MSHA Underground Electrical Safety Certification Mock
Exam
Practice Questions with Answers and Explanations
Question 1. Which statement best reflects safe practice for Ohm's law: voltage in an underground mine?
A. calculate voltage by adding current and resistance
B. calculate voltage as current multiplied by resistance (V = I × R)
C. calculate voltage as current divided by resistance
D. calculate voltage as resistance divided by current
Correct Answer: B. calculate voltage as current multiplied by resistance (V = I × R)
Explanation: The best answer is to calculate voltage as current multiplied by resistance (V = I × R). This is important
because Ohm's law relates voltage, current, and resistance, so V = I × R. The other choices either defeat a protective
measure, misuse equipment, or introduce an avoidable electrical hazard. On an MSHA-style safety question, the preferred
choice is the one that controls the hazard before exposure occurs.
Question 2. A circuit has 120 V applied across a 20-ohm load. What current should an electrician expect?
A. 12 A
B. 2,400 A
C. 20 A
D. 6 A
Correct Answer: D. 6 A
Explanation: Using Ohm's law, current equals voltage divided by resistance. 120 V ÷ 20 Ω equals 6 A. The other values
result from using the wrong operation or ignoring the resistance. A calculated value should still be compared with equipment
ratings and actual field measurements.
Question 3. A supervisor is reviewing work practices related to Ohm's law: voltage. Which action
requires immediate correction?
A. Stop and reassess if conditions change while addressing Ohm's law: voltage.
B. calculate voltage as current multiplied by resistance (V = I × R)
C. calculate voltage as current divided by resistance
D. Verify the condition before work and document any defect related to Ohm's law: voltage.
Correct Answer: C. calculate voltage as current divided by resistance
Explanation: The action requiring correction is to calculate voltage as current divided by resistance. A safer approach is to
calculate voltage as current multiplied by resistance (V = I × R). That approach matters because Ohm's law relates voltage,
current, and resistance, so V = I × R. Unsafe shortcuts around electrical protection can turn an equipment problem into a
serious worker-exposure or ignition event.
Page 1
,Question 4. Why is the recommended practice for Ohm's law: voltage important in underground
electrical safety?
A. because any conductor below high voltage is incapable of causing serious injury
B. because electrical hazards are eliminated whenever a machine stops moving
C. Because Ohm's law relates voltage, current, and resistance, so V = I × R.
D. because production continuity is more important than protective-device operation
Correct Answer: C. Because Ohm's law relates voltage, current, and resistance, so V = I × R.
Explanation: The controlling reason is that Ohm's law relates voltage, current, and resistance, so V = I × R. Accordingly, the
worker should calculate voltage as current multiplied by resistance (V = I × R). The other choices rely on unsafe assumptions
about voltage, machine status, or production needs. Effective mine electrical safety depends on engineered protection,
positive verification, and disciplined work practices.
Question 5. Which statement best reflects safe practice for Ohm's law: current in an underground mine?
A. calculate current as voltage multiplied by resistance
B. calculate current as voltage divided by resistance (I = V ÷ R)
C. calculate current as resistance divided by voltage
D. calculate current by adding voltage and resistance
Correct Answer: B. calculate current as voltage divided by resistance (I = V ÷ R)
Explanation: The best answer is to calculate current as voltage divided by resistance (I = V ÷ R). This is important because
rearranging Ohm's law gives I = V ÷ R. The other choices either defeat a protective measure, misuse equipment, or introduce
an avoidable electrical hazard. On an MSHA-style safety question, the preferred choice is the one that controls the hazard
before exposure occurs.
Question 6. A 480-V load draws 15 A in a basic single-phase power calculation. What is the apparent
power using P = V × I?
A. 495 W
B. 32 W
C. 7,200 W
D. 465 W
Correct Answer: C. 7,200 W
Explanation: For the basic relationship, power equals voltage multiplied by current. 480 V × 15 A equals 7,200 W. The
distractors come from addition, subtraction, or division rather than multiplication. Actual AC three-phase power calculations
may also require phase and power-factor terms.
