Journeyman Electrician’s Exam Journeyman Electrician's Overcurrent Protection 5

Question 1

Which of the following is an acceptable location for an overcurrent device per NEC 240.24(D)?

Accepted Answer

In a dedicated electrical room with restricted access

Answer

NEC 240.24(D) prohibits OCPDs in bathrooms, and 240.24(E) prohibits them in clothes closets; a dedicated electrical room is permitted.

Question 2

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?

Accepted Answer

175 amperes

Answer

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.

Question 3

What is the purpose of a 'selective coordination' study in an electrical distribution system?

Accepted Answer

To ensure the OCPD closest to a fault operates before upstream devices

Answer

Selective coordination ensures that only the OCPD nearest to the fault clears it, keeping the rest of the system energized.

Question 4

Under NEC 210.20, a branch circuit OCPD must have a rating of at least what percentage of a continuous load?

Accepted Answer

125%

Answer

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.

Question 5

A cartridge fuse that shows signs of overheating at its ferrule ends should be:

Accepted Answer

Replaced and the fuse holder inspected for high-resistance connections

Answer

Overheated ferrules indicate high-resistance connections; both the fuse and the fuse holder must be inspected and replaced as needed.

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Journeyman Electrician's Overcurrent Protection 5