џWPCL ћџ2BJ|xа HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаа АА X агга ХА6p&А6p&Х аб cмˆ4 PŽТ б вЦ‚HјР!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаааб cмˆ4 PŽТ бIMPORT R:\\ART\\WMF\\ITU.WMF \* mergeformatУ Уб cмˆ4 PŽТ б аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHP И XА`ИhР!Р!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф б cмˆ4 PŽТ бINTERNATIONAL TELECOMMUNICATION UNIONб cмˆ4 PŽТ бУ У а јА ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџјP И XА`ИhР!Р!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаˆа HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјpи (#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ЬаТа ТТ№ ТТ№јТб cмˆ4 PŽТ бCCITTб cмˆ4 PŽТ бСHШ CСƒб cмˆ4 PŽТ бK.27б cмˆ4 PŽТ бЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјpи А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ЬаТа ТТ№ ТТ№јТ‚б cмˆ4 PŽТ бФ ФTHE INTERNATIONALЦЦ Та ТТ№ ТТ№јТTELEGRAPH AND TELEPHONEЦЦ Та ТТ№ ТТ№јТCONSULTATIVE COMMITTEEЦЦ Та ТТ№ ТТ№јТб cмˆ4 PŽТ бЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјpи А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ ЬаТа ТТ№ ТТ№јТб cмˆ4 PŽТ бУ УPROTECTION AGAINST INTERFERENCEЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТб cмˆ4 PŽТ бЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТBONDING CONFIGURATIONSЦЦ Та ТТ№ ТТ№јТAND EARTHING INSIDEЦЦ Та ТТ№ ТТ№јТA TELECOMMUNICATION BUILDINGЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТб cмˆ4 PŽТ бЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТб cмˆ4 PŽТ бRecommendation K.27б cмˆ4 PŽТ бЦЦ Та ТТ№ ТТ№јТЦЦ Та ТТ№ ТТ№јТб cмˆ4 PŽТ бФ ФЦЦ Та ТТ№ ТТ№јТб cмˆ4 PŽТ бвЦ‚HјР!Цв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјpи џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаIMPORT R:\\ART\\WMF\\CCITTRUF.WMF \* mergeformatб cмˆ4 PŽТ бУ УЦЦТа ТТ№ ТТ№јТ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP И XА`ИhР!Р!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ ФGeneva, 1991б cмˆ4 PŽТ бУ УЦЦ а јА ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџјP И XА`ИhР!Р!џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаˆФ Фа HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б ‚С`(#5СPrinted in Switzerland аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаУ У Та ТС€ HССр8NСFOREWORDФ ФЦЦ а H№ аС СThe CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988). а H аС СRecommendation K.27 was prepared by Study Group V and was approved under the Resolution No. 2 procedure on the 18 of March 1991. ‚Ср PС___________________  аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС‚Ср TСб cмˆ4 PŽТ бCCITT NOTEУ Уб cмˆ4 PŽТ бЦЦ б cмˆ4 PŽТ бФ ФС СIn this Recommendation, the expression Р"РAdministrationР"Р is used for conciseness to indicate both a telecommunication Administration and a recognized private operating agency. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа ‚Ср UСРMР  ITU  1991 а H аAll rights reserved. No part of this 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 ITU.‚У У PAGE BLANCHEб cмˆ4 PŽТ б ггеУI а Hx аУ Уб cмˆ4 PŽТ б styleref head_footRecommendation K.27Ф ФPAGE19У Уб cмˆ4 PŽТ бУееŸ† а HH аб cмˆ4 PŽТ бPAGE20У Уб cмˆ4 PŽТ б styleref head_footRecommendation K.27 Ÿеа X Ш аб cмˆ4 PŽТ бRecommendation K.27Ф Ф аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бRecommendation K.27 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚Ср BСб cмˆ4 PŽТ бУ УBONDING CONFIGURATIONS AND EARTHING INSIDE Ср JСA TELECOMMUNICATION BUILDING аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б1ТX ТIntroductionФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe main subject of the CCITT Handbook on Р"РEarthing of telecommunication installationsР"Р [1], 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 transition 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 CCITT Recommendation on bonding configurations and earthing inside a telecommunication building. а H аС СWithin the field of EMC, regulations restricting electromagnetic emissions must be satisfied, and for acceptable performance, equipment must possess a specific level of immunity. Electromagnetic compatibility 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 Р"РsingleЉpointР"Р connections to the CBN. These singleЉpoint 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 (meshЉBN) or by a single point connection (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 important 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 РSР 6 and Annex A. As part of its shielding function, the bonding and earthing network provides for personnel safety and lightning protection, and helps control electrostatic discharge (ESD). а H аС СSince 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 these 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. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У2ТX ТScopeФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СExperience in the operation of telecommunication centres shows that the use of a bonding and earthing network that is coordinated with equipment capability and with electrical protection devices, has the following attributes: Та ТРIРТ№ Тpromotes personnel safety and reduces fire hazards;ЦЦ Та ТРIРТ№ Тenables signalling with earth return;ЦЦ Та ТРIРТ№ Тminimizes service interruptions and equipment damage;ЦЦ Та ТРIРТ№ Тminimizes radiated and conducted electromagnetic emissions;ЦЦ а Hр аТа ТРIРТ№ Тreduces radiated and conducted electromagnetic susceptibility;ЦЦ а H аТа ТРIРТ№ Тimproves system tolerance to discharge of electrostatic energy, and lightning interference.ЦЦа HH а С СWithin this framework, this Recommendation: а H аТа ТТ№ ТС€ Сa)СpСis a guide to bonding and earthing of telecommunication equipment in telephone exchanges and similar telecommunication switching centres;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСis intended to comply with safety requirements imposed by IEC [2] or national standardizing bodies on a.c. power installations;ЦЦ а H аТа ТТ№ ТС€ Сc)СpСcan be used for installation of new telecommunication centres, and, if possible, for expansion and replacement of systems in existing centres;ЦЦ а H аТа ТТ№ ТС€ Сd)СpСtreats coordination with external lightning protection, but does not provide details of protective measures specific to telecommunication buildings;ЦЦ а H аТа ТТ№ ТС€ Сe)СpСaddresses the shielding contribution of the effective elements of the building;ЦЦ а H аТа ТТ№ ТС€ Сf)СpСaddresses shielding provided by cabinets, cable trays and cable shields;ЦЦ а H аТа ТТ№ ТС€ Сg)СpСis intended to encourage EMC planning, which should include bonding and earthing arrangements that accommodate installation tests and routine diagnostics;ЦЦ Та ТТ№ ТС€ Сh)СpСdoes not include:ЦЦ а H аТа ТТ№ ТРIРТhpТrequired values of surge current immunity and insulation withstand voltages,ЦЦ а H№ аТа ТТ№ ТРIРТhpТlimits of radiated and conducted electromagnetic emission or immunity,ЦЦ а Hx аТа ТТ№ ТРIРТhpТtechniques for verifying and maintaining bonding and earthing networks.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У3ТX ТDefinitionsФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn this Recommendation, definitions with respect to earthing already introduced by the IEC [3] are used to maintain conformity. For convenience, they are reproduced in РSР 3.1. Definitions specific to telecommunication installations, and not covered by the IEC, are added in РSР 3.2. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа3.1Тh  ТУУIEC definitionsФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe following definitions are taken from IEC 50 [3]. The term Р"Рearthing networkР"Р is defined in Chapter 604, all others are in Chapter 826. