Fuses and Isolators — MCQs – EE

1. The primary function of a fuse is to:
(A) Protect electrical circuits from overcurrent and short-circuit faults
(B) Control voltage
(C) Regulate frequency
(D) Convert AC to DC

2. A fuse works on the principle of:
(A) Heating effect of electric current
(B) Magnetic effect of current
(C) Chemical effect of current
(D) Inductive effect of current

3. The material used for the fuse element should have:
(A) Low melting point and high conductivity
(B) High melting point
(C) High resistivity
(D) Magnetic properties

4. Which of the following materials is commonly used as a fuse element?
(A) Tin-lead alloy
(B) Silver
(C) Copper
(D) All of the above

5. The fuse element is always connected in:
(A) Series with the circuit
(B) Parallel with the circuit
(C) Across the load
(D) To the ground

6. When current exceeds the rated value, the fuse:
(A) Melts and opens the circuit
(B) Reduces resistance
(C) Starts oscillating
(D) Increases current

7. The fusing current of a fuse depends on:
(A) Material, cross-sectional area, and length
(B) Voltage only
(C) Frequency only
(D) Ambient temperature only

8. A low current rating fuse should have:
(A) Thin wire and small cross-sectional area
(B) Thick wire
(C) Long wire
(D) High resistance

9. The function of a fuse carrier is to:
(A) Hold the fuse element and enable safe replacement
(B) Conduct current directly
(C) Measure voltage
(D) Reduce arc length

10. The main disadvantage of a rewirable fuse is:
(A) Possibility of using wrong wire during replacement
(B) High cost
(C) Slow operation
(D) Poor sensitivity

11. HRC (High Rupturing Capacity) fuses are designed to:
(A) Interrupt high fault currents safely without explosion
(B) Operate at low currents only
(C) Reduce voltage drop
(D) Control power factor

12. The material inside an HRC fuse is usually:
(A) Quartz powder or silica sand
(B) Oil
(C) Air
(D) Mica

13. The arc in an HRC fuse is extinguished by:
(A) The formation of non-conducting gases and cooling by filler material
(B) Increasing current
(C) Reducing voltage
(D) Magnetic fields

14. HRC fuses are mainly used in:
(A) High voltage circuits
(B) Domestic low-voltage circuits
(C) Communication circuits
(D) DC batteries

15. The breaking capacity of a fuse refers to:
(A) The maximum fault current it can safely interrupt
(B) The maximum operating voltage
(C) The minimum current rating
(D) The load current

16. A fuse should have:
(A) Inverse time-current characteristic
(B) Linear time-current characteristic
(C) Constant operating time
(D) Fixed delay

17. Which of the following is NOT a type of fuse?
(A) Cartridge fuse
(B) HRC fuse
(C) Isolator fuse
(D) Rewirable fuse

18. An isolator is used to:
(A) Provide safe disconnection of a circuit when there is no current flow
(B) Interrupt current during fault
(C) Measure voltage
(D) Control frequency

19. Isolators are generally operated:
(A) When the circuit is completely de-energized
(B) During fault conditions
(C) During short circuits
(D) Under full load

20. Isolators are also known as:
(A) Disconnectors
(B) Regulators
(C) Reactors
(D) Compensators

21. Isolators are used in conjunction with:
(A) Circuit breakers
(B) Transformers
(C) Motors
(D) Capacitors

22. The isolator provides:
(A) Visible isolation for maintenance work
(B) Automatic fault clearance
(C) Protection against overcurrent
(D) Voltage regulation

23. The main difference between a circuit breaker and an isolator is:
(A) Isolator cannot interrupt load current
(B) Both operate under the same condition
(C) Isolator provides faster tripping
(D) Circuit breaker has no protective function

24. Isolators are generally installed:
(A) On both sides of a circuit breaker
(B) On only one side of the line
(C) Near the load
(D) Across the generator terminals

25. The isolator is operated:
(A) After the circuit breaker is opened
(B) Before opening the breaker
(C) Simultaneously with the breaker
(D) Automatically

26. A load break switch differs from an isolator because it:
(A) Can open and close a circuit under small load conditions
(B) Cannot interrupt current at all
(C) Is manually operated only
(D) Has no arc quenching mechanism

27. Isolators are used in substations to:
(A) Ensure complete de-energization of equipment before maintenance
(B) Increase system voltage
(C) Regulate frequency
(D) Control reactive power

28. The operation of an isolator should always follow:
(A) Circuit breaker tripping
(B) Transformer energization
(C) Motor start
(D) Load switching

29. Isolators are mainly classified as:
(A) Single-break, double-break, and pantograph type
(B) Oil and SF₆ type
(C) Manual and automatic type
(D) Indoor and outdoor circuit breakers

30. The overall purpose of using fuses and isolators is to:
(A) Protect and safely disconnect electrical systems during faults or maintenance
(B) Increase current flow
(C) Improve power factor
(D) Control voltage