NEBOSH Certificate in Electrical Safety
Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of an earth
(ground) connection in an electrical system?
A) To increase current flow
B) To prevent voltage drops
C) To provide a path for fault currents to protect users and
equipment
D) To improve efficiency
C) To provide a path for fault currents to protect users and equipment
Rationale: The earth connection allows fault currents to flow safely to
the ground, reducing the risk of electric shock and preventing damage
to equipment. It is a fundamental safety measure in electrical systems.
2. What is the main hazard associated with overhead power lines?
A) Fire from electrical surges
, B) Electrocution from contact or arcing
C) Water contamination
D) Mechanical injury from vibrations
B) Electrocution from contact or arcing
Rationale: Overhead lines carry high voltage. Contact, even indirectly,
can lead to severe electrical shock or fatal electrocution. Arcing can
occur without direct contact, creating additional risk.
3. Residual Current Devices (RCDs) are designed to:
A) Stop overcurrent conditions
B) Detect and disconnect the supply when leakage current occurs
C) Control voltage fluctuations
D) Increase system efficiency
B) Detect and disconnect the supply when leakage current occurs
Rationale: RCDs monitor current imbalance between live conductors
and disconnect the circuit quickly if a leakage current (often through a
human body) is detected, preventing electric shock.
4. Which of the following types of insulation failure is most likely to
result in a fire?
A) Conductor breakage
B) Insulation overheating
, C) Moisture ingress
D) Short-term voltage spikes
B) Insulation overheating
Rationale: Overheating damages insulation, which can ignite
surrounding materials, leading to fire. While moisture or voltage
spikes can cause shocks, sustained overheating is the primary fire risk.
5. What is the maximum safe working voltage for a low-voltage
electrical system under NEBOSH definitions?
A) 50 V AC
B) 230 V AC
C) 1000 V AC
D) 5000 V AC
C) 1000 V AC
Rationale: Low-voltage systems are defined as up to 1000 V AC or
1500 V DC. Voltages above this threshold are considered high-voltage
and require more stringent safety measures.
6. Which type of PPE is most appropriate for protection against
electrical shock during live work?
A) Safety glasses
B) Insulating gloves
, C) Hard hats
D) Steel-toe boots
B) Insulating gloves
Rationale: Insulating gloves provide a barrier between the worker and
live conductors, reducing the risk of electrical shock. Other PPE may
protect against physical injuries but not electric current.
7. Which of the following is the safest method for verifying the
absence of voltage?
A) Visual inspection of cables
B) Using a voltage tester after isolating the circuit
C) Measuring current flow with a clamp meter
D) Touching the conductor with a dry hand
B) Using a voltage tester after isolating the circuit
Rationale: Always isolate the circuit and use a correctly rated voltage
tester to verify de-energization. Visual inspection or physical contact is
unsafe and unreliable.
8. What is the primary function of a circuit breaker in electrical
systems?
A) To reduce electrical resistance
B) To limit current during normal operation
Exam Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of an earth
(ground) connection in an electrical system?
A) To increase current flow
B) To prevent voltage drops
C) To provide a path for fault currents to protect users and
equipment
D) To improve efficiency
C) To provide a path for fault currents to protect users and equipment
Rationale: The earth connection allows fault currents to flow safely to
the ground, reducing the risk of electric shock and preventing damage
to equipment. It is a fundamental safety measure in electrical systems.
2. What is the main hazard associated with overhead power lines?
A) Fire from electrical surges
, B) Electrocution from contact or arcing
C) Water contamination
D) Mechanical injury from vibrations
B) Electrocution from contact or arcing
Rationale: Overhead lines carry high voltage. Contact, even indirectly,
can lead to severe electrical shock or fatal electrocution. Arcing can
occur without direct contact, creating additional risk.
3. Residual Current Devices (RCDs) are designed to:
A) Stop overcurrent conditions
B) Detect and disconnect the supply when leakage current occurs
C) Control voltage fluctuations
D) Increase system efficiency
B) Detect and disconnect the supply when leakage current occurs
Rationale: RCDs monitor current imbalance between live conductors
and disconnect the circuit quickly if a leakage current (often through a
human body) is detected, preventing electric shock.
4. Which of the following types of insulation failure is most likely to
result in a fire?
A) Conductor breakage
B) Insulation overheating
, C) Moisture ingress
D) Short-term voltage spikes
B) Insulation overheating
Rationale: Overheating damages insulation, which can ignite
surrounding materials, leading to fire. While moisture or voltage
spikes can cause shocks, sustained overheating is the primary fire risk.
5. What is the maximum safe working voltage for a low-voltage
electrical system under NEBOSH definitions?
A) 50 V AC
B) 230 V AC
C) 1000 V AC
D) 5000 V AC
C) 1000 V AC
Rationale: Low-voltage systems are defined as up to 1000 V AC or
1500 V DC. Voltages above this threshold are considered high-voltage
and require more stringent safety measures.
6. Which type of PPE is most appropriate for protection against
electrical shock during live work?
A) Safety glasses
B) Insulating gloves
, C) Hard hats
D) Steel-toe boots
B) Insulating gloves
Rationale: Insulating gloves provide a barrier between the worker and
live conductors, reducing the risk of electrical shock. Other PPE may
protect against physical injuries but not electric current.
7. Which of the following is the safest method for verifying the
absence of voltage?
A) Visual inspection of cables
B) Using a voltage tester after isolating the circuit
C) Measuring current flow with a clamp meter
D) Touching the conductor with a dry hand
B) Using a voltage tester after isolating the circuit
Rationale: Always isolate the circuit and use a correctly rated voltage
tester to verify de-energization. Visual inspection or physical contact is
unsafe and unreliable.
8. What is the primary function of a circuit breaker in electrical
systems?
A) To reduce electrical resistance
B) To limit current during normal operation