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.1С јСУ УearthФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe conductive mass of the earth, whose electric potential at any point is conventionally taken as equal to zero (in some countries the term Р"РgroundР"Р is used instead of Р"РearthР"Р). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.2С јСУ Уearth electrodeФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA conductive part or a group of conductive parts in intimate contact with and providing an electrical connection with earth. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.3С јСУ Уearthing networkФ ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe part of an earthing installation that is restricted to the earth electrodes and their interconnections. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.4С јСУ Уmain earthing terminalФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA terminal or bar provided for the connection of protective conductors, including equipotential bonding conductors and conductors for functional earthing, if any, to the means of earthing.аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа Та Т3.1.5СP СУ Уearthing conductorФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA protective conductor connecting the main earthing terminal or bar to the earth electrode. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.6С јСУ Уequipotential bondingФ ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СElectrical connection putting various exposed conductive parts and extraneous conductive parts at a substantially equal potential. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.7С јСУ Уequipotential bonding conductorФ ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA protective conductor for ensuring equipotential bonding. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.8С јСУ Уneutral conductor (N)Ф ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA conductor connected to the neutral point of a system and capable of contributing to the transmission of electrical energy. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.9С јСУ Уprotective conductor (PE)Ф ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA conductor required by some measures for protection against electric shock by electrically connecting any of the following parts: Та ТРIРТ№ Тexposed conductive parts;ЦЦ Та ТРIРТ№ Тextraneous conductive parts;ЦЦ Та ТРIРТ№ Тmain earthing terminal;ЦЦ Та ТРIРТ№ Тearth electrode;ЦЦ Та ТРIРТ№ Тearthed point of the source or artificial neutral.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.1.10У УС јСPEN conductorФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СAn earthed conductor combining the functions of both protective conductor and neutral conductor. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа3.2Тh  ТУУDefinitions for telecommunication earthing installationsФФЦЦ Та ТС€ HС3.2.1С јСУ Уbonding network (BN)Ф ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA 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 Р"Рelectromagnetic shieldР"Р, denotes any structure used 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. а H аС СThe following definitions of BN configurations are illustrated in Figure 1/K.27. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.2С јСУ Уcommon bonding network (CBN)Ф ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe 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 reinforcing 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. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.3С јСУ УmeshЉBN (MBN)Ф ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA bonding network in which all associated equipment frames, racks and cabinets, and usually, the d.c. power return conductor, are bonded together as well as at multiple points to the CBN. Consequently, the meshЉBN augments the CBN (see Figure 1e)/K.27). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.4С јСУ Уisolated bonding network (IBN)Ф ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA bonding network that has a single point of connection (Р"РSPCР"Р) to either the common bonding network or another isolated bonding network. All IBNs considered here will have a connection to earth via the SPC [see Figures 1c)/K.27 and 1d)/K.27]. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.5С јСУ Уsingle point connection (SPC)Ф ФггУУЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаФФС СThe unique location in an IBN where a connection is made to the CBN. In reality, the SPC is not a Р"РpointР"Р but, of necessity, has sufficient size to accommodate the connection of conductors. Usually, the SPC takes the form of а H аa copper busЉbar. 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. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.6С јСУ УSPC window (SPCW)Ф ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe interface or transition region between an IBN and the CBN. Its maximum dimension is typically 2 metres. The SPC busЉbar (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 busЉbar or frame [see Figures 1c)/K.27 and 1d)/K.27]. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.7С јСУ УmeshЉIBNФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA type of IBN in which the components of the IBN (e.g. equipment frames) are interconnected to form a meshЉlike structure. This may, for example, be achieved by multiple interconnections between cabinet rows, or by connecting all equipment frames to a metallic grid (a Р"Рbonding matР"Р) 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 FaradayЉcage. The spacing of the grid is chosen according to the frequency range of the electromagnetic environment [see Figure 1d)/K.27]. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.8С јСУ Уstar IBNФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA type of IBN comprising clustered or nested IBNs sharing a common SPC [see Figure 1c)/K.27]. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.9С јСУ Уsystem blockФ ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СAll the equipment whose frames and associated conductive parts form a defined BN. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.10У УС јСisolated d.c. return (d.c.ЉI)Ф ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA d.c. power system in which the return conductor has a single point connection to a BN. More complex configurations are possible, see РSР 5.2. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС3.2.11У УС јСcommon d.c. return (d.c.ЉC)Ф ФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA d.cУ У. Ф Фpower system in which the return conductor is connected to the surrounding BN at many locations. This BN could be either a meshЉBN (resulting in a d.c.ЉCЉMBN system) or an IBN (resulting in a d.c.ЉCЉIBN system). More complex configurations are possible (see РSР 5.2). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У4ТX ТPrinciples of bonding and earthingФ ФЦЦ 4.1Тh  ТУУSummary of theoryФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СBonding and earthing refer to the construction and maintenance of bonding networks (BNs) and their connection to earth. In this document the acronym BN implies that a connection to earth exists. Also, BN is used to refer to CBNs and IBNs collectively.‚б cмˆ4 PŽТ б Ср OСFigure 1/K.27 = 23 cm б cмˆ4 PŽТ б а H аС СThe 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 concern are quasi steadyЉstate sources such as a.c. power harmonics, and Р"Рfunction sourcesР"Р such as clock signals from digital equipment. All of these sources will be referred to generically as Р"РemittersР"Р. People and equipment that suffer adversely from the energy from the emitters will be referred to as Р"РsusceptorsР"Р. 