CME Grounding, Bonding & Overcurrent Protection 2 — Questions and Answers
Question 1: Per NEC 240.4(D), what is the maximum overcurrent protection permitted for a 12 AWG copper branch-circuit conductor?
- 15A
- 20A (Correct answer)
- 25A
- 30A
Correct answer: 20A
NEC 240.4(D)(5) limits overcurrent protection for 12 AWG copper conductors to a maximum of 20A.
Question 2: What is the minimum burial depth for a ground ring below the surface of the earth per NEC 250.52(A)(4)?
- 18 inches
- 24 inches
- 30 inches (Correct answer)
- 36 inches
Correct answer: 30 inches
NEC 250.52(A)(4) requires a ground ring to be installed at least 2½ feet (30 inches) below the surface of the earth.
Question 3: When conductors are installed in parallel in multiple raceways, how must equipment grounding conductors be installed per NEC 250.122(F)?
- In only one raceway, sized for total combined load
- In each raceway, each sized per Table 250.122 based on the overcurrent device (Correct answer)
- Only required in raceways containing the largest conductor
- Not required if metallic raceways serve as the EGC
Correct answer: In each raceway, each sized per Table 250.122 based on the overcurrent device
NEC 250.122(F) requires an EGC to be installed in each raceway when parallel conductors are used, with each EGC sized per Table 250.122 for the circuit overcurrent device.
Question 4: A concrete-encased electrode (Ufer ground) must contain at least how many feet of bare copper conductor or steel rebar per NEC 250.52(A)(3)?
- 10 feet
- 15 feet
- 20 feet (Correct answer)
- 25 feet
Correct answer: 20 feet
NEC 250.52(A)(3) requires at least 20 feet of bare copper conductor (4 AWG or larger) or 20 feet of steel rebar (½ inch or larger) encased in concrete for a concrete-encased electrode.
Question 5: What is the primary function of the equipment grounding conductor (EGC) in a branch circuit?
- To carry normal load current back to the neutral bus
- To provide a low-impedance fault current path that enables overcurrent device operation (Correct answer)
- To equalize voltage between ungrounded phase conductors
- To reduce electromagnetic interference in the wiring system
Correct answer: To provide a low-impedance fault current path that enables overcurrent device operation
The EGC provides a low-impedance path for fault current to return to the source, ensuring sufficient current flows to operate the overcurrent protective device and clear the fault.
Question 6: Per NEC 230.95, ground-fault protection of equipment (GFPE) is required for solidly grounded wye services exceeding 150V to ground but not exceeding 600V phase-to-phase when the service disconnect is rated at or above:
- 100A
- 600A
- 800A
- 1000A (Correct answer)
Correct answer: 1000A
NEC 230.95 requires GFPE for solidly grounded wye services with service disconnecting means rated 1000A or more to protect against high-level arcing ground faults.
Question 7: A supply-side bonding jumper is used to bond metal enclosures on which side of the service or separately derived system?
- The load side of all distribution panelboards
- The supply side, between the service or separately derived system source and the first disconnecting means (Correct answer)
- The load side of the main service disconnect only
- Only at grounding electrode connections
Correct answer: The supply side, between the service or separately derived system source and the first disconnecting means
Per NEC 250.102(C), supply-side bonding jumpers bond metal enclosures and raceways on the supply side of the service or between a separately derived system and its first disconnecting means.
CME Grounding, Bonding & Overcurrent Protection 2
Per NEC 240.4(D), what is the maximum overcurrent protection permitted for a 12 AWG copper branch-circuit conductor?