1、 STD-ITU-T RECMN K-35-ENGL L99b = 48b2571 Ob21789 7T7 M INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU PROTECTION AGAINST INTERFERENCE K.35 (05196) BONDING CONFIGURATIONS AND EARTHING AT REMOTE ELECTRONIC SITES ITU-T Recommendation K.35 (Previously “CCITT
2、 Recommendation”) STD.ITU-T RECMN K.35-ENGL 177b VBb25L b21770 b17 m FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (Ir). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recom
3、men- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the -T Study Groups which, in their turn, produce Recommendations on these topic
4、s. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation K.35 was prepared by ITU-T Study Group 5 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 8th
5、of May 1996. NOTES 1. telecommunication administration and a recognized operating agency. 2. follows: In this Recommendation, the expression “Administration” is used for conciseness to indicate both a The status of annexes and appendices attached to the Series K Recommendations should be interpreted
6、 as - - an annex to a Recommendation forms 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
7、 publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the . CONTENTS Introduction Scope Definitions Earthing network for EEEs 4.1 Earthing ring for AGREES and BGIEEEs . 4.2 Earthing r
8、ing for EEC . 4.3 Concrete-encased earth electrode . a.c. power distribution 5.1 d.c. power distribution Bonding configuration . a.c. power line surge protective device . 7.1 Main Earthing Terminal 7.3 Outside-plant cable entrance . 7.2 Interior bonding-bus . 7.4 Equipment framework 7.5 Surge protec
9、tors on communication pairs 7.6 Metallic wails References . Appendix I . Page 1 1 2 2 2 3 3 3 3 5 5 5 5 6 7 7 7 7 8 Recommendation K.35 (05/96) 1 STD-ITU-T RECMN K-35-ENGL L77b Li8b259L Ob21792 471 Recommendation K.35 BONDING CONFIGURATIONS AND EARTHING AT REMOTE ELECTRONIC SITES (Geneva, 1996) 1 In
10、troduction Electronic Equipment Enclosures remotely located from telecommunication buildings increasingly are being used to contain a variety of telecommunication equipment. Differences such as size, shape and local environmental stresses give rise to the need for electromagnetic compatibility measu
11、res that differ from those at telecommunication buildings i or at subscribers premises 2. The nomenclature and measures of this Recommendation are intended to promote harmony of installation and equipment configurations while providing for personnel safety and electromagnetic compatibility. Although
12、 the bonding configurations and earthing measures of this Recommendation contribute to the reduction of electrical surge energy that reaches installed equipment, surge protectors, as described in Recommendation K.11 3, may be needed on the conductors of wire-line cables. Furthermore, the equipment m
13、ust be capable of resisting the residual surges that reach it; equipment resistibility is described in Recommendation K.20 4. 2 Scope This Recommendation covers bonding configurations and earthing for equipment located at remote electronic sites such as switching or transmission huts, cabinets or co
14、ntrolled environmental vaults with only one level, a need for a.c. mains power service, and a floor space of about 100 m2 without an antenna tower on the roof of the building as well as nearby; but are more substantial than small electronic housings, such as carrier repeaters or distribution termina
15、ls. Experience in the operation of Electronic Equipment Enclosures shows that the use of a bonding configuration and earthing that are coordinated with equipment capability and with electrical protection devices has the following attributes: - - - promotes personnel safety and reduces fire hazards;
16、enables signalling with earth return (functional earthing); minimizes service interruptions and equipment damage caused by lightning, exposures to power lines and faults in internal d.c. power supplies; minimizes radiated and conducted emissions and susceptibility; - - improves system tolerance to d
17、ischarge of electrostatic energy. Within this framework, this Recommendation: is a guide to bonding configurations and earthing of telecommunication equipment in Electronic Equipment Enclosures; is intended to comply with safety requirements imposed by IEC 5 or national standardizing bodies on a.c.
