Journeyman Electrician's Overcurrent Protection Flashcards
7 cards from real Journeyman Electrician’s Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Journeyman Electrician's Overcurrent Protection flashcards as text
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?
Answer: 30 amperes
Per NEC 240.4(D), 10 AWG copper conductors are protected at a maximum of 30 amperes.
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?
Answer: 70 amperes
NEC 430.52 allows inverse-time breakers up to 250% of FLC for single-phase motors, and 28A × 2.5 = 70A.
Which NEC article governs overcurrent protection for panelboards?
Answer: Article 408
NEC Article 408 covers switchboards, switchgear, and panelboards, including their overcurrent protection requirements.
A 20-ampere, 120-volt branch circuit supplies a single receptacle. What is the minimum ampere rating required for that receptacle?
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.
When is it permissible to use the next higher standard OCPD size above a conductor's ampacity?
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.
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?
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.
Type S fuses are designed to prevent which of the following problems?
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.