Individual insulated conductors are twisted together with a uniform lay to form a pair. The length of the lay of each pair is different from that of the adjacent pair to enable the cable to meet the capacitance unbalance and cross talk requirements of the specifications. The Pairs are colour coded for easy identification.
The twisted Pairs are stranded in a single unit of 10,20&25 Pairs, Wrapped helically with an identification colour binder. For higher number of Pairs cable, a number of units are stranded together to form a super unit. A coloured identification binder is wrapped around the super units for easy identification.
These units or super units are then laid up to form the core of cable. During this operation a water resistant filling compound is introduced to fully fill the interstices of the laid up core. This filling compound acts as a dielectric between the pairs as well as a moisture barrier. The filling compound is compatible with the polyethylene insulation whereby the cable's electrical and physical characteristics are not affected. Solid polyethylene insulated cables without moisture resistant filling compound as an air core cable can also manufactured.
The jelly laid up cable is then covered with layer of hygroscopic polyester tape to contain the jelly. This also sets as a mechanical protection to the cable core, and act as a dielectric.
Aluminium poly-laminate screen:
An aluminium tape coated on both sides with polyethylene is applied longitudinally over the core wrap. This helps in preventing electrical interface by other power cables laid in parallel. It also as a moisture barrier.
A tight fitting sheath of black virgin polyethylene is then extruded over the aluminium polyethylene screen which offers protection to the cable.
Bedding and armouring:
A double polyethylene tape is applied helically over the sheath with a suitable overlap. This acts as a bedding for the steel tape. The cable is then helically armoured with double galvanized steel tapes with a suitable overlap. This offers mechanical protection to the cable.
A tight fitting jacket of specially formulated black virgin polyethylene is extruded over the armoured cable this acts as mechanical protection and also protection against ultra-violet rays.
Cables are tested or electrical and transmission parameters, as per routine test or customer specifications (special, if any) before offered to the customer.
Foam Skin Cable:
Foam skin cable is a technologically upgraded version of Jelly Filled Telephone Cables. These are of two types Air Fire & Filled Type. The conductor is insulated with Foam polyethylene coated by dual extrusion, providing a protective layer of solid colour skin insulation. As a result, there is considerable saving in raw material and the cable size is reduced. Since the wire diameter of the cable is reduced, the overall diameter is proportionately smaller, thereby more number of Pairs / Cables can be accommodated in smaller ducts without changing its electrical and transmission parameters.
In this type, four wires are twisted to form two pairs and two circuits. The diameter of single wire is reduced in this configuration, but the electrical parameters remain unchanged. This cable is basically used for Trunk / Carrier communication.
This Cable is a high frequency cable, which is divided in two compartments, one is to carry signal and the second is to bring back the signal. It withstands more circuits on the same pair. Constructionally it consist of 4 mil polyethylene coated flat aluminium screen which divides the cable core in two compartments. The integral screen / shield is formed in such a manner that it shields the compartment and isolates each other. In addition to this one more aluminium shield is applied over the cable core for preventing electrical interference from outside sources. The cable satisfies the original requirement of two cables under one sheath for Pulse Code Modular carrier application.