The resistance of earth is the resistance between infinite earth and earth electrode. It is depending on the condition of the soil, moisture content, dissolved salts and temperature of the soil.

There are several ways we can improve earth electrode resistance:

• By pouring water in the earth pit at repeated intervals
• By increasing the plate area
• By using longer rod deeper into the earth
• By using multiple rods
• To reduce soil resistivity, it is necessary to dissolve in the moisture particle in the soil; Some substance like salt/charcoal is highly conductive in water solution.

Important Point:

Methods of earth resistance measurement:

• 2-point dead earth method
• 3-point or fall of potential method
• 4-point method
• Clamp-on method

• As per IE rules, the resistance between the consumer earth terminal and the earth continuity conductor must be less than 1 ohms
• The cross-sectional area of the earth wire must be less than half of the cross-sectional area of the thickest wire used in the electrical wiring installation
• Generally, the size of the copper wire used as earth continuity conductor is 3SWG
• Earth wires smaller than 14SWG must not be used

Concept:

As per IE rules, insulation Resistance between earth and conductor should not exceed the 1/5000 time of the current flowing through the conductor.

That is to be measured by the ‘Megger’ instrument.

As per IE rules, 1956 insulation Resistance between earth and conductor should in range of mega Ohms.

IMPORTANT TO REMEMBER:-

One Mega ohm Rule for IR Value for Equipment

Based upon equipment rating:

• < 1K V = 1 MΩ minimum
• >1KV = 1 MΩ /1KV

Therefore, based on this analogy for Medium and High voltages there is need for Insulation –

Therefore,

Value of insulation Resistance between earth and conductor should not be less than 100 M ohm.

The resistance of earth is the resistance between the earth and earth electrode. It depends on three factors.

• The resistance of the earth electrode
• The contact resistance between electrode surface and soil
• The resistivity of soil between the electrode and earth

Resistivity of soil depends upon

• The electrical conductivity offered by a soil mainly due to electrolysis i.e. the resistivity of soil is mainly electrolytic in nature; So, the concentration of water, salt (NaCl) and other chemical components in the soil largely determines its resistivity
• The chemical composition of the soil
• The temperature of the soil
• Moisture; moist soil is best suited for earthing purpose
• It is normal practice to insert an earth electrode well below the ground level, to get a stable moist soil in depth
• Wet marshy land, loamy soil land, arable land, clayey land or land with loam mixed with small quantities of sand, gravel and stones are the best choice for the purpose
• Land with entirely dry sand, gravel chalk, limestone, granite, and very stony ground should be avoided

Out of the given options, the wet marshy ground offers more moisture. Hence it is best preferred for earthing.

HT Consumer:

High Tension (HT) consumer means a consumer who obtains supply from the Licensee at High Voltage.

Indian Electricity Act for HT consumer:

• According to Indian Electricity Act, HT consumers should maintain Power Factor 0.9 – 0.99.
• All new HT Consumers Electrical drawings should be approved by CEIG (Chief Electrical Inspector to Government) against the available proper Capacitors and Automatic Power Factor Controller in their Electrical systems for maintaining ZERO level KVAR losses (Maintaining Unity Power Factor).
• All Existing HT Consumers if not maintain the Unity Power Factor, they should be implemented by adequate Capacitors with Automatic Power Factor Controller in their electrical systems for maintaining ZERO level KVAR losses (Maintaining Unity Power Factor) within three months period time.
• All HT consumers’ consumptions should be billed through KVAH Units, not by KWH Units.
• In HT Consumer also Government required Power Factor is 0.9, i.e. 10% KVAR loss.

Requirement of Meters:

• For HT/EHT consumers – 3 Phase Tri-vector meters with MDI(Maximum Demand Indiactor). The meters shall have a facility for “Time of the Day” metering and storage of at least 45 days. The consumer shall have the option to install meter having facility to record peak hours MDI in addition to above features.
• For HT/ EHT loads Circuit Breakers (CBs) of appropriate rating and specifications shall be installed along with the meter.
• In a situation where the licensee is facing problems in collection of energy dues,the licensee may install pre-paid meters. The meters shall conform to the technical requirements as prescribed in Central Electricity Authority (Installation and Operation of meters) Regulations 2006.
• If supply to an HT/EHT consumer is given on an independent feeder for his exclusive use the metering arrangement shall be installed at the consumer’s premises or, if mutually agreed, the metering arrangement at the sub-station of the licensee may be used for billing and no meter need be installed at the premises of the consumer.

Disconnection on Consumer’s Request:

• HT/EHT consumers shall also bear the estimated expenditure on removal of the apparatus and service line.
• The licensee shall issue a demand note to the consumer in writing, under acknowledgment, within 10 working days of receipt of request.

Rules of the electricity board

• Light and fans wired on a common circuit. Such sub-circuit shall not have more than a total of 10 points of light, fan, and 5 A socket outlets. A load of such a circuit restricted to 800 Watts.
• Power sub-circuit shall be designed according to the load but in no case shall there be more than two 15 A outlets on each sub-circuit.
• In a power circuit, the maximum load that can be permitted is around 3000 watts

IE Rule 44: Instruction for the restoration of persons suffering from electric shock

IE Rule 46: Periodical Inspection and testing of consumer’s Installation

IE Rule 37: Supply to vehicles cranes etc.

Concept:

Purpose of Earthing:

• To save human life from the danger of electrical shock or death by blowing a fuse.
• It provides 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 i.e. to ensure that all exposed conductive parts do not reach a dangerous potential.
• To provide a safe path to dissipate lightning and short circuit currents.

An earth electrode is a conducting element buried directly in the ground, facilitating the flow of fault currents towards the ground.

Earth electrode can be in the form of metallic rod, pipe, strip or plate which has very low resistance in order to carry the fault current to the ground safely.

Depending upon the type of earthing electrode, the methods of earthing are:

• Plate earthing
• Pipe earthing
• Rod earthing
• Strip or wire earthing

Pipe earthing is the most common type used for residential quarters and strip earthing is used for 11 kV substation.