EARTHING SYSTEM

EARTHING SYSTEM

EARTHING SYSTEM
The meaning of earthing or grounding is to connect the electrical equipment to the general mass of earth by wire of negligible resistance.
This brings the body of the electrical equipment to zero potential and thus will avoid the sock to the operator. The neutral of the supply system is also solidly earthed to ensure equal to zero.
WHY IS EARTHING NECESSARY?
If all electrical equipment produced was totally insulated, then there would be no need for earthing.
Unfortunately up to now, insulated covers or casings have been expensive to produce and so metal has been used. The use of metal means that if a fault occurred, the metal could become alive at anything up to mains voltage.
HOW DOES EARTHING GIVE PROTECTION?
The usual method of earthing is to join to exposed metal work to earth to earth via an earth continuity conductor connected to an electrode burried in the earth.
In conjunction with a fuse, or other sillar device, this then forms a protective system. Thus if a live conductor accidentally comes into contact with any exposed metal, it is effectively connected to earth.
WHY IS EARTHING SO IMPORTANT?
Human life is involved where electrical apparatus is used, and an electric shock can be fatal.
Also a violent short circuit can easily start a disastrous fire on a premises.
These are well known facts that are often forgotten when electricity is being used every day.
A can be now, tomorrow, five years time, or possible even never.
It is because an emergency might never occur that an efficient earthing system is often neither installed nor maintained.
Many installations in pakistan have totally inadequate earthin systems, but this is not realized since a fault has not yet occurred.
It is only after someone has been electrocuted or a building is gutted by fire, that it is realized that little or no protection had been given by the protective system.
COMPONENTS / PARTS OF EARTHINGS SYSTEM:
(1) Earthing Continuity Conductor
(2) Earthing Lead or Earth Conductor
(3) Earth Electro ac
EARTH CONTINUITY CONDUCTOR
This is the part of the earthing system, which joinjs or bends together all the metal parts of an insulation.
Conduits, ducts, boxes, metal casings of switches fuse distribution  boards, regulating and controlling apparatus, exposed metal work machines and any metal frame work on which electrical apparatus is mounted.
EARTH LEAD OR EARTH CONDUCTOR:
The earth conductor is the conductor, which provides connection between earth electrode and earth connecting point (Main Earth Point). The earthing conductor must be short and straight with the minimum number of joints. Two forms of earthing conductors, depending upon the load, are commonly used.
these are copper wire and copper strip. Copper strip is used on very large installations.
The usual practice in Pakistan is use to hard drawn copper wire, In case of copper wire duplicating earthing conductor should be run up to the earth electrode in order to increase the protection of installation. If there are two earth plates there should be four earthing conductors.
The area of each of the earthing conductor should not be less than half the area of the largest current path.
When copper wire is installed, it should be enclosed in the G.I Pipes. This gives protection against mechanical damage and corrosion and also can used to guide water to the plate in order to keep the plate and surrounding artificially damped.
EARTH ELECTRODE:
An earth electrode provides connection between the installation metal work and general mass of earth. For domestic installation main water pipe was used as earth electrode. Big installation (over 21 kW) has to have its own earth electrode.
The most common type of electrode is plate of either galvanized iron or copper, Cast iron pipes can also be used in place but are not as efficient as plates.
The main purpose of an electrode is to provide good conductivity with earth at all time.
The way is to install the electrode well below water level. The plate should be placed in an upright position and surrounded by a bed of at least on ft.
REQUIREMENTS FOR EARTHING:
A complete protective system consists of two parts a protective device connected in the supply conductor (such as re-wireable fuse, or overload circuit breaker.
And  a low resistance earth return path bonded to all exposed metal work and earth.
A protective system must be able to deal efficiently with either one or all of the possible circuit faults .
METHODS OF EARTHING:
There are three methods of earthing.
 1.  EARTHING THROUGH A WATER MAIN
 2.  PIPE EARTHING
 3.  PLATE EARTHING:
EARTHING THROUGH A WATER MAIN
Before making an earthing connection to the water main, it must be ascertained that throughout G.I Pipes have been used, otherwise of the cement concrete popes have been used, the earthing will not be effective.
When making an earthing connection, care must be taken to limit the contact resistance to the minimum.
For that purpose properly designed earthing clamp should be used. The stranded copper lead is fanned out and is soldered to make it solid.
Then the lead strip is bent round the pipe so that it may be seated properly over the pipe.
The surface of the pipe is cleaned properly, and all traces or grease are removed and then over it is placed the clamp.
This method is however not popular as water means are of concrete or cement.

PIPE EARTHING:
If the water-pipe cannot be used as an earth, a galvanized iron pipe of approved length and diameter can be sued. The size of the pipe depends upon (a) the current to be, carried (b) the type of soil.
According to I.S.I.  Standard No. 732-1963 the galvanized iron pipe shall not be less than 38.1 mm.
Diameter and 2m. Long for ordinary soil but if the soil is dry and rocky, the length of the pipe should be increased to 2.75m.

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