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. а H аС СOther purposes of a BN are to function as a Р"РreturnР"Р conductor in some signalling applications, and as a path for power fault currents. The capability of the BN to handle large currents helps to rapidly deЉenergize faulted power circuits. Also the BN and its connection to earth is used in Р"Рground returnР"Р signalling (see РSР 4.5). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа4.2Тh  ТУУImplementation principlesФФЦЦ Та ТС€ HС4.2.1С јСУУImplementation principles for the CBNФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe theoretical concepts of Annex A are confirmed by practical experience and lead to the general principles listed below. A consequence of applying these principles is that the number of conductors and interconnections in the CBN is increased until adequate shielding is achieved. Concerning the important issue of electric shock, the following implementation principles apply to mitigation of electric shock as well as to equipment malfunction. Electric shock is discussed further in РSР 4.3. Та ТТ№ ТС€ Сa)СpСAll elements of the CBN shall be interconnected. Multiple interconnections resulting in a threeЉdimensional mesh are especially desirable. Increasing the number of CBN conductors and their interconnections, increases the CBN shielding capability and extends the upper frequency limit of this capability.ЦЦ а H аТа ТТ№ ТС€ Сb)СpСIt is desirable that the egress points for all conductors leaving the building (including the earthing conductor), be located close together. In particular, the a.c. power entrance facilities, telecommunications cable entrance facilities, and the earthing conductor entry point, should be close together.ЦЦ а H аТа ТТ№ ТС€ Сc)СpСThe facility should be provided with a main earthing terminal located as close as possible to the a.c. power and telecommunications cable entrance facilities. The main earthing terminal shall connect to:ЦЦ а Hh аТа ТТ№ ТРIРТhpТan earthing electrode(s) via a conductor of shortest length;ЦЦ а H№ аТа ТТ№ ТРIРТhpТthe neutral conductor of the a.c. power feed (in TN systems);ЦЦ а H№ аТа ТТ№ ТРIРТhpТcable shields (at the cable entrance) either directly or via arresters or capacitors if required by corrosion considerations.ЦЦ а H аТа ТТ№ ТС€ Сd)СpСThe CBN shall be connected to the main earthing terminal. Multiple conductors between CBN and the main earthing terminal are desirable.ЦЦ а H аТа ТТ№ ТС€ Сe)СpСAs contributors to the shielding capability of the CBN, interconnection of the following items of the CBN is important:ЦЦ а H аТа ТТ№ ТТhpТС€С1)Си Сmetallic structural parts of the building including IЉbeams and concrete reinforcement where accessible;ЦЦ а H аТа ТТ№ ТТhpТС€С2)Си Сcable supports, trays, racks, raceways, and a.c. power conduit.ЦЦ а H аТа ТТ№ Тf)Си СThe coupling of surges into indoor cabling (signal or power) is reduced, in general, by running the cables in close proximity to CBN elements. However, in the case of external surge sources, the currents in the CBN will tend to be greater in peripheral CBN conductors. This is especially true of lightning downЉconductors. Thus, it is best to avoid routing cables in the periphery of the building. When this is unavoidable, metallic ducts that fully enclose the cables may be needed. In general, the shielding effect of cable trays (etc.) is especially useful, and metallic ducts or conduit that fully enclose the cables provide near perfect shielding.ЦЦ а H аТа ТТ№ ТС€ Сg)СpСIn steel frame highЉrise buildings, advantage may be taken of the shielding effects that the steel frame provides against lightning strokes. For cables extending between floors, maximum shielding is obtained by locating the cables near the centre of the building. However, as implied above, cables enclosed in metallic ducts may be located anywhere.ЦЦ а H аТа ТТ№ ТС€ Сh)СpСWhere the facility to use overЉvoltage primary protection [4] on telecommunication wires is provided, it should have a low impedance connection to the cable shield, if it exists, and also to the surrounding CBN.ЦЦ а H аТа ТТ№ ТС€ Сi)СpСOverЉvoltage protectors may be provided at the a.c. power entrance facility if the telecommunication building is located in an area where power lines are exposed to lightning. These protectors should be bonded with low impedance to the CBN.ЦЦ а H аТа ТТ№ ТС€ Сj)СpСMechanical connections in a protection path of the CBN whose electrical continuity is questionable shall be bypassed by jumpers that are visible to inspectors. These jumpers shall comply with IEC requirements for safety. However, for EMC applications, the jumpers should have low impedance.ЦЦ а H аТа ТТ№ ТС€ Сk)СpСThe CBN facilitates the bonding of cable shields or outer conductors of coaxial cables at both ends by providing a low impedance path in parallel and in proximity to the cable shields and outer conductors. Thus most of the current driven by potential differences is carried by the highly conductive members of the CBN. Disconnection of one cable shield for inspection should minimally affect the current distribution in the CBN. ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС4.2.2С јСУУImplementation principles for a meshЉBNФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe main feature of a meshЉBN is the interconnection, at many points, of cabinets and racks of telecommunications and other electrical equipment, and also multiple interconnections to the CBN. а H аС СIf the outer conductor of a coaxial cable interconnection between meshЉBN equipment has multiple connections to the CBN, it may need additional shielding. If the shielding provided by a cable tray is insufficient, additional shielding may be provided by use of shielded coaxial cable (Р"РtriaxР"Р), enclosing ducts, or conduit. а H аС СBonding methods, in increasing order of EMC quality are: screw fastenings, spot welds, and welded seams. The highest level of EMC shielding is provided by equipment cabinets and any sheetЉmetal enclosures within these cabinets. С СA proven countermeasure to undesirable emission or reception of electromagnetic energy, especially at high frequencies, is a shield that totally encloses the electronic circuit. Effective shielding of cables, especially when the shields are extensions of shielding cabinets, depends on shielding material, shield geometry, and especially the connection of the shield to the cabinet panels at which the shield terminates. С СIt is easy to add shielding to a meshЉBN configuration. The need for additional shielding may arise for example, if a broadcast transmitter were installed nearby. С СIn some situations, it may be advantageous to augment the meshЉBN by connecting all equipment frames of a system block to a conductive grid (a bonding mat) located either below or above a collection of equipment cabinets. This optional use of a bonding mat is shown in Figure BЉ1/K.27. