1、 International Telecommunication Union ITU-T K.64TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2011) SERIES K: PROTECTION AGAINST INTERFERENCE Safe working practices for outside equipment installed in particular environments Recommendation ITU-T K.64 Rec. ITU-T K.64 (01/2011) i Recommendation
2、ITU-T K.64 Safe working practices for outside equipment installed in particular environments Summary Recommendation ITU-T K.64 describes working practices for service personnel to help them work safely in telecommunication installations in three specific environments. The specific environments cover
3、ed in this Recommendation are characterized by wet conditions or close proximity to exposed metallic parts. The working practices apply to telecommunication plants with voltage levels higher than the limits defined for analogue PSTN circuits, such as remote feeding telecommunication current or volta
4、ge (RFT-C or RFT-V) circuits. This version of Recommendation ITU-T K.64 includes a warning regarding contact with terminals carrying RFT circuits with small parts of the body, e.g., back of the hand. The references have been updated. History Edition Recommendation Approval Study Group 1.0 ITU-T K.64
5、 2004-02-29 5 2.0 ITU-T K.64 2011-01-13 5 ii Rec. ITU-T K.64 (01/2011) FOREWORD 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 Se
6、ctor (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying 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 eve
7、ry four years, establishes the topics for study by the ITU-T study groups which, 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 purvie
8、w, the necessary standards are prepared on a collaborative basis with ISO and 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 volunt
9、ary. However, the Recommendation may contain certain mandatory provisions (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
10、 negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve
11、the use of a claimed Intellectual Property Right. 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 Recommen
12、dation, ITU had not received notice of intellectual property, protected by patents, 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 ht
13、tp:/www.itu.int/ITU-T/ipr/. The ITU-T thanks the International Electrotechnical Commission (IEC) for permission to reproduce information from IEC Technical Report 60479-1. All such extracts are copyright of IEC, Geneva, Switzerland. All rights reserved. Further information on the IEC is available fr
14、om http:/www.iec.ch/. IEC has no responsibility for the placement and context in which the extracts and contents are reproduced by ITU-T, nor is IEC in any way responsible for the other content or accuracy therein. ITU 2011 All rights reserved. No part of this publication may be reproduced, by any m
15、eans whatsoever, without the prior written permission of ITU. Rec. ITU-T K.64 (01/2011) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations 2 5 Telecommunication particular workplaces . 3 6 Voltage levels on TLC installations . 3 7 Work practices on TLC plants in par
16、ticular environments . 5 7.1 Switching off the power supply 5 7.2 Practices to be used when working on live telecommunication circuits 5 8 Work on telecommunication installations at risk of electric shock 7 8.1 Work on equipment or devices (terminal box, etc.) . 7 8.2 Work on cables . 8 Appendix I R
17、ationale of safe voltage limit values for workplace at major risk of electric shock . 9 I.1 Operating cases . 9 I.2 Calculation assumption 9 I.3 Limit current calculation 11 I.4 Voltage limit calculation 14 Bibliography. 18 iv Rec. ITU-T K.64 (01/2011) Introduction Network operators, in their teleco
18、mmunication infrastructure, use equipment that is remotely powered by symmetrical or coaxial pair cables. The voltages and currents that power these systems differ among them, and comply with the limit values defined in standards IEC 60950-1 and IEC 60950-21 for symmetrical pair cables and in standa
19、rd IEC 60728-11 for coaxial cables. The limits in these standards have been defined to allow service personnel to work safely on these lines without de-energizing the circuits. Nevertheless, there are telecommunication environments that necessitate additional precautions to enable service personnel
20、to work safely on circuits that are usually considered safe to touch. These environments are characterized as wet conditions, sometimes associated with standing water. This Recommendation lists three practical situations where additional precautions are needed and defines how the service personnel s
21、hould perform work to reduce risk associated with these situations. Specific applications, local conditions or regulations may give rise to a need for additional safeguards or modifications to practices presented in this Recommendation. Rec. ITU-T K.64 (01/2011) 1 Recommendation ITU-T K.64 Safe work
22、ing practices for outside equipment installed in particular environments 1 Scope The scope of this Recommendation is to provide working procedures for maintenance activities in specific environments for telecommunication plants with voltage levels higher than the limits defined for analogue PSTN cir
23、cuits. The specific environments covered in this Recommendation are characterized by wet conditions or close proximity to exposed metallic parts. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of t
24、his Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and oth
25、er references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T K.50 Recommendation ITU-T K.50 (2000), Safe limits of oper
26、ating voltages and currents for telecommunication systems powered over the network. IEC TS 60479-1 IEC/TS 60479-1 ed 4.0 (2005), Effects of current on human beings and livestock Part 1: General aspects. IEC 60728-11 IEC 60728-11 ed 3.0 (2010), Cable networks for television signals, sound signals and
27、 interactive services Part 11: Safety. IEC 60950-1 IEC 60950-1 ed 2.0 (2005), Information technology equipment Safety Part 1: General requirements. IEC 60950-21 IEC 60950-21 ed 1.0 (2002), Information technology equipment Safety Part 21: Remote power feeding. 3 Definitions This Recommendation define
28、s the following terms: 3.1 analogue PSTN circuit: A telecommunication network voltage (TNV) circuit (see clause 3.9) operating at voltages less than or equal to 90 V d.c. with cadenced ringing signals complying with IEC 60950-1. 3.2 CATV circuit: An interface circuit for a cable distribution system
