Voltage Drop Calculations (NEC Chapter 9) — NEC 2023 Edition

Question 1: What is the minimum NEC recommended voltage for a 230 volt load connected to 240 v source?

• 230 V
• 228 V
• 232 V
• 225 V

Question 2: If a 115 volt load is connected to 120 V source. What is minimum voltage that is supplied to the load as recommended by NEC?

• 114 V.
• 115 V
• 120 V
• 117 V

Question 3: What is the voltage drop of two 10 AWH THHN conductors that supply 16 A, 115 V load located 50 ft from the source?

• 1.92 V
• 0,96
• 2.4 V
• 1.8 V

Question 4: Two 12 AWG THHN conductors are placed to connect 8A, 120 V load to the source which is 100 ft distance. What is maximum voltage drop in conductor?

• 3.2 Volts
• 6.4 Volts
• 1.92 Volts
• 2.4 Volts

NEC Reference: NEC Chapter 9, Table 8 / Informational Note to 215.2(A)

Question 5: A 3 phase 18 KVA, 208 volts load is connected to panel board with 100 ft length of 2AWG THHN copper conductor. What is the approximate voltage drop in the conductor?

• 1.68 volts
• 3.2 Volts
• 2.4 volts
• 3.8 volts

NEC Reference: NEC Chapter 9, Table 8 / Informational Note to 215.2(A)

Question 6: A 12 KVA , 3 phase 480 Volts load should be connected to panel board with a distance of 220 ft. What size conductor is required to prevent the voltage drop from exceeding 3 %?

• 12 AWG
• 10 AWG
• 8 AWG
• 14 AWG

NEC Reference: NEC Chapter 9, Table 8 / Informational Note to 215.2(A)

Question 7: A 4 AWG THHN is used to connect a 480 V 3 phase 35 kVA transformer to panel board. what is the maximum length of conductor that can be used in which the voltage drop doesn't cross 3% ?

• 640 ft
• 320 ft
• 720 ft
• 540 ft

NEC Reference: NEC 14.4

Question 8: What is the maximum voltage drop that is recommended by NEC for both branch and feeder conductors?

• 3 %
• 4 %
• 5 %
• 6 %

NEC Reference: NEC Chapter 9, Table 8 / Informational Note to 215.2(A)

Question 9: What is 3 phase load that can be connected to a 220 ft, 8 THHN, 480 V conductor with out exceeding the NEC recommended voltage drop?

• 40 KVA
• 42 KVA
• 48 KVA
• 53 KVA

NEC Reference: NEC 12.9

Question 10: What is maximum voltage drop in percentage recommended by NEC for branch circuit conductors?

• 3 %
• 5 %
• 2 %
• 4 %

Question 11: The NEC's 3% and 5% voltage drop recommendations are found in Informational Notes. What does that generally mean about their enforceability?

• They are recommendations, not mandatory requirements
• They are mandatory and always enforced
• They apply only to service conductors
• They were removed from the NEC entirely

NEC Reference: NEC Informational Note to 210.19(A) / 215.2(A)

Question 12: Two 8 AWG THHN copper conductors supply a 20 A, 120 V load located 75 ft from the source. Using R = 0.78 ohm/1000 ft for 8 AWG, what is the approximate voltage drop?

• 2.34 volts
• 1.56 volts
• 3.12 volts
• 4.68 volts

NEC Reference: NEC Chapter 9, Table 8

Question 13: A calculated voltage drop of 2.34 volts on a 120-volt circuit represents approximately what percentage voltage drop?

• About 1.95%
• About 5%
• About 10%
• About 0.5%

NEC Reference: NEC Informational Note to 210.19(A)

Question 14: What is "voltage drop," in the context of conductor sizing?

• Loss of voltage along a conductor due to its resistance
• A type of overcurrent protection device
• A required grounding method
• A conduit fill calculation

NEC Reference: NEC Chapter 9

Question 15: Which of the following generally INCREASES voltage drop on a circuit, all else being equal?

• Increasing conductor length
• Increasing conductor size (larger CM area)
• Decreasing load current
• None of these affect voltage drop

NEC Reference: NEC Chapter 9

Question 16: Increasing the conductor size (using a larger AWG/kcmil conductor than the minimum required for ampacity) generally has what effect on voltage drop?

