Different Types of Earthing

Different Types of Earthing Points : different types of earthing, earthing through a water main, g.i. pipe earthing, g.i. plate of copper plate earthing, besides electrical appliances the article to be earthed, use of earth leakage circuit breaker, earth leakage trip or circuit breaker A house wiring or a factory wiring may be earthed in three different ways: (i) Earthing through a Water Main Before connecting an earthing system to a water main, it must be ascertained that all throughout galvanized iron pipes have been used. If any portion of the water main is made of cement concrete, eat-thing resistance will be high and the earthing arrangement will not be effective.

While connecting earth wire with the water main, care must be take to see that the contact resistance is minimized. For this purpose specially made earthing clamps are used. If a standard conductor is used as earth wire, all the strands should be made straight and placed parallel and soldered together to make it solid at that end which is to be connected with the water main. A lead strip is bent round the pipe so that the earth wire can be properly placed over it and the contact between the wire and the pipe is perfect. Before placing the lead strip the surface of the pipe should be thoroughly cleaned, and all traces of dirt and grease are removed.

Sometimes the earthing clamp is tightened over the water main and the end of the earth wire is soldered to a thimble or a lug fixed with the earthing clamp. If the water main is the property of municipally or some other person, the consumer must not connect his earth wire with the water main without written consent of the over and the electrical Inspector.

(ii) G.I. Pipe Earthing For earthing house wiring, factory wiring (specially electrical installations of big factories), neutral wire of the supply line etc., galvanized iron pipe is generally used as earth electrode. The size of the pipe depends upon fault current and the condition of the soil. If moist and soft soil is available in, the earth pit, the length of the pipe should be at least metres and its diameter 38.1 mm. If the soil is dry and rocky, the length of the pipe should be increased to 2.75 metres. In order that the contact between inner surface of the pipe and the soil is perfect, some holes of diameter 12 mm. arc made on the pipe at equal intervals along the length.

The pipe is placed upright in the pit as shown in figure. It must be placed in permanently wet ground. The depth at which the pipe should be buried depends upon the condition of the ground moisture. According to Indian Code of Practice the pipe should be placed at a depth of 4.75 metres below the ground level. But this depth can be surrounded if sufficient moisture of soil is available earlier. The pipe at bottom should be rounded by charcoal or broken pieces of coke and salt for a distance up to 15 cm around the pipe. With this arrangement, on one side, charcoal increased the contact surface between the pipe and the earth, on the other side, salt decreased the earthing resistance. Generally alternate layers of salt and charcoal are arranged in the earth pit for best results, in the first layer there is salt, in the second layer there is charcoal, in the third layer there is salt again, in the fourth layer there is charcoal again, and so on. The practice is to use galvanized iron wire or strip as earth lead where galvanized iron pipe is used as earth electrode. The size of the earth lead or earth wire depends upon maximum current that will flow through it when a fault will occur anywhere in the installation. But generally the cross-section of this wire is 0.645 square centimeter. One and of the earth wire is connected to iron pipe of diameter 19.05 mm placed at the top of, the earth electrode. It is then carried in a galvanized iron pipe of diameter 12.7 mm placed at a depth not less than 60 cm below the ground level. Further, when the earth wire is carried over from one machine or apparatus to another, it should be protected from external injury by carrying it through a pipe or in a recessed portion.

(iii) G.I. Plate of Copper Plate Earthing In case of plate earthing if galvanized iron plate is used as earth electrode, its size shall not be less than 60 cm x6Ocmx 6.35 mm(2 ft x 2 ft x ½ in) according to Indian Standard. With this plate galvanized iron wire is used as earth lead. If copper plate is used, its size must be at least 60 cm x 60 cm x 3.18 mm (2 ft x 2 ft x 1/8 in), and copper wire should be used as earth lead with this plate. In both cases plate is kept vertically in the earth pit at a depth of at least 3 metres (10 ft) below ground level.

The depth at which the plate is kept in the earth pit depends upon the condition of the soil. It must be placed in a permanently wet ground. If the soil surrounding the plate becomes dry and hard, the earthing itself becomes a source of danger. For this reason pcriodical testing of earthing arrangement is necessary. At first a socket is soldered at the end of the earth wire. This socket is securely bolted to the earth plate with the help of two lock nuts, bolts and washers. At the top of the earth plate a G.I. pipe of diameter 12.7 mm (Yz inch) is placed, and through his pipe earth wire is drawn upto earthing busbar or main switch.

In the soil this pipe should remain at least 60 cm below ground level. The metallic frames of all instruments and switches mounted on the main switch board and other distribution boards should remain connected with the earth wire. Another G.I. pipe of diameter 19.05 (3/4 inch) is also placed at the top of the earth plate. At the top of the pipe there is a funnel the mouth of which is covered with a wire mesh so that a piece of solid cannot be dropped into the pipe. The top of the pipe with funnel remains in reservoir of size 30 cm x 30cm x 30 cm (1 ft x 1 ft x 1ft) four sides of which have brick walls and the top remains covered with a cast iron plate. Periodically three or four buckets of water is poured into the earth pit through the funnel in order to keep the sol in the pit moist. The Article is not to be Earthed The following articles need not be earthed:
i) Small pieces of metal conduits used to protect small pieces of C.T.S. or PV.C. wires.
ii) Metal conduit pipes used as wall tubes for the protection of cleat wiring passing through partition wall.
iii) Metal box covered with non-conducting substance and used in connection with C.T.. or P.V.C. wiring.
iv) Lamp caps.
v) Name plate separated by insulating substance, screws and other small substances.
vi) Metal chain (with which pendant lamp fitting is suspended) not touched with flexible cord of twisted type.
vii) Lamp fitting in a room the floor of which is made of non-conducting substance (the fitting must remain at a height out of reach and away from any earthed body). Besides Electrical Appliances the Article to be Earthed When it is not possible to maintain an electrical wiring system isolated from water pipe, gas pipe, telephone wire etc., these must be properly connected to earth by means of binding with earth continuity conductor.
The article to be connected to earth through bonding in such cases are as follows:
i) Both tub, bare metallic pipe, water tank etc. of bath room.
ii) If possible all iron or steel frame, joist, girder, etc. coming within reach.
iii) Electric crane, lift etc. moving on iron frame.