NEC Overcurrent Protection & Grounding 3 — Questions and Answers
Question 1: Which NEC section requires Arc-Fault Circuit-Interrupter (AFCI) protection for bedroom branch circuits in dwelling units?
- 210.12 (Correct answer)
- 240.87
- 250.30
- 230.95
Correct answer: 210.12
NEC 210.12 mandates AFCI protection for branch circuits supplying outlets in dwelling unit bedrooms and other specified areas.
Question 2: Under NEC 250.52, which of the following is a permitted grounding electrode?
- A concrete-encased electrode (Ufer ground) (Correct answer)
- PVC water pipe buried 8 feet
- Aluminum rod electrode
- A gas piping system
Correct answer: A concrete-encased electrode (Ufer ground)
NEC 250.52(A)(3) recognizes concrete-encased electrodes (Ufer grounds) as a permitted grounding electrode type.
Question 3: What is the maximum rating of a fuse or inverse-time circuit breaker that may be used to protect a 10 AWG copper conductor (ampacity 30A) under NEC 240.4(B)?
- 30 amperes (Correct answer)
- 25 amperes
- 40 amperes
- 20 amperes
Correct answer: 30 amperes
Under 240.4(B), the next standard size above conductor ampacity is permitted, but 30A is the exact ampacity so 30A is used directly.
Question 4: Per NEC 250.66, the size of the grounding electrode conductor (GEC) for a service is based on:
- The size of the largest service-entrance conductor (Correct answer)
- The total connected load in amperes
- The rating of the main service overcurrent device
- The number of grounding electrodes installed
Correct answer: The size of the largest service-entrance conductor
NEC Table 250.66 sizes the GEC based on the largest service-entrance conductor or equivalent area for parallel conductors.
Question 5: Which statement about double-pole (2-pole) circuit breakers is correct per NEC requirements?
- They must simultaneously disconnect both ungrounded conductors (Correct answer)
- They may trip independently on each pole under overload
- They are not permitted in residential panelboards
- They require a neutral wire connection to operate
Correct answer: They must simultaneously disconnect both ungrounded conductors
NEC 240.20(B) requires multipole breakers to simultaneously open all ungrounded conductors of the circuit.
Question 6: NEC 250.4(A)(1) states the purpose of grounding electrical systems is to:
- Limit voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines (Correct answer)
- Reduce power consumption by equipment
- Eliminate the need for surge protection devices
- Provide a return path for normal operating current
Correct answer: Limit voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines
NEC 250.4(A)(1) specifies grounding limits overvoltage from lightning and other surge events to protect equipment and personnel.
Question 7: What is the maximum length of a 25-foot feeder tap conductor permitted under NEC 240.21(B)(2) if it terminates in a single circuit breaker?
- 25 feet (Correct answer)
- 10 feet
- 50 feet
- 100 feet
Correct answer: 25 feet
NEC 240.21(B)(2) allows up to 25-foot tap conductors when the tap terminates in a single overcurrent device and specific ampacity conditions are met.
NEC Overcurrent Protection & Grounding 3
Which NEC section requires Arc-Fault Circuit-Interrupter (AFCI) protection for bedroom branch circuits in dwelling units?