Question 7. A supervisor is reviewing work practices related to Ohm's law: current. Which action
requires immediate correction?
A. calculate current as resistance divided by voltage
B. Stop and reassess if conditions change while addressing Ohm's law: current.
C. Verify the condition before work and document any defect related to Ohm's law: current.
D. calculate current as voltage divided by resistance (I = V ÷ R)
Correct Answer: A. calculate current as resistance divided by voltage
Explanation: The action requiring correction is to calculate current as resistance divided by voltage. A safer approach is to
calculate current as voltage divided by resistance (I = V ÷ R). That approach matters because rearranging Ohm's law gives I
= V ÷ R. Unsafe shortcuts around electrical protection can turn an equipment problem into a serious worker-exposure or
ignition event.
Page 2
,Question 8. Why is the recommended practice for Ohm's law: current important in underground
electrical safety?
A. because any conductor below high voltage is incapable of causing serious injury
B. because electrical hazards are eliminated whenever a machine stops moving
C. because production continuity is more important than protective-device operation
D. Because rearranging Ohm's law gives I = V ÷ R.
Correct Answer: D. Because rearranging Ohm's law gives I = V ÷ R.
Explanation: The controlling reason is that rearranging Ohm's law gives I = V ÷ R. Accordingly, the worker should calculate
current as voltage divided by resistance (I = V ÷ R). The other choices rely on unsafe assumptions about voltage, machine
status, or production needs. Effective mine electrical safety depends on engineered protection, positive verification, and
disciplined work practices.
Question 9. Which statement best reflects safe practice for Ohm's law: resistance in an underground
mine?
A. calculate resistance as voltage multiplied by current
B. calculate resistance as voltage divided by current (R = V ÷ I)
C. calculate resistance as current divided by voltage
D. calculate resistance by subtracting current from voltage
Correct Answer: B. calculate resistance as voltage divided by current (R = V ÷ I)
Explanation: The best answer is to calculate resistance as voltage divided by current (R = V ÷ I). This is important because
rearranging Ohm's law gives R = V ÷ I. The other choices either defeat a protective measure, misuse equipment, or introduce
an avoidable electrical hazard. On an MSHA-style safety question, the preferred choice is the one that controls the hazard
before exposure occurs.
Question 10. A 24-V control circuit has a 6-ohm load. What current flows under ideal conditions?
A. 4 A
B. 0.25 A
C. 18 A
D. 144 A
Correct Answer: A. 4 A
Explanation: Ohm's law gives I = V ÷ R. 24 V ÷ 6 Ω equals 4 A. The other answers use incorrect arithmetic relationships.
Unexpected current in the field should prompt a check for wiring, resistance, or supply problems.
Question 11. A supervisor is reviewing work practices related to Ohm's law: resistance. Which action
requires immediate correction?
A. Stop and reassess if conditions change while addressing Ohm's law: resistance.
B. calculate resistance by subtracting current from voltage
C. calculate resistance as voltage divided by current (R = V ÷ I)
D. Verify the condition before work and document any defect related to Ohm's law: resistance.
Correct Answer: B. calculate resistance by subtracting current from voltage
Explanation: The action requiring correction is to calculate resistance by subtracting current from voltage. A safer approach
is to calculate resistance as voltage divided by current (R = V ÷ I). That approach matters because rearranging Ohm's law
gives R = V ÷ I. Unsafe shortcuts around electrical protection can turn an equipment problem into a serious worker-exposure
or ignition event.
Page 3
, Question 12. Why is the recommended practice for Ohm's law: resistance important in underground
electrical safety?
A. Because rearranging Ohm's law gives R = V ÷ I.
B. because production continuity is more important than protective-device operation
C. because electrical hazards are eliminated whenever a machine stops moving
D. because any conductor below high voltage is incapable of causing serious injury
Correct Answer: A. Because rearranging Ohm's law gives R = V ÷ I.
