E2 Overcurrent Protection Devices 1 — Questions and Answers
Question 1: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 14 AWG copper conductors in a commercial installation?
- 20 amperes
- 25 amperes
- 15 amperes (Correct answer)
- 30 amperes
Correct answer: 15 amperes
NEC 240.4(D) limits overcurrent protection for 14 AWG copper conductors to a maximum of 15 amperes to prevent conductor damage from overheating.
Question 2: According to NEC 240.4(D), what is the maximum overcurrent protection allowed for 12 AWG copper conductors?
- 15 amperes
- 20 amperes (Correct answer)
- 25 amperes
- 30 amperes
Correct answer: 20 amperes
NEC 240.4(D) specifies that 12 AWG copper conductors shall not be protected by overcurrent devices rated more than 20 amperes.
Question 3: Under NEC 240.4(D), what is the maximum overcurrent protection for 10 AWG copper conductors?
- 20 amperes
- 25 amperes
- 35 amperes
- 30 amperes (Correct answer)
Correct answer: 30 amperes
NEC 240.4(D) limits overcurrent protection for 10 AWG copper conductors to a maximum of 30 amperes.
Question 4: Which of the following is a standard ampere rating for overcurrent devices per NEC 240.6(A)?
- 55 amperes
- 65 amperes
- 45 amperes (Correct answer)
- 85 amperes
Correct answer: 45 amperes
NEC 240.6(A) lists 45 amperes as a standard overcurrent device rating; 55, 65, and 85 amperes do not appear in the standard rating sequence.
Question 5: Per NEC 240.21, overcurrent protection for conductors shall generally be provided at:
- The load end of the conductor run
- The point where the conductor receives its supply (Correct answer)
- The midpoint of long conductor runs
- The main service disconnect only
Correct answer: The point where the conductor receives its supply
NEC 240.21 requires overcurrent protection at the point where the conductor receives its supply from the feeder or service, protecting the entire conductor run.
Question 6: Under NEC 240.21(B)(1), what is the maximum length of a feeder tap conductor that does not require overcurrent protection at the tap point, provided it is enclosed in a raceway and meets all other conditions?
- 10 feet (Correct answer)
- 15 feet
- 25 feet
- 50 feet
Correct answer: 10 feet
NEC 240.21(B)(1) permits unprotected tap conductors up to 10 feet when all specified conditions are met, including enclosure in a raceway and termination in a single circuit breaker or set of fuses.
Question 7: Per NEC 240.21(B)(2), what is the maximum length for a feeder tap conductor whose ampacity is not less than 1/3 the rating of the overcurrent device protecting the feeder?
- 10 feet
- 15 feet
- 25 feet (Correct answer)
- 50 feet
Correct answer: 25 feet
NEC 240.21(B)(2) allows tap conductors up to 25 feet when their ampacity is at least 1/3 the feeder's OCPD rating and conditions including physical protection are satisfied.
E2 Overcurrent Protection Devices 1
Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 14 AWG copper conductors in a commercial installation?