Journeyman Electrician’s Exam Journeyman Electrician's Overcurrent Protection 4 — Questions and Answers
Question 1: A dual-element time-delay fuse is particularly useful for protecting circuits with:
- Purely resistive heating loads
- Motor loads with high inrush currents (Correct answer)
- Lighting circuits at unity power factor
- Solar PV array circuits
Correct answer: Motor loads with high inrush currents
Dual-element time-delay fuses tolerate the high inrush current of motor starting while still protecting against sustained overloads.
Question 2: Under NEC 230.91, where must the service overcurrent protective device be installed?
- At the meter socket
- At the first accessible point after the service entrance conductors enter the building (Correct answer)
- Outdoors on the utility pole
- At the load center on any floor of the building
Correct answer: At the first accessible point after the service entrance conductors enter the building
NEC 230.91 requires the service OCPD to be an integral part of the service disconnecting means located at the first accessible point of entry.
Question 3: What maximum number of overcurrent devices may serve as the service disconnecting means for a single building under NEC 230.71?
- Two
- Four
- Six (Correct answer)
- Eight
Correct answer: Six
NEC 230.71(A) limits the service disconnecting means to a maximum of six switches or circuit breakers for a single service.
Question 4: A 40-ampere, 240-volt branch circuit feeds an electric range. The range's nameplate rating is 8.75 kW. Is this circuit properly protected?
- No, a 50-ampere breaker is required
- Yes, 40 amperes satisfies the demand calculation (Correct answer)
- No, a 30-ampere breaker must be used
- Yes, but only if a GFCI breaker is installed
Correct answer: Yes, 40 amperes satisfies the demand calculation
NEC 220.55 and Table 220.55 allow demand factors; a 40A circuit is the minimum required for an 8.75 kW range and is acceptable.
Question 5: Current-limiting fuses reduce the let-through energy during a fault primarily by:
- Increasing the fault current path impedance before arcing begins
- Clearing the fault in less than one-half cycle (Correct answer)
- Opening the circuit after a time delay
- Sensing voltage drop across the fuse element
Correct answer: Clearing the fault in less than one-half cycle
Current-limiting fuses clear high-magnitude faults in less than a half cycle (0.00833 s), drastically reducing let-through I²t energy.
Question 6: When a circuit breaker is used in a location that is inaccessible except by portable means (e.g., ladders), it:
- May not be used as a disconnecting means
- Must be replaced with a fusible switch
- Is still permitted as an OCPD but not as the sole disconnect (Correct answer)
- Complies fully if rated for the calculated load
Correct answer: Is still permitted as an OCPD but not as the sole disconnect
NEC 240.24(A) requires OCPDs to be readily accessible; a breaker that requires a ladder is not readily accessible and cannot serve as the disconnect.
Question 7: An OCPD for a storage battery system must be installed within how many inches of the battery terminals per NEC 480.5?
- 6 inches
- 12 inches (Correct answer)
- 18 inches
- 24 inches
Correct answer: 12 inches
NEC 480.5 requires the OCPD for battery systems to be installed within 12 inches of the battery terminals to protect the short unprotected conductor.