Explanation: The controlling reason is that rearranging Ohm's law gives R = V ÷ I. Accordingly, the worker should calculate
resistance as voltage divided by current (R = V ÷ I). The other choices rely on unsafe assumptions about voltage, machine
status, or production needs. Effective mine electrical safety depends on engineered protection, positive verification, and
disciplined work practices.
Question 13. Which statement best reflects safe practice for electrical power in an underground mine?
A. calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I)
B. calculate power as resistance plus current
C. calculate power as current divided by voltage
D. calculate power as voltage divided by current
Correct Answer: A. calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I)
Explanation: The best answer is to calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I).
This is important because for the basic power relationship used in simple exam problems, watts equal volts multiplied by
amperes. The other choices either defeat a protective measure, misuse equipment, or introduce an avoidable electrical
hazard. On an MSHA-style safety question, the preferred choice is the one that controls the hazard before exposure occurs.
Question 14. A heater draws 10 A from a 240-V source. Using the basic power formula, how much power
is consumed?
A. 2.4 W
B. 250 W
C. 2,400 W
D. 24 W
Correct Answer: C. 2,400 W
Explanation: The basic power formula is P = V × I. 240 V × 10 A equals 2,400 W. The alternative answers do not follow the
voltage-current power relationship. Load and conductor ratings must be evaluated using the actual circuit configuration and
applicable requirements.
Question 15. A supervisor is reviewing work practices related to electrical power. Which action requires
immediate correction?
A. calculate power as voltage divided by current
B. Stop and reassess if conditions change while addressing electrical power.
C. calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I)
D. Verify the condition before work and document any defect related to electrical power.
Correct Answer: A. calculate power as voltage divided by current
Explanation: The action requiring correction is to calculate power as voltage divided by current. A safer approach is to
calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I). That approach matters because for
the basic power relationship used in simple exam problems, watts equal volts multiplied by amperes. Unsafe shortcuts
around electrical protection can turn an equipment problem into a serious worker-exposure or ignition event.
Page 4
Exam
Practice Questions with Answers and Explanations
Question 1. Which statement best reflects safe practice for Ohm's law: voltage in an underground mine?
A. calculate voltage by adding current and resistance
B. calculate voltage as current multiplied by resistance (V = I × R)
C. calculate voltage as current divided by resistance
D. calculate voltage as resistance divided by current
Correct Answer: B. calculate voltage as current multiplied by resistance (V = I × R)
Explanation: The best answer is to calculate voltage as current multiplied by resistance (V = I × R). This is important
because Ohm's law relates voltage, current, and resistance, so V = I × R. The other choices either defeat a protective
measure, misuse equipment, or introduce an avoidable electrical hazard. On an MSHA-style safety question, the preferred
choice is the one that controls the hazard before exposure occurs.
Question 2. A circuit has 120 V applied across a 20-ohm load. What current should an electrician expect?
A. 12 A
B. 2,400 A
C. 20 A
D. 6 A
Correct Answer: D. 6 A
Explanation: Using Ohm's law, current equals voltage divided by resistance. 120 V ÷ 20 Ω equals 6 A. The other values
result from using the wrong operation or ignoring the resistance. A calculated value should still be compared with equipment
ratings and actual field measurements.
Question 3. A supervisor is reviewing work practices related to Ohm's law: voltage. Which action
requires immediate correction?
A. Stop and reassess if conditions change while addressing Ohm's law: voltage.
B. calculate voltage as current multiplied by resistance (V = I × R)
C. calculate voltage as current divided by resistance
D. Verify the condition before work and document any defect related to Ohm's law: voltage.
Correct Answer: C. calculate voltage as current divided by resistance
Explanation: The action requiring correction is to calculate voltage as current divided by resistance. A safer approach is to
calculate voltage as current multiplied by resistance (V = I × R). That approach matters because Ohm's law relates voltage,
current, and resistance, so V = I × R. Unsafe shortcuts around electrical protection can turn an equipment problem into a
serious worker-exposure or ignition event.
