Type of line supports:
1) Wooden pole.
2) Steel (Tubular) pole.
3) Reinforced concrete (RCC) pole.
1) Wooden pole
it is made up of sal or chair wood. Its use is limited to low voltage distribution work (230 to 440 V). These are used for shorter spans (40 to 50 m). These are generally used in rural areas. These poles are cheap and provide good insulating property. The portion of the pole, buried underground is treated with preservatives like creosote oil. This is done to increase the life of the pole because the portion of the pole below the ground level tends to rot and preservatives prevent this happening, Fig.1. show types of a wooden pole.
The drawbacks of wooden poles are :
(i) These cannot be used for higher voltages (above 20 kV)
(ii) Life is less because of the natural decaying process.
(iii) Mechanical strength is less.
(iv) Preservative processing is required.
(v) The condition of the pole is to be inspected frequently.
2) Steel (Tubular) poles
These are stronger than wooden poles. So these are suitable for longer spans (50 to 80 m). The surface of steel poles is galvanized or painted to prevent rusting and corrosion. This enhances the life of the pole in galvanizing Zink is used. These are used for distribution purposes in cities. The area of cross-section reduces from bottom to top. These are hollow poles. Refer Fig.2.
3.Reinforced Concrete (RCC) Pole
These are popular and have replaced wooden and tubular poles.
They have greater mechanical strength, longer life, and good appearance.
The span between poles is between 80-100 meters. However, these are heavy due to the use of concrete, hence transportation cost is more. So these are manufactured at the site to reduce the cost of transportation. Fig. 3. shows the RCC pole.