33 Earthing, Lightning & Safety Design questions from the Electrical Design bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
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A.IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
B.four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
C.connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault
D.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
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2. Which term means: "IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral"?
Junior
A.Fall-of-potential test
B.TN, TT and IT systems
C.Wenner method
D.Earth electrode types
Answer + AI explanation with Pro
3. Which statement is correct?
Junior
A.TN, TT and IT systems — metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4
B.TN, TT and IT systems — IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
C.TN, TT and IT systems — residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
D.TN, TT and IT systems — Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures
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4. What is Surge arrester?
Junior
A.voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
B.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
C.metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4
D.residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
Answer + AI explanation with Pro
5. Which term means: "metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4"?
Junior
A.Step vs touch voltage
B.Equipotential bonding
C.Surge arrester
D.Fall-of-potential test
Answer + AI explanation with Pro
6. Which statement is correct?
Junior
A.Surge arrester — step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg
B.Surge arrester — metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4
C.Surge arrester — distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
D.Surge arrester — voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
Answer + AI explanation with Pro
7. What is Earth electrode types?
Junior
A.Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures
B.voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
C.IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
D.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
Answer + AI explanation with Pro
8. Which term means: "IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils"?
Junior
A.Earth electrode types
B.TN, TT and IT systems
C.Ground potential rise
D.Step vs touch voltage
Answer + AI explanation with Pro
9. Which statement is correct?
Junior
A.Earth electrode types — three-terminal earth resistance test where the potential probe placed at about 62% of the current-probe distance gives the true electrode resistance
B.Earth electrode types — voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
C.Earth electrode types — IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
D.Earth electrode types — IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
Answer + AI explanation with Pro
10. What is Equipotential bonding?
Junior
A.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
B.three-terminal earth resistance test where the potential probe placed at about 62% of the current-probe distance gives the true electrode resistance
C.connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault
D.four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
Answer + AI explanation with Pro
11. Which term means: "connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault"?
Junior
A.Arc flash boundary
B.Fall-of-potential test
C.Equipotential bonding
D.RCD
Answer + AI explanation with Pro
12. Which statement is correct?
Junior
A.Equipotential bonding — connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault
B.Equipotential bonding — residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
C.Equipotential bonding — three-terminal earth resistance test where the potential probe placed at about 62% of the current-probe distance gives the true electrode resistance
D.Equipotential bonding — four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
Answer + AI explanation with Pro
13. What is Wenner method?
Mid
A.IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
B.metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4
C.four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
D.residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
Answer + AI explanation with Pro
14. Which term means: "four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design"?
Mid
A.Ground potential rise
B.Step vs touch voltage
C.RCD
D.Wenner method
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
A.Wenner method — metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4
B.Wenner method — four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
C.Wenner method — residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
D.Wenner method — step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg
Answer + AI explanation with Pro
16. What is Ground potential rise?
Mid
A.voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
B.IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
C.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
D.IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
Answer + AI explanation with Pro
17. Which term means: "voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design"?
Mid
A.Ground potential rise
B.Arc flash boundary
C.Equipotential bonding
D.Step vs touch voltage
Answer + AI explanation with Pro
18. Which statement is correct?
Mid
A.Ground potential rise — three-terminal earth resistance test where the potential probe placed at about 62% of the current-probe distance gives the true electrode resistance
B.Ground potential rise — voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
C.Ground potential rise — Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures
D.Ground potential rise — connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault
Answer + AI explanation with Pro
19. What is Step vs touch voltage?
Mid
A.step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg
B.residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
C.voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
D.metal-oxide (ZnO) varistor that conducts above its rated voltage to clamp surges, selected by MCOV, residual voltage and energy class per IEC 60099-4
Answer + AI explanation with Pro
20. Which term means: "step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg"?
Mid
A.Fall-of-potential test
B.Wenner method
C.RCD
D.Step vs touch voltage
Answer + AI explanation with Pro
21. Which statement is correct?
Mid
A.Step vs touch voltage — step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg
B.Step vs touch voltage — three-terminal earth resistance test where the potential probe placed at about 62% of the current-probe distance gives the true electrode resistance
C.Step vs touch voltage — distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
D.Step vs touch voltage — Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures
Answer + AI explanation with Pro
22. What is IEC 62305 LPS classes?
Mid
A.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
B.IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
C.Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures
D.four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
Answer + AI explanation with Pro
23. Which term means: "Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures"?
Mid
A.IEC 62305 LPS classes
B.Surge arrester
C.Fall-of-potential test
D.Earth electrode types
Answer + AI explanation with Pro
24. Which statement is correct?
Mid
A.IEC 62305 LPS classes — step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg
B.IEC 62305 LPS classes — IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
C.IEC 62305 LPS classes — Class I to IV with rolling-sphere radius 20, 30, 45 and 60 m and mesh 5×5 to 20×20 m, Class I for explosive or critical structures
D.IEC 62305 LPS classes — connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault
Answer + AI explanation with Pro
25. What is RCD?
Mid
A.step is between feet 1 m apart; touch is hand-to-feet at 1 m reach; IEEE 80 tolerable limits use a 1000 Ω body and 0.116/√t for 50 kg
B.IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
C.residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
D.IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
Answer + AI explanation with Pro
26. Which term means: "residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations"?
Mid
A.Earth electrode types
B.Arc flash boundary
C.TN, TT and IT systems
D.RCD
Answer + AI explanation with Pro
27. Which statement is correct?
Mid
A.RCD — residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
B.RCD — IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
C.RCD — voltage the grid reaches relative to remote earth during a fault, equal to fault current times grid resistance, driving touch, step and telecom design
D.RCD — IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
Answer + AI explanation with Pro
28. What is Arc flash boundary?
Senior
A.distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
B.connecting all exposed and extraneous conductive parts to the main earthing terminal so no dangerous potential difference appears during a fault
C.three-terminal earth resistance test where the potential probe placed at about 62% of the current-probe distance gives the true electrode resistance
D.four equally spaced probes give soil resistivity ρ = 2πaR averaged to a depth about equal to the spacing a, the input for grid design
Answer + AI explanation with Pro
29. Which term means: "distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584"?
Senior
A.IEC 62305 LPS classes
B.Surge arrester
C.Arc flash boundary
D.Fall-of-potential test
Answer + AI explanation with Pro
30. Which statement is correct?
Senior
A.Arc flash boundary — IEC 60364 earthing arrangements: TN uses a supply-earthed neutral with separate or combined PE, TT a local electrode, IT an isolated or impedance-earthed neutral
B.Arc flash boundary — IS 3043 electrodes: plate (600 × 600 mm), pipe, rod and strip, with chemical maintenance-free electrodes now common in poor soils
C.Arc flash boundary — residual current device tripping on line-neutral imbalance, 30 mA for personnel and 100–300 mA for fire protection, mandated by CEA regulations
D.Arc flash boundary — distance at which incident energy falls to 1.2 cal/cm², the onset of a second-degree burn, computed per IEEE 1584
Answer + AI explanation with Pro
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