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HС4.2.3С јСУУImplementation principles for an IBNФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe main feature of an IBN is that it is isolated from the surrounding CBN except for a singleЉpoint connection where conductors entering the system block enter via the transition region between the IBN and CBN (see definition of SPCW). а H аС СWithin the confines of an IBN, the importance of multiple interconnections between cabinets and racks, etc., depends on the details of d.c. power distribution and signal interconnection. For example, if the d.c. power return conductor has multiple connections to cabinet frames, then multiple interconnection of cabinet frames and racks is desirable for the following reason: it will tend to reduce surge coupling in the event of a d.c. fault in equipment within the IBN. а H аС СConcerning cable shields of twisted pair cables, if a shield is left openЉcircuit at the end that terminates on IBN equipment, while the other end is connected to the CBN, surges in the CBN may result in induced common mode surges on the pairs in that cable. If those pairs terminate on devices that can operate satisfactorily in the presence of a steady state common mode (e.g. optoЉisolators, transformers, or surge protectors), and if those devices can also withstand common mode surges, then there may be an advantage in having the electrostatic shielding afforded by an open circuited shield. С СIn the case of coaxial cable, the outer conductor will, of necessity, terminate on the interface circuits at each end. Interface circuits containing transformers or optoЉisolators may be used to isolate the outer conductor. If a shielded cable or waveguide enters the IBN from the CBN, the most generally effective strategy is to connect each end of the shield or waveguide to the equipment frame and to bond the shield or waveguide to the single point connection. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа4.3Тh  ТУУProtection against electric shockФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA densely interconnected BN, together with its connection to earth, substantially reduces the likelihood of significant voltages appearing а H аbetween adjacent metallic components. However, additional measures need to be taken, especially in regard to a.c. power distribution (see РSР 5.1). IEC [2] discusses protection against electric shock, and installations should conform to its recommendations. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа4.4Тh  ТУУProtection against lightningФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA CBN conforming to РSР 4.2.1 should adequately shield against lightning surges arriving at the building on conductors such as cable shields and power lines. However, in the event of a direct stroke to the building, the CBN may not provide sufficient shielding. Consequently, buildings without steel frames or reinforcements may require external lightning protection; especially so if the building has a radio tower on its roof. Concerning the protective measures against the effects of a direct lightning stroke to a building, refer to IEC [5]. Where necessary to further reduce risk, these protective measures may have to be enhanced, e.g. by conductive roof layers, closer spacing of downЉconductors, interconnection of the reinforcement of concrete buildings, and interconnection of metallic facade elements. It is advantageous to introduce all conductive elements of services, e.g. cables and pipes, into the building at one location and in close proximity. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа4.5Тh  ТУУFunctional earthingФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СTelecommunication techniques sometimes use circuits for signalling with earth return, e.g. lines with ground start, three wire interЉexchange connection, etc. Equipment interconnected by these circuits needs functional earthing.The signalling range is normally determined by the resistance of the current path. Most of this resistance is contributed by the earth electrodes. The performance provided by the earthing network via the main earthing terminal is generally sufficient for this signalling purpose [1].аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У Та Т5СјСPower distributionФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA.c. and d.c. power distribution in telecommunication buildings should be designed to limit coupling to telecommunication circuits arising from: Та ТРIРТ№ Тmutual impedance of shared conductors;ЦЦ а H аТа ТРIРТ№ Тmutual inductive coupling (especially during short circuit conditions);ЦЦ Та ТРIРТ№ Тcommon source impedances.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа5.1Тh  ТУУA.c. power distributionФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIt is recommended that the a.c. power distribution system in a telecommunication building be of type TNЉS as specified by the IEC [2]. This requires that there be no PEN conductor within the building. If the neutral conductor is bonded to the main earthing terminal, this conductor is otherwise given the same treatment as the phase conductors. Consequently, a three phase network in a telecommunication building is, physically, a five wire installation (L1, L2, L3, N, PE). а H аС СIt is recognized that both TTЉtype and ITЉtype systems are in use for public power distribution. However, this Recommendation does not fully address bonding and earthing of such systems. If power is served to the telecommunications building by a TT or IT distribution network, a separation transformer dedicated to that building allows for the recommended TNЉS installation. Other methods not using a separation transformer are under study. ITЉtype systems are under further study. С СTo avoid interference caused by magnetic fields of currents on power cables, it is usual practice to separate telecommunication cables from unshielded power cables by at least 10 cm, even if both have partial shielding in the form of the recommended metallic support structure. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа5.2Тh  ТУУD.c. power distributionФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn telecommunication buildings, d.c. power is generally distributed from a centralized d.c. power plant, with the positive terminal connected to the CBN. This polarity is chosen to minimize corrosion in the outside cable plant. There may be exceptions for specific transmission systems. а H аС СThe d.c. power return network may be connected to its surrounding BNs at a single point only. This case will be referred to as an Р"Рisolated d.c.Љ returnР"Р system (d.c.ЉI). а H аС СAlternatively, the d.c. return may connect to the BN at multiple points (in which case some d.c. current will be conducted by the BN). This system will be referred to as a Р"Рd.c. return common to a BNР"Р and denoted by Р"Рd.c. C-BNР"Р. Typical configurations are d.c. CЉCBN (d.c. return common to the CBN), and d.c. CЉIBN (d.c. return common only to an IBN). Also, a d.c. return could, for example, traverse both the CBN and an IBN, and be common to the CBN but isolated from the IBN. This case is denoted by d.c. CЉCBN : d.c. IЉIBN. These are discussed in Annex B. Other more complicated interconnections of BNs and d.c. returns are also in use. а H аС СThe advantage of a d.c.ЉCЉBN system is that it cannot support a d.c. feed commonЉmode and hence unwanted coupling via this mode cannot occur. On the other hand, there will be coupling between the BN and the d.c. feed. The advantage of the d.c. IЉBN system is that it avoids BN to d.c. feed coupling. However, it supports a commonЉmode and may introduce unwanted coupling. The choice between the two systems depends on the overall design strategy. Some recommendations are given below. а H аС СA d.c.ЉCЉCBN feed may be used in systems in which the d.c. feedЉtoЉCBN coupling has been minimized by the following measures: а H аТа ТРIРТ№ Тd.c. feed conductors have large crossЉsections enabling them to carry high currents with minimal temperature rise;ЦЦ Та ТРIРТ№ Тvoltage drop at maximum load current is low;ЦЦ а H аТа ТРIРТ№ Тthere is low source impedance, and low mutual impedance between the branches of the d.c. feed system.