Journeyman Electrician’s Exam Journeyman Electrician's Overcurrent Protection 2 — Questions and Answers
Question 1: What is the maximum standard fuse or circuit breaker size permitted for a 10 AWG copper conductor with 30A ampacity used in a branch circuit?
- 20 amperes
- 25 amperes
- 30 amperes (Correct answer)
- 40 amperes
Correct answer: 30 amperes
Per NEC 240.4(D), 10 AWG copper conductors are protected at a maximum of 30 amperes.
Question 2: A 240-volt, single-phase motor draws 28 amperes at full load. What is the maximum rating of an inverse-time circuit breaker permitted for branch-circuit protection of this motor?
- 40 amperes
- 50 amperes
- 70 amperes (Correct answer)
- 100 amperes
Correct answer: 70 amperes
NEC 430.52 allows inverse-time breakers up to 250% of FLC for single-phase motors, and 28A × 2.5 = 70A.
Question 3: Which NEC article governs overcurrent protection for panelboards?
- Article 240
- Article 408 (Correct answer)
- Article 230
- Article 310
Correct answer: Article 408
NEC Article 408 covers switchboards, switchgear, and panelboards, including their overcurrent protection requirements.
Question 4: A 20-ampere, 120-volt branch circuit supplies a single receptacle. What is the minimum ampere rating required for that receptacle?
- 15 amperes
- 20 amperes (Correct answer)
- 25 amperes
- 30 amperes
Correct answer: 20 amperes
NEC 210.21(B)(1) requires a single receptacle on a branch circuit to have an ampere rating not less than the branch-circuit rating.
Question 5: When is it permissible to use the next higher standard OCPD size above a conductor's ampacity?
- Whenever the load is continuous
- When the conductor ampacity does not correspond to a standard OCPD rating (Correct answer)
- Only for motor circuits
- Only when the conductor is #12 AWG or larger
Correct answer: When the conductor ampacity does not correspond to a standard OCPD rating
NEC 240.4(B) allows the next higher standard OCPD rating when the conductor's ampacity does not correspond to a standard rating, provided the OCPD is 800A or less.
Question 6: A service entrance has a calculated load of 175 amperes. Which standard-size OCPD is the smallest that may be used to protect this service?
- 150 amperes
- 175 amperes
- 200 amperes (Correct answer)
- 225 amperes
Correct answer: 200 amperes
Standard OCPD sizes per NEC 240.6 jump from 175A to 200A, so 200A is the next available standard size above 175A.
Question 7: Type S fuses are designed to prevent which of the following problems?
- Overheating at the fuse holder terminals
- Overfusing by substituting a higher-rated fuse (Correct answer)
- Voltage surges damaging appliances
- Ground faults on 240-volt circuits
Correct answer: Overfusing by substituting a higher-rated fuse
Type S fuses have a rejection feature that prevents inserting a fuse rated higher than the adapter allows, stopping overfusing.
