1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T K.50 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2016) SERIES K: PROTECTION AGAINST INTERFERENCE Safe limits for operating voltages and currents in telecommunication systems powered over the network Recommendation I
2、TU-T K.50 Rec. ITU-T K.50 (07/2016) i Recommendation ITU-T K.50 Safe limits for operating voltages and currents in telecommunication systems powered over the network Summary Recommendation ITU-T K.50 provides guidance on voltages and currents that may safely be used to power telecommunication system
3、s that are part of the network of telecommunications service providers. 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
4、 state by service or skilled personnel without using insulated gloves or tools. For safety reasons, system types operating at hazardous voltages are not intended to pass beyond the public network interface (PNI) between the service provider and the end customer. These hazardous voltage systems are n
5、ot 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, between a telecommunication centre and a telecommunications access facility/node, and between a telecommunication cent
6、re and PNIs. Recommendation ITU-T K.50 only covers systems that use continuous dcpowering. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T K.50 2000-02-25 5 11.1002/1000/4913 2.0 ITU-T K.50 2016-07-14 5 11.1002/1000/12871 Keywords IEC 60950-1, IEC 62368-1, RFT-C, RFT, RFT-V,
7、 remote power feeding, safety, telecommunication systems. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T K.50 (07/2016) FORE
8、WORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying
9、 technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups w
10、hich, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO a
11、nd IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (
12、to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such wor
13、ds does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position conc
14、erning 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, ITU had not received notice of intellectual property, protected by p
15、atents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2016 All rights reserved. No part of this pu
16、blication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T K.50 (07/2016) iii Table of Contents Page 1 Scope . 1 2 References . 2 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 5 4 Abbreviations and acronyms
17、 6 5 Conventions 7 6 Voltage and current limits 7 6.1 General . 7 6.2 Method 1: Voltage-limited RFT (RFT-V) circuits . 8 6.3 Method 2: Current-limited RFT (RFT-C) circuits 11 7 Work practices 15 7.1 General work practices . 15 7.2 Special work practices 16 Bibliography. 17 iv Rec. ITU-T K.50 (07/201
18、6) Introduction Telecommunication networks sometimes use equipment that generates voltages and currents that exceed TNV-1, TNV-2, TNV-3 (defined in IEC 60950-1) and ES1, ES2 (defined in IEC 62368-1) to provide power to remote equipment over paired-conductor network telecommunications cables. Example
19、s of this type of equipment are x-type digital subscriber line (xDSL) powering units, xDSL remote terminating units, line power up-converters, repeaters, regenerators, or remote cabinet or enclosure equipment. The voltages and currents that power these systems differ from those of telecommunication
20、services provided to end users or subscribers. To help ensure that service or skilled personnel can safely work on these lines without de-energizing the circuits or using insulated gloves, this Recommendation provides guidance not only on the voltage and current limits for these systems, but also th
21、e associated work practices required. Voltages and currents that may be applied to a telecommunication network by equipment forming part of a subscribers installation are covered in IEC 60950-1 and IEC 62368-1. Rec. ITU-T K.50 (07/2016) 1 Recommendation ITU-T K.50 Safe limits for operating voltages
22、and currents in telecommunication systems powered over the network 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 of telecommunications service providers. These systems use the paired-cond
23、uctor cables of the network to provide power to communications-related equipment at remote locations. This equipment and the current-carrying conductors can be accessed in the energized state by service or skilled personnel without using insulated gloves or tools. These systems are not intended to e
24、xtend a voltage-limited remote feeding telecommunication (RFT-V) or a current-limited RFT (RFT-C) circuit beyond the point of demarcation between the service provider and the end user or ordinary people. In addition, exposed RFT-V and RFT-C circuits are not allowed to be accessible to ordinary peopl
25、e or end users. The systems that use RFT-C and RFT-V are located in the network between different telecommunication centres, between a telecommunication centre and a telecommunications access facility or node, and between a telecommunication centre and public network interfaces (PNIs). This Recommen
26、dation covers only systems that use continuous direct current (d.c.) powering. RFT circuits sometimes carry signalling or data on the conductors, as well as delivering power. However, in many cases the conductors are used to simply provide d.c. power and no signalling or data is present. This is bec
27、oming more commonplace, as fibre is used more and more to transmit broadband data and twisted pair copper cable pairs are used to power remote telecommunications equipment. Figure 1-a shows the field of application in the network between different telecommunication centres. Figure 1-b shows the part
28、 of the access network where this Recommendation is applicable. If there is no access network equipment between the local exchange and the customer premises equipment to convert the RFT-V or RFT-C to telecommunication network voltage-1 (TNV-1), TNV-2, TNV-3, energy source class 1 (ES1) or energy sou
