# Earthing And Grounding Objective Type Questions With Explanations

1. The Soil resistance depends on .......
A. Nacl
B. Moisture
C. Depth of the electrode
D. All of the above

Answer: D. All of the above

Explanations:
The resistance of earth is the resistance between the earth and earth electrode. It depends on three factors.
• The resistance of earth electrode
• The contact resistance between electrode surface and soil
• The resistivity of soil between the electrode and earth

The resistivity of soil depends upon
• The electrical conductivity offered by a soil mainly due to electrolysis i.e., the resistivity of a soil is mainly electrolytic in nature
• So, 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
• Earth resistance depends on the depth of the earth electrode, moisture, temperature but it does not depend on operating time.

2. Ground resistance should be designed such that
A. Grounding resistance should be always zero
B. Grounding resistance should be as low as possible
C. Grounding resistance should be as high as possible
D. All of the above

Answer: B. Grounding resistance should be as low as possible

Explanation:
• 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 grounding system basically provides a low resistance path for the fault and lightning currents in order to maintain the safe potential with respect to the zero potential. High grounding resistance of more than 100 Î© often shows a capacitive type and a low resistance of less than 10Î© in the inductive type.
• Thus, the grounding resistance should be treated as impedance. The steady-state grounding resistance is designed to be as low as possible.
• In order to achieve low resistance, grounding systems are designed in a way to achieve as large as possible contact surface between the grounding system conductors and the surrounding soil.
• Ideally, the ground should be of zero ohms resistance. However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less.
• The grounding resistance is lower as the grounding electrode is larger. Therefore, high cost is required

3. The earthing rod orientation in the pit should be:
A. 45°
B. Horizontal
C. Vertical
D. 75°

Explanation:
• The earthing rod orientation in the pit should be Vertical.
• Salt and charcoal are added in the earth pit for improving conductivity.
• Earthing wire is used in the electric circuit to prevent damage to equipment or personnel handling it. The minimum size of earthing wire is dependent on the current through it.
• The area of cross section of the earthing lead should not be less than half of area of cross section of the thickest wire used in the installation.
• The size of these conductors depends on the size of the cable used for the wiring circuit.
• 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 3 SWG. Earth wires smaller than 14 SWG must not be used.
• The minimum size of the earth lead should not be smaller than 8 SWG.

4. Which one is the easiest method for earth resistance measurement?
A. Fall of potential
B. Selective measurement
C. Stake less measurement
D. All are equally easy

Explanation:
• Stake less measurement only measures individual ground rod resistances in parallel to earth grounding systems.
• If the ground system is not parallel to earth, then you will either have an open circuit or be measuring ground loop resistance.
• The most commonly used method of measuring the earth resistance of an earth electrode is the 3-point method or "fall of potential" method.
• It comprises the Earth Electrode to be measured and two other electrically independent test electrodes usually labeled P (Potential) and C (Current).
• An alternating current (I) is passed through the outer electrode C and the voltage is measured, by means of an inner electrode P, at some intermediary point between them.
• A wattmeter is used for the measurement of power.
• Kelvin double bridge is used for the measurement of resistance.
• Schering bridge is used for the measurement of capacitance.

5. In any system (grounding or ungrounding), a ____ coupling exist between the system conductors and the adjacent grounding surfaces:
A. Capacitance
D. Inductance
C. Resistance
D. None of the above

Explanation:
In any system a coupling Capacitance exist between the system conductors and the adjacent grounding surfaces
Electrical earthing:
• The process of transferring the immediate discharge of the electrical energy directly to the earth with the help of the low resistance wire is known as Electrical earthing.
• The electrical earthing is done by connecting the non-current carrying part of the equipment or neutral supply system to the ground.
There are two types of electrical earthing named
• Neutral earthing
• Equipment earthing

Neutral earthing:
• The neutral earthing is also called the system earthing.
• In neutral earthing, the neutral of the system is directly connected to the earth with the help of the GI wire.
• This type of earthing is mostly provided to the system which has star winding.

