Basic Construction of Electrical Cables

The basic construction of electrical cables involves six parts. Given below is a basic introduction to these:

Core or Conductors

Any type of cable is intended to serve a particular application. Depending on the specific application a cable can contain one, two, or three conductors/cores. E.g a 10 kVA, 3 phase AHU demands a three-core cable, while a small exhaust fan might require a single core cable. Conductors used in cables are stranded and are generally made of tinned copper.


Next to core, insulation is applied. The thickness of insulation depends on the supply voltage. Impregnated paper, varnished cambric or rubber mineral are the common materials employed for fabricating insulation.

Filler material

In case of multicore cables, gaps around the cables can result in deformed shape of cables. In order to provide proper shape to cable, the filler material is used. The filler material takes the extra space around cables and provides proper shape to cable.

Metallic sheath

The ingress of liquids, gases, moisture or dust is damaging for cables. In order to avoid this, the metallic sheath is provided over the insulation. The metallic sheath is made from aluminum or lead.


A layer of bedding is applied over the metallic sheath. Bedding primarily serves two purposes:

  1. It protects metallic sheath against corrosion
  2. It serves as protection blanket against mechanical injury that might result from armoring


Once bedding is done, armoring is the next step. The armor generally made of galvanized steel can be single or multi-layer steel tape that protects cable against mechanical damages at the time of laying and while handling it during installation time.


Serving is the final layer applied on the armoring with the sole purpose of providing protection to armor against atmospheric conditions. The serving is generally made of fibrous material.

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