Telephone Cables
Outdoor Telephone Cables Indoor Telephone Cables Indoor/Outdoor Telephone Cables Special Telephone Cables

Ordering Information

 Foam Skin Insulated & AP Sheathed (ALPETH) Jelly Filled Cables to GR-421


The cables are designed for use in access or trunk networks, from telephone exchange to subscriber area. The cables are suitable for installation in ducts, direct burial in the ground and also for aerial installation with integral suspension strand.Jelly filled option is for subscriber’s cables installed underground or along the edge of pavement. An armoured option is offered for direct burial installations where additional mechanical or rodent protection is required. A figure-8 self support option is offered for aerial installation.


Telcordia (Bellcore) GR-421


Telephone Cables

Telephone Cables


Solid annealed bare copper, 0.4/0.5/0.63/0.9mm as per ASTM B-3/class 1 of IEC 60028


Foam Skin which is a composite polyethylene insulation made of an inner cellular layer and an outer solid skin as per ASTM D 1248/IEC 60708

Twisted Pairs

Insulated conductors are twisted into pairs with varying lay length to minimize crosstalk

Cabling Element

Twisted Pairs

Cable Core Assembly

Cables with up to 400 pairs are composed of 25-pair units or 12/13-pair units; cables with over 400 pairs are composed of 50 or 100-pair units. Any extra pairs form a separate unit. Units are identified by colour coded binders. Standard construction is per GR-421 given in Cable Make Up Diagram

Core Wrapping(optional)

One or more non-hygroscopic polyester tapes are helically or longitudinally laid with an overlap. These tapes furnish thermal, mechanical as well as high dielectric protection between shielding and individual conductors

Moisture Barrier

A layer of bare aluminium tape (0.2mm/8mil) is applied longitudinally with overlap over the cable core to provide 100% electrical shielding coverage and ensures a barrier against water vapor. In cables with more than 200 pairs, the aluminum tape may be corrugated for improved cable flexibility


The cable core interstices are filled with petroleum jelly to avoid longitudinal water penetration within the cable.
The water resistant filling compound is applied to the air space between non-hygroscopic tape and shield, shield and sheath within the cable core


Black low density polyethylene as per ASTM D 1248/IEC 60708, being able to withstand exposure to sunlight,
temperature variations, ground chemicals and other environmental contaminants


Ripcord may be provided for slitting the sheath longitudinally to facilitate its removal

Spare Pairs (optional)

Spare pairs may be incorporated for large pair cables

Continuity Wire (optional)

One tinned copper drain wire may be longitudinally laid to ensure electrical continuity of the screen

Telephone Cables

Telephone Cables

Optional Construction

Armoured Cable

Steel wire armour or corrugated steel tape armour applied over an optional inner polyethylene sheath.For steel tape version, the 0.15mm/6mil thick steel tape is coated with a copolymer and applied with an overlap. An outer polyethylene sheath is applied over the armour

Self-Support Cables

A 7-strand galvanized steel strand is used as support wire. Black polyethylene sheath covers both core and support wire in a figure-8 construction

Electrical Properties

Nominal Conductor Diameter mm 0.4 0.5 0.63 0.9
Conductor Gauge Size AWG 26 24 22 19
Maximum Average DC Resistance Ω/km / Ω/mile 140/225 87/140 55/88.6 27.0/43.4
Maximum Individual DC Resistance Ω/km / Ω/mile 144.2/232 89.5/144 56.5/91.0 28.0/45.0
Minimum Insulation Resistance @500V DC MΩ.km / MΩ.mile 1600/1000 1600/1000 1600/1000 1600/1000
Maximum Average Resistance Unbalance % 1.5 1.5 1.5 1.5
Maximum Individual Resistance Unbalance % 5 5 5 5
Average Mutual Capacitance nF/km / nF/kft 48.5-54.0
Maximum Individual Mutual Capacitance nF/km / nF/kft 57/17.4 57/17.4 57/17.4 57/17.4
Maximum Individual Capacitance Unbalance pair-to-pair pF/km / pF/kft 145/44 145/44 145/44 145/44
Capacitance Unbalance RMS pair-to-pair pF/km / pF/kft 45/13.7 45/13.7 45/13.7 45/13.7
Maximum Individual Capacitance Unbalance pair-to-ground pF/km / pF/kft 2625/800 2625/800 2625/800 2625/800
Maximum Average Capacitance Unbalance pair-to-ground pF/km / pF/kft 574/175 574/175 574/175 574/175
Maximum Conductor Loop Resistance @20°C Ω/km / Ω/mile 300/482 192/309 114/183.6 60/96.4
Impedance @1KHz 994 796 660 445
Impedance @100KHz 147 134 125 122
Impedance @512KHz 120 118 117 116
Impedance @1MHz 117 115 114 113
Maximum Average Attenuation @0.8KHz dB/km / dB/kft 1.64/0.5 1.30/0.39 1.04/0.32 0.74/0.22
Maximum Average Attenuation @1KHz dB/km / dB/kft 1.68/0.51 1.35/0.41 1.08/0.33 0.76/0.23
Maximum Average Attenuation @3KHz dB/km / dB/kft 3.18/0.97 2.52/0.77 2.01/0.61 1.42/0.43
Maximum Average Attenuation @150KHz dB/km / dB/kft 11.4/3.47 8.3/2.53 6.2/1.89 4.4/1.34
Maximum Average Attenuation @772KHz dB/km / dB/kft 24.3/7.4 19.4/5.9 15.4/4.7 10.8/3.3
Maximum Average Attenuation @1000KHz dB/km / dB/kft 27.1/8.25 21.4/6.52 17.5/5.33 12.8/3.89
Dielectric Strength
Conductor to Conductor (3secs) V DC 2400 3000 4000 5000
Conductor to Screen (3secs) V DC 10000 10000 10000 10000

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