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.64 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2016) SERIES K: PROTECTION AGAINST INTERFERENCE Safe working practices for outside equipment installed in particular environments Recommendation ITU-T K.64 Rec. ITU-T
2、 K.64 (06/2016) i Recommendation 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
3、. The specific environments covered 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 t
4、elecommunication current or voltage (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 Ap
5、proval Study Group Unique ID* 1.0 ITU-T K.64 2004-02-29 5 11.1002/1000/7147 2.0 ITU-T K.64 2011-01-13 5 11.1002/1000/11035 3.0 ITU-T K.64 2016-06-29 5 11.1002/1000/12874 Keywords K.50, RFT, RFT-C, RFT-V, safe, TNV, work practices. * To access the Recommendation, type the URL http:/handle.itu.int/ in
6、 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.64 (06/2016) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunication
7、s, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (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
8、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 which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid
9、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 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunicati
10、on administration and a recognized operating agency. Compliance with this Recommendation is voluntary. 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 mandat
11、ory 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 words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU draws att
12、ention 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 concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or othe
13、rs 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 patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent
14、 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 publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T K.64 (06/2016) ii
15、i Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 4 Abbreviations and acronyms 2 5 Telecommunication particular workplaces . 3 6 Voltage levels on TLC installations . 3 7 Work practices on TLC plants in particular environments . 5 7.1 Switching off the power supply 5 7.2 Practice
16、s 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 Rationale of safe voltage limit values for workplace at major risk of elect
17、ric 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. 17 iv Rec. ITU-T K.64 (06/2016) Introduction Network operators, in their telecommunication infrastructure, use equipment that is remotely powered by symm
18、etrical 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 standard IEC 60728-11 for coaxial cables. The limits in these standards have bee
19、n 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 to work safely on circuits that are usually considered safe to touch. Thes
20、e 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 should perform work to reduce risk associated with these situations. Specif
21、ic 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 (06/2016) 1 Recommendation ITU-T K.64 Safe working practices for outside equipment installed in particular environments 1
22、 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 public switched telephone network (PSTN) circuits. The specific environments cover
23、ed 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 this Recommendation. At the time of pub
24、lication, 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 other references listed below. A list of
25、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 operating voltages and currents for teleco
26、mmunication 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 interactive services Part 11: Safet
27、y. 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 defines the following terms: 3.1 analogu
28、e 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 intended for transmission of video
29、, 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 dry conditions: An environmental
30、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 (06/2016) 3.4 environment classification: The environments considered by this Recommendation are classified as follows: Environment type 1: environment
31、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 and producing (in the case of hand
32、 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 area of the metallic parts (e.g., m
33、etallic 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 cable. 3.6 RFT-C circuit: A remote fee
34、ding 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 conditions are specified in ITU-T K.50
35、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 voltage limit values under normal oper
36、ating 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 measures to minimize the risks to tha
37、t 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 limit values. 3.10 user: Any perso
38、n 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 equipment installed in the external plant e
39、nvironment. 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 and acronyms This Recommendation uses the following abbreviations and acronyms: CATV Cable TV CCP Cross-Conne
40、ction Point MDF Main Distribution Frame PSTN Public Switched Telephone Network RFT-C Remote Feeding Telecommunication Current circuit Rec. ITU-T K.64 (06/2016) 3 RFT-V Remote Feeding Telecommunication Voltage circuit rms Root Mean Square SELV Safety Extra Low Voltage TLC Telecommunication TNV Teleco
41、mmunication 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 safety extra low voltage (SELV) cir
42、cuit limits may present 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 volta
43、ges usually present 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 prev
44、ent injury. Therefore, 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 man
45、hole or, in general, 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 b
46、ody will differ from 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 i
47、n full contact with an earthed conductor. Summarizing, there are three particular environments that may present safety hazards to the service personnel that operates a telecommunication (TLC) plant: 1) Environment type 1: wet conditions (see clause 3.4); 2) Environment type 2: confined working space
48、 in wet conditions (see clause 3.4); 3) 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 effect
49、ive working practices, as described in 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
