommendation ITU-T K.73 analyses the situation in which equipment, connected together, is installed in different buildings with different earthing and power feeding conditions. Thi
4、s Recommendation also includes installation requirements for equipment located in different buildings, having the same earthing and feeding power conditions, to improve the shielding and bonding of telecommunication and power cable between buildings. Other Recommendations dealing with bonding and ea
5、rthing are Recommendation ITU-T K.27, Bonding configurations and earthing inside a telecommunication building, Recommendation ITU-T K.35, Bonding configurations and earthing at remote electronic sites and Recommendation ITU-T K.66, Protection of customer premises from overvoltages. These Recommendat
6、ions do not cover how equipment installed in these different environments can be interconnected. Source Recommendation ITU-T K.73 was approved on 13 April 2008 by ITU-T Study Group 5 (2005-2008) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T K.73 (04/2008) FOREWORD The International Telecom
7、munication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tari
8、ff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recomme
9、ndations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommend
10、ation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperabilit
11、y or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that complia
12、nce with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity o
13、r applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required t
14、o implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2009 All rights reserved. No part of this publication may be reproduced, by
15、 any means whatsoever, without the prior written permission of ITU. Rec. ITU-T K.73 (04/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined in this Recommendation. 2 4 Abbreviations 2 5 Description of the problem . 2 5.1 a.c. current (for different main distribution s
16、ystems). 3 5.2 Lightning current 3 6 Solutions . 3 6.1 Galvanic isolation. 3 6.2 Parallel bonding conductor (PBC) 4 7 Responsibility . 4 8 Bonding between buildings under different earthing and power feeding conditions. 4 8.1 Consideration in case of lightning flash on the building 8 9 Bonding betwe
17、en buildings under the same earthing and power feeding conditions. 8 9.1 Consideration in case of fault to ground in a LV power feeding . 9 9.2 Consideration in case of lightning flash on the building 9 Appendix I Consideration in case of fault to ground in a MV power feeding 10 Bibliography. 13 iv
18、Rec. ITU-T K.73 (04/2008) Introduction The equipment installed inside a building is generally connected to the earthing system of the building and can be also connected to other equipment inside or outside the building. The outdoors mains distribution network serving a building can be a TN (TN-S or
19、TN-C), TT or IT system; but the a.c. power distribution inside the building may be different depending on the customer needs. A d.c. power distribution inside a building can be an “isolated d.c. return“ system or a “d.c. return common“ system. To cover these different distribution situations, bondin
20、g and earthing configurations need to be defined to ensure that adequate reliability and safety are maintained. This Recommendation has the following objectives: 1) contribute to safety by reducing potential differences between telecommunications equipment units and earthed systems; 2) mitigate dama
21、ge caused by lightning and other surges on the mains and telecommunications cables; 3) allow rapid de-energization of power lines that accidentally contact telecommunications equipment or cables, thereby reducing hazards and damage; 4) provide paths to divert to earth the surge currents entering the
22、 premises on cable screens; 5) provide a low-resistance circuit to earth for systems that use signalling with earth return. This Recommendation requires the connection to the main earthing terminal of the following elements: both ends of metallic cable screens, if high unbalanced currents are expect
23、ed due to different earthing potentials. Precautions should be taken to limit such currents; conductive parts of entry, distribution and termination points, including metallic cabinets, covers and other metallic parts of the cable management system. In this Recommendation, the term “different earthi
24、ng and power feeding conditions“ means that each building is fed by an outdoor mains distribution and the earthing systems of each building are not intentionally connected, regardless of both the distance or the power feeding conditions. In this Recommendation, the term “same earthing and power feed
25、ing conditions“ means that there is only one outdoor mains distribution and only one earthing system for all buildings. Rec. ITU-T K.73 (04/2008) 1 Recommendation ITU-T K.73 Shielding and bonding for cables between buildings 1 Scope This Recommendation provides bonding configurations and earthing fo
26、r telecommunication equipment installed inside different buildings in the following cases: 1) buildings with different earthing and power feeding conditions; 2) buildings with the same earthing and power feeding conditions. This Recommendation: is intended to facilitate the internetworking between d
27、ifferent equipment (interconnected by metallic links); can be used for new installations and, if possible, for the expansion and replacement of the existing installations; is not intended to replace national regulations on bonding and earthing. The user should refer to ITU-T K.27 for bonding configu
28、rations and earthing inside the telecommunication building; to ITU-T K.35 for bonding configurations and earthing at remote sites; to ITU-T K.66 for bonding and earthing of telecommunication installations inside a customer premises. Bonding requirements between a building and an adjacent tower are o
