============================================================ Question 1/V - Arrangement and purpose of protective components fitted at main distribution frames and other connection points (Continuation of Question 1/V, 1985-1988; revised wording) (See also Questions 5/V and 7/V) The following questions concern protective components of all types (over-voltage or over-current) fitted at MDFs, subscriber's premises or other points in the line network. a) What types of protective components are used? b) Against what conditions are they intened to protect? (e.g. lightning, mains induction, mains contacts). c) Under what circumstances is protection provided? d) Where and how are protective components accommodated? e) What are the technical and economic reasons which have led to the practices described and what results have been experienced? The particular problems of - relationships between MDF protection and printed circuit-board protection, and - problems of equipment and network protection caused by the liberalization of equipment in subscribers premises should be studied. Note 1 - This Question is to be studied in collaboration with CCIR Study Groups 1, 3, 9 and 10. ============================================================ Question 5/V - Protection policy aginst over-voltages (Continuation of Question 5/V, 1985-1988; revised wording) (See also Questions 1/V and 7/V) The object of this Question is to produce new Recommendations on the resistibility of equipment to over-voltage or over-currents. All types of telecommunication equipment, except that covered by Question 21/V, should be included. All types of abnormal conditions should be covered - lightning, mains induction, mains contacts, mains transients, rise of earth potential and electrostatic discharges. The questions are: a) What are the statistics of voltage, current, source impedance, waveform and duration of abnormal conditions encountered at exchange terminations, subscriber's terminations and other significant points in the line network? What methods of measurement are used and what parameters should be measured? b) What levels and durations of over-voltage or over-current should equipment be designed to resist? Economic considerations should be taken into account. Experiences of equipment failures due to surges would assist study of this Question? c) What testing procedures should be used to measure the resistibility of equipment to abnormal conditions? d) What problems arise of coordination of protective components, including those built into equipment? Is operation of protective components affected by the telecommunication equipment? How are these problems dealt with? Note 1 - The particular requirements of equipment resistibility at subscriber installations where, for any reason, the earths of telecommunications equipment cannot be simply bonded to the mains power earth should be studied. Note 2 - This Question covers the safety of telecommunications networks. CCITT should cooperate with IEC and other standardization bodies on matters of electrical safety in relation to telecommunications networks. It may be necessary to establish supporting Recommendations on this subject. ============================================================ Question 6/V - Coordinated protection schemes for telecommunication cables (Continuation of Question 6/V. 1985-1988; revised wording) (To be coordinated with Question 4/VI) In the cases where telecommunication cables need protection against the effects of the electromagnetic induction by a.c. power and traction lines, against lightning and against corrosion, it may be convenient to provide coordinated measures to give protection against all these factors. Studies under this Question should be directed to coordinated protection schemes for optical fibre cables, in particular coordinating the protection of cables and working staff against overvoltages due to electromagnetic induction by power and traction lines with that for lightning protection (see also Recommendation K.25 "Lightning protection of optical fibre cables"). Note - Studies on this Question should also include the revision of the reply annexed to the Question. ANNEX (to Question 6/V) Coordinated protection schemes for telecommunication cables 1.Introduction In the cases where telecommunication cables need protection against dangers and interference, from a.c. power and traction lines, against lightning and against corrosion, it is convenient to provide coordinated measures to give protection against all these factors. The environment, where the cable is laid, is the main factor to be considered to decide whether or not protection is necessary, in particular, the following criteria should be taken into consideration: a) for protection against lightning -keraunic level, -orographic conditions, -altitude, -soil resistivity; b) for protection against effects of electric lines -soil resistivity, -inducing current, -distance between the telecommunication cable and the electric line; c) for protection against corrosion -soil resistivity, -corrosive components (ions) in the soil, -stray currents in the soil (d.c. sources are d.c. traction rails, d.c. earthing electrodes, metallic structures with cathodic protection and the like). Protection of underground communication cables against corrosion is mainly achieved with protective plastic coverings on the metal cable sheath. As regards the environment, the installed cable behaviour is different if an insulating or conductive plastic material is used as protective covering. Therefore, coordinated protection schemes are also different and the two cases should be separately considered. 