Circuit breakers are essential components that protect against potential hazards, ensuring people’s and property’s safety. Circuit breakers are critical for providing safe and reliable operation of electrical systems installed in residential, commercial, and industrial settings. They protect against potential hazards caused by overloads, short circuits, and other abnormal conditions by interrupting the circuit when necessary. There are different categories of circuit breakers employed in power systems. Examples include miniature circuit breakers (MCBs) for residential and commercial settings, molded case circuit breakers (MCCBs) for heavy-duty applications, and vacuum circuit breakers (VCBs) for high-voltage applications. Electrical Engineering Online shares the top 10 MCQ Questions with explanations for your job tests, college/university exams, and for your concept development on fundamentals of Circuit breakers.
Also see: Complete list of Electrical Engineering MCQs Online here
The primary role of a circuit breaker is to
The primary role of a circuit breaker is to:
- Regulate current flow
- Protect electrical equipment
- Generate electricity
- To store electrical energy
Correct answer: 2. Protect electrical equipment
Explanation: The primary function of a circuit breaker is to protect electrical equipment and circuits from overcurrent and short circuits by interrupting the current flow when necessary.
Circuit breakers are used to prevent
Circuit breakers are used to prevent
- Overvoltage
- Short circuits
- Power outages
- Electromagnetic interference
Correct answer: 2. Short circuits
Explanation: Circuit breakers are designed to detect and interrupt excessive current flow, including short circuits, to prevent damage to electrical equipment and potential hazards.
The most popular type of circuit breaker that is most commonly used in residential applications
The most popular type of circuit breaker that is most commonly used in residential applications
- Miniature circuit breaker (MCB)
- Molded case circuit breaker (MCCB)
- Vacuum circuit breaker (VCB)
- Oil circuit breaker (OCB)
Correct answer: 1. Miniature circuit breaker (MCB)
Explanation: MCBs are commonly used in residential applications because of their compact size, ease of installation, and ability to protect against overloads and short circuits.
Which of the below-mentioned is NOT a typical circuit breaker trip unit
Which of the below-mentioned is NOT a typical circuit breaker trip unit
- Thermal
- Magnetic
- Electronic
- Oil
Correct answer: 4. Oil
Explanation: Oil circuit breakers use oil as an arc-quenching medium and do not have a trip unit. Trip units are typically found in circuit breakers that use different technologies, such as thermal, magnetic, or electronic.
The function of a thermal trip unit in a circuit breaker
The function of a thermal trip unit in a circuit breaker
- To control the flow of current
- To regulate voltage levels
- To protect against overcurrents
- To prevent short circuits
Correct answer: 3. To protect against overcurrents
Explanation: A thermal trip unit in a circuit breaker is designed to detect excessive heat caused by prolonged overcurrent conditions. It protects against overload by tripping the circuit breaker when the temperature rises beyond a specified threshold.
Which type of circuit breaker provides the fastest response time
Which type of circuit breaker provides the fastest response time
- Thermal circuit breaker
- Magnetic circuit breaker
- Electronic circuit breaker
- All provide similar response times
Correct answer: 2. Magnetic circuit breaker
Explanation: Magnetic circuit breakers use magnetic fields to detect and trip in response to short-circuit currents. They offer rapid response times to protect against high fault currents.
What is the function of a ground fault circuit interrupter (GFCI)
What is the function of a ground fault circuit interrupter (GFCI)
- To regulate voltage fluctuations
- To control the current flow
- To prevent power outages
- To protect against electric shock
Correct answer: 4. To protect against electric shock
Explanation: GFCIs are specialized circuit breakers that monitor the flow of electric current between the phase and neutral wires. They quickly trip the circuit when an imbalance is detected, protecting against electric shock.
What is the typical voltage rating for a low-voltage circuit breaker
What is the typical voltage rating for a low-voltage circuit breaker
- 120 volts
- 600 volts or below
- 1,000 volts
- 10,000 volts
Correct answer: 2. 600 volts or below
Explanation: Low-voltage circuit breakers are designed to handle voltages up to 600 volts. They are commonly used in residential.
The type of circuit breaker is commonly used in high-voltage applications, such as power transmission.
The type of circuit breaker is commonly used in high-voltage applications, such as power transmission?
- Miniature circuit breaker (MCB)
- Molded case circuit breaker (MCCB)
- Vacuum circuit breaker (VCB)
- Oil circuit breaker (OCB)
Correct answer: 3. Vacuum circuit breaker (VCB)
Explanation: Vacuum circuit breakers are commonly used in high-voltage applications due to their ability to extinguish arcs in a vacuum, making them suitable for interrupting high currents.
What is the main advantage of a gas-insulated circuit breaker (GCB)
What is the main advantage of a gas-insulated circuit breaker (GCB)
- Compact size
- Low cost
- High interrupting capacity
- Easy maintenance
Correct answer: 3. High interrupting capacity
Explanation: Gas-insulated circuit breakers provide high interrupting capacity. It employs insulating gas (such as sulfur hexafluoride -SF6), allowing for compact design and efficient interruption of high currents.
The circuit breaker that is commonly used in industrial applications, such as factories and power plants
The circuit breaker that is commonly used in industrial applications, such as factories and power plants
- Miniature circuit breaker (MCB)
- Molded case circuit breaker (MCCB)
- Vacuum circuit breaker (VCB)
- Oil circuit breaker (OCB)
Correct answer: 2. Molded case circuit breaker (MCCB)
Explanation: MCCBs are commonly used in industrial applications due to their higher current ratings, robust construction, and ability to protect against overloads and short circuits.
What is the typical operating principle of an electronic circuit breaker
What is the typical operating principle of an electronic circuit breaker
- Electromagnetic induction
- Arc quenching
- Electronic sensing and control
- Thermal expansion
Correct answer: 3. Electronic sensing and control
Explanation: Electronic circuit breakers use electronic components, such as sensors and microprocessors, to detect overcurrent conditions and govern the opening and closing of circuit breaker contacts.
The role of a time-delay feature in some circuit breakers is
The role of a time-delay feature in some circuit breakers is
- To ensure immediate tripping for all overcurrents
- To allow for temporary overcurrents without tripping
- To protect short circuits only
- To prevent damage from voltage surges
Correct answer: 2. To allow for temporary overcurrents without tripping
Explanation: Time-delay features in circuit breakers are designed to tolerate temporary overcurrent conditions, such as inrush currents during motor starting, without unnecessary tripping.
The role of a shunt trip accessory in a circuit breaker is
The role of a shunt trip accessory in a circuit breaker is
- To provide the remote-tripping capability
- To increase the interrupting capacity
- To monitor power quality parameters
- To improve the thermal performance
Correct answer: 1. To provide remote tripping capability
Explanation: A shunt trip accessory is an additional feature in a circuit breaker that allows for remote tripping of the circuit breaker by applying an external voltage or signal.
The feature of a circuit breaker determines its ability to interrupt fault currents
The feature of a circuit breaker determines its ability to interrupt fault currents
- Voltage rating
- Current rating
- Trip curve
- Number of poles
Correct answer: 2. Current rating
Explanation: The current rating of a circuit breaker indicates its maximum capability to interrupt fault currents and is an important consideration when selecting a circuit breaker for specific applications.