29、utside the scope of this Recommendation. NOTE In this case, the user should refer to b-ITU-T K.47, b-ITU-T K.56 and ITU-T K.71. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation
30、. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references list
31、ed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T K.27 Recommendation ITU-T K.27 (1996), Bonding configurations and earthing i
32、nside a telecommunication building. ITU-T K.35 Recommendation ITU-T K.35 (1996), Bonding configurations and earthing at remote electronic site. ITU-T K.66 Recommendation ITU-T K.66 (2004), Protection of customer premises from overvoltages. ITU-T K.71 Recommendation ITU-T K.71 (2007), Protection of c
33、ustomer antenna installations. EN 50174-2 EN 50174-2 (2001), Information technology Cabling installation. Part 2: Installation planning and practices inside buildings. EN 50174-3 EN 50174-3 (2003), Information technology Cabling installation. Part 3: Installation planning and practices outside build
34、ings. 2 Rec. ITU-T K.73 (04/2008) EN 50310 EN 50310 (2006), Application of equipotential bonding and earthing in buildings with information technology equipment. IEC 62305-1 IEC 62305-1 (2006), Protection against lightning Part 1: General principles. IEC 62305-2 IEC 62305-2 (2006), Protection agains
35、t lightning Part 2: Risk management. IEC 62305-3 IEC 62305-3 (2006), Protection against lightning Part 3: Physical damage to structures and life hazard. 3 Definitions In this Recommendation, the b-IEC 60050 earthing definitions are used. The definitions of ITU-T K.27 for bonding configurations and e
36、arthing are also used. 3.1 Terms defined in this Recommendation This Recommendation defines the following terms: 3.1.1 bonding terminal: This is a terminal provided to allow easy connection of bonding conductors at the entry point of services. The bonding terminal is connected to a MET or to an EBB.
37、 3.1.2 functional earth: A functional earth (FE) is used for the purpose of allowing the intended signalling function of telecommunication equipment to be fulfilled. The signalling function may include signalling with earth return. 3.1.3 parallel bonding conductor: Bonding conductor that is parallel
38、 to the cable. 4 Abbreviations This Recommendation uses the following abbreviations: EBB Equipotential Bonding Bar FE Functional Earth MET Main Earthing Terminal PBC Parallel Bonding Conductor PE Protective Conductor RCD Residual Current Device SPD Surge Protection Device 5 Description of the proble
39、m Equipment and persons in a building are exposed to externally produced energy because conductive services such as telecommunications lines, power lines, antenna leads, waveguides, earthing conductors, and metallic pipes penetrate the shell of the building. The penetration of conducted energy is mi
40、tigated by interconnecting all of these conductors at their entry points with low-impedance bonding conductors or voltage-limiting devices referred to the main earthing terminal. The building should be provided with a main earthing terminal, located as close as possible to the a.c. power and telecom
41、munication cable entrance facilities. In order to minimize surge currents and voltages in the building, the shields of all cables entering the building shall be bonded to the main Rec. ITU-T K.73 (04/2008) 3 earthing terminal, preferably directly or by means of monitoring the current interrupters. A
42、rresters or capacitors may be used for this connection, if required by corrosion considerations. In case of connection between equipments installed in different buildings, the current could flow on the cable screen laid for the connection between the equipments due to the potential difference betwee
43、n the earthing systems of the buildings. The current can cause a damage to the cable, and or to the equipment and injury to the people. 5.1 a.c. current (for different main distribution systems) The main distribution network can service the building by a TN (TN-S or TN-C), TT or IT system; the a.c.
44、power distribution inside the building can be different from the one that depends on the demands of the customer. TN-S earthing system is recommended and is specified in some standards EN 50174 series and EN 50310. If the different earthing systems of different buildings which are connected by means
45、 of a cable screen, the following situations have to be considered: current on the cable screen in case of power fault between the different buildings; transferred potential. The same situation has to be considered in the case of different buildings with the same earthing system. The following aspec
46、ts should be considered: Power, I/O, etc., links between buildings (existing or future ones). Safety of those involved with connecting or disconnecting of cables between buildings for provisioning, repair or maintenance. Failure of the fault protection systems (RCDs, insulation monitoring devices, e
47、tc.). The quantity and types of other cables interconnecting different buildings (in the whole life of the buildings to avoid any later risk). If people decide in one building to modify the earthing system without consulting any involved people in the other buildings (for example, if the buildings h
48、ave different owners or if those knowledgeable about the earthing systems are not available). 5.2 Lightning current If the lightning flash strikes a building, a part of the lightning current flows through the cable screen and that can cause damage to the cable, to the equipment and to the people. 6
49、Solutions 6.1 Galvanic isolation This solution consists in maintaining the cable screen isolated from the earthing system; in this case, the cable covering shall be able to bear the potential difference between the cable screen and the earthing system produced both by fault or by lightning. NOTE If the insulation level of the cable covering cannot withstand the expected lightning overvoltage, an appropriate SPD shall be placed across the screen and the earth. In some situations, the cable screen could be bonded