2.Combined protection with insulating plastic coverings1 Combined protection of telecommunication cables against induction, lightning and corrosion with insulating plastic coverings requires: -suitable metal sheath; -adequate covering with right value of dielectric strength; -ground connections of metal sheath; -use of shield wire. Periodic supervision of the insulating covering does not seem to be necessary because the administrations had a positive experience concerning corrosion. Such a control could be recommended only in the areas where stray current or interference current corrosion have been observed. The distance (d) between electrodes and their resistance (R) can be established using specific methods and considering thunderstorm activity, induction from electric lines and electric characteristics of telecommunication cables. Nevertheless, the following indications about the values of (d) and (R) can be taken into account: -local cables are usually earthed only at each end; -long-distance cables can be earthed only at the repeater stations with about 10-20 ohm of earth electrode resistance or more frequently (at each joint) but with no excellent value of (R). Multipoint sacrificial anodes may be considered as earth electrodes; in such cases, the earth resistance values have to be controlled during their lifetime. Shield wires are used for both local and long-distance cables when conditions warrant. Generally their use is considered: -for local cables when the soil resistivity is greater than 1,000 ohm m in rural areas only; -for long-distance cables when the soil resistivity exceeds 100 ohm m. The Handbook "The protection of telecommunication lines and equipment against lightning discharges" contains useful information for determining the need for shield wires. 3. Combined protection with conductive plastic coverings Combined protection of telecommunication cables against induction, lightning and corrosion with conductive plastic covering requires: -suitable covering characteristics, -use of shield wires when conditions warrant. Generally their use is considered, as well as for bare cables, when the soil resistivity is greater than 1000 ohm.m. The Handbook "The protection of telecommunication lines and equipment against lightning discharges" contains useful information for determining the need for shield wires. Ground connections of the metal sheath are not necessary. The covering thickness and compound type are the same as for insulating coverings. On the basis of experience of one Administration, the possible limit values of the main properties of the conductive plastic covering to be considered are shown in Tables 1 and 2. In particular the chemical characteristics in Table 1 are recommended to make negligible the effects of the galvanic corrosion between conductive plastic covering and metals used in buried telephone plants. TABLE 1 Limit values of conductive plastic covering characteristics + + Conductive covering Properties + Test method PE PVC + + - + + Carbon black contest (%) < 13 < 25 ASTM D 1603-76 modified* Polymer density (g/cm3) 0,920-0,935 1,3-1,4 IEC 811 p. 5.3 Melting temperature ( C) _ 115 - ASTM E 793-85 Cold bend test at -15 C no visible no visible ASTM D 2633-82 crack crack Melt flow index (g/10 min) 0,05-0,1 - IEC 811 App. B + + * Thermogravimetric analysis TABLE 2 Limit values of electrical, mechanical and physical characteristics of the conductive plastic covering + + Conductive covering Properties + Test method PE PVC + - + - + + - Volume resistivity (ohm.m) < 10 < 10 IEC 93 Transversal resistivity (ohm.m) < 20 < 20 - Tensile strength at break (MPa) > 9 > 9 IEC 811 Percent elongation at break (%) > 200 > 130 IEC 811 Environmental stress > 200 - COM VI n. 26 cracking resistance (h) 1968-72 Water absorption < 1 < 1 IEC 811 - 24h; 100 C - (%) + + The periodic supervision of the covering is not possible but this fact is not important because the low corrosion rate of the metal sheath make negligible the corrosion damages. The protection need against electromagnetic induction is unlikely and the personal safety is assured by the continuous earthing of the metal sheath. The conductive plastic covering can be also used above a metal moisture barrier of an optical fibre cable; up to now this coordinated protection scheme has not been experienced in optical cable plants. ============================================================ Question 7/V - Characteristics and testing of protective components and assemblies (Continuation of Question 7/V, 1985-1988; revised wording) (See also Questions 1/V and 5/V) The purpose of this Question is to establish standard tests for selected characteristics for protective components so as to make comparison and selection easier. The following should be considered: a) components for over-current and over-voltage protection b) complete assemblies including mountings c) protective components which are intended to be used as integral parts of equipment d) combinations of protective components. The question to be considered is: What are the characteristics of protective components and what tests should be made on them? Note 1 - This Question is to be studied in collaboration with CCIR Study Groups 1, 3, 9 and 10. ============================================================ Question 8/V - Interference testing and measurement (New Question) The CCITT intends to collect together testing and measurement methods for interference and protection techniques in a single document, by assembling, harmonizing and where necessary completing the documents listed below, for publication in a Handbook: - The Directives, - K-Series Recommendations, - Recommendation P.36, - Contributions COM V-67*, 68*, (Period 1985-1988). ============================================================ Question 11/V - Disturbance to telecommunications circuits from power- line carrier systems (Continuation of Question 11/V, 1985-1988) (Audio frequency and high-frequency systems should be included) The following points should be studied: 1. What is the mechanism by which interference to telecommunication circuits arises from power-line carrier systems? 