ЦЦ а H аС СThe use of a d.c.ЉI feed results in a much lower d.c. feedЉtoЉCBN coupling and is preferable in d.c. distribution networks designed with: а H аТа ТРIРТ№ Тloads in more than one system of electronic equipment (i.e. shared battery plant), andЦЦ а H аТа ТРIРТ№ Тloads that are sensitive to transients occurring during short circuit conditions.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У6ТX ТComparison between IBN and meshЉBN installationsФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe advantage of installing equipment in an IBN is that a high level of shielding is attainable from d.c. through tens of kilohertz or perhaps hundreds of kilohertz depending on the size of the IBN (see РSР A.1.2). The reason is that, within this frequency range, the single point connection between the IBN and CBN results in negligible current flowing between CBN and IBN. Some digital switches are designed specifically for installation within an IBN. а H аС СMesh IBNs and star IBNs are both currently in use. Paragraph B.2 describes a mesh IBN in the form of a Р"РbondingЉmatР"Р, and РSР B.3 describes a star IBN system. Sparsely interconnected mesh IBNs have also been used successfully, and this is mentioned in РSР B.3. а H аС СTo limit the risk of electric shock between an IBN and the surrounding CBN, it is necessary to limit the size of the IBN (both horizontal and vertical extent). Passageways that form the boundary between IBN and CBN, should have a minimum width imposed. а H аС СDisadvantages of IBN installation are cable routing restrictions and the additional expense (compared to meshЉBN) of maintaining the isolation. а H аС СThe advantage of installing equipment in a meshЉBN configuration is that equipment frames may be connected to the surrounding CBN without restriction. Also, shielded cables and coaxial cables may be routed, and their shields or outer conductors connected to cabinet frames, without restriction. If the CBN design and equipment susceptibility has been coordinated, the CBN provides shielding from d.c. through several megahertz. A meshЉBN installation also has maintenance advantages as described in the next section. а H аС СA disadvantage of the meshЉBN installation is the need for quantitative design procedures and appropriate immunity data for equipment. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У7ТX ТMaintenance of bonding networksФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СOne advantage of meshЉBN installation is that small changes that occur in the CBN generally have only a small effect on its shielding capability. Moreover, when necessary, additional shielding may be obtained by introduction of additional conductors (e.g. bonding conductors, cable trays, and conduit). Such modifications are usually straightforward. а H аС СIBN systems are more difficult to maintain, because craftЉperson activity is liable to result in inadvertent interconnections between IBN and CBN, violating the desired singleЉpoint connection, and introducing surge currents into the IBN. Closely related to this is maintenance of d.c.ЉI power а H аsystems. Verification of singleЉpoint connection in a d.c.ЉI system is facilitated if this connection is made with a conductor, around which, a d.c. clampЉon ammeter can be clamped. Zero current confirms singleЉpoint connection. а H аС СIt is recommended that systematic verification be performed on all bonding configurations and earthing connections inside a telecommunications building. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У8ТX ТExamples of connecting equipment configurations to the CBNФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe bonding configuration that is used depends upon the type of equipment to be connected to the CBN. С СThree examples are described in Annex B. They are: Та ТРIРТ№ ТmeshЉBN (see РSР B.1);ЦЦ Та ТРIРТ№ ТmeshЉIBN with a bonding mat configuration (see РSР B.2);ЦЦ а H аТа ТРIРТ№ Тstar, or sparseЉmeshЉIBN with isolation of d.c. power return (see РSР B.3).ЦЦ а HH а‚Ср8OСб cмˆ4 PŽТ бANNEX A Ср8FСб cмˆ4 PŽТ б(to Recommendation K.27) Ср8<СУ УBrief theory of bonding and earthing networksФ Ф аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаA.1Тh  ТУУOverviewФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe basic theoretical notions of shielding apply to the entire electromagnetic spectrum extending from d.c. through microwave frequencies. The essence of these basic notions is represented by the circuit model of Figure A-1a)/K.27. The description of energy sources as Р"РemittersР"Р, and susceptible equipment (and people) as Р"РsusceptorsР"Р is taken from KeiserУУ ФФ[6]. In Figure AЉ1a)/K.27, УУVУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ is the frequency domain representation of the emitter (e.g. a Laplace or Fourier transform), and УУZУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ is the emitter source impedance. The susceptor is represented by its impedance УУZУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ. The electromagnetic interaction between emitter and susceptor is modelled by a twoЉport network (port A with terminals A0, and A1, and port B with terminals B0, and B1). In Figure AЉ1a)/K.27 this twoЉport is represented by a TЉnetwork, but a p representation is often useful, as is a Norton equivalent for the emitter. а H аС СAlthough Figure AЉ1a)/K.27 is a simplification of reality, it is usually an adequate model for any specific emitterЉsusceptor pair. Moreover, it can be used as the starting point whenever a more complex model is necessary. а H аС СFigure AЉ1a)/K.27 illuminates the two main strategies for increasing the shielding of the susceptor from the emitter: the Р"РshortЉcircuitР"Р and Р"РopenЉcircuitР"Р strategies. It is clear that if УУZУУб cмˆ4 PŽТ бCб cмˆ4 PŽТ бФФФФ is zero, no energy from the emitter УУVУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ can reach the susceptor and УУVУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ = 0. The energy that leaves the emitter is Р"Рreflected by the shortЉcircuitР"Р and dissipates in the resistive components of УУZУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ and УУZУУб cмˆ4 PŽТ бAб cмˆ4 PŽТ бФФФФ. (Energy can also be returned to the source but this is not significant here.) Similarly, it is clear that if either УУZУУб cмˆ4 PŽТ бAб cмˆ4 PŽТ бФФФФ or УУZУУб cмˆ4 PŽТ бBб cмˆ4 PŽТ бФФФФ are infinite in magnitude (i.e. open circuit), no emitter energy will reach the susceptor (and again УУVУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ = 0). In this case, the energy that leaves the emitter is reflected by the open circuit. Suppose УУZУУб cмˆ4 PŽТ бBб cмˆ4 PŽТ бФФФФ is the open circuit. Then УУZУУб cмˆ4 PŽТ бBб cмˆ4 PŽТ бФФФФ = Р8Р, and the energy will dissipate in the resistive parts of УУZУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ, УУZУУб cмˆ4 PŽТ бAб cмˆ4 PŽТ бФФФФ and УУZУУб cмˆ4 PŽТ бCб cмˆ4 PŽТ бФФФФ. Note that in general, УУVУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ and all impedances are functions of frequency. а H аС СThe twoЉport in Figure AЉ1a)/K.27 (A1, A0, B1, B0) will be referred to as the shielding network relative to some specific emitter and susceptor. If a different emitter or susceptor were considered, new impedance functions УУZУУб cмˆ4 PŽТ бAб cмˆ4 PŽТ бФФФФ, УУZУУб cмˆ4 PŽТ бBб cмˆ4 PŽТ бФФ ФФand УУZУУб cмˆ4 PŽТ бCб cмˆ4 PŽТ бФФФФ would apply. а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH€pи P №hР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA