Journeyman Electrician’s Exam Journeyman Electrician's Overcurrent Protection 3 — Questions and Answers
Question 1: Where must an overcurrent device be located relative to the point where a conductor receives its supply?
- Within 6 feet of the supply point
- At the point where the conductor receives its supply (Correct answer)
- At the load end of the conductor
- Within 10 feet of the supply point
Correct answer: At the point where the conductor receives its supply
NEC 240.21 requires OCPDs to be placed at the point where the conductor receives its supply unless a tap rule exception applies.
Question 2: A feeder tap conductor using the 10-foot tap rule must have an ampacity of at least what percentage of the overcurrent device protecting the feeder?
- 100%
- 33% (Correct answer)
- 10%
- 50%
Correct answer: 33%
NEC 240.21(B)(1) requires the tap conductor's ampacity to be at least one-third (33%) of the feeder OCPD rating for the 10-foot tap rule.
Question 3: Which of the following best describes an 'inverse-time' circuit breaker?
- It trips faster as the current increases (Correct answer)
- It trips at a fixed time regardless of current
- It trips only on ground faults
- It trips only when current drops below rated value
Correct answer: It trips faster as the current increases
An inverse-time breaker has a trip time that decreases as the overcurrent magnitude increases, providing time-current coordination.
Question 4: A fused disconnect for an air-conditioning unit must be installed within sight of and readily accessible from the unit. Which article covers this requirement?
- Article 230
- Article 240
- Article 440 (Correct answer)
- Article 430
Correct answer: Article 440
NEC Article 440 covers air-conditioning and refrigerating equipment, including the disconnecting means and overcurrent protection requirements.
Question 5: What is the maximum OCPD size allowed for a 15 AWG copper conductor used in a branch circuit?
- 10 amperes
- 15 amperes (Correct answer)
- 20 amperes
- 25 amperes
Correct answer: 15 amperes
NEC 240.4(D)(3) limits the OCPD for 14 AWG to 15A; 15 AWG is not a standard branch-circuit size, so 14 AWG rules (15A max) apply.
Question 6: Ground-fault circuit interrupter (GFCI) protection detects current imbalances as small as:
- 5 milliamperes (±1 mA) (Correct answer)
- 15 milliamperes
- 30 milliamperes
- 100 milliamperes
Correct answer: 5 milliamperes (±1 mA)
GFCI devices are designed to trip when they sense a ground-fault current of approximately 4–6 mA (nominally 5 mA ±1 mA).
Question 7: Which conductor is NOT required to be protected by an overcurrent device under NEC 240.22?
- Grounded (neutral) conductors (Correct answer)
- Ungrounded phase conductors
- Travelers in 3-way switch circuits
- Equipment grounding conductors
Correct answer: Grounded (neutral) conductors
NEC 240.22 prohibits placing an OCPD in series with the grounded conductor unless the device opens all conductors simultaneously.