18、power installations; is intended for installation of new Electronic Equipment Enclosures; treats coordination with electrical protection devices, but does not provide details of protective measures specific to Electronic Equipment Enclosures; utilizes the shielding contribution of effective elements
19、 of the structure and its contents; addresses the bonding of cable shields; is intended to facilitate electromagnetic compatibility of telecommunications equipment; does not include protection against LEMP (Lightening Electromagnetic Pulse). Recommendation K.35 (05196) I 3 Definitions In this Recomm
20、endation, definitions with respect to bonding configurations and earthing already introduced by the IEC 6 and Recommendation K.27 i are used to maintain conformity. Additional definitions needed for remote electronic sites are in this clause. 3.1 electronic communication equipment, and that: electro
21、nic equipment enclosure (EEE): A structure that provides physical and environmental protection for - has only one level; - has a floor space of no more than about 100 m2; - has a need for a.c. mains power service. 3.2 above-ground electronic equipment enclosure (AGEEE): An EEE that is wholly or part
22、ially above ground level. Installed equipment is fully accessible from the interior area. The AG/EEE subcategory includes transportable structures as well as structures partially or fully constructed or assembled on-site. 3.3 below-ground electronic equipment enclosure (BGEEE): An EEE that is comple
23、tely below ground level except possibly for an entryway, a.c. power service, and environmental control equipment. Installed equipment is fully accessible from the interior area. 3.4 the outside without having to enter an intenor area. electronic equipment cabinet (EEC): An EEE for which all installe
24、d equipment can be fully accessed from 3.5 bonding-bus: A conductor, or group of conductors, that serves as a common connection between the Main Earthing Terminal 6 and metallic assemblies in the EEE. The bonding-bus may also be connected to other busbars or -terminals connected to the Earthing Netw
25、ork 6 or structural steel. 3.6 ring bonding-bus: A bonding-bus whose conductors form a closed, connected nng. An example of bonding configurations and earthing of EEEs by use of ring bonding-bus is shown in Appendix I. 4 Earthing network for EEEs 4.1 Earthing ring for AG/EEEs and BG/EEEs An AGEEE or
26、 BGEEE should be provided with a buried exterior earthing ring that satisfies at least the following conditions: - the ring should be uninsulated and buried at approximately 0.75 m; - the ring should encircle the EEE with a spacing, where practical, of about 0.65 m or more from the exterior walls: -
27、 one earthing conductor should connect the ring to the Main Earthing Terminal 6. NOTE - National safety rules may require additional rod electrodes andior additional connections to the a.c. power service entrance. An alternative to the foregoing attachments to the earthing ring is to connect the neu
28、tral busbar to a separate earthing network using a separate earthing conductor; the earthing conductor from the Main Earthing Terminal to the earthing ring remains. The Main Earthing Terminal and the neutral busbar are connected within the EEE. This alternative arrangement permits occasional isolati
29、on of the earthing ring to monitor its condition without disconnecting the earthing connection on the neutral conductor. 2 Recommendation K.35 (0996) STD*ITU-T RECMN K.35-ENGL 199b = qBb259L Ob21795 LTO = 4.2 Earthing ring for EEC The earthing network provides some voltage equalization in the earth
30、near an EEC. The EEC should be provided with a buried exterior earthing ring that satisfies at least the following conditions: - - the ring should be uninsulated, buried at a depth of 0.3 - 0.5 m; the ring should encircle the foundation pad of the EEC or be located below the perimeter of the pad; -
31、NOTE - National safety rules may require additional rod electrodes and/or additional connections to the a.c. power service one uninsulated earthing conductor should connect the ring to the Main Earthing Terminal 6. entrance. 4.3 Concrete-encased earth electrode An EEE often rests on a foundation ear
32、th electrode 7, or is itself constructed of concrete. In this case, the reinforcement or conductor may be used in place of the earthing ring of subclauses 4.1 and 4.2. 5 a.c. power distribution It is recommended that the indoor mains installation within a telecommunication building be of type TN-S a
33、s specified by the IEC 5 in order to improve the EMC performance of the telecommunication installation. This requires that there shall be no PEN conductor within the building. Consequently, a three phase network within a telecommunication building is, physically, a five-wire installation (Ll, L2, L3
