CEA NEC Code and Calculations 4 — Questions and Answers
Question 1: Under NEC 230.79, what is the minimum ampacity of a service disconnect for a one-family dwelling?
- 100 amperes (Correct answer)
- 60 amperes
- 200 amperes
- 150 amperes
Correct answer: 100 amperes
NEC 230.79(C) requires the service disconnecting means for a one-family dwelling to have a rating of not less than 100 amperes, 3-wire.
Question 2: According to NEC 314.16, the minimum box fill for a 14 AWG conductor is how many cubic inches?
- 2 cubic inches (Correct answer)
- 1.5 cubic inches
- 2.5 cubic inches
- 3 cubic inches
Correct answer: 2 cubic inches
NEC Table 314.16(B) assigns a volume allowance of 2.0 cubic inches per 14 AWG conductor for box fill calculations.
Question 3: What NEC rule governs the use of extension cords in lieu of permanent wiring?
- Extension cords must not be used as a substitute for permanent wiring (Correct answer)
- Extension cords are allowed if protected by a 20A GFCI breaker
- Extension cords may be used permanently if rated for the load
- Extension cords are acceptable behind walls with a cover plate
Correct answer: Extension cords must not be used as a substitute for permanent wiring
NEC 400.12 prohibits the use of flexible cords and cables, including extension cords, as a substitute for permanent wiring.
Question 4: A 240-volt, single-phase motor draws 18 amperes. What is the minimum branch circuit conductor ampacity required by the NEC?
- 22.5 amperes (Correct answer)
- 18 amperes
- 20 amperes
- 25 amperes
Correct answer: 22.5 amperes
NEC 430.22 requires motor branch circuit conductors to have an ampacity of at least 125% of the motor's full-load current: 18 × 1.25 = 22.5 amperes.
Question 5: Under the NEC, arc-fault circuit interrupter (AFCI) protection is required in which location of a dwelling unit?
- All 120-volt, 15- and 20-ampere branch circuits in kitchens and living areas (Correct answer)
- Only in bedrooms
- Only in garages and outdoors
- Only in laundry rooms
Correct answer: All 120-volt, 15- and 20-ampere branch circuits in kitchens and living areas
NEC 210.12 has expanded AFCI requirements to cover all 120-volt, 15- and 20-ampere branch circuits throughout dwelling units including kitchens, family rooms, and living areas.
Question 6: According to the NEC, what is the maximum number of overcurrent devices (excluding the main) permitted in a single panelboard?
- 42 overcurrent devices (Correct answer)
- 30 overcurrent devices
- 20 overcurrent devices
- No specific NEC limit
Correct answer: 42 overcurrent devices
NEC 408.54 limits the number of overcurrent devices in a panelboard to 42, not counting the main overcurrent device.
Question 7: What is the calculated load in volt-amperes for a 1,500 square foot dwelling's general lighting and receptacle load using the NEC unit load method?
- 4,500 VA (Correct answer)
- 3,000 VA
- 6,000 VA
- 1,500 VA
Correct answer: 4,500 VA
NEC Table 220.12 assigns 3 VA per square foot for dwelling units; 1,500 sq ft × 3 VA = 4,500 VA.
CEA NEC Code and Calculations 4
Under NEC 230.79, what is the minimum ampacity of a service disconnect for a one-family dwelling?