NABCEP Code Requirements 3 — Questions and Answers
Question 1: Under NEC 690.47, which grounding method is acceptable for a transformerless (non-isolated) utility-interactive inverter PV system?
- Functional ground only with no equipment grounding conductor
- Equipment grounding conductors with no grounding electrode system
- A grounding electrode system connected at the inverter with equipment grounding conductors throughout (Correct answer)
- Floating (ungrounded) array with double insulation only
Correct answer: A grounding electrode system connected at the inverter with equipment grounding conductors throughout
NEC 690.47 requires a grounding electrode system and equipment grounding conductors throughout for transformerless inverter systems.
Question 2: NEC 690.15 requires a means to disconnect all ungrounded conductors of a PV system from all other conductors. What is this device commonly called?
- Rapid shutdown initiator
- PV system disconnecting means (Correct answer)
- Overcurrent protection device
- Ground fault protection device
Correct answer: PV system disconnecting means
NEC 690.15 mandates a PV system disconnecting means to isolate PV conductors from other wiring.
Question 3: Per NEC 705.12(B)(2), the sum of ampere ratings of overcurrent devices supplying power to a busbar or conductor shall not exceed what percentage of the busbar or conductor ampere rating?
- 100%
- 110%
- 120% (Correct answer)
- 125%
Correct answer: 120%
NEC 705.12(B)(2) limits the total supply to 120% of the busbar rating when the back-fed breaker is at the opposite end from the main breaker.
Question 4: According to UL 1741, inverters intended for utility-interactive operation must have anti-islanding protection to disconnect within how many seconds when grid power is lost?
- 0.1 seconds
- 2 seconds (Correct answer)
- 5 seconds
- 10 seconds
Correct answer: 2 seconds
UL 1741 and IEEE 1547 require anti-islanding disconnection within 2 seconds of detecting loss of grid voltage.
Question 5: Under NEC 690.56, what marking is required on the exterior of a one- or two-family dwelling that has a PV system with rapid shutdown?
- A yellow warning placard indicating high voltage
- A rapid shutdown switch location label and a label indicating PV system is present (Correct answer)
- A red tag on the utility meter
- An OSHA lockout/tagout sign
Correct answer: A rapid shutdown switch location label and a label indicating PV system is present
NEC 690.56 requires a permanent label indicating the location of the rapid shutdown switch and that a PV system is present.
Question 6: What is the minimum wire bending space and clearance requirement that must be maintained at all PV disconnects per the NEC?
- The disconnect can be mounted in any orientation with no clearance requirement
- Working space per NEC Article 110.26 must be maintained in front of all disconnects (Correct answer)
- Only a 12-inch clearance above the disconnect is required
- PV disconnects are exempt from NEC 110 working space requirements
Correct answer: Working space per NEC Article 110.26 must be maintained in front of all disconnects
NEC 110.26 working space requirements apply to all PV disconnects just as they do to any electrical equipment.
Question 7: Which NFPA standard specifically addresses the installation requirements for stationary energy storage systems, including lithium-ion batteries paired with residential solar?
- NFPA 70 (NEC)
- NFPA 72
- NFPA 855 (Correct answer)
- NFPA 101
Correct answer: NFPA 855
NFPA 855 sets installation requirements and size limits for stationary energy storage systems including residential battery storage.
NABCEP Code Requirements 3
Under NEC 690.47, which grounding method is acceptable for a transformerless (non-isolated) utility-interactive inverter PV system?