2. What guidelines can be given to minimize the problem? ============================================================ Question 13/V - Unbalance of telephone installations (Continuation of Question 13/V, 1985-1988; revised wording) (See also Question 30/XII) From the point of view of noise and other disturbances in telecommunication systems due to interferences by electric power systems and HF-transmitters, is it necessary to specify values and measuring methods of unbalance about earth for: a) terminal and intermediate equipment? b) telecommunication lines? c) the line from subscriber to subscriber within a local network including the exchange? If so: - Which frequency range should be considered? Is it necessary to take into account in addition to the audio- frequency-transmission, digital transmission and carrier frequency systems on balanced lines. -Which unbalance values should be recommended above the audio frequency range? -Which methods are suitable for unbalance measurements with regard to the frequency range and to the transmission system? -Which method is suitable and sufficient for reducing unbalance, to achieve the necessary characteristics? -Which is the statistical distribution of unbalance parameters of equipment if manufactured in large quantities? -What is the distribution of unbalance parameters statistical or uniform along a telecommunication line which should be used for calculation of transverse voltages? ============================================================ Question 15/V - Magnitudes of harmonics in power and traction lines and methods to reduce their effects (Continuation of Question 15/V, 1985-1988) Study of the characteristics of harmonic currents circulating either in power lines or traction lines and the methods to reduce the effects of these currents on telecommunications circuits. Note 1 - The study should include, for both a.c. and d.c. cases: - possibility to reduce the level of harmonic currents circulating in power lines and traction lines; -the possibility to have some recommendation for the power and traction organizations or companies to limit the equivalent disturbing currents to reasonable values; -specific arrangements enabling a reduction to be made in the noise appearing in the telecommunication network; - calculation of the longitudinal and transverse voltages appearing in telecommunication circuits exposed to induction from these lines. -methods to measure harmonic currents and voltages; -propagation (including resonance effects) of harmonic currents and voltages in power and traction lines. Note 2 - Account should be taken of the information on Question 15/V contained in the following documents: - CCITT Contributions COM V-11, 28, 55, 56 and 78 (1977-1980) - CCITT Contributions COM V-3, 17 and 25 (1981-1984) Note 3 - The study of this Question involves close collaboration with UIC, CIGRE and other organizations and the Special Rapporteur will act as the representative of CCITT on these matters. ============================================================ Question 16/V - Levels of voltages and currents related to disturbances from power and traction installations (Continuation of Question 16/V, 1985-1988; revised wording) It is necessary to: -study the amplitude, waveshape, spectral content, duration, conditions and rate of occurrence of voltages and currents induced or impressed on telecommunications installations from power and traction installations, which may cause danger or impairment to the operation of the telecommunications installations; -determine if any new or more detailed guidelines for dealing with such voltages or currents should be established. Note 1 - The study should be carried out with the cooperation of CIGRE and UIC. Note 2 - (This note is not limitative.) As regards the dangers: the Question should preferably be confined to the dangers to persons, the danger of damage to equipment being considered in connection with other Questions: 5/V and 21/V. Contributions COM V-81, COM V-101, COM V-102 and COM V-R 9 (1985-1988) should be considered for the study. It would also be advisable to obtain the views of appropriate organs of the IEC and of medical authorities, whose collaboration the CCITT should seek to enlist, as far as possible at the international level. As regards noise induced in telecommunication circuits: reference should be made to the G and Q-Series Recommendations. The view of the Study Groups concerned with telecommunication quality (XII, XVII) will be sought on any proposals Study Group V may propose to adopt. ============================================================ Question 17/V - Electromagnetic compatibility (EMC) of telecommunications networks and equipment (New Question) CCITT should establish Recommendations on the overall subject of Electromagnetic Compatibility (EMC) to guide equipment designers and network operators on all aspects of this subject. Some separate parts will be studied under other specialized Questions in CCITT Study Group V (e.g. lightning surge disturbances, conducted and radiated radio- frequency interference). Other parts, (e.g. electrostatic discharges, mains-borne transients) will be studied only under this Question. CCITT should: 1) study emission control factors, e.g., longitudional conversion losses in telecommunications lines, screening factors, signal pulse mask characteristics. 