Stranding of Conductors
A large cross-section of a conductor gets rigid. During handling, it is prone to kinking and breaking. Conductors are stranded to prevent this. Stranded conductors are lightweight and easy to coil. The layers of a stranded conductor are formed by twisting small wires called strands together. Each layer's wires are helical-wrapped around the layer before them. For each layer, stranding is done in the opposite direction. If the wires in one layer are twisted left to right, the wires in the following layer will be twisted right to left, and so on. A central wire or strand is frequently twisted around which additional layers of strands are wound.
6 wires wrap around 1 wire, 12 wires wrap around the preceding 6, 18 wires wrap around 12, 24 wires wrap around 18, and so on. The number of layers available will be determined by the number of wires available. A layer isn't counted if the centre wire isn't present. Three or four-stranded wires can be placed in the centre instead of a single wire, and layers can be constructed over them. If you add two stranded wires in the middle, the first layer will have 9 wires, the second layer will have 15, and so on. The number of wires in each consecutive layer increases by 6 in each of the examples above. The number of wires in each layer, the total number of wires, and the overall diameter of the stranded conductor are shown in the table below.
Details of Stranded Conductor
|
No: of wires in the
centre |
1 wire |
3 wires |
4 wires |
|
The number of wires
in the nth layer from the centre |
6n |
3 + 6n |
4 + 6n |
|
The total number of
wires in an n-layer stranded conductor |
1 + 3n ( 1 + n) |
3 (1 + n)2 |
(4 + 3n) ( 1 + n) |
|
Diameter in
centimetres over the nth layer, where d is the diameter of each
wire in centimetres. |
(1 + 2n) d |
(2.155 + 2n) d |
(2.414 + 2n) din |