A. Grounding resistance should be always zeroB. Grounding resistance should be as low as possibleC. Grounding resistance should be as high as possibleD. All of the aboveAnswer: B. Grounding resistance should be as low as possibleExplanation: - 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 Ω often shows a capacitive type and a low resistance of less than 10Ω 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
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 Ω often shows a capacitive type and a low resistance of less than 10Ω 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