Free Wiring, Installation and Safety MCQs with Answers

• A. Yes
• B. No

Explanation: Capacitance grading uses layers of different dielectric materials, or sometimes graded insulation, to distribute electric stress more…

• A. Yes
• B. No

Explanation: Natural rubber is latex obtained from the milky sap of tropical rubber trees, mainly Hevea brasiliensis.

• A. Yes
• B. No

Explanation: Polyethylene has good dielectric strength, low dielectric loss and comparatively good resistance to ageing, so the statement that these…

• A. Yes
• B. No

Explanation: Oil-filled cables require regular monitoring for oil pressure, leakage and replenishment, making their maintenance more difficult than…

• A. becomes one-fourth
• B. becomes one-half
• C. becomes double
• D. remains unchanged

Explanation: Cable capacitance is proportional to its length because doubling the length doubles the area over which capacitive coupling occurs.

• A. prevent the moisture from entering the cable
• B. provide enough strength
• C. provide proper insulation
• D. none of the above

Explanation: The outer sheath primarily prevents moisture and other contaminants from entering the cable.

• A. inter-sheaths
• B. insulating materials with different dielectric constants
• C. both (A) and (B)
• D. none of the above

Explanation: Inter-sheaths and graded insulation using materials with different permittivities redistribute the electric field and reduce peak stress…

• A. minimize the stress
• B. avoid the requirement of good insulation
• C. provide proper stress distribution
• D. none of the above

Explanation: Inter-sheaths divide the insulation into sections and control the potential distribution, thereby making the electric stress more uniform.

• A. lags the voltage by 90°
• B. leads the voltage by 90°
• C. lags the voltage by 180°
• D. leads the voltage by 180°

Explanation: A cable behaves capacitively, and current in a capacitor leads its voltage by 90 degrees. Therefore, the charging current leads the voltage.

• A. insulation may melt due to higher temperature
• B. skin effect dominates on the conductor
• C. of corona loss between conductor and sheath material
• D. there is a danger of breakdown of insulation due to the presence of voids

Explanation: Voids in solid insulation can ionise under high electric stress, producing partial discharges that gradually damage the insulation and…

• A. one half
• B. double
• C. four times
• D. none of the above

Explanation: Cable capacitance is directly proportional to the insulation permittivity, with geometry unchanged.

• A. 11 kV
• B. 33 kV
• C. 66 kV
• D. 132 kV

Explanation: Pressure cables use pressurised insulating material to suppress ionisation and void formation, but their construction becomes impractical…

• A. between 2 and 3
• B. between 5 and 6
• C. between 8 and 10
• D. between 12 and 14

Explanation: Rubber has a relatively low relative permittivity, typically about 2 to 3, unlike materials such as mica or porcelain whose values are…

• A. steel tape
• B. galvanised steel wire
• C. any of the above
• D. none of the above

Explanation: Cable armour is commonly made from steel tape or galvanised steel wire, depending on the cable construction and required mechanical…

• A. unsheathed cables
• B. armoured
• C. PVC sheathed cables
• D. all of the above

Explanation: Conduits provide mechanical protection and enclosure for unsheathed wires or cables, which otherwise lack a protective outer sheath.

• A. polyvinyl chloride
• B. post varnish conductor
• C. pressed and varnished cloth
• D. positive voltage conductor
• E. none of the above

Explanation: PVC is the standard abbreviation for polyvinyl chloride, a thermoplastic widely used as cable insulation and sheathing because it is…

• A. composite
• B. porous
• C. homogeneous
• D. hygroscopic

Explanation: Capacitance grading uses layers of different permittivities arranged so the electric stress is distributed more uniformly across the…

• A. 5 ohms
• B. 20 ohms
• C. 50 ohms
• D. 100 ohms

Explanation: The surge impedance of a power cable is low compared with that of an overhead line because the cable has high capacitance and low…

• A. armour
• B. bedding
• C. conductor surface
• D. lead sheath

Explanation: For a cable, dielectric stress is greatest at the conductor surface and decreases outward, reaching its minimum at the outer conducting…

• A. the resistance of the conductor
• B. the inductance of conductors
• C. the capacitances of insulated conductors
• D. all above parameters

Explanation: A cable fault changes the capacitance distribution between its insulated conductors, so comparing their capacitances helps locate the…