21. In practice, earth is chosen as a place of zero electric potential because it
- is non-conducting
- is easily available reference
- keeps losing and gaining electric charge everyday
- has almost constant potential
22. Third pin in a 3-pin plug is provided so as to
- Provide an earth connection
- Provide a 3-phase supply when required
- Provide a spare phase when required
- Prevent the plug being reversed in the socket
23. Resistivity of earth increases sharply when moisture falls below
24. What is the diameter of the GI pipe through which the earth wire needs to be taken to?
- 13 mm diameter
- 15 mm diameter
- 19 mm diameter
- 6 mm diameter
25. What should be the value of earthing resistance for large power stations?
- 1 Ω
- 0.5 Ω
- 2 Ω
- 5 Ω
26. What type of earthing is used by transmission lines?
- Plate earthing
- Rod earthing
- Strip earthing
- Both plate and strip earthing
27. Which type of earthing is also called as ‘fire earthing’?
- plate earthing
- rod earthing
- strip earthing
- only i
- only ii
- only iii
- i, ii and iii
28. What is the dimension of the copper strips used for the strip earthing?
- 25 mm x 4 mm
- 25 mm x 3 mm
- 30 mm x 4 mm
- 30 mm x 3 mm
29. In the earthed neutral system, the magnitude of transient voltage is
- Very small
- Very high
30. Risk of Broken neutral is maximum in _________ earthing system.