NABCEP Installation & Safety 3 — Questions and Answers
Question 1: What is the correct procedure for locking out a grid-tied PV system before performing maintenance on the inverter?
- Turn off the inverter's power switch only
- Open the AC disconnect, apply lockout/tagout, then open the DC disconnect and apply lockout/tagout (Correct answer)
- Remove fuses from the combiner box only
- Disconnect the battery bank if present
Correct answer: Open the AC disconnect, apply lockout/tagout, then open the DC disconnect and apply lockout/tagout
Proper LOTO requires isolating both AC and DC sides: open the AC disconnect first, apply lockout/tagout, then open the DC disconnect and apply lockout/tagout.
Question 2: What does the NEC term 'identified' mean when referring to equipment in Article 690?
- Listed by a NRTL for its intended use (Correct answer)
- Labeled with the installer's name and license number
- Marked with the system voltage
- Approved by the local AHJ only
Correct answer: Listed by a NRTL for its intended use
'Identified' in the NEC means the equipment is recognized as suitable for the specific purpose, function, or environment, typically by being listed by a Nationally Recognized Testing Laboratory.
Question 3: What is the purpose of a rapid shutdown system (RSS) in a PV installation per NEC 690.12?
- To reduce the inverter output during peak demand
- To de-energize conductors in or on a building to protect first responders (Correct answer)
- To automatically restart the system after a grid outage
- To limit the maximum power output to the rated system size
Correct answer: To de-energize conductors in or on a building to protect first responders
Rapid shutdown systems reduce the voltage and current in PV conductors inside and on buildings to protect firefighters and other first responders from electrocution.
Question 4: Under NEC 690, which conductor color is required for the grounded conductor (negative) in a DC PV circuit?
- Red
- White or gray (Correct answer)
- Green
- Black
Correct answer: White or gray
NEC requires white or gray insulation to identify the grounded conductor in DC PV circuits, consistent with general NEC grounded-conductor color coding.
Question 5: A PV module's Voc is rated at 25°C. How does the open-circuit voltage change when the module temperature drops to -10°C?
- It decreases significantly
- It increases, and this higher voltage must be considered in system design (Correct answer)
- It remains the same because Voc is temperature-independent
- It decreases slightly and has no safety impact
Correct answer: It increases, and this higher voltage must be considered in system design
PV module Voc increases as temperature decreases; designers must calculate the maximum Voc at the lowest expected ambient temperature to avoid exceeding equipment ratings.
Question 6: Which NFPA standard covers electrical safety requirements for employee workplaces and informs PV installation safety practices?
- NFPA 13
- NFPA 70E (Correct answer)
- NFPA 72
- NFPA 101
Correct answer: NFPA 70E
NFPA 70E, the Standard for Electrical Safety in the Workplace, establishes arc-flash and shock hazard boundaries and required PPE for workers on energized electrical systems.
Question 7: What is the minimum burial depth for a PV system DC circuit cable in rigid metal conduit (RMC) per NEC Table 300.5?
- 6 inches (Correct answer)
- 12 inches
- 18 inches
- 24 inches
Correct answer: 6 inches
NEC Table 300.5 requires a minimum burial depth of only 6 inches for wiring in rigid metal conduit because the conduit itself provides mechanical protection.
NABCEP Installation & Safety 3
What is the correct procedure for locking out a grid-tied PV system before performing maintenance on the inverter?