Free Wiring, Installation and Safety MCQs with Answers

• A. oil filled
• B. S.L. type
• C. belted
• D. armoured

Explanation: For voltages above about 66 kV, oil-filled cables are commonly used because the oil improves insulation and helps remove heat.

• A. 200 V
• B. 500 V
• C. 700 V
• D. 1000 V

Explanation: Low-tension cable classification generally covers voltages up to 1,000 V.

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

Explanation: In the conventional cable classification, high-tension cables are used up to 11 kV; higher ranges are classified as super-tension or…

• A. 5 kV/mm
• B. 15 kV/mm
• C. 30 kV/mm
• D. 200 kV/mm

Explanation: Rubber has a dielectric strength of approximately 30 kV/mm, meaning a 1 mm layer can withstand about 30 kV before electrical breakdown.

• A. insulation layer
• B. sheath
• C. armour
• D. conductor surface

Explanation: The radial electric stress in a cable is greatest at the conductor surface because stress decreases as the distance from the conductor…

• A. blue
• B. black
• C. brown
• D. none of the above

Explanation: Under the modern harmonized cable colour code, the neutral conductor is identified by blue insulation.

• A. be acid proof
• B. be non-inflammable
• C. be non-hygroscopic
• D. have all above properties

Explanation: Good cable insulation should resist chemical attack, absorb little moisture, and not readily support combustion.

• A. absence of harmonics
• B. non-existence of any stability limit
• C. smaller dielectric loss
• D. absence of ripples
• E. none of the above

Explanation: A DC cable has no alternating electric field and therefore does not suffer AC dielectric loss; it also avoids AC charging-current effects.

• A. hessian cloth
• B. jute
• C. any of the above
• D. none of the above

Explanation: Cable bedding is commonly made from fibrous materials such as jute or hessian cloth, placed over the metallic sheath before armouring.

• A. earthing connection
• B. bedding
• C. armouring
• D. none of the above

Explanation: Bedding is placed immediately over the metallic sheath to protect it from mechanical damage by the armour.

• A. varnished cambric
• B. vulcanised rubber
• C. impregnated paper
• D. none of the above

Explanation: Empire tape is varnished cambric, a flexible insulating tape used in electrical insulation. It is not ordinary rubber or impregnated paper.

• A. Bedding
• B. Sheath
• C. Armouring
• D. None of the above

Explanation: Armouring, usually made from steel wires or strips, provides the cable with mechanical protection against impact and pulling forces.

• A. low cost
• B. high dielectric strength
• C. high mechanical strength
• D. all of the above

Explanation: A practical cable insulator should be economical, withstand high electric stress, and resist mechanical damage.

• A. reactive power
• B. power factor
• C. voltage
• D. current carrying capacity

Explanation: Insulation thickness is primarily determined by the voltage stress that the insulation must withstand.

• A. Varnished cambric
• B. Rubber
• C. Paper
• D. Any of the above

Explanation: Varnished cambric, rubber, and impregnated paper have all been used as cable-insulation materials.

• A. 4 mA
• B. 9 mA
• C. 15 mA
• D. 25 mA

Explanation: About 9 mA is commonly taken as the maximum current a person can tolerate for several seconds without severe physiological effects.

• A. current
• B. voltage
• C. duration of contact
• D. all of the above

Explanation: Shock severity is governed mainly by the current through the body, while voltage determines the current that can flow and contact duration…

• A. Television set
• B. Toaster
• C. Vacuum cleaner
• D. Washing machine

Explanation: A toaster commonly consumes about 1,000 to 2,000 W, more than a television, vacuum cleaner, or washing machine in this comparison.

• A. Vacuum cleaner
• B. Television
• C. Hair dryer
• D. Electric shaver

Explanation: An electric shaver usually has a small motor and typically consumes only a few watts, much less than a television, vacuum cleaner, or hair…

• A. Suppressing emissions
• B. Reducing the efficiency of the coupling path
• C. Reducing the susceptibility of the receptor
• D. All of these

Explanation: EMI can be reduced at any of its three stages: suppress the emission source, weaken the coupling path, or make the receiving circuit less…