29、intended for transmission of video, data and/or audio signals between separate buildings or between outdoor antennas and buildings. NOTE CATV circuits remotely powered, i.e., circuits on feeder between the optical node unit and the last line amplifier, are only considered in this Recommendation. 3.3
30、 dry conditions: An environmental condition in which the resistance of the skin and to the body is not reduced with respect to the value defined in IEC TS 60479-1. 2 Rec. ITU-T K.64 (01/2011) 3.4 environment classification: The environments considered by this Recommendation are classified as follows
31、: Environment type 1: environment with the floor in wet conditions, sometimes with standing water (for example, manholes, vaults, trenches); Environment type 2: environment with wet walls and confined working space (for example, vaults) such that the wet wall may be in contact with the persons body
32、and producing (in the case of hand contact with an energized part) a current path different to the hand-to-feet current path; Environment type 3: environment with confined working space and existing extraneous metallic parts (for example, facilities of other services); during the operations, large a
33、rea of the metallic parts (e.g., metallic tower for radio link) are in continuous contact with the body. 3.5 insulated tool: A tool, such as a screwdriver, scissor or pliers, having an insulated handle, that may be used by service personnel during his operations on telecommunication equipment or cab
34、le. 3.6 RFT-C circuit: A remote feeding telecommunication circuit that is so designed and protected that under normal operating conditions and single fault conditions, the currents in the circuit do not exceed defined values. NOTE The current limit values under normal operating and single fault cond
35、itions are specified in ITU-T K.50 or IEC 60950-21. 3.7 RFT-V circuit: A remote feeding telecommunication circuit that is so designed and protected that under normal operating conditions and single fault conditions, the voltages are limited and the accessible area of contact is limited. NOTE The vol
36、tage limit values under normal operating and single fault conditions are specified in ITU-T K.50 or IEC 60950-21. 3.8 service personnel: A person having appropriate technical training and experience necessary to be aware of hazards, to which that person may be exposed in performing a task, and of me
37、asures to minimize the risks to that person or other persons. 3.9 TNV circuit: A circuit in the equipment to which the accessible area of contact is limited and that is so designed and protected that, under normal operating conditions and single fault conditions, the voltages do not exceed specified
38、 limit values. 3.10 user: Any person other than service personnel. 3.11 vault: An underground chamber (manhole, pit, exchange or high rise building cable entry) or above ground pedestal or cabinet used to accommodate communication equipment such as joint closures, housings and/or electronic equipmen
39、t installed in the external plant environment. 3.12 wet condition: An environmental condition in which the resistance of the skin and to the body is reduced with respect to the value defined in IEC TS 60479-1. 4 Abbreviations This Recommendation uses the following abbreviations: CATV Cable TV CCP Cr
40、oss-Connection Point MDF Main Distribution Frame PSTN Public Switched Telephone Network RFT-C Remote Feeding Telecommunication Current circuit Rec. ITU-T K.64 (01/2011) 3 RFT-V Remote Feeding Telecommunication Voltage circuit rms Root Mean Square SELV Safety Extra Low Voltage TLC Telecommunication T
41、NV Telecommunication Network Voltage 5 Telecommunication particular workplaces Safety standards recognize that voltage levels defined as safe to touch in normal conditions may present a hazard to service personnel in damp conditions. For example, it is recognized that even SELV circuit limits may pr
42、esent a risk of electric shock for a person when such circuits are used in a wet environment. For this reason, the voltage limit for parts touchable by a person is equal to half the value of the limit applicable in dry environments. Obviously, it is not possible to reduce the voltages usually presen
43、t on a telecommunication line in order to have the same safe conditions within a wet environment when contacted by service personnel. In such cases, recognizing the presence of potentially harmful energy sources, the behaviour of service personnel becomes an effective means to prevent injury. Theref
44、ore, there is the need to follow safe working practices when equipment maintenance is necessary and a dry environment is not possible. This approach is possible because the service personnel are skilled and trained. An example of such work is the maintenance activities inside a manhole or, in genera
45、l, in a vault where the presence of water at the bottom is as likely as that of infiltration water on the internal walls. Sometimes, the confined space of the workplace hinders the maintenance of the equipment and increases the likelihood that the current path through the persons body will differ fr
46、om the hand-to-feet current path. Lastly, service personnel may accidentally make an adverse, large-area contact with energized conductors. This could happen, for instance, if one hand holds a tool fastened to the energized conductor while the other hand, or another body part, is in full contact wit
47、h an earthed conductor. Summarizing, there are three particular environments that may present safety hazards to the service personnel that operates a TLC plant: 1) Environment type 1: wet conditions (see clause 3.4); 2) Environment type 2: confined working space in wet conditions (see clause 3.4); 3
48、) Environment type 3: confined working space contacting extraneous metallic parts (see clause 3.4). To reduce the risk of electric shock associated with the maintenance activities performed in such an environment, service personnel shall follow simple and effective working practices, as described in
49、 clause 7. 6 Voltage levels on TLC installations IEC 60950-1 allows voltage levels, not higher than 70.7 V (peak) or 120 V d.c., on symmetrical pair cables of telecommunication networks. TNV circuits, accessible to skilled personnel only, are safe for an ordinary environment (dry conditions) but in wet conditions the contact with TNV circuits at voltages greater than analogue PSTN voltages (see 3.1) may be dangerous for service personnel due to a reduction of the contact impedance. 4 Rec. ITU-T K.64 (01/2011) The voltage
