Rule 90 is about earthing and states that all metal supports and metallic fittings should be permanently and efficiently earthed. Each stay-wire should be efficiently earthed or an insulator provided in it at a height not less than 3.0 m from the ground.
Thumb Rule for Calculate Number of Earthing Rod
- ρ = Resistivity of earth in Ohm-Meter.
- L = Length of the electrode in Meter.
- d = Diameter of the electrode in Meter.
- K = 0.75 if 25< L/d < 100.
- K = 1 if 100 < L/d < 600.
- K = 1.2 o/L if 600 < L/d < 300.
There are five types of neutral earthing:
- Solid-earthed neutral.
- Unearthed neutral.
- Resistance-earthed neutral. Low-resistance earthing. High-resistance earthing.
- Reactance-earthed neutral.
- Using earthing transformers (such as the Zigzag transformer)
Earthing Charcoal & Salt are used in Conventional Pipe & Plate Earthing. The layer of charcoal and salt helps to maintain low resistance for earth fault currents. Because of ionic behavior of salt and charcoal they will maintain moisture.
The key difference between earthing and grounding is that the term “Earthing” means that the circuit is physically connected to the ground which is Zero Volt Potential to the Ground (Earth). Whereas in “Grounding” the circuit is not physically connected to ground, but its potential is zero with respect to other points.
IR Value for Transformer. Insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. Insulation resistance tests are commonly measured directly in megohms or may be calculated from measurements of applied voltage and leakage current.
Earthing is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault.
Plate earthing is the best earthing.
Mostly, the galvanised iron is used for the earthing. The earthing provides the simple path to the leakage current. The shortcircuit current of the equipment passes to the earth which has zero potential.
2. Equipment Earthing. This is the prime type of earthing for homes and other buildings. It deals with the safeguarding of noncurrent carrying apparatus and metallic conductors.
Earthing of a system is done in the installation to connect the respective parts with electrical conductors or electrodes. The electrode is placed near the soil or below the ground level, which has flat iron riser under the ground. The noncurrent-carrying parts are connected with the flat iron.
0.3 The subject of earthing covers the problems relating to conduction of electricity through earth. The terms earth and earthing have been used in this code irrespective of reliance being placed on the earth itself as a low impedance return path of the fault current.
3 good ways to improve earth electrode resistance
- Lengthen the earth electrode in the earth.
- Use multiple rods.
- Treat the soil.
This is basically to have additional and fail-safe earthing in all eventualities. It is statutory obligation under IE rules,1956 , which provides that all non current carrying metallic parts of an electrical tools, plants, equipments, apparatus will be connected to earth by two separate and distinct earthing points.
Strip or wire earthing. Plate Earthing. In this type of earthing, a plate made up of galvanized iron or copper is buried vertically at a depth not less than 3m from the ground level.
The Earth Resistance profile varies between 10 Ohms and 20 Ohms. Soil identifications as well as programmed intensive field measurements of soil resistivity and earthing system at selected sites proves that soil resistivity values' depend on the type of soil.
The “total body resistance” of the person is composed of the very low (approximately 300 Ω) internal body resistance plus the 2 skin contact resistances. The skin contact resistance will usually be between 1000 and 100,000 Ω, depending on contact area, moisture, condition of the skin, and other factors.
Earth resistivity is usually measured using the Wenner method, which involves the use of four temporary earth spikes. The spikes do not need to be moved as part of the testing procedure however – their location and spacing is determined by the depth at which it is required to determine the earth resistivity.
The problem with adding moisture to the soil is that it's not a practical option in most cases. Another way to lower earth resistivity is to treat the soil with a salt, such as copper sulfate, magnesium sulfate, or sodium chloride. Combined with moisture, the salts leach into the soil to reduce earth resistivity.
Factors affecting on Earth resistivity
- Soil Resistivity. It is the resistance of soil to the passage of electric current.
- Soil Condition.
- Moisture.
- Dissolved salts.
- Climate Condition.
- Physical Composition.
- Location of Earth Pit.
- Effect of grain size and its distribution.
Step 1: Touch the BLACK probe to the EARTH terminal and touch the RED probe to the NEUTRAL terminal on the switching mode power supply unit. Step 2: Switch ON the power supply, and you will be able to read the voltage values displayed on screen.
