NEC Code Test — Questions and Answers
Question 1: A cord-and-plug-attached appliance is linked to a 25 ampere branch circuit. What is the maximum ampere rating that the appliance can handle?
- 20 amperes (Correct answer)
- 22.5 amperes
- 18.5 amperes
- 25 amperes
Correct answer: 20 amperes
According to NEC 210.23(A)(2), for branch circuits supplying two or more receptacles or outlets, the total cord-and-plug-connected load must not exceed 80% of the branch-circuit ampere rating. For a 25-ampere circuit, 80% of 25 A is 20 A. Therefore, the maximum ampere rating for a cord-and-plug-attached appliance connected to a 25-ampere branch circuit is 20 amperes.
Question 2: On a 15 amp branch circuit operating at 120 volts, what is the maximum number of receptacles that can be installed?
- 11
- 12
- 10 (Correct answer)
- 13
Correct answer: 10
The National Electrical Code (NEC) does not explicitly limit the number of receptacles on a general-purpose branch circuit. However, for planning purposes, especially in residential applications, a common guideline is to allocate 1.5 amperes (or 180 VA) per receptacle. For a 15-ampere, 120-volt circuit, the total capacity is 15 A * 120 V = 1800 VA. Dividing 1800 VA by 180 VA per receptacle yields 10 receptacles.
Question 3: The branch conductor's ampacity, which supplies power to the motor with an FLC of 25 amperes, is
- 28 amperes
- 30 amperes
- 25 amperes
- 32 amperes (Correct answer)
Correct answer: 32 amperes
According to NEC 430.22(A), the branch-circuit conductors supplying a single motor must have an ampacity not less than 125% of the motor's full-load current (FLC). For a motor with an FLC of 25 amperes, the required conductor ampacity would be 1.25 * 25 A = 31.25 A. The next standard conductor ampacity rating above 31.25 A is 32 amperes.
Question 4: A 2/0 THWN conductor is placed in a dry area at a temperature of 450 degrees Celsius. What is the conductor's corrected ampacity?
- 165 Amperes
- 170 Amperes (Correct answer)
- 175 Amperes
- 160 Amperes
Correct answer: 170 Amperes
Assuming the ambient temperature of '450 degrees Celsius' is a typo and meant '45 degrees Celsius' (as 450°C is far beyond conductor limits), we calculate the corrected ampacity. A 2/0 AWG THWN conductor is often dual-rated as THHN/THWN, allowing for a 90°C ampacity of 195 A (from NEC Table 310.16). Applying the temperature correction factor for 45°C from the 90°C column (Table 310.15(B)(2)(a)), which is 0.87, results in 195 A * 0.87 = 169.65 A, which rounds to 170 Amperes.
Question 5: A 1/0 THWN in a wet location has a rated ampacity of 150 amperes. If the same conductor is used at a temperature of 400 degrees Celsius. What is the corrected ampacity?
- 142 amperes
- 138 amperes
- 132 amperes (Correct answer)
- 150 amperes
Correct answer: 132 amperes
Temperature correction factor of 1/0 THWN Conductor for 40-750 C = 0.88 The corrected ampacity = 0.88 * 150 = 132 amperes
Question 6: The entry points of underground ducts or conduits into the building must be sealed.
- True (Correct answer)
- False
Correct answer: True
These must be sealed to prevent the entry of gases or moisture in to the building.
Question 7: If the raceway contains four 1/0 THWN conductors, what is the ampacity of a 1/0 THWN conductor in a dry location at a temperature of 1040 F?
- 132
- 124 (Correct answer)
- 165
- 170
Correct answer: 124
The conductor ampacity of 1/0 THWN in dry location ( 900C) = 170 amperes ( NEC Table 310.15(B)(16)) Ambient temperature correction factor at 1080F = 0.91 ( NEC Table 310.15(B)(2)) Raceway conductor bundle adjustment factor for 4 conductors = 0.8 ( NEC Table 310.15(B)(3)(a)) corrected ampacity = 170 * 0.8*0.91 = 124 amperes
Question 8: What conductor size is needed for a single-family housing unit with an estimated load of 220 amps and a maximum unbalanced neutral load of 110 amps?
