1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU K.50 (02/2000) SERIES K: PROTECTION AGAINST INTERFERENCE Safe limits of operating voltages and currents for telecommunication systems powered over the network ITU -T Recommend at ion K. 50 (Formerly CCITT Rec
2、ommendation) ITU-T RECOMMENDATION K.50 SAFE LIMITS OF OPERATING VOLTAGES AND CURRENTS FOR TELECOMMUNICATION SYSTEMS POWERED OVER THE NETWORK Summary This Recommendation provides guidance on voltages and currents that may safely be used to power telecommunication systems that are part of the network.
3、 These systems use the paired-conductor cables of the network or specific power feeding cables to provide power to equipment at remote locations. This equipment and the current carrying conductors can be accessed in the energized state by service personnel without using insulated gloves or tools. Th
4、ese systems are not intended to be part of the subscribers installation, and are not accessible to users of the network. They are located in the networks between different telecommunication centres and between a telecommunication centre and public network interfaces. This Recommendation covers only
5、systems that use continuous dc powering. Source ITU-T Recommendation K.50 was prepared by ITU-T Study Group 5 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on 25 February 2000. Keywords Remote power feeding, safety. Recommendation K.50 (02/2000) 1 FOREWORD ITU (International
6、 Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations
7、 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 ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The ap
8、proval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation,
9、 the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a
10、claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, t
11、he ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. o ITU 200
12、0 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 fi-om the ITU. 11 Recommendation K.50 (02/2000) CONTENTS 1 2 3 4 5 5.1 5.2 5.3 6 6.1 6.2 Scope .
13、 References . Abbreviations Definitions Voltage and current limits . Method 1 : Voltage limited RFT circuits . General Method 2: Current limited RFT circuits . Work practices General work practices . Special work practices Annex A . RFT-V circuits . A . 1 Limits under normal operating conditions A.2
14、 Limits under single fault conditions . A.3 Coordination with surge protective devices A.4 Installation instructions . Annex B - RFT-C circuits . B . 1 Limits under normal operating conditions B.2 B.3 Limits with one conductor earthed . B.4 Installation instructions . Appendix I - Bibliography . Lim
15、its under single fault conditions . Recommendation K.50 (02/2000) Page 1 9 . 111 Introduction and background Telecommunication networks use repeaters, regenerators, or multiplexers that sometimes are powered over the paired-conductor cables of the network. The voltages and currents that power these
16、systems differ rom those of telecommunication services provided to users. To help ensure that service personnel can safely work on these lines without de-energizing the circuits or using insulated gloves, this Recommendation provides guidance on the voltage and current limits for these systems, as w
17、ell as on associated work practices. Voltages and currents that may be applied to a telecommunication network by equipment forming part of a subscribers installation are covered in IEC 60950, Safety of Information Technolou Equipment 2. iv Recommendation K.50 (02/2000) Recommendation K.50 SAFE LIMIT
18、S OF OPERATING VOLTAGES AND CURRENTS FOR TELECOMMUNICATION SYSTEMS POWERED OVER THE NETWORK (Geneva, 2000) 1 Scope This Recommendation provides guidance on voltages and currents that may safely be used to power telecommunication systems that are part of the network. These systems are not intended to
19、 be part of the subscribers installation, and are not accessible to users of the network. They are located in the networks between different telecommunication centres and between a telecommunication centre and public network interfaces. Figure la shows the field of application in the network between
20、 different telecommunication centres. Figure lb shows the part of the access network where K.50 is applicable. If there is no access network equipment between the local exchange and the customer premises equipment, this Recommendation does not apply. NOTE 1 - Example for the ISDN basic rate network
21、termination (NT 1): a) When the NT1 is owned by the operator, it is an equipment in the access network and it is within the scope of K.50. b) When the NT1 is owned by the customer, it is customer premises equipment and K.50 does not apply to it. These systems use the paired-conductor cables of the n
22、etwork or specific power feeding cables to provide power to equipment at remote locations. This equipment and the current carrying conductors can be accessed in the energized state by service personnel without using insulated gloves or tools. This Recommendation covers only systems that use continuo
23、us dc powering. If voltages and currents that exceed the limits of this Recommendation are used, then this Recommendation does not apply. Guidance on work practices, if these limits are exceeded, can be found in Volumes VI and VII of the Directives 3 and 4. NOTE 2 - Limits on permissible voltages th
24、at may occur because of exposure to power or traction lines are provided in Recommendation K.33 i and in the ITU-T Directives. NOTE 3 -Requirements for the safety of equipment that is part of the telecommunications network infiastructure are provided in ITU-T Recommendation K.51 SI and IEC 60950 2.
