Earthing MCQ Quiz - Objective Question with Answer for Earthing - Download Free PDF

The correct answer is option 2.

The fundamental principle for electrical installations aligns directly with international safety standards such as IEC 60364 and NFPA 70 (NEC), which emphasize:

• Protection against electric shock
• Overcurrent protection (including overloads and short circuits)
• Protection against fault currents
• Proper grounding and bonding

These are foundational principles to prevent injury, fire, and equipment damage. The other options contradict safety standards and could pose serious hazards if followed.

• Induced low voltage on metal equipment which causes low shock can be prevented using earthing.
• The main function of the earth wire is to prevent the live wire from overloading and absorbs the excess electrons & flows to the ground.
• Earthing is necessary to give protection against the danger of electric shock.
• The earthing protects the apparatus and personnel from the high voltage surges and lightning discharge.
• The earthing provides the easiest path to the flow of short circuit current even after the failure of the insulation.
• The earthing protects the personnel from the short circuit current hence it provides safety against shock.

• The pipe earthing resistance can be regulated by adding salt and water.
• In pipe earthing method the galvanized steel and perforated pipe of approved length and diameter in place upright in permanently wet soil.
• The size of the pipe depends upon the current to be carried and the type of soil.
• The size of the pipe uses for earthing is of diameter 40 mm and 2.5 meters in length for ordinary soil or greater length in case of dry and rocky soil.
• The depth at which the pipe must be buried depends on the moistures of the ground.
• The pipe is placed at 3.75 meters.
• The bottom of the pipe is surrounded by small pieces of coke or charcoal at a distance of about 15 cm.
• Alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth's resistance respectively.
• Generally, 10 kg of charcoal and 10 kg of salt are used for this purpose.
• Another pipe of 19 mm diameter and a minimum length of 1.25 meters are connected at the top of the GI pipe by reducing the socket.

• Hollow GI rod electrode is used for pipe earthing.
• In pipe earthing method the galvanized steel and perforated pipe of approved length and diameter in place upright in permanently wet soil.
• The size of the pipe depends upon the current to be carried and the type of soil.
• The size of the pipe uses for earthing is of diameter 40 mm and 2.5 meters in length for ordinary soil or greater length in case of dry and rocky soil.
• The depth at which the pipe must be buried depends on the moistures of the ground.
• The pipe is placed at 3.75 meters.
• The bottom of the pipe is surrounded by small pieces of coke or charcoal at a distance of about 15 cm.
• Alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth's resistance respectively.
• Generally, 10 kg of charcoal and 10 kg of salt are used for this purpose.
• Another pipe of 19 mm diameter and a minimum length of 1.25 meters are connected at the top of the GI pipe by reducing the socket.

Concept:-
When a pipe electrode is used for earthing, the length of the pipe should be at least 2.5 m, while for a plate electrode, the size of the plate should be at least 60 cm x 60 cm (2 ft x 2 ft) and the thickness should be 3.15 mm (for GI plates) or 6.35 mm (for copper plates).

Correct Answer: 3) 2.5 m, 1.5 m

Explanation:

Pipe Electrode:

A pipe electrode typically consists of a galvanized iron (GI) or steel pipe with a minimum length of 2.5 m and a diameter ranging from 38 mm to 75 mm.

It is placed vertically into the ground for efficient earthing.

Plate Electrode:

The standard size for a plate electrode is:

Copper Plate: At least 60 cm x 60 cm x 3.15 mm

GI Plate: At least 60 cm x 60 cm x 6.35 mm

The plate is buried vertically at a depth of at least 1.5 m.

Thus, when a pipe electrode is used for earthing, the length of the pipe should be at least 2.5 m, and for a plate electrode, the size should be at least 1.5 m.

Symbols of switchgear equipment:

1.) Grounding:

2.) Earthing:

3.) Lightning arrester:

4.) ​Circuit breaker:

Earthing is used to protect from an electric shock. It helps by providing a path for a fault current to flow to earth. Earth wire is made of galvanized steel because of good mechanical properties.

