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
Which of the following is an acceptable location for an overcurrent device per NEC 240.24(D)?
Answer: In a dedicated electrical room with restricted access
NEC 240.24(D) prohibits OCPDs in bathrooms, and 240.24(E) prohibits them in clothes closets; a dedicated electrical room is permitted.
A 3-phase, 480-volt, 50 HP motor has a full-load current of 65 amperes. What is the maximum non-time-delay fuse size allowed for branch-circuit short-circuit and ground-fault protection?
Answer: 175 amperes
NEC Table 430.52 allows non-time-delay fuses up to 300% of FLC; 65A × 3.0 = 195A, so the next standard size of 200A applies — but 175A is the largest standard size that does not exceed 300% if we round down: 65 × 3 = 195, nearest standard ≤ 195 is 175A.
What is the purpose of a 'selective coordination' study in an electrical distribution system?
Answer: To ensure the OCPD closest to a fault operates before upstream devices
Selective coordination ensures that only the OCPD nearest to the fault clears it, keeping the rest of the system energized.
Under NEC 210.20, a branch circuit OCPD must have a rating of at least what percentage of a continuous load?
Answer: 125%
NEC 210.20(A) requires the branch-circuit OCPD to be rated at not less than 125% of the continuous load plus 100% of the non-continuous load.
A cartridge fuse that shows signs of overheating at its ferrule ends should be:
Answer: Replaced and the fuse holder inspected for high-resistance connections
Overheated ferrules indicate high-resistance connections; both the fuse and the fuse holder must be inspected and replaced as needed.
For a 100-ampere feeder, what is the minimum ampacity required for the feeder tap conductor using the 25-foot tap rule per NEC 240.21(B)(2)?
Answer: 33 amperes
The 25-foot tap rule requires the tap conductor's ampacity to be at least 1/3 of the feeder OCPD rating; 100A ÷ 3 = 33.3A.
Which statement correctly describes the difference between an overload and a short circuit?
Answer: An overload is a sustained excess current within the circuit path; a short circuit is an unintended low-impedance fault
An overload is excess current flowing through the normal circuit path; a short circuit is an unintended connection creating a low-impedance path with very high fault current.