25、Exchange Trunk network Exchange TNV-1 TNV-3 RFT-c RFT-v T0508800-99 Field of application of K.50 in the trunk network Figure laK.50 - Field of application of IC50 in the trunk network Recommendation K.50 (02/2000) 1 Telecommunication equipment in the access network TNV-1 TNV-3 RFT-C RFT-V Public Cus
26、tomer interface equipment - network - premise Field of application of K.50 in the access network T0508810-99 Figure lbK.50 - Field of application of IC50 in the access network 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this te
27、xt, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edit
28、ion of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. ITU-T Recommendation K.33 (1996), Limits for people safety related to coupling into telecommunications systems from a. c. electric power and a.c. electriped railw
29、ay installations in fault conditions. IEC 60950 (1999), Safety of information technology equipment, Ed. 3. Danger and disturbance, Directives of the CCITT, Volume VI, 1990. Protective measures and safety precautions, Directives of the CCITT, Volume VII, 1990. IEC/TR2 60479-1 (1994), Efects of curren
30、t on human beings and livestock, Part 1: General aspects. ITU-T Recommendation K. 12 (2000), Characteristics of gas discharge tubes for the protection of telecommunications installations. ITU-T Recommendation K.28 ( 1993), Characteristics of semi-conductor arrester assemblies for the protection of t
31、elecommunications installations. ITU-T Recommendation K. 5 1 (2000), Safety criteria for telecommunication equipment. Abbreviations This Recommendation uses the following abbreviations: PNI RFT RFT-C RFT-V SELV SPD TNV 2 Public Network Interface Remote Feeding Telecommunication circuit Remote Feedin
32、g Telecommunication circuit - Current limited Remote Feeding Telecommunication Circuit - Voltage limited Safety Extra Low Voltage Surge Protective Device Telecommunication Network Voltage Recommendation K.50 (02/2000) 4 Definitions In this Recommendation, definitions introduced by the IEC 2 are used
33、 to maintain conformity. For convenience, they are reproduced here. Other definitions, currently under study in IEC, have been added. NOTE - The definition of circuits in IEC 60950 is limited to circuits internal to equipment. For this Recommendation, the definition of circuits is extended to includ
34、e conductors that carry the same voltages/currents. 4.1 Service personnel 2 : Persons having appropriate technical training and experience necessary to be aware of hazards to which they are exposed in performing a task and of measures to minimize the danger to themselves or other persons. NOTE - In
35、the context of this Recommendation, service personnel must be authorized by the network operator. 4.2 User 2 : Any person other than service personnel. 4.3 SELV circuit 2: A secondary circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not excee
36、d a safe value. 4.4 TNV circuit 2: A circuit to which the accessible area of contact is limited and that is so designed and protected that, under normal operating and single fault conditions, the voltages do not exceed specified limiting values. TNV circuits are classified as TNV-1, TNV-2 and TNV-3
37、circuits. 4.5 - TNV-1 circuit 2: A TNV circuit: whose normal operating voltages do not exceed the limits for an SELV circuit under normal operating conditions; on which overvoltages rom telecommunication networks are possible. TNV-2 circuit 2: A TNV circuit: whose normal operating voltages exceed th
38、e limits for an SELV circuit under normal operating conditions; which is not subject to overvoltages rom telecommunication networks. TNV-3 circuit 2: A TNV circuit: whose normal operating voltages exceed the limits for an SELV circuit under normal operating conditions; - on which overvoltages rom te
39、lecommunication networks are possible. 4.8 RFT circuit: A circuit, other than SELV or TNV circuit, intended for the supply of power to equipment via a paired-conductor network, and which is so designed and protected that under normal operating and single fault conditions the voltages or currents do
40、not exceed defined values. The circuit in the equipment that receives power rom an RFT circuit is also considered to be an RFT circuit. 4.9 RFT-C circuit: A current limited RFT circuit. The detailed characteristics of an RFT-C circuit are described in Annex B. 4.10 RFT-V circuit: A voltage limited R
41、FT circuit. The detailed characteristics of an RFT-V circuit are described in Annex A. 4.11 Public network interface ISO/IEC 118011: A point of demarcation between public and private network. In many cases the public network interface is the point of connection between the network providers faciliti
42、es and the customer premises cabling. - 4.6 - - 4.7 - Recommendation K.50 (02/2000) 3 5 Voltage and current limits 5.1 General This Recommendation defines two methods for safe powering of telecommunication systems over the network. They are both based on IEC/TR2 60479-1 5. The first method limits th
43、e voltage so that the insulation or the resistance of the body limits the current conducted by service personnel to tolerable levels. The second method limits the current of the remote power feeding circuit so that higher voltages can be allowed. Both methods are being used for many years by various
44、 operators. Examples of existing national standards are given in the Bibliography (Appendix I). 5.2 Method 1: Voltage limited RFT circuits This method is defined as the RFT-V circuit in Annex A. 5.3 This method is defined as the RFT-C circuit in Annex B. Method 2: Current limited RFT circuits 6 Work
45、 practices 6.1 General work practices The RFT circuits have been defined so that the equipment and the current carrying conductors can be accessed in the energized state by service personnel without de-energizing the circuits or using insulated gloves or tools. Therefore normal work practices are ap
46、plicable for working on RFT circuits. When RFT circuits are used, it is recommended to inform the service personnel that RFT voltages and currents can be present on circuits in the network. Guidance on work practices, if the limits of RFT circuits are exceeded, can be found in Volumes VI and VII of
47、the Directives 3 and 4. 6.2 Special work practices If service personnel, working e.g. at the MDF, can contact simultaneously several terminals that are connected to RFT-C circuits, these terminals shall be suitably labelled or appropriately marked to alert service personnel. ANNEX A RFT-V circuits A
48、.l Under normal operating conditions, a RFT-V circuit shall comply with all of the following requirements: a) the steady state open circuit voltage from each conductor to earth that is supplied to a telecommunication network shall not exceed: 140 V d.c.; or Limits under normal operating conditions 2
49、00 V d.c. if the short circuit current is limited to 10 mA d.c.; 4 Recommendation K.50 (02/2000) b) c) the maximum power that can be delivered to any load connected to the telecommunication network shall be limited to 100 VA after 1 s (steady state condition in operation); the steady state current that can flow into the telecommunication network shall comply with clause 6.3 of IEC 60950 2. (“Equipment intended to provide power over the telecommunication wiring system to remote equipment shall limit the output current to a value that does not cau