29、rce class 2 (ES2), this Recommendation does not apply. Guidance on work practices, if these limits are exceeded, can be found in b-ITU-T Directives Vol. VI and b-ITU-T Directives Vol. VII. NOTE 1 Limits on permissible voltages that may occur because of exposure to power or electrified railway lines
30、are provided in b-ITU-T Directives. NOTE 2 Requirements for the safety of equipment that is part of the telecommunications network infrastructure are provided in b-ITU-T K.51, IEC 60950-1 and IEC 62368-1. 2 Rec. ITU-T K.50 (07/2016) a) b) NOTE 1 ES1, PS1 connected to information and communications t
31、echnology (ICT) cabling with overvoltage protection (OVP) would be equivalent to TNV-1. NOTE 2 ES2, PS1 connected to ICT cabling with OVP would be equivalent to TNV-3. NOTE 3 ES1, PS1 connected to ICT cabling with OVP would be equivalent to TNV-1. Figure 1 Field of application of this Recommendation
32、: a) in the trunk network; b) in the access network 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recomme
33、ndations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly p
34、ublished. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. IEC 60950-1 IEC 60950-1 (2013), Information technology equipment Safety Part 1: General requirements. IEC 62368-1 IEC 62368-1 (2014), Audio/video, information
35、 and communication technology equipment Part 1: Safety requirements. 3 Definitions 3.1 Terms defined elsewhere NOTE The definition of circuits in IEC 60950-1 is limited to circuits internal to equipment. In IEC 62368-1 the definition of circuits is limited to circuits external to equipment, which ar
36、e normally considered to be a telecommunication network. For this Recommendation, the definition of circuits is extended to include network cable conductors that carry the same voltages/currents. Rec. ITU-T K.50 (07/2016) 3 This Recommendation uses the following terms defined elsewhere: 3.1.1 basic
37、insulation IEC 60950-1: Insulation to provide basic protection against electric shock. NOTE IEC 62368-1 refers to “basic safeguard“ rather than “basic protection“ and notes “This concept does not apply to insulation used exclusively for functional purposes“. 3.1.2 double insulation IEC 60950-1: Insu
38、lation comprising both basic insulation and supplementary insulation. 3.1.3 ELV circuit IEC 60950-1: Secondary circuit with voltages between any two conductors of the circuit, and between any one such conductor and earth, not exceeding 42.4 V peak, or 60 V d.c., under normal operating conditions, wh
39、ich is separated from hazardous voltage by basic insulation, and which neither meets all of the requirements for an SELV circuit nor meets all of the requirements for a limited current circuit. 3.1.4 external circuit IEC 62368-1: Electrical circuit that is external to the equipment and is not mains.
40、 NOTE An external circuit is classified as ES1, ES2 or ES3, and PS1, PS2 or PS3. 3.1.5 functional insulation IEC 62368-1: Insulation between conductive parts which is necessary only for the proper functioning of the equipment. NOTE IEC 60950-1 adds the informative note “functional insulation by defi
41、nition does not protect against electric shock. It may, however, reduce the likelihood of ignition and fire“. 3.1.6 hazardous voltage IEC 60950-1: Voltage exceeding 42.4 V peak, or 60 V d.c., existing in a circuit that does not meet the requirements for either a limited current circuit or a TNV circ
42、uit. NOTE The corresponding IEC 62368-1 requirement would be voltages exceeding ES1. 3.1.7 instructed person IEC 62368-1: Person instructed or supervised by a skilled person as to energy sources and who can responsibly use equipment safeguards and precautionary safeguards with respect to those energ
43、y sources. NOTE 1 Supervised, as used in the definition, means having the direction and oversight of the performance of others. NOTE 2 In the context of this Recommendation, the term instructed person is synonymous with user IEC 60950-1. 3.1.8 limited current circuit IEC 60950-1: Circuit that is so
44、designed and protected that, under both normal operating conditions and single fault conditions, the current that can be drawn is not hazardous. NOTE 1 Simulated faults and abnormal conditions are defined in clause 1.4.14 of IEC 60950-1. NOTE 2 The limit value of d.c. is defined as 2 mA d.c. through
45、 a 2 k resistor connected between any two parts of a limited current circuit or between any such part and earth in clause 2.4 of IEC 60950-1. 3.1.9 ordinary person b-IEC 60050-826: Person who is neither a skilled person nor an instructed person. NOTE In the context of this Recommendation, the term o
46、rdinary person is synonymous with user IEC 60950-1. 3.1.10 overvoltage b-IEC/TR 60664-2-1: Any voltage having a peak value exceeding the corresponding peak value of maximum steady-state voltage at normal operating conditions. 3.1.11 primary circuit IEC 60950-1: Circuit that is directly connected to
47、the a.c. mains supply. 3.1.12 prospective touch voltage IEC 62368-1: Voltage between simultaneously accessible conductive parts when those conductive parts are not being touched. 3.1.13 reinforced insulation IEC 62368-1: Single insulation system that provides a degree of protection against electric
48、shock equivalent to double insulation. 4 Rec. ITU-T K.50 (07/2016) NOTE IEC 60950-1 adds the informative note The term “insulation system“ does not imply that the insulation has to be in one homogeneous piece. It may comprise several layers that cannot be tested as basic insulation and supplementary
49、 insulation. 3.1.14 secondary circuit IEC 60950-1: Circuit that has no direct connection to a primary circuit and derives its power from a transformer, converter or equivalent isolation device, or from a battery. NOTE 1 In the context of this Recommendation, the definition of circuits is extended to include network cable conductors that carry the same voltages/currents. NOTE 2 IEC 62368-1 does not define the term secondary circuit, but refers to it as