34、, N, PE), Depending on the type of outdoor mains distribution network serving a telecommunication building, one of the following requirements shall apply: a) Service by a TN-S section of the outdoor mains distribution network: 1) solely the protective conductor (PE) shall be connected to the main ea
35、rthing terminal (see Figure 1, mode 1). b) Service by a TN-C section of the outdoor mains distribution network: 1) 2) the PEN conductor shall be connected to the main earthing terminal only; from the main earthing terminal to and within customer locations inside the building, the neutral conductor (
36、N) shall be treated as a live conductor; a dedicated PE shall be provided (see Figure 1, mode 2). 3) Service by a T or IT section of the outdoor mains distribution network: 1) 2) c) the PE shall be derived via the main earthing terminal from the earthing network: the dimensioning of the PE shall fol
37、low the rules of the TN-S system. If the outdoor mains distribution is of type IT or TT, a separation transformer dedicated to that building allows for the recommended TN-S installation. In this case the indoor mains installation must conform to mode 1, Figure 1. 5.1 a.c. power line surge protective
38、 device The a.c. mains input to the EEE should be equipped with a surge protective device. A specification for a low-voltage surge protective device is in advanced stages of preparation by IEC Subcommittee 37A. The surge protective device should be connected to the mains conductors on the load side
39、of the circuit breaker. The surge protective device should be located where the leads for connection to the mains conductors, including the earthed (neutral) conductor, are as short as possible. Lead lengths that are less than 0.5 m are recommended. Recommendation K.35 (0996) 3 fl II I mains Inputfr
40、omwtdoor distribution (TN-S) Main earthing terminal Earthing network NOTE - Mode 1 is obligatory if a separation transformer is dedicated to the building and the TN-S system consequently originates at the transformer load side. L 0uqX.lt to indoor mains installation (TN-S) PE DC-return ring conducto
41、r I I - - Main earthing terminal input from outdoor Earthing network mains distribution (TN-C) Mode 3: ITAT or TTfil DC-return ring conductor i Output to indoor mains installation (IT or Tr) n L input from outdoor mains distribution (IT or l-r) Main earthing terminal Earthing network FIGURE 1K.35 Ar
42、rangements for the transition from the outdoor mains distribution network to the indoor mains 4 Recommendation K.35 (05196) STD-ITU-T RECMN K.35-ENGL L77b 48b257L Ob21777 T73 6 d.c. power distribution in many EEEs, d.c. power is generally distributed from a centralized d.c. power plant (bulk power p
43、lant), with the positive terminal connected to the common bonding network i of the structure. This polarity is chosen to minimize corrosion in the outside cable plant, but there may be exceptions for specific transmission systems. The return conductor of the d.c. distribution system may be connected
44、 to the Common Bonding Network (CBN) in either of two manners. It may be connected at only one location as an isolated d.c. return system (dc-I). Or the d.c. return may connect to the CBN at several locations (in which case some d.c. current is conducted by the CBN), as a d.c. return common to a CBN
45、 (dc C-CBN). Because of the small size of an EEE, the common-mode voltages (and the conversion to transverse mode voltage) supported by either of these two distribution systems should be comparable. NOTE - The Common Bonding Network of an EEE comprises the bonding-bus conductors, a.c. power conduit,
46、 PE conductors, structural steel, and cable and racks i. The bonding conductor that connects the return side of the d.c. power source to the interior bonding-bus should be capable of conducting the maximum fault current of the power system. Rapid operation of overcurrent protective devices is aided
47、by connecting cable racks to the bonding-bus and providing electrical continuity between rack sections. Because of the close proximity of equipment in an EEE, it is important that equipment not be sensitive to voltage surges on the d.c. power caused by short-circuits in other equipment. 7 Bonding co
48、nfiguration The bonding configuration in the EEE makes use of a CBN that includes all available metallic structural components and metallic cable trays and supports, augmented by an interior ring bonding-bus. The interconnected CBN reduces the magnitude of external surge current that is conducted on
49、 the framework of the enclosed equipment. This Recommendation covers the case where equipment is connected to the CBN in a Mesh-BN configuration i. This bonding configuration helps provide an equipotential environment for personnel in the close confines of the EEE. It also assures the presence of many parallel current paths to help de-energize a short-circuit in the d.c. supply and to mitigate the effects of surge currents. (Equipment can be connected to the CBN using other bonding configurations, but such cases are not covered in this Re