Equipment earthing:
• This type of earthing is provided to the electrical equipment for the safety of operating personnel.
• The non-current carrying part of the equipment like their metallic frame is connected to the earth with the help of the conducting wire.
• If any fault occurs in the apparatus, the short-circuit current passes the earth with the help of a wire. Thus, protecting the system from damage.

6. Earthing is necessary to give protection against ___.
A. Danger of electric shock
B. Voltage fluctuation
D. High temperature of the conductors

Answer: A. Danger of electric shock

Explanation:
• 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.

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.
• To provide protection against static electricity from friction.

7. The advantage of neutral earthing is:
A. Freedom from persistent arcing grounds
B. Over voltages due to lightning can be discharged to earth
C. Simplified design earth fault protection
D. All of the above

Answer: D. All of the above

Explanation:
Earthing:
• The process of connecting the metallic frame (i.e. non-current carrying part) of electrical equipment or some electrical part of the system (e.g. neutral point in a star-connected system, one conductor of the secondary of a transformer etc.) to earth (i.e. soil) is called grounding or earthing.
• Earthing is generally done in the transmission line at the supply end to safeguard the whole system from flowing high fault currents whenever any fault occurs in the system.

• Voltages of the healthy phases do not exceed line to ground voltages i.e. they remain nearly constant.
• The high voltages due to arcing grounds are eliminated.
• The protective relays can be used to provide protection against earth faults.
• In case an earth fault occurs on any line, the protective relay will operate to isolate the faulty line.
• The over-voltages due to lightning are discharged to earth.
• It provides greater safety to personnel and equipment.
• It provides improved service reliability.
• Operating and maintenance expenditures are reduced.
• The simplified design of earth fault protection.
• Over-voltages due to lightning can be discharged to the earth.
• Freedom from persistent arcing grounds.

8. Which one of the following is used in earth pit?
A. Salt and charcoal
B. Graphite and magnesium
C. Graphite and Silver
D. Aluminum and Iron

Explanation:
• Salt and charcoal are added in the earth pit for improving conductivity.
• Salt and charcoal increase the conductivity of the soil in the earth pit.
• As a result, the fault current finds it easy path through equipment to the earth.
• The alternate layers of charcoal and salt maintain low resistance for earth fault currents.

9. Moisture content in the soil _______ the earth soil resistance.
A. increase
B. decrease
C. does not affect
D. none of the above

Explanation:
• The measure of the resistance offered by the soil in the flow of electricity, is called the soil resistivity.
• The resistivity of the soil depends on the various factors like soil composition, moisture, temperature, etc.
• The resistivity of the soil varies with the depth.
• The lower layers of the soil have greater moisture content and lower resistivity.
• With the increase in moisture content, the resistivity decreases and hence soil resistance decreases.

10. Generally grounding is provided for:
A. only for the safety of the equipment
B. only for the safety of the operating personnel
C. Both (A) and (B)
D. None of the above

Answer: C. Both (A) and (B)

Explanation:
Grounding:
• The process of connecting the metallic frame (i.e. non-current carrying part) of electrical equipment or some electrical part of the system (e.g. neutral point in a star-connected system, one conductor of the secondary of a transformer etc.) to earth (i.e. soil) is called grounding or earthing.
• Grounding is generally done in transmission line at the supply end to safeguard the whole system from flowing high fault currents whenever any fault occurs in the system.
• Generally grounding is provided for the safety of the equipment and only for the safety of the operating personnel.

Important Points:
The following are the advantages of neutral grounding:
• Voltages of the healthy phases do not exceed line to ground voltages i.e., they remain nearly constant.
• The high voltages due to arcing grounds are eliminated.
• The protective relays can be used to provide protection against earth faults. In case earth fault occurs on any line, the protective relay will operate to isolate the faulty line.
• The over voltages due to lightning are discharged to earth.
• It provides greater safety to personnel and equipment.
• It provides improved service reliability.
• Operating and maintenance expenditures are reduced.