most useful characterization of the shielding network is a frequency domain transfer function. Here, the transfer function УУTФФ(w) will be defined as either УУIУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w)/УУVУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ(w) or УУVУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w)/УУVУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ(w). Thus УУTФФ(w), as defined here, is a function of УУZУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ and УУZУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ as well as УУZУУб cмˆ4 PŽТ бAб cмˆ4 PŽТ бФФФФ, УУZУУб cмˆ4 PŽТ бBб cмˆ4 PŽТ бФФФФ and УУZУУб cмˆ4 PŽТ бCб cмˆ4 PŽТ бФФФФ. а H аС СTo summarize, for each emitterЉsusceptor pair there is a transfer function УУTФФ(w) that characterizes the shielding network. С СReturning to the topic of shielding strategies, note that in general, perfect short and open circuits are not possible to achieve, since the best implementations possess inductance and capacitance respectively. As a result, instead of perfect shielding, the most that can be achieved is a transfer function УУTФФ(w) whose magnitude is less than some prescribed value over some prescribed frequency range. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСA.1.1С јСУУApplication to BNs in generalФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn typical bonding networks, resistive components are small, and for transient events with spectra in the 1 kHz to 1 MHz range, the shielding network is primarily inductive. Consequently, the general representation of Figure AЉ1a)/K.27 reduces to Figure AЉ1b)/K.27. As noted above, the specific component values depend on a particular emitterЉsusceptor pair. However, the УУLФФs in Figure AЉ1b)/K.27 are constants: they are not functions of frequency. An observation of fundamental importance is as follows: Increasing the number of conductors and interconnections in the BN (especially in the region lying between the emitter and susceptor) will, in general, reduce УУLУУб cмˆ4 PŽТ бCб cмˆ4 PŽТ бФФФФ and hence reduce the transfer function of the BN relative to that emitterЉsusceptor pair. In the limiting case, the susceptor could be given nearЉtotal shielding by enclosing it in an unbroken sheet of metal (i.e. a Faraday cage). а H аС СA susceptor may be characterized by a Р"Рsusceptibility thresholdР"Р УУIУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w), or УУVУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w). Sinusoidal excitation will be assumed, but the following theory may be adaptable to pulse excitation. As an example, consider as a susceptor, equipment whose frame is connected to the CBN at several points. Choose one of these points to be the test point. Suppose the CBN connection at the test point is made by a conductor, around which splitЉcore transformers can be clamped for purposes of excitation and current measurement. Let the current at the test point be sinusoidal with angular frequency w and amplitude УУIУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w). [УУIУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w) real and positive.] С СSuppose that for each w, an УУIУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w) is found such that the equipment functions normally for those УУIУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w) that satisfy аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚Ср JСУУIУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w) < УУIУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w)СЈ СС СС X%Сfor wУУб cмˆ4 PŽТ б1б cмˆ4 PŽТ бФФ < w < wУУб cмˆ4 PŽТ б2б cмˆ4 PŽТ бФФ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаand functions abnormally for УУIУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ(w) that fails to satisfy this inequality. Then УУIУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w) is the equipment susceptibility threshold for the frequency range [wУУб cмˆ4 PŽТ б1б cмˆ4 PŽТ бФФ, wУУб cмˆ4 PŽТ б2б cмˆ4 PŽТ бФФ], and for that specific test point and connection configuration. а H аС СAlso, suppose a worstЉcase emitter has been characterized (e.g. let УУVУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ be that worst case), then the design of a bonding and earthing network may now be expressed quantitatively as follows: for every emitterЉsusceptor pair of concern, the network's transfer function shall satisfy the following inequality: аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚Ср GСР$РУУTФФ(w)УУVУУб cмˆ4 PŽТ бemб cмˆ4 PŽТ бФФФФ(w)Р$Р < УУIУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w)С СС X%Сfor wУУб cмˆ4 PŽТ б1б cмˆ4 PŽТ бФФ < w < wУУб cмˆ4 PŽТ б2б cмˆ4 PŽТ бФФ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаwhere wб cмˆ4 PŽТ бУУ1ФФб cмˆ4 PŽТ б and wб cмˆ4 PŽТ бУУ2ФФб cмˆ4 PŽТ б specify the frequency range of concern. Typically, wб cмˆ4 PŽТ бУУ1ФФб cмˆ4 PŽТ б ~ 0 and wб cмˆ4 PŽТ бУУ2ФФб cмˆ4 PŽТ б ~ 1 MHz. С СNote that УУIУУб cмˆ4 PŽТ бsutб cмˆ4 PŽТ бФФФФ(w) is specific to a particular test point, and to the particular configuration of equipmentЉtoЉCBN interconnections. It may not apply if the equipment or its interconnections are modified.аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа Та ТA.1.2СP СУУSome important features of IBNsФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIsolated bonding networks use an openЉcircuit shielding strategy. However, because IBNs are invariably installed within an enclosing CBN, short and open circuit strategies operate in cascade as shown in Figure AЉ1c)/K.27. Here, node B2 could, for example, represent the frame of an equipment (УУZУУб cмˆ4 PŽТ бsuб cмˆ4 PŽТ бФФФФ) that is isolated except for a singleЉpointЉconnection to the CBN at node B0. Node B1 represents all of the immediately surrounding CBN metalwork. The capacitor C represents the capacitance between the equipment frame and the surrounding CBN. Figure AЉ1c)/K.27 shows clearly that for low frequencies, Р$РУУTФФ(w)Р$Р will be small (it has a zero at w = 0), but at a sufficiently high frequency there will be one or more resonances where Р$РУУTФФ(w)Р$Р will have maxima. In the neighbourhood of these resonant frequencies, shielding will be poor. However, if there are no significant emitters in these spectral regions, or if the equipment has additional shielding that is effective in these spectral regions, then no malfunctions will occur. ‚ Ср NСб cмˆ4 PŽТ бFigure AЉ1/K.27 = 20 cm б cмˆ4 PŽТ бб cмˆ4 PŽТ б Ср VСANNEX B Ср MСб cмˆ4 PŽТ б(to Recommendation K.27) Ср HСУ УExamples of bonding configurationsФ Ф аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаB.1Тh  ТУУMeshЉBNФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA meshЉBN is a densely interconnected BN in which equipment frames are an extension of the CBN. In this example, which is shown in Figure BЉ1/K.27, the d.c. power system is of type d.c.ЉCЉMBN. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.1.1С јСУУComponents of a meshЉBNФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn meshЉBNs, extensive interconnection among the following conductive elements is recommended: а Hр аТа ТРIРТ№ Тcabinets and cable racks of telecommunications and peripheral equipment;ЦЦ а H аТа ТРIРТ№ Тframes of all systems housed within the telecommunication building;ЦЦ а H аТа ТРIРТ№ Тthe protective conductor PE of the TNЉS type a.c. power installation;ЦЦ а Hx аТа ТРIРТ№ Тall metal parts, which according to IEC Publications [2] must be connected to the protective conductor (PE);ЦЦ а H аТа ТРIРТ№ Тthe main earthing terminal, including earthing conductors and earth electrodes;ЦЦ Та ТРIРТ№ Тeach d.c. power return conductor along its entire length.