• It decreases voltage drop
• It increases voltage drop
• It has no effect at all
• It always doubles the voltage drop

NEC Reference: NEC Chapter 9

Question 17: What is a common practical consequence of excessive voltage drop on a branch circuit supplying a motor load?

• The motor runs hot, inefficiently, with reduced starting torque
• The motor becomes more efficient
• There is no practical consequence
• The circuit breaker size must be reduced

NEC Reference: NEC Chapter 9 (general design consideration)

Question 18: In the three-phase voltage drop formula VD = 1.732 x K x I x D / CM, what does the constant 1.732 represent?

• The square root of 3, for balanced three-phase systems
• The number of conductors in the circuit
• The power factor of the load
• A safety margin with no mathematical basis

NEC Reference: NEC Chapter 9, Table 8

Question 19: In a single-phase voltage drop calculation using conductor resistance from Table 9, why is the one-way distance generally doubled (multiplied by 2)?

• The circuit includes both the outgoing and returning conductor
• It is just an arbitrary safety factor
• It accounts for three-phase power only
• It has nothing to do with circuit length

NEC Reference: NEC Chapter 9, Table 9

Question 20: In the voltage drop formula, the resistivity constant K is approximately 12.9 for copper. Is the K value for aluminum higher or lower?

• Higher (aluminum has more resistance)
• Lower
• Exactly the same
• Aluminum has no K value

NEC Reference: NEC Chapter 9, Table 8

Question 21: Two 6 AWG THHN copper conductors supply a 30 A, 240 V load located 150 ft from the source. Using R = 0.49 ohm/1000 ft for 6 AWG, what is the approximate voltage drop?

• 4.41 volts
• 2.94 volts
• 5.88 volts
• 3.5 volts

NEC Reference: NEC Chapter 9, Table 8

Question 22: A three-phase, 480V circuit has a calculated voltage drop of 9.6 volts. What percentage voltage drop does this represent?

• 2%
• 5%
• 10%
• 0.2%

NEC Reference: NEC Informational Note to 215.2(A)

Question 23: If a feeder has a 2% voltage drop, what is generally the maximum recommended voltage drop remaining for the branch circuit, to stay within the combined 5% NEC recommendation?

• 3%
• 5%
• 1%
• 8%

NEC Reference: NEC Informational Note to 210.19(A)

Question 24: In the voltage drop formula VD = 1.732 x K x I x D / CM, what does "CM" represent?

• The conductor's circular mil area
• The conduit fill percentage
• The number of current-carrying conductors
• The ambient temperature

NEC Reference: NEC Chapter 9, Table 8

Question 25: True or false: voltage drop calculations become more important as the distance between the source and the load increases.

• True
• False
• Only for three-phase circuits
• Distance has no effect on voltage drop

NEC Reference: NEC Chapter 9

Question 26: A calculated voltage drop of 6 volts on a 120-volt circuit exceeds the 3% branch-circuit recommendation. What is the generally recommended remedy?

• Use a larger conductor to reduce resistance
• Use a smaller conductor
• Increase the circuit breaker size
• Nothing can be done

NEC Reference: NEC Chapter 9 / Informational Note to 210.19(A)

Question 27: A three-phase, 24 kVA load operates at 208 volts. What is the approximate load current?

• About 66.6 amperes
• About 115 amperes
• About 40 amperes
• About 24 amperes

NEC Reference: NEC Chapter 9 (three-phase power formula)

Question 28: For circuits supplying sensitive electronic equipment, why might a design engineer choose to target voltage drop well BELOW the NEC's 3%/5% recommendations?

• Sensitive equipment can be more susceptible to voltage variation
• The NEC requires a stricter limit for electronics
• It has no practical benefit
• It is required only for motors, not electronics

NEC Reference: NEC Informational Note to 210.19(A)

Question 29: True or false: a conductor sized correctly for ampacity is automatically guaranteed to meet the NEC's recommended voltage drop limits.

• False -- they are separate checks
• True -- ampacity sizing always covers voltage drop
• Voltage drop is not a real concern
• Ampacity and voltage drop are the same calculation

NEC Reference: NEC Chapter 9 / 310.14

Question 30: A single-phase, 120V, 12A load is supplied by two 10 AWG THHN conductors (R = 1.2 ohm/1000 ft). What is the maximum one-way distance to keep voltage drop at or under 3% (3.6 volts)?

• 125 ft
• 250 ft
• 62.5 ft
• 100 ft

NEC Reference: NEC Chapter 9, Table 9