Types of Earthing
1). Plate Earthing:
2). Pipe Earthing:
3). Rod Earthing
4). Earthing through the Waterman
5). Strip or Wire Earthing
What is Grounding or Earthing?
To connect the metallic (conductive) Parts of an Electric appliance or installations to the earth (ground) is called Earthing or Grounding.
In other words, to connect the metallic parts of electric machinery and devices to the earth plate or earth electrode (which is buried in the moisture earth) through a thick conductor wire (which has very low resistance) for safety purpose is known as Earthing or grounding.
To earth or earthing rather, means to connect the part of electrical apparatus such as metallic covering of metals, earth terminal of socket cables, stay wires that do not carry current to the earth. Earthing can be said as the connection of the neutral point of a power supply system to the earth so as to avoid or minimize danger during discharge of electrical energy.
Difference between Earthing, Grounding and Bonding.
Let me clear the confusion among earhing, grounding and bonding.
Earthing and Grounding is the same terms used for earthing. Grounding is the commonly word used for earthing in the North American standards like IEEE, NEC, ANSI and UL etc while, Earthing is used in European, Common wealth countries and Britain standards like IS and IEC etc.
The word Bonding used for jointing two wires (as well as conductors, pipes or appliances together. Bonding is known as connecting the metallic parts of different machines which is not considered to be carrying electric current during normal operation of the machines to bring them at the same level of electric potential.
Need of Earthing or Grounding. Why Earthing is Important?
The primary purpose of earthing is to avoid or minimize the danger of electrocution, fire due to earth leakage of current through undesired path and to ensure that the potential of a current carrying conductor does not rise with respect to the earth than its designed insulation.
When the metallic part of electrical appliances (parts that can conduct or allow passage of electric current) comes in contact with a live wire, maybe due to failure of installations or failure in cable insulation, the metal become charged and static charge accumulates on it. If a person touches such a charged metal, the result is a severe shock.
To avoid such instances, the power supply systems and parts of appliances have to be earthed so as to transfer the charge directly to the earth.
Below are the basic needs of Earthing.
To protect human lives as well as provide safety to electrical devices and appliances from leakage current.
To keep voltage as constant in the healthy phase (If fault occurs on any one phase).
To Protect Electric system and buildings form lighting.
To serve as a return conductor in electric traction system and communication.
To avoid the risk of fire in electrical installation systems.
Different Terms used in Electrical Earthing
Earth: The proper connection between electrical installation systems via conductor to the buried plate in the earth is known as Earth.
Earthed: When an electrical device, appliance or wiring system connected to the earth through earth electrode, it is known as earthed device or simple “Earthed”.
Solidly Earthed: When an electric device, appliance or electrical installation is connected to the earth electrode without a fuse, circuit breaker or resistance/Impedance, It is called “solidly earthed”.
Earth Electrode: When a conductor (or conductive plate) buried in the earth for electrical earthing system. It is known to be Earth Electrode. Earth electrodes are in different shapes like, conductive plate, conductive rod, metal water pipe or any other conductor with low resistance.
Earthing Lead: The conductor wire or conductive strip connected between Earth electrode and Electrical installation system and devices in called Earthing lead.
Earth Continuity Conductor: The conductor wire, which is connected among different electrical devices and appliances like, distribution board, different plugs and appliances etc. in other words, the wire between earthing lead and electrical device or appliance is called earth continuity conductor. It may be in the shape of metal pipe (fully or partial), or cable metallic sheath or flexible wire.
Sub Main Earthing Conductor: A wire connected between switch board and distribution board i.e. that conductor is related to sub main circuits.
Earth Resistance: This is the total resistance between earth electrode and earth in Ω (Ohms). Earth resistance is the algebraic sum of the resistances of earth continuity conductor, earthing lead, earth electrode and earth.
POINTS TO BE EARTHED
Earthing is not done anyhow. According to IE rules and IEE (Institute of Electrical Engineers) regulations,
Earth pin of 3-pin lighting plug sockets and 4-pin power plug should be efficiently and permanently earthed.
All metal casing or metallic coverings containing or protecting any electric supply line or apparatus such as GI pipes and conduits enclosing VIR or PVC cables, iron clad switches, iron clad distribution fuse boards etc should be earthed (connected to earth).
The frame of every generator, stationary motors and metallic parts of all transformers used for controlling energy should be earthed by two separate and yet distinct connections with the earth.
In a dc 3-wire system, the middle conductors should be earthed at the generating station.
Stay wires that are for overhead lines should be connected to earth by connecting at least one strand to the earth wires.
Components of Earthing System
A complete electrical earthing system consists on the following basic components.
Earth Continuity Conductor
Earth Continuity Conductor or Earth Wire
That part of the earthing system which interconnects the overall metallic parts of electrical installation e.g. conduit, ducts, boxes, metallic shells of the switches, distribution boards, Switches, fuses, Regulating and controlling devices, metallic parts of electrical machines such as, motors, generators, transformers and the metallic framework where electrical devices and components are installed is known as earth wire or earth continuity conductor as shown in the above fig.
The resistance of the earth continuity conductor is very low. According to IEEE rules, resistance between consumer earth terminal and earth Continuity conductor (at the end) should not be increased than 1Ω. In simple words, resistance of earth wire should be less than 1Ω.
Size of the Earth Continuity Conductor or Earth Wire depends on the cable size used in the wiring circuit.
Size of Earth Continuity Conductor
The cross sectional area of the Earth Continuity Conductor should not be less than the half of the cross sectional area of the thickest wire used in the electrical wiring installation.
Generally, the size of the bare copper wire used as earth continuity conductor is 3SWG. But keep in mind that, don’t use less than 14SWG as earth wire. Copper strip is also can be used as earth continuity conductor instead of bare copper wire but don’t go for it until manufacture recommend it.
Earthing Lead or Earthing Joint
The conductor wire connected between earth continuity conductor and earth electrode or earth plate is called earthing joint or “Earthing lead”. The point where earth continuity conductor and earth electrode meet is known as “connecting point” as shown in the above fig.
Earthing lead is the final part of the earthing system which is connected to the earth electrode (which is underground) through earth connecting point.
There should be minimum joints in earthing lead as well as lower in size and straight in the direction.
Generally, copper wire can be used as earthing lead but, copper strip is also used for high installation and it can handle the high fault current because of wider area than the copper wire.
A hard drawn bare copper wire is also used as an earthing lead. In this method, all earth conductors connected to a common (one or more) connecting points and then, earthing lead is used to connect earth electrode (earth plat) to the connecting point.
To increase the safety factor of installation, two copper wires are used as earthing lead to connect the device metallic body to the earth electrode or earth plate. I.e. if we use two earth electrodes or earth plats, there would be four earthing leads. It should not be considered that the two earth leads are used as parallel paths to flow the fault currents but both paths should work properly to carry the fault current because it is important for better safety.
Size of the Earthing Lead
The size or area of earthing lead should not be less than the half of the thickest wire used in the installation.
The largest size for earthing lead is 3SWG and the minimum size should not be less than 8SWG. If 37/.083 wire is used or the load current is 200A from the supply voltage, then it is recommended to use copper strip