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Option 3 : Armouring
Construction of Cables:
The various parts are :
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(i) Cores or Conductors: A cable may have one or more than one core (conductor) depending upon the type of service for which it is intended.
(ii) Insulation:
- Each core or conductor is provided with a suitable thickness of insulation, the thickness of the layer depending upon the voltage to be withstood by the cable.
- The commonly used materials for insulation are impregnated paper, varnished cambric, or rubber mineral compound.
(iii) Metallic sheath: In order to protect the cable from moisture, gases, or other damaging liquids (acids or alkalies) in the soil and atmosphere, a metallic sheath of lead or aluminum is provided over the insulation.
(iv) Bedding: Over the metallic sheath is applied a layer of bedding which consists of fibrous material like jute or hessian tape. The purpose of bedding is to protect the metallic sheath against corrosion and from mechanical injury due to armoring.
(v) Armouring:
- Over the bedding, armoring is provided which consists of one or two layers of galvanized steel wire or steel tape.
- Its purpose is to protect the cable from mechanical injury while laying it and during the course of handling.
- Armoring may not be done in the case of some cables such as low voltage to avoid excessive sheath losses.
(vi) Serving. In order to protect armoring from atmospheric conditions, a layer of fibrous material (like jute) similar to bedding is provided over the armoring. This is known as serving.