- 3/0 AWG and 3 AWG (Correct answer)
- 3/0 AWG and 2 AWG
- 2/0 AWG and 2 AWG
- 1/0 AWG and 4 AWG
Correct answer: 3/0 AWG and 3 AWG
Service conductor for 225 Amperes load = 3/0 AWG neutral conductor for unbalanced load 110 = 3 AWG
Question 9: Which of the following is the minimum size of a single supply-side bonding jumper for three metal raceways with 300 kcmil service conductors each?
- 1 AWG
- 3 AWG
- 1/0 AWG
- 2 AWG (Correct answer)
Correct answer: 2 AWG
NEC Table 250.102(C)(1) For over 3/0 AWG and 350 kcmil the required bonding jumper size is 2 AWG
Question 10: The connected load of a single family dwelling unit is 4000 VA. The calculated demand load is which of the following?
- 4000 VA
- 3350 VA (Correct answer)
- 3550 VA
- 3850 VA
Correct answer: 3350 VA
First 3000 VA the demand factor is 100% = 3000 * 100 % = 3000 VA remaining (4000-3000) = 1000 ( demand factor = 35%) = 1000 * 0.35 = 350 VA total demand load = 3000 + 350 = 3350 VA
Question 11: What is the adjustment ampacity of a 3/0 THWN conductor in a wet location with an ambient temperature of 1080F? There are four 3/0 THWN conductors in the raceway.
- 153 amperes
- 133 amperes
- 119 amperes (Correct answer)
- 144 amperes
Correct answer: 119 amperes
3/0 THWN conductor ampacity in wet location (750C) = 175 Amperes ( NEC 310.15(B)(16)) Ambient temperature correction factor at 1080F = 0.85 ( NEC 310.15(B)(2)) raceway conductor bundle adjustment factor for 4 conductors= 0.8 ( NEC 310.15(B)(3)(a)) The conductor ampacity = 175 * 0.85 * 0.8 = 119 Amperes
Question 12: The voltmeter at one end of the feeder reads 240 volts. What is the volt-minimum meter's reading voltage at the outlet of lighting loads?
- 240 volts
- 228 volts
- 232.8 volts (Correct answer)
- 235 volts
Correct answer: 232.8 volts
The maximum voltage drop in feeder is 3 % the voltmeter reading = 240 – 0.03 * 240 = 240 – 7.2 = 232.8 volts
Question 13: The capacity of the conductor is 150 amperes. If five conductors are placed in a flexible cord, what is the maximum conductor ampacity allowed for each conductor?
- 135 amperes
- 105 amperes
- 140 ampere
- 120 amperes (Correct answer)
Correct answer: 120 amperes
For 5 conductors in flexible cord allowed ampacity percentage = 80 % of rated amapcity Allowed amapcity of each conductor with 150 Ampere rating = 150 * 0.8 = 120 amperes.
Question 14: For a 4200 W, 240 V electric water heater connected in a building, what is the maximum size over current device required?
- 25 A
- 30 A (Correct answer)
- 35 A
- 40 A
Correct answer: 30 A
Protection rating for an electric water heater should be less than 150% of the rating of device. Protection size = 4200 / 240 * 1.5 Protections size = 26.25 A The nearest next size over current device is 30 A.
Question 15: In a 3/4 EMT trade size, how many 10 AWG RHH conductors may be installed?
- 8 conductors
- 3 conductors
- 5 conductors
- 6 conductors (Correct answer)
Correct answer: 6 conductors
Total 6 10 AWG RHH conductors can be installed in trade size ¾ EMT.
Question 16: What size service conductors are needed for a 190 A calculated load in a dwelling? The service disconnect breaker has a 200-amp rating.
- 2/0 AWG (Correct answer)
- 1/0 AWG
- 4/0 AWG
- 3/0 AWG
Correct answer: 2/0 AWG
Answer : 2/0 AWG Note : Service conductors that supply individual dwelling unit or single dwelling unit can have ampacity rating of 83% of service disconnect. The conductor ampacity for 200 A service disconnect = 0.83 * 200 = 166 amperes Refer : NEC Table 310.15(B)(16) 2/0 AWG with ampacity 175 amperes ( 750 C) is suitable as service conductor
NEC Code Test
A cord-and-plug-attached appliance is linked to a 25 ampere branch circuit.
What is the maximum ampere rating that the appliance can handle?
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