2) examine the immunity requirements of telecommunication equipment to limit malfunction and transmission quality degradation due to external interference. The work under this Question should assist in harmonizing liaison on EMC work between CCITT, CCIR (Study Group 1), IEC and other international organizations to ensure the maximum participation of Telecommunication Administrations with the minimum overlap or duplication. ============================================================ Question 18/V - Radiated radio frequency interference and telecommunications equipment and systems (New Question) The purpose of this Question is to establish Recommendation(s) on the subject of radiated radio frequency interference for telecommunications equipment. Guidelines on improving the design of telecommunications equipment and systems along with advice on precautionary measures shall be developed. Both emission and immunity aspects are to be studied. The work shall address: i) what parameters should be considered when testing telecommunications equipment to ensure compatibility with other telecommunications systems and national EMC regulations; ii) what measuring procedures should be adopted; iii) the definition of acceptable immunity performance; iv) the failure criteria of equipment when subjected to interference; v) protection methods that may be adopted to improve the performance of telecommunications equipment and systems. Note 1 - In the study of this Question the work of other standards organizations such as IEC (CISPR and other bodies) along with national regulations, as well as of CCIR (Study Group 1) shall be considered to avoid the duplication of work. Note 2 - Particular attention shall be paid to the different requirements of customer terminal, roadside and central office equipment. ============================================================ Question 19/V - Conducted radio frequency interference on telecommunication equipment and systems (Continuation of Question 19/V, 1985-1988; revised title and wording) The purpose of this Question is to establish Recommendation(s) on the subject of conducted radio frequency interference on telecommunications equipment and systems. Guidelines on improving the design of telecommunication line and equipment along with advice on precautionary measures shall be developed. Both emission and immunity aspects are to be studied. All types of conducted radio frequency interference should be covered, including continuous wave and high frequency impulsive noise, except those covered by Questions 13, 15, and 16/V. The questions are: i) Measurement method - what parameters of conducted radio frequency interference voltage on telecommunication lines at a frequency above 30 MHz should be measured? -what procedure should be used to measure this type of interference? ii) Immunity test -what levels of conducted radio frequency interference in telecommunication lines should equipment or systems be immune to? -what testing procedure should be used? -what kinds of protection method can efficiently improve immunity of telecom equipment or systems? iii) Updating Recommendation K.18 -what calculating method should be added to Recommendation K.18 to evaluate induced noise voltage on subscriber circuits due to radio broadcast waves. iv) Conducted emmision -is there any disturbance to other telecommunication systems or radio receivers caused by emissions from telecommunication lines? If so, what guidelines on emission control factors should be established? Note 1 - This Question is to be studied in liaison with CISPR/SCG, IEC/TC77 and CCIR/Study Group 1, and CCITT Study Groups XI, XII, XV and XVIII to establish effective standard. Note 2 - Longitudinal conversion loss to telecommunication lines, which is one of the emission control factors, should be studied in connection with Question 13/V. ============================================================ Question 20/V - Survey on provisions intended to mitigate adverse effects (danger and disturbance) of electromagnetic origin (New Question) Considering - that adverse effects caused by electromagnetic fields are dealt with in detail in several CCITT documents (Recommendations and Manuals); - that some interdependence between effects generated by different sources of inducing electromagnetic fields exists; - that measures to mitigate adverse effects caused by one source may influence such effects originated from other sources; CCITT should establish guidelines on the following points in connection with the application of relevant Recommendations and Manuals concerning the mitigation of danger and disturbance: 1. classification of disturbances in telecommunication services and danger to telecommunications equipment and personnel; 2. specification of the sources of danger and disturbance and ways to control them; 3. tolerable levels of adverse effects; 4. reference to CCITT related documents. Note - In the study of this Question, the work of IEC (CISPR and other bodies) should be taken into account. ============================================================ Question 21/V - Test to be carried out on repeaters or regenerators to check the efficiency of protection from external interference with local or remote power feeding (Continuation of Question 21/V, 1985-1988; revised title and wording) The study of this Question may entail amendments to Recommendation K.17 based on problems listed below: -are there any reasons for modifications of existing specifications for tests on coaxial-pair and symmetric-pair repeaters or regenerators? -is it useful to extend specifications given in Recommendation K.17 for power feeding paths and power feeding equipments of optical fibre systems due to modifications in existing systems. Note - Broadband ISDN systems with optical fibres may need reconsidering of existing specifications. -is it useful to specify testing methods and limits for interference sources causing no damage but malfunction of power- fed repeaters or regenerators? If so, which of the transient sources should be considered: - transients due to switching operations in power network? - transients due to discharge of static electricity? -transients due to partial discharges caused by power feeding voltages or induced voltages of power lines? -transients due to operation of lightning arresters in adjacent telecommunication lines? -is it necessary to consider the interfering effect of transients only for digital systems? -is it advisable to study the interfering effect of steady-state of electromagnetic fields to power-fed repeaters or regenerators? ============================================================ Question 22/V - Protection of telecommunication lines and installations against lightning (Continuation of Question 22/V. 1985-1988; revised wording) Revision of the Handbook "Protection of telecommunication lines and installations against lightning". Studies should be directed to the revision of the Handbook on the basis of the submitted suggestions, if any, and to the editing of additional parts of the Handbook concerning: i) the prediction of trouble rates expected on optical fibre cables due to lightning; ii) characteristics of the overvoltages and overcurrents caused by lightning on telecommunication lines, in particular on subscriber loops; iii) portection of electronic equipment against the effects caused by lightning which strikes the building where the equipment is installed. Note 1 - Contribution D.38 (1985-1988) suggests amendments to the Handbook. Contribution COM V-3 (1977-1980) gives information about protection of waveguides against lightning. Contributions COM V-8 and 39 (1985-88) give imformation about protection of cables against lightning by means of the gas-filled arresters. Contribution COM V-10 (1985-1988) describes the application of the storm warning technique for the protection of telecommunication stations. Note 2 - Attention is drawn to the following points: -for study on part 1, Contribution D.38 (1985-1988) should be taken into account; -for study on part 2, Contribution COM V-36 (1985-1988) should be considered; -for study on part 3, reference should be made to the activity on this field of IEC TC 81 and to Contribution COM V-26 (1985-1988). ============================================================ Question 24/V - Earthing in telecommunication systems (Continuation of Question 24/V, 1985-1988; revised title and wording) The main purpose of this Question is to establish Recommendations on the earthing of electronic equipment inside telecommunication buildings and subscriber premises. The further items related on earthing have to be considered with lower priority: - effectiveness of earth electrodes treated with salts or colloids; - life of electrodes; - methods of calculation for long-rod electrodes; -joint use of earth electrodes (telecommunication and power installations); -development of practical methods of electrode installation; - experience obtained with concrete-covered electrodes; - earth electrodes for submarine cable telecommunication systems which use the ground as a conductor for remote feeding of line repeaters; -problems of compatibility originated by the presence of earthing connections within the near electromagnetic field created by radio station broadcasts. Note 1 - It is desirable to prepare Recommendations and keep updated the Handbook on "Earthing of telecommunication installations". Note 2 - As background, the following documents have to be taken into account: COM V-22, 23, 38, 47, 48, 49, 50, 73, 82, 83 (1985-1988) ============================================================ Question 26/V - Directives concerning the protection of telecommunication lines against harmful effects from electric power and electrified railway lines (Continuation of Question 26/V, 1985-1988; revised title and wording) The nine Volumes of the Directives (1988 edition) should be updated whenever necessary. For this reason Contributions submitted to Study Group V relevant to the contents and presentation of the Directives are to be reviewed. Considering that - the Directives (1988 edition) differ significantly from the former editions; -inducing and induced installations are described in detail; -new methods of estimating and calculating the results of capacitive, inductive and conductive coupling have been inserted; -more comprehensive information on protective measures and devices is given. Information dealing with observations based on practical experiences or new results of studies should be submitted by the users of the Directives. 1 Coordinated protection schemes for optical fibre cables are under study.