What is Earthing:
The main reason for doing earthing in electrical network is for the safety. When all metallic parts in electrical equipment’s are grounded then if the insulation inside the equipment’s fails there are no dangerous voltages present in the equipment case. If the live wire touches the grounded case then the circuit is effectively shorted and fuse will immediately blow. When the fuse is blown then the dangerous voltages are away.
(1) Safety for Human life/ Building/Equipment’s:
- To save human life from danger of electrical shock or death by blowing a fuse i.e. To provide an alternative path for the fault current to flow so that it will not endanger the user
- To protect buildings, machinery & appliances under fault conditions.
- To ensure that all exposed conductive parts do not reach a dangerous potential.
- To provide safe path to dissipate lightning and short circuit currents.
- To provide stable platform for operation of sensitive electronic equipment’s i.e. To maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment .
- Lightning, line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system. Earthing provides an alternative path around the electrical system to minimize damages in the System.
(3) Voltage stabilization:
- There are many sources of electricity. Every transformer can be considered a separate source. If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other. The earth is the most omnipresent conductive surface, and so it was adopted in the very beginnings of electrical distribution systems as a nearly universal standard for all electric systems.
There are 3 types of earthing techniques available. they are given below,
- TN-S system
- TT system
- TN-C-S system
TN-S earthing system:
A TN-S system has the supply source directly connected to earth, the installation metalwork connected to the neutral of the supply source via the lead sheath of the supply cable, and the neutral and protective conductors throughout the whole system performing separate functions.
TT Earthing system:
A TT system has a direct connection to the supply source to earth and a direct connection of the installation metalwork to earth. An example is an overhead line supply with earth electrodes, and the mass of earth as a return path as shown below.
TN-C-S Earthing system:
A TN-C-S system is as the TN-S but the supply cable sheath is also the neutral, i.e. it forms a combined earth/neutral conductor known as a PEN (protective earthed neutral) conductor.
The installation earth and neutral are separate conductors.
This system is also known as PME (protective multiple earthing).
Conventional methods of earthing:
(1) Plate type Earthing:
- Generally for plate type earthing normal Practice is to use
- Cast iron plate of size 600 mm x600 mm x12 mm. OR
- Galvanized iron plate of size 600 mm x600 mm x6 mm. OR
- Copper plate of size 600 mm * 600 mm * 3.15 mm
- Plate burred at the depth of 8 feet in the vertical position and GI strip of size 50 mmx6 mm bolted with the plate is brought up to the ground level.
- These types of earth pit are generally filled with alternate layer of charcoal & salt up to 4 feet from the bottom of the pit.
(2) Pipe type Earthing:
- For Pipe type earthing normal practice is to use
- GI pipe [C-class] of 75 mm diameter, 10 feet long welded with 75 mm diameter GI flange having 6 numbers of holes for the connection of earth wires and inserted in ground by auger method.
- These types of earth pit are generally filled with alternate layer of charcoal & salt or earth reactivation compound.