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Telephone-A Summary of IEC 60708

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A Summary of IEC 60708 LOW-FREQUENCY CABLES WITH POLYOLEFIN INSULATION AND MOISTURE BARRIER POLYOLEFIN SHEATH Scope This standard is intended to define polyolefin insulated cables for insertion into local outdoor networks. This standard is applicable to polyolefin insulated and moisture barrier polyolefin sheathed telephone cables, filled or unfilled with copper conductors, and used as: a) Cables suitable for installation in ducts. b) Cables suitable for direct burial in the ground. c) Cables with integral suspension strand for aerial installations. This standard is in accordance with ITU-T Recommendations. This standard includes general design details and requirements for dimensions and other constructional details as well as mechanical, electrical and environmental characteristics for ail types of low-frequency cables with polyolefin insulation (solid or cellular), filled or unfilled, and moisture barrier polyolefin sheath (with integral suspension strand). 1) Conductor - Conductor material The conductor shall consist of annealed copper, uniform in quality and free from defects. The properties of the copper shall be in accordance with IEC 60028. - Type of conductor The conductor shall consist of a single strand, circular in section. -Conductor finish The conductor shall be plain. -Conductor dimensions The conductor is designated by its nominal diameter. Nominal Diameters are 0.4,0.5,0.6,0.8 mm . The nominal diameter shall be at least 0.4 mm . -Continuity of conductor Joints in the conductor are permitted provided that the tensile strength of a joint is not less than 90 % of the tensile strength of the unjointed conductor.
2) Insulation -Insulation material The conductor shall be covered with solid or cellular polyolefin insulation or any combination thereof. - (Polyethylene or Polypropylene)
3)Cabling element A cabling element shall be – a pair of two insulated conductors twisted together and Designated wire a and wire b
4)Stranding The cable elements shall be formed into a number of sub-units or units which can be stranded into a regular make up to produce the required number of pairs. -25 pair count The pairs shall be identified by each insulated conductor having a single colour in accordance with the colour scheme given in Annex C. Sub-units shall be identified by coloured bindings of tape or threads. Each group of sub-units making up a 25 pair count shall be identified by a common colour of bindings.
5)Filling For filled cables, the interstices of the cable core shall be filled continuously with a compound suitable to prevent water penetration within the cable. 6)Core protection The core of the cable may have a protective layer (e.g. a helical or longitudinal lapping of one or more tapes).
7)Sheath -General: A moisture barrier aluminium laminated polyethylene sheath construction is specified for both underground and aerial cables. This type of sheath will also provide screening. For aerial cables a figure “8” construction is specified. Circular sheath cables can also be used as aerial cables. -Sheath material : Aluminium Tape bonded to Polyethylene sheath . -Aluminium tape: The aluminium tape shall be coated on at least one side with a polymer film. The aluminium tape without the polymer layer shall have a nominal thickness of at least 0.15 mm. -Polyethylene: The polyethylene shall have a minimum carbon black content of 2.0 %.
8)Cable protection According to ITT Recommendation L.3, armouring can be applied over the sheath to improve the strength of the cable against mechanical damage, rodents and insect attack and/or to improve the screening efficiency against electromagnetic interference and lightning discharges. The armouring may be made by metallic tape (or tapes) or wires with a protective layer .
A Summary of IEC 60708 (Electrical Requirements) LOW-FREQUENCY CABLES WITH POLYOLEFIN INSULATION AND MOISTURE BARRIER POLYOLEFIN SHEATH
1) Electrical resistance of conductor
2) Dielectric strength The dielectric strength of the insulation shall be checked on the finished cable. The insulation shall withstand the application of a d.c. test voltage. The test voltages for alternative durations are given in following table .
3) Insulation resistance The insulation resistance at a temperature of 20 °C shall be not less than: - for filled cables 1 500 MOhm x km - or unfilled cables 5000 MOhm x km 4) Mutual capacitance The mutual capacitance shall not exceed the values given in following Table.

5) Capacitance unbalance The capacitance unbalance shall not exceed the values given in following Table per 500 m length of cable:

*** Following Parameters aren’t applicable to A-2Y(St)2Y cables with static screen. 6) Attenuation Attenuation values depend on cable design and should be given by the manufacturer. Measurement method according to IEC 61156-1, 3.3.2. 7) Near End Crosstalk (NEXT) NEXT values are given in Table 6. Measurement method according to IEC 61156-1, 3.3.3. 8) Equal Level Far-end Crosstalk (ELFEXT) ELFEXT values are given in following Table. Measurement method according to IEC 61156-1, 3.3.5. 9) Power sum (PS) of crosstalk loss Power sum values of near-end and equal-level far-end crosstalk loss are given in following Table. Measurement method according to IEC 61156-1

10) Characteristic impedance The nominal value of characteristic impedance Z0 of the cable shall be in the range from 80 Ohms to 130 Ohms at 1 MHz, depending on the design. The maximum deviation from the nominal characteristic impedance shall be within ±15 %. Measurement method according to IEC 61156-1, 3.3.6. 11) Velocity of propagation The velocity of propagation shall be >60 % at 1 MHz. Measurement method according to IEC 61156-1, 3.3.1.