Page 1
,Question 4. Why is the recommended practice for Ohm's law: voltage important in underground
electrical safety?
A. because any conductor below high voltage is incapable of causing serious injury
B. because electrical hazards are eliminated whenever a machine stops moving
C. Because Ohm's law relates voltage, current, and resistance, so V = I × R.
D. because production continuity is more important than protective-device operation
Correct Answer: C. Because Ohm's law relates voltage, current, and resistance, so V = I × R.
Explanation: The controlling reason is that Ohm's law relates voltage, current, and resistance, so V = I × R. Accordingly, the
worker should calculate voltage as current multiplied by resistance (V = I × R). The other choices rely on unsafe assumptions
about voltage, machine status, or production needs. Effective mine electrical safety depends on engineered protection,
positive verification, and disciplined work practices.
Question 5. Which statement best reflects safe practice for Ohm's law: current in an underground mine?
A. calculate current as voltage multiplied by resistance
B. calculate current as voltage divided by resistance (I = V ÷ R)
C. calculate current as resistance divided by voltage
D. calculate current by adding voltage and resistance
Correct Answer: B. calculate current as voltage divided by resistance (I = V ÷ R)
Explanation: The best answer is to calculate current as voltage divided by resistance (I = V ÷ R). This is important because
rearranging Ohm's law gives I = V ÷ R. The other choices either defeat a protective measure, misuse equipment, or introduce
an avoidable electrical hazard. On an MSHA-style safety question, the preferred choice is the one that controls the hazard
before exposure occurs.
Question 6. A 480-V load draws 15 A in a basic single-phase power calculation. What is the apparent
power using P = V × I?
A. 495 W
B. 32 W
C. 7,200 W
D. 465 W
Correct Answer: C. 7,200 W
Explanation: For the basic relationship, power equals voltage multiplied by current. 480 V × 15 A equals 7,200 W. The
distractors come from addition, subtraction, or division rather than multiplication. Actual AC three-phase power calculations
may also require phase and power-factor terms.
Question 7. A supervisor is reviewing work practices related to Ohm's law: current. Which action
requires immediate correction?
A. calculate current as resistance divided by voltage
B. Stop and reassess if conditions change while addressing Ohm's law: current.
C. Verify the condition before work and document any defect related to Ohm's law: current.
D. calculate current as voltage divided by resistance (I = V ÷ R)
Correct Answer: A. calculate current as resistance divided by voltage
Explanation: The action requiring correction is to calculate current as resistance divided by voltage. A safer approach is to
calculate current as voltage divided by resistance (I = V ÷ R). That approach matters because rearranging Ohm's law gives I
= V ÷ R. Unsafe shortcuts around electrical protection can turn an equipment problem into a serious worker-exposure or
ignition event.
Page 2
,Question 8. Why is the recommended practice for Ohm's law: current important in underground
electrical safety?
A. because any conductor below high voltage is incapable of causing serious injury
B. because electrical hazards are eliminated whenever a machine stops moving
C. because production continuity is more important than protective-device operation
D. Because rearranging Ohm's law gives I = V ÷ R.
Correct Answer: D. Because rearranging Ohm's law gives I = V ÷ R.
Explanation: The controlling reason is that rearranging Ohm's law gives I = V ÷ R. Accordingly, the worker should calculate
current as voltage divided by resistance (I = V ÷ R). The other choices rely on unsafe assumptions about voltage, machine
status, or production needs. Effective mine electrical safety depends on engineered protection, positive verification, and
disciplined work practices.
Question 9. Which statement best reflects safe practice for Ohm's law: resistance in an underground
mine?
A. calculate resistance as voltage multiplied by current
B. calculate resistance as voltage divided by current (R = V ÷ I)
C. calculate resistance as current divided by voltage
D. calculate resistance by subtracting current from voltage
Correct Answer: B. calculate resistance as voltage divided by current (R = V ÷ I)
Explanation: The best answer is to calculate resistance as voltage divided by current (R = V ÷ I). This is important because
rearranging Ohm's law gives R = V ÷ I. The other choices either defeat a protective measure, misuse equipment, or introduce
an avoidable electrical hazard. On an MSHA-style safety question, the preferred choice is the one that controls the hazard
before exposure occurs.
