NEC Overcurrent Protection & Controls 2 — Questions and Answers
Question 1: Per NEC 240.4(D), what is the maximum overcurrent protection for a 12 AWG copper conductor?
- 15 amperes
- 20 amperes (Correct answer)
- 25 amperes
- 30 amperes
Correct answer: 20 amperes
NEC 240.4(D) limits 12 AWG copper to a maximum overcurrent device of 20 amperes.
Question 2: What is the standard ampere rating immediately above 100 A in the NEC 240.6(A) list of standard fuse and circuit breaker ratings?
- 110 amperes (Correct answer)
- 115 amperes
- 125 amperes
- 150 amperes
Correct answer: 110 amperes
NEC 240.6(A) lists 110 A as the standard rating directly above 100 A.
Question 3: When the ampacity of a conductor does not match a standard overcurrent device rating, 240.4(B) generally allows what for circuits 800 A or less?
- Using the next lower standard rating only
- Using the next higher standard rating (Correct answer)
- Doubling the conductor size
- No deviation is permitted
Correct answer: Using the next higher standard rating
NEC 240.4(B) permits the next higher standard overcurrent device rating for circuits 800 A and below under specified conditions.
Question 4: Per NEC 240.4(D), what is the maximum overcurrent protection for a 14 AWG copper conductor?
- 10 amperes
- 15 amperes (Correct answer)
- 20 amperes
- 25 amperes
Correct answer: 15 amperes
14 AWG copper is limited to a maximum 15-ampere overcurrent device.
Question 5: Overcurrent protection for conductors and equipment is provided to open the circuit if current reaches a value that would cause what, per 240.1?
- A voltage drop above 3%
- An excessive or dangerous temperature in conductors or insulation (Correct answer)
- Harmonic distortion
- A power factor below 0.9
Correct answer: An excessive or dangerous temperature in conductors or insulation
Per the 240.1 informational note, overcurrent protection limits current to prevent dangerous temperatures in conductors and insulation.
Question 6: Per NEC 240.4(D), what is the maximum overcurrent protection for a 10 AWG copper conductor?
- 20 amperes
- 25 amperes
- 30 amperes (Correct answer)
- 40 amperes
Correct answer: 30 amperes
10 AWG copper is limited to a maximum 30-ampere overcurrent device.
Question 7: Which of the following is NOT a standard ampere rating for fuses and inverse-time circuit breakers under 240.6(A)?
- 45 amperes
- 70 amperes
- 85 amperes (Correct answer)
- 90 amperes
Correct answer: 85 amperes
85 A is not a listed standard rating; 45, 70, and 90 A are all standard.
NEC Overcurrent Protection & Controls 2
Per NEC 240.4(D), what is the maximum overcurrent protection for a 12 AWG copper conductor?