Methods of Earthing

METHODS OF EARTHING

The various methods of earthing in common use are

(i) Plate earthing

(ii) Pipe earthing

(iii) Rod earthing

(iv) Strip or wire earthing

1. Plate earthing

In this method either a copper plate of 60 cm × 60 cm × 3.18 or GI plate of 60 cm × 60 cm × 6.35 is used for earthing. The plate is buried into the ground not less than 3 m from the ground level. The earth plate is embedded in alternate layers of coal and salt for a thickness of 15 cm as shown in figure (7.6). In addition, water is poured for keeping the earth's electrode resistance value below a maximum of 5 Ω. The earth wire securely bolted to the earth plate.

A cement masonry chamber is built with a cast iron cover for easy regular maintenance.

2. Pipe earthing

Earth electrode made of a GI (galvanized iron) pipe of 38 mm in diameter and length of 2 m (depending on the current) with 12 mm holes on the surface is placed upright at a depth of 4.75 cm in a permanently wet ground. To keep the value of the earth resistance at the desired level, the area (15 cm) surrounding the GI pipe is filled with a mixture of salt and coal. The efficiency of the earthing system is improved by pouring water through the Funnel periodically. The GI earth wires of sufficient cross‒sectional area are run through a 12.7 mm diameter pipe (at 60 cm below) from the 19mm diameter pipe and secured tightly at the top‒as‒shown in figure (7.7).

When compared to the plate earth system the pipe earth system can carry larger leakage currents due to larger surface area is in contact with the soil for given electrode size. This system also enables easy maintenance as the earth wire connection is housed at the ground levels.

3. Rod earthing

It is the same method as pipe earthing, A copper rod of 12.5 cm (1/2 inch) diameter or 16 mm (0.6 in) diameter of galvanized steel or hollow section 25 mm (1 inch) of GI pipe of length above 2.5 m (8.2 ft) are buried upright in the earth manually or with the help of a pneumatic, hammer. The length of embedded electrodes in the soil reduces earth resistance of a desired value.

4. Strip or wire earthing

In this method of earthing strip electrodes of cross‒section not less than 25 mm (1 in × 0.06 in) is buried in a horizontal trenches of a minimum depth of 0.5 m. If copper with a cross‒section of 25 mm × 4 mm (1 in × 0.15 in) is used and a dimension of 3.0 mm² if it's a galvanized iron or steel.

If at all round conductors are used, their cross‒section area should not be too small, say less than 6.0 mm² if it's a galvanized iron or steel. The length of the conductor buried in the ground would give a sufficient earth resistance and this length should not be less than 15 m. The electrodes shall be as widely distributed as possible in a single straigth or circular trenches radiating from a point. This type of earthing is used where the earth bed has a rocky soil and excavation work is difficult.