All Free Electrical Engineering MCQs with Answers

• A. only for the safety of the equipment
• B. only for the safety of the operating personnel
• C. both (A) and (B)
• D. none of the above

Explanation: Grounding protects equipment by limiting dangerous voltages and enables protective devices to clear faults, while also reducing shock risk…

• A. depth of the electrode
• B. moisture
• C. Nacl
• D. all the above

Explanation: Soil resistance varies with electrode depth, moisture content, and dissolved salts such as sodium chloride.

• A. to provide as low resistance possible to the ground
• B. to provide as high resistance possible to the ground
• C. to provide flow of positive, negative and zero sequence currents
• D. none of the above

Explanation: Earthing provides a low-resistance path for fault current to flow safely into the ground, allowing protective devices to operate quickly.

• A. to provide low impedance
• B. to discharge the charging capacitance to ground
• C. protection for operating personnel
• D. both (B) and (C)

Explanation: An isolated EHV apparatus may retain charge on its capacitance even after disconnection.

• A. increase
• B. decrease
• C. does not affect
• D. none of the above

Explanation: Moisture increases the soil's conductivity by providing ions for current flow, so the earth resistance decreases.

• A. voltage potential at the earth mat increases due to grounding
• B. voltage potential at the earth mat decreases due to grounding
• C. voltage potential at the earth mat remains zero irrespective of fault
• D. none of the above

Explanation: During an earth fault, fault current flows through the grounding conductor and earth mat, producing a voltage rise relative to remote…

• A. grounding resistance should be as low as possible
• B. grounding resistance should be as high as possible
• C. grounding resistance should be always zero
• D. none of the above

Explanation: Low grounding resistance keeps fault current high enough to operate protective devices and limits the voltage rise of exposed metalwork.

• 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.