NABCEP NEC Article 690 Applications 3 — Questions and Answers
Question 1: NEC 690.47(C) addresses DC grounding electrode systems for ungrounded PV systems. What does it require?
- No grounding electrode is required for ungrounded systems
- A separate dc grounding electrode system or bonding to the ac grounding electrode system (Correct answer)
- Only lightning rods are needed
- The negative conductor must be grounded at the array
Correct answer: A separate dc grounding electrode system or bonding to the ac grounding electrode system
NEC 690.47(C) requires ungrounded PV systems to have either a separate dc grounding electrode or a bond to the existing ac grounding electrode system.
Question 2: According to NEC 690.41, a PV system arc-fault circuit interrupter (AFCI) is required to protect which conductors?
- Only the ac output conductors of the inverter
- PV source circuits, PV output circuits, and inverter input and output circuits (Correct answer)
- Only the dc conductors within 1 ft of the inverter
- Only conductors in conduit inside the building
Correct answer: PV source circuits, PV output circuits, and inverter input and output circuits
NEC 690.41 requires AFCI protection for PV source circuits, output circuits, and inverter input/output to detect and interrupt arc faults in the PV system.
Question 3: What is the primary purpose of the Ground-Fault Protection (GFP) required by NEC 690.41 for grounded PV arrays?
- To limit system voltage during a fault
- To detect ground faults and disable the array or disconnect faulted circuits (Correct answer)
- To prevent reverse current through the modules
- To balance current between parallel source circuits
Correct answer: To detect ground faults and disable the array or disconnect faulted circuits
The GFP device detects ground faults in the array and disables the array or disconnects faulted circuits to prevent fire and equipment damage.
Question 4: NEC 690.43 requires exposed non-current-carrying metal parts of PV equipment to be grounded or bonded. Which conductor size requirement applies to the equipment grounding conductor?
- It must be sized per NEC Table 250.122 based on the overcurrent device rating (Correct answer)
- It must match the size of the grounded conductor
- It must be at least 6 AWG copper regardless of circuit size
- It must be 10 AWG minimum for all PV circuits
Correct answer: It must be sized per NEC Table 250.122 based on the overcurrent device rating
NEC 690.43 requires equipment grounding conductors to be sized per NEC Table 250.122, based on the rating of the overcurrent protective device for the circuit.
Question 5: According to NEC 690.47(A), a grounding electrode conductor for a dc PV system must be sized per which NEC table?
- Table 250.66 (Correct answer)
- Table 250.122
- Table 310.15(B)(16)
- Table 690.31
Correct answer: Table 250.66
NEC 690.47(A) references Table 250.66 for sizing the grounding electrode conductor for dc PV systems, same as for ac services.
Question 6: For an ungrounded PV system, NEC 690.35 requires which of the following protection measures?
- A fuse in every module string only
- Ground-fault protection, arc-fault protection, and marking as an ungrounded system (Correct answer)
- The negative conductor must be bonded to ground at one point
- An isolation transformer between array and inverter
Correct answer: Ground-fault protection, arc-fault protection, and marking as an ungrounded system
NEC 690.35 requires ungrounded PV systems to include ground-fault protection, arc-fault protection, and proper labeling indicating the system is ungrounded.
Question 7: When bonding PV module frames and racking to form a grounding system, NEC 690.43(B) permits listed grounding clips or lugs to bond to which part of the racking?
- Only the end clamps of each module
- The metal structural framing members of the racking system (Correct answer)
- The module glass surface
- The rooftop flashing only
Correct answer: The metal structural framing members of the racking system
NEC 690.43(B) permits listed grounding clips or lugs to bond module frames and equipment to the metal structural members of the racking system.
NABCEP NEC Article 690 Applications 3
NEC 690.47(C) addresses DC grounding electrode systems for ungrounded PV systems.
What does it require?