Free Wiring, Installation and Safety MCQs with Answers

• A. 500 ohms
• B. 1000 ohms
• C. 1500 ohms
• D. 2000 ohms

Explanation: For basic shock calculations, the human body is commonly approximated by a resistance of about 1,000 ohms, although actual resistance…

• A. burning
• B. arcing
• C. melting
• D. none of the above

Explanation: A fuse element is designed to heat up under excessive current until it reaches its melting point and opens the circuit.

• A. no ageing effect
• B. high speed of operation
• C. high rupturing capacity
• D. all of the above

Explanation: An H.R.C. fuse has a sealed element that avoids ageing, operates quickly, and can safely interrupt very large fault currents.

• A. to operate the relay of circuit breaker
• B. as a substitute for circuit breaker
• C. always independent of the position of circuit breaker
• D. generally on both sides of a circuit breaker

Explanation: An isolator provides visible disconnection for maintenance and is not intended to interrupt fault current like a circuit breaker.

• A. 20 A
• B. 50 A
• C. 100 A
• D. 200 A

Explanation: Fuse protection is commonly used for lower current ratings, while circuit breakers are preferred above about 100 A because they are more…

• A. low currents circuits
• B. low voltages circuits
• C. high voltages and large currents circuits
• D. all circuits

Explanation: Oil switches use insulating oil to provide arc extinction, making them suitable for switching high voltages and large currents.

• A. overload
• B. short-circuit and overload
• C. open circuit, short-circuit and overload
• D. none of the above

Explanation: A fuse opens the motor circuit when excessive current flows, covering short-circuit current and sufficiently sustained overload current.

• A. Photoelectric effect
• B. Electrostatic effect
• C. Heating effect
• D. Magnetic effect

Explanation: Current produces heat according to the Joule-heating relation, and the fuse element is chosen to melt when this heating exceeds its safe…

• A. current
• B. voltage
• C. VAR
• D. kVA

Explanation: A fuse rating specifies the maximum continuous current it can carry without melting under stated conditions.

• A. low melting point and high specific resistance
• B. low melting point and -low specific resistance
• C. high melting point and low specific resistance
• D. low melting point and any specific resistance

Explanation: A fuse element should melt at the required fault current, so it needs a low melting point; high resistivity produces greater heating for a…

• A. in series with circuit
• B. in parallel with circuit
• C. either in series or in parallel with circuit
• D. none of the above

Explanation: The fuse must carry the circuit current and interrupt that same current when it becomes excessive, so it is placed in series with the…

• A. neutral wire
• B. negative of D.C. circuit
• C. positive of D.C. circuit
• D. phase dine

Explanation: A fuse must be placed in the live or phase conductor so that blowing it disconnects the appliance from the supply.

• A. interrupting an electrical circuit
• B. switching an electrical circuit 111.
• C. switching and controlling an electrical circuit
• D. switching, controlling and protecting the electrical circuit and equipment

Explanation: Switchgear is a collective term for equipment that switches, controls, and protects electrical circuits and connected apparatus.

• A. Radiation
• B. Convection
• C. Conduction
• D. All of the above

Explanation: The fuse element transfers most of its generated heat to the surrounding filler and fuse body by conduction, which then carries it away.

• A. overload
• B. reverse current
• C. open-circuits
• D. short-circuits

Explanation: An H.R.C. fuse has a high rupturing capacity, so its enclosed fuse element and filling can safely interrupt very large fault currents.

• A. Rewireable fuse
• B. Isolator
• C. Oil circuit breaker
• D. Air break circuit breaker
• E. None of the above

Explanation: A rewireable fuse is the simplest and least costly low-voltage overcurrent device, since its fuse wire can be replaced after operation.

• A. motors
• B. power outlet circuits
• C. fluorescent lamps
• D. light circuits

Explanation: Delay or time-delay fuses tolerate the brief high inrush current drawn when a motor starts, while still operating during a sustained…

• A. 2
• B. 4
• C. 6
• D. 10

Explanation: A grounding conductor must have sufficient cross-sectional area to carry fault current safely without overheating; the stated minimum in…

• A. Inverse time trip
• B. Time-delay trip
• C. Shunt trip
• D. None of the above
• E. All of the above

Explanation: A shunt trip releases a circuit breaker when an external control voltage is applied, allowing it to be operated remotely.

• A. construct insulated cabins
• B. insulate the machinery
• C. ground the framework
• D. humidify the surroundings

Explanation: Connecting the machinery framework to earth provides a path for accumulated static charge to drain safely.