Question 10. A 24-V control circuit has a 6-ohm load. What current flows under ideal conditions?
A. 4 A
B. 0.25 A
C. 18 A
D. 144 A
Correct Answer: A. 4 A
Explanation: Ohm's law gives I = V ÷ R. 24 V ÷ 6 Ω equals 4 A. The other answers use incorrect arithmetic relationships.
Unexpected current in the field should prompt a check for wiring, resistance, or supply problems.
Question 11. A supervisor is reviewing work practices related to Ohm's law: resistance. Which action
requires immediate correction?
A. Stop and reassess if conditions change while addressing Ohm's law: resistance.
B. calculate resistance by subtracting current from voltage
C. calculate resistance as voltage divided by current (R = V ÷ I)
D. Verify the condition before work and document any defect related to Ohm's law: resistance.
Correct Answer: B. calculate resistance by subtracting current from voltage
Explanation: The action requiring correction is to calculate resistance by subtracting current from voltage. A safer approach
is to calculate resistance as voltage divided by current (R = V ÷ I). That approach matters because rearranging Ohm's law
gives R = V ÷ I. Unsafe shortcuts around electrical protection can turn an equipment problem into a serious worker-exposure
or ignition event.
Page 3
, Question 12. Why is the recommended practice for Ohm's law: resistance important in underground
electrical safety?
A. Because rearranging Ohm's law gives R = V ÷ I.
B. because production continuity is more important than protective-device operation
C. because electrical hazards are eliminated whenever a machine stops moving
D. because any conductor below high voltage is incapable of causing serious injury
Correct Answer: A. Because rearranging Ohm's law gives R = V ÷ I.
Explanation: The controlling reason is that rearranging Ohm's law gives R = V ÷ I. Accordingly, the worker should calculate
resistance as voltage divided by current (R = V ÷ I). The other choices rely on unsafe assumptions about voltage, machine
status, or production needs. Effective mine electrical safety depends on engineered protection, positive verification, and
disciplined work practices.
Question 13. Which statement best reflects safe practice for electrical power in an underground mine?
A. calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I)
B. calculate power as resistance plus current
C. calculate power as current divided by voltage
D. calculate power as voltage divided by current
Correct Answer: A. calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I)
Explanation: The best answer is to calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I).
This is important because for the basic power relationship used in simple exam problems, watts equal volts multiplied by
amperes. The other choices either defeat a protective measure, misuse equipment, or introduce an avoidable electrical
hazard. On an MSHA-style safety question, the preferred choice is the one that controls the hazard before exposure occurs.
Question 14. A heater draws 10 A from a 240-V source. Using the basic power formula, how much power
is consumed?
A. 2.4 W
B. 250 W
C. 2,400 W
D. 24 W
Correct Answer: C. 2,400 W
Explanation: The basic power formula is P = V × I. 240 V × 10 A equals 2,400 W. The alternative answers do not follow the
voltage-current power relationship. Load and conductor ratings must be evaluated using the actual circuit configuration and
applicable requirements.
Question 15. A supervisor is reviewing work practices related to electrical power. Which action requires
immediate correction?
A. calculate power as voltage divided by current
B. Stop and reassess if conditions change while addressing electrical power.
C. calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I)
D. Verify the condition before work and document any defect related to electrical power.
Correct Answer: A. calculate power as voltage divided by current
Explanation: The action requiring correction is to calculate power as voltage divided by current. A safer approach is to
calculate single-phase DC-equivalent power as voltage multiplied by current (P = V × I). That approach matters because for
the basic power relationship used in simple exam problems, watts equal volts multiplied by amperes. Unsafe shortcuts
around electrical protection can turn an equipment problem into a serious worker-exposure or ignition event.
Page 4
