CEI Renewable Energy System Inspection 3 — Questions and Answers
Question 1: What is the maximum voltage permitted for a PV system installed on a one- or two-family dwelling under NEC 690.7?
- 300V
- 600V (Correct answer)
- 1000V
- 1500V
Correct answer: 600V
NEC 690.7(A) limits PV system voltage to 600V DC for systems on one- and two-family dwellings to reduce shock hazard risk.
Question 2: A rapid shutdown system (RSS) is required for PV systems on buildings. Within how many seconds must conductors outside the array boundary be de-energized after initiating shutdown?
- 10 seconds
- 30 seconds (Correct answer)
- 60 seconds
- 90 seconds
Correct answer: 30 seconds
NEC 690.12 requires that conductors outside the PV array boundary be de-energized to 30V or less within 30 seconds of rapid shutdown initiation.
Question 3: Which conductor color is required by NEC for the grounded conductor in a DC PV system?
- Green
- White or gray (Correct answer)
- Red
- Bare copper
Correct answer: White or gray
NEC 200.6 requires grounded conductors (including the negative conductor in a DC system) to be identified with white or gray insulation.
Question 4: An inspector finds a PV system with a string inverter where the output circuit conductors run through an attic space. What NEC requirement must be verified?
- Conductors must be in metallic conduit only
- Conductors must be rated for the maximum attic temperature encountered (Correct answer)
- Conductors must be 10 AWG minimum
- Conductors must have a dedicated circuit breaker in the attic
Correct answer: Conductors must be rated for the maximum attic temperature encountered
NEC 690.31 requires PV system conductors to be rated for the temperatures they will encounter, and attic spaces can reach extreme temperatures requiring high-temp rated conductors.
Question 5: What is the purpose of a combiner box in a large PV array installation?
- Convert DC power to AC power
- Combine multiple PV source circuits into a single PV output circuit (Correct answer)
- Provide battery backup capability
- Monitor grid frequency and voltage
Correct answer: Combine multiple PV source circuits into a single PV output circuit
A combiner box aggregates the output of multiple PV source circuits (strings) into a single PV output circuit, typically including fuses or breakers for each string.
Question 6: Under NEC 690.47, what type of grounding electrode system is required for a PV system with a transformer isolating it from the utility grid?
- A separate grounding electrode for the PV system DC side only
- Connection to the building's existing grounding electrode system (Correct answer)
- A dedicated ground ring electrode around the array
- No grounding electrode is required if isolated by transformer
Correct answer: Connection to the building's existing grounding electrode system
NEC 690.47 requires the PV system grounding electrode to be bonded to the building's existing grounding electrode system to create a unified system.
Question 7: When inspecting a microinverter-based PV system, what is the key difference from a string inverter system that affects the DC wiring inspection?
- Microinverter systems operate at higher DC voltages
- DC wiring is confined to the module-level and operates at low module voltage (Correct answer)
- Microinverter systems do not require a rapid shutdown system
- DC conductors in microinverter systems are ungrounded
Correct answer: DC wiring is confined to the module-level and operates at low module voltage
With microinverters, each module has its own inverter, so DC wiring is only at the individual module level and remains at low module voltage rather than accumulated string voltage.
CEI Renewable Energy System Inspection 3
What is the maximum voltage permitted for a PV system installed on a one- or two-family dwelling under NEC 690.7?