ЦЦ а H аС СMultiple interconnections between CBN and each d.c. return along its entire length is usually a feature of the meshЉBN configuration. The d.c. return conductor of such a configuration may be entrusted with the functions of protective conductor (PE) for systems associated with a.c. loads or sockets, provided that continuity and reliability complies with the IEC Publications [2]. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.1.2С јСУУGeneral design objectivesФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СSafety requirements supersede all other requirements. To ensure continuity of bonding conductors, reliable connection methods shall be used, e.g. crimping, welding, etc. However, if several options exist for fulfilling safety requirements, only that one shall be used which best coordinates with EMC requirements. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТHТС€HСB.1.2.1СјСУУNonЉtelecommunication installationsФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СWithin the whole telecommunication building, there shall be no exception from the TNЉSЉtype a.c. power installation [2]. This requires, except at the main earthing terminal for a TNЉC to TNЉS transition at the entrance of the building, that the neutral conductor (N) and protective conductor (PE) are nowhere interconnected in the building, neither in permanently connected equipment, nor in equipment connected by plug and socket. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТHТС€HСB.1.2.2СјСУУTelecommunication equipment and systemsФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СTelecommunication equipment with electronic circuitry is generally provided with a Р"Рpotential referenceР"Р metallization that extends widely over the surface of the printed circuit boards (PCBs). If PCBs are connectorized, a number of pins are used to interconnect to adjoining cabling, backplanes, or motherboards. At this interface there starts the interconnection to the meshЉBN via equipment frames, shelfЉracks, etc.‚б cмˆ4 PŽТ б Ср NСFigure BЉ1/K.27 = 23 cm б cмˆ4 PŽТ б С СThe equipment racks shall be interconnected by low impedance leads or copper bars. Since the meshЉBN technique usually incorporates the d.c. а H аreturn conductor into the CBN, the leads or bars can serve as the d.c. return. The leads or bars of each row have to be interconnected via the shortest route to minimize inductance. One or more d.c. return conductors may be used to interconnect the system to the centralized common power distribution cabinet or an intermediate power distribution panel. It is recommended that these leads be paired in close proximity with the corresponding negative d.c. power feed leads to reduce loop areas and enhance EMC. Small gauge d.c. power conductors should be twisted. а H аС СD.c./d.c. converters generally have one input conductor and one output conductor connected to the meshЉBN. There may be exceptions in specific equipment. а H аС СAn independent a.c. power supply network, derived from the d.c. supply by d.c./a.c. converters, is best implemented as a TNЉS type [2]. а H аС СUnrestricted fastening of the system to the floor and walls provides, in general, sufficient bypassing of stray capacitance for acceptable EMC performance of the system. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.1.3С јСУУCablingФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СRegarding EMC, cables can act as antennas, and support common modes than can transport extraneous energy into otherwise wellЉdesigned equipment. а H аThis antenna and commonЉmode propagation phenomenon can be mitigated by proper routing and shielding. С СRouting of indoor cabling shall be in close proximity to conductive elements of the CBN and follow the shortest possible path. The shielding afforded by interconnected cable racks, trays, raceways, etc. shall be intentionally used. This shielding is effective only if it is continuous. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.1.4С јСУУEMC performanceФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СEquipment in an appropriately designed meshЉBN configuration, together with the use of d.c. power distribution with a return that is common to the meshЉBN (i.e., d.c.ЉCЉMBN), is known to give acceptable EMC performance. а H аС СThe incorporation of d.c. power return conductors into the meshЉBN limits voltage drops caused by short circuit currents in the d.c. power distribution network. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаB.2Тh  ТУУMeshЉIBN with a bonding mat configurationФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СA high level of shielding may be obtained by connecting all equipment frames within a systemЉblock into a bondingЉmat configuration. This configuration is isolated from the surrounding CBN. The result is a very effective type of meshЉIBN; an example is shown in Figure BЉ2/K.27. С СThe technical goals of this installation method are: а H аТа ТТ№ ТС€ Сa)СpСprevention of CBN currents from flowing in the bondingЉmat or any other part of the systemЉblock;ЦЦ Та ТТ№ ТС€ Сb)СpСachievement of satisfactory EMC performance by controlled interconnection of systemЉblocks;ЦЦ а Hр аТа ТТ№ ТС€ Сc)СpСprovision of bonding and cabling facilities that allow for:ЦЦ Та ТТ№ ТРIРТhpТsystematic EMC planning;ЦЦ Та ТТ№ ТРIРТhpТuse of wellЉdefined and reproducible EMC test methods.ЦЦ а HH а‚Ср8FСб cмˆ4 PŽТ бFigure BЉ2/K.27 = 23 cm б cмˆ4 PŽТ б аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.2.1С јСУУEquipment configurationФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe systemЉblock comprises equipment agreed by the operating agencies and manufacturer(s) to be interconnected to the meshЉIBN (Figure 1d)/K.27). (Note that this agreement facilitates assignment of responsibility to either the supplier or the operating agency.) а H аС СPeripheral equipment denotes equipment location beyond the boundaries of the systemЉblock, but which relies functionally on a connection to the IBN. а H аС СEquipment serving air conditioning, lighting, etc., is considered to be external to the systemЉblock and may be installed or operated as part of the CBN of the building. С СHowever, provision for the following is recommended: Та ТРIРТ№ Тprotective earthing;ЦЦ Та ТРIРТ№ Тa.c. power distribution;ЦЦ а H аТа ТРIРТ№ Тd.c. power distribution up to the SPC, with the d.c. power return conductor(s) incorporated into the CBN (d.c.ЉCЉCBN).ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТHТС€HСB.2.1.1СјСУУSingle point connectionФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIt is recommended that the SPC be established in the vicinity of its system, serving as the only connection between IBN and CBN. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТHТС€HСB.2.1.2СјСУУCablingФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СAll conductors and cables connecting to the system block shall pass near to the SPC (i.e. through the SPCЉwindow). Metalwork near the system block shall be bonded to the SPC to avoid electric shock or flashЉover in the event of a lightning strike to the building. Installation of a distribution frame at the SPC is recommended since this facilitates connection of cable shields to the SPC. It is recommended that the shields of all cables passing the SPC be connected to the SPC. а H аС СAlien cables crossing the area of the IBN must be spaced sufficiently from cables connecting to the SPC and the system block. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТHТС€HСB.2.1.3СјСУУEquipment powered by external a.c. sourcesФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СEquipment with IEC class II certification (no PE connected) may be used without restriction within the system block area or at its periphery. С СEquipment with IEC class I certification (relying on PE protection methods) shall be powered via isolating transformers, if not connected to d.c./a.c. converters or a.c. power sockets belonging to the system block. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.2.2С јСУУEMC performanceФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СEquipment in an appropriately designed meshЉIBN configuration, together with the use of the d.c. power distribution with a return that is common to the meshЉIBN (i.e., d.c.ЉCЉIBN), is known to give acceptable EMC performance. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаB.3Тh  ТУУStar or sparseЉmesh IBN with isolation of d.c. power returnФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn this configuration, the framework of the switch is connected to form either a star or a meshЉIBN (see Figure 1/K.27). The cabinet framework and metallic panels are the major components of this IBN (there is no bonding mat). This type of IBN (whether star or mesh) will be denoted by Р"РframeЉIBNР"Р. The mesh topology is typically achieved by the crossЉaisle interconnections afforded by cable trays. The result is a Р"РsparseЉmeshР"Р IBN. The single point interconnection between a Р"РframeЉIBNР"Р and the CBN is made at the SPC busЉbar (SPCB) located within the SPC window (SPCW). The SPCW has a fixed dimension that allows the SPCB to be of sufficient size for connecting conductors, while limiting the voltage drop across the SPCB in the event of lightning surges or power system faults. а H аС СAn example of this configuration (in its star form) is shown in Figure BЉ3/K.27. The d.c. feed section leaving the power plant is isolated (i.e. of type d.c.ЉIЉCBN). This feed splits into a d.c.ЉIЉIBN feed serving the frameЉIBN equipment (the system block), and a d.c.ЉCЉCBN feed serving meshЉBN equipment. For the branch feeding the meshЉBN equipment, a connection between d.c. return and CBN is made at the SPCB. Beyond the SPCW, this branch is of type d.c.ЉCЉCBN (i.e. it has multiple connections to the CBN). The d.c. feed to the frameЉIBN equipment need not pass through the SPCW since, within the frameЉIBN, it is isolated. However, it is advantageous if most of the d.c. feed cable is in close proximity to bonding conductors, because this will reduce surge voltages that appear across the isolation barriers of the d.c./d.c. converters on which the d.c. feed terminates. С СTo summarize, the main features of the system are: Та ТРIРТ№ Тinsulation of the frameЉIBN from the surrounding CBN;ЦЦ Та ТРIРТ№ Тconnection of the frameЉIBN to the CBN only at the SPCB;ЦЦ а H аТа ТРIРТ№ Тisolation of the d.c. return within the frameЉIBN and between the power plant and the SPCW.ЦЦ а H аС СSystems of this type (both star and mesh configurations) have shown satisfactory EMC performance. а H аС СNote that this example demonstrates how this bonding and earthing network combines, in one building, systems using IBNs and meshЉBNs. The example also shows how all systems may share one d.c. power plant. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.3.1С јСУУThe d.c. power return configurationФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIn the d.c. power system, the frameЉIBN branch and the power plant branch are isolated, resulting in no conductive coupling from the CBN in these branches. However, surges (e.g. lightning and short circuit fault currents) arising in the d.c.ЉCЉCBN branch (that feeds meshЉBN equipment) can couple УУindirectlyФФ into the frameЉIBN equipment via the common source impedance presented by the power plant and the d.c.ЉIЉCBN section. This impedance is kept to a low value by running the Љ48 V conductors and d.c. return conductors in close proximity. а H аС СThe bonding conductor from the SPCB to the frame of the power plant is run in close proximity to all d.c. feed conductors in the d.c.ЉIЉCBN section. This reduces d.c. feed commonЉmode surge voltages at the power plant and enables fault clearing in the event of a fault between Љ48 V and frame in the power plant. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.3.2С јСУУSystem installationФФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СCable shields from outside the IBN that terminate within the IBN (i.e. on the system block) have their shields: а H аТа ТТ№ ТС€ Сa)СpСbonded to the frameЉIBN and to no other point (such cables shall not extend more than one floor from the SPC), orЦЦ а H аТа ТТ№ ТС€ Сb)СpСbonded to the frameЉIBN, bonded to the SPCB, and, outside of the system block, bonded to the CBN.ЦЦ а H аС СSubЉsystems that are part of the system block should be located within one floor of the SPC of the main system. This avoids excessive voltage differences between the extremities of the IBN and nearby CBN. а H аС СPeripheral equipment that is to use an IBN and that is located more than one floor from the SPC of the main system shall use a dedicated SPC that is within one floor. The equipment shall be powered through an isolation barrier, e.g., by using d.c./d.c. or a.c./d.c. converters. а H аС СThe isolation barrier inside any d.c. power equipment must have sufficient voltage withstand capability to meet local authority requirements. Installation and wiring of converters should comply with these isolation requirements.‚б cмˆ4 PŽТ б Ср MСFigure BЉ3/K.27 = 23 cm аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СFramework of equipment, and metal structural components, in a CBN that is located within 2 metres of an IBN should be bonded to the SPCB for reasons of personnel safety. а H аС СOther equipment that is in the telecommunications building, and that uses the meshЉBN configuration, is installed using the techniques of РSР B.1, with or without an isolated d.c. return. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHјP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТС€ HСB.3.3С јСУУMaintainability of isolated bonding networksФФЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIBNs need careful installation and ongoing surveillance to assure isolation. Also, the use of an isolated d.c. power return may require ongoing monitoring to check its isolation, especially if maintenance work is performed on different or mixed configurations by the same personnel. Violation of isolation during, or as a consequence of, maintenance work, may lead to failures in system operation or even to physical damage during lightning or power fault events. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТ‚У УReferencesФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа[1]Тh  ТCCITT Handbook УУEarthing of telecommunication installationФФ Geneva, 1976.ЦЦ ‚[2]Тh  ТIEC Publication 364 УУElectrical installations of buildingsФФ.ЦЦ IEC Publication 364Љ4Љ41 УУProtection against electric shock,ФФ 1982. IEC Publication 364Љ5Љ54 УУEarthing arrangements and protective conductors,ФФ 1980, Amendment 1, 1982. а H а[3]Тh  ТIEC Publication 50 УУInternational electrotechnical vocabularyФФ; Chapter 826, 1982 and Chapter 604, 1987.ЦЦ ‚[4]Тh  ТCCITT Recommendation УУResistibility of telecommunication switching equipment to overvoltages and overcurrentsФФ, Blue Book, Volume IX, Geneva 1989, Rec. K.20ЦЦ [5]Тh  ТIEC Publication 1024 УУProtection of structures against lightningФФ.ЦЦ IEC Publication 1024Љ1 УУGeneral principlesФФ 1990, Part 1. а H а[6]Тh  ТKEISER (B.): УУPrinciples of electromagnetic compatibilityФФ, 3rd edition, Artech, 1987.ЦЦ