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Thursday, 25 July 2019

Stranding of Conductors

A conductor of large cross section becomes rigid. It is liable to kink and break during handling. To avoid this, conductors are stranded. Stranded conductors are flexible and can be coiled easily. A stranded conductor is made by twisting thin wires called strands together to form layers. The wires of each layer are held in helical fashion round the preceding layer. Stranding is done in opposite directions for successive layers. If the wires in one layer are twisted in left hand direction, the next layer of wires will be twisted in the right hand direction and so on. The conductors usually have a central wire or strand around which successive layers of strands are wound.




A standard stranding consists of 6 wires around 1 wire then 12 wires around the previous 6, then 18 wires around 12, then 24 wires around 18 and so on. The number of layers to be provided will depend on the number of wires to be provided. The centre wire is not counted as a layer. Instead of putting a single wire in the centre three or four stranded wires may also be put in the centre and over them layers may be formed. If 2 stranded wires are put in the centre, 9 wires will be in the first layer, then 15 wires in second layer and so on. In each of the above cases the increase in the number of wires in each successive layers is 6. The below table shows the number of wires in different layers, total number of wires and over all diameter of the stranded conductor.

Details of Stranded Conductor

No: of wires in the centre
1 wire
3 wires
4 wires
No: of wires in the nth layers from centre
6n
3 + 6n
4 + 6n
Total No. of wires in a stranded conductor having n - layers
1 + 3n ( 1 + n)
3 (1 + n)2
(4 + 3n) ( 1 + n)
Diameter over the nth layer centimetres, where d indica-tes the diameter of each wire in centimetres.
(1 + 2n) d
(2.155 + 2n) d
(2.414 + 2n) din

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