• The grounding to any device will provide the lowest resistance path possible to the ground.
• When there is a fault in the circuit, the earth or ground wire provides a path for the current to flow to the ground.
• So that the user will not get shocked when touches the metal parts. Hence to flow sufficient current it should offer low resistance to passes more current to ground.
• Ideally, earth resistance should be zero & practically it should be as low as possible.

• Hollow GI rod electrode is used for pipe earthing.
• In pipe earthing method the galvanized steel and perforated pipe of approved length and diameter in place upright in permanently wet soil.
• The size of the pipe depends upon the current to be carried and the type of soil.
• The size of the pipe uses for earthing is of diameter 40 mm and 2.5 meters in length for ordinary soil or greater length in case of dry and rocky soil.
• The depth at which the pipe must be buried depends on the moistures of the ground.
• The pipe is placed at 3.75 meters.
• The bottom of the pipe is surrounded by small pieces of coke or charcoal at a distance of about 15 cm.
• Alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth's resistance respectively.
• Generally, 10 kg of charcoal and 10 kg of salt are used for this purpose.
• Another pipe of 19 mm diameter and a minimum length of 1.25 meters are connected at the top of the GI pipe by reducing the socket.

One Mega ohm Rule for IR Value for Equipment:

Based upon equipment rating:

For the voltage < 1 kV = 1 MΩ minimum

For the voltage level > 1 kV = 1 MΩ /1 kV

As per IE Rules-1956,

• At a pressure of 1000 V applied between each live conductor and earth for a period of one minute the insulation resistance of HV installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards.
• Medium and Low Voltage Installations: At a pressure of 500 V applied between each live conductor and earth for a period of one minute, the insulation resistance of medium and low voltage installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards] from time to time.

When there is a fault in the circuit the earthing wire provides a path for the current to flow to ground. Hence the user will not get shocked when touches the metal parts. So to drive sufficient current it should offer low resistance to drive more current to ground. Ideally, resistance should be zero, practically it should be as low as possible.

• The pipe earthing resistance can be regulated by adding salt and water.
• In pipe earthing method the galvanized steel and perforated pipe of approved length and diameter in place upright in permanently wet soil.
• The size of the pipe depends upon the current to be carried and the type of soil.
• The size of the pipe uses for earthing is of diameter 40 mm and 2.5 meters in length for ordinary soil or greater length in case of dry and rocky soil.
• The depth at which the pipe must be buried depends on the moistures of the ground.
• The pipe is placed at 3.75 meters.
• The bottom of the pipe is surrounded by small pieces of coke or charcoal at a distance of about 15 cm.
• Alternate layers of coke and salt are used to increase the effective area of the earth and to decrease the earth's resistance respectively.
• Generally, 10 kg of charcoal and 10 kg of salt are used for this purpose.
• Another pipe of 19 mm diameter and a minimum length of 1.25 meters are connected at the top of the GI pipe by reducing the socket.

• Induced low voltage on metal equipment which causes low shock can be prevented using earthing.
• The main function of the earth wire is to prevent the live wire from overloading and absorbs the excess electrons & flows to the ground.
• Earthing is necessary to give protection against the danger of electric shock.
• The earthing protects the apparatus and personnel from the high voltage surges and lightning discharge.
• The earthing provides the easiest path to the flow of short circuit current even after the failure of the insulation.
• The earthing protects the personnel from the short circuit current hence it provides safety against shock.

• Increase in voltage potential at the earth mat caused by electrical faults that occur at electrical substations, power plants, or high voltage transmission lines.
• When fault occurs, short circuit current flows through the equipment and into the grounding electrode. The resistance of the Earth is non-zero, so current injected into the earth at the grounding electrode produces a potential rise with respect to a distant reference point.

Concept:

The standard wire gauge earthing lead is not thinner than 8 SWG due to the following reasons:

• Earthing wire prevents damage to equipment or personnel handling it.
• The minimum size of earthing wire is dependent on the current flowing through it.
• The cross-section area of the earthing lead should not be less than half of the area of the cross-section of the thickest wire used in the installation.
• The size of these conductors is dependent on the cable size that is employed in the wiring. 
• The copper wire used as an earth continuity conductor has a size of 3 SWG.