NABCEP Installation & Safety 5 — Questions and Answers
Question 1: When torquing module mounting hardware, why is it important to follow the manufacturer's specified torque values?
- To comply with aesthetic requirements of the rail manufacturer
- To ensure structural integrity without stripping threads or cracking frames, while maintaining warranty (Correct answer)
- To satisfy NEC electrical code requirements for conductors
- To meet the minimum wind-uplift calculation only
Correct answer: To ensure structural integrity without stripping threads or cracking frames, while maintaining warranty
Proper torque prevents under-tightening (which allows loosening) and over-tightening (which strips threads or cracks aluminum frames), and manufacturer specs are required to maintain equipment warranties.
Question 2: A worker is about to connect a second PV string to a combiner box that already has one string energized. What hazard must they address first?
- Voltage drop from the first string
- Backfeed current from the existing string through the new fuse position during connection (Correct answer)
- Grounding of the new string's racking
- The need to re-label the junction box
Correct answer: Backfeed current from the existing string through the new fuse position during connection
When one string is energized in the combiner, connecting a second string can create backfeed current through the new fuse position, risking arcing and injury during connection.
Question 3: What is the primary reason PV wire (USE-2/PV Wire) is used instead of standard THWN-2 wire for module-level wiring?
- PV wire is less expensive than THWN-2
- PV wire is rated for direct sunlight exposure and wet locations at elevated temperatures (Correct answer)
- THWN-2 cannot be used in conduit
- PV wire has lower resistance than THWN-2
Correct answer: PV wire is rated for direct sunlight exposure and wet locations at elevated temperatures
PV wire and USE-2 are specifically rated for prolonged sunlight exposure, wet locations, and higher temperature ratings, making them suitable for outdoor array wiring.
Question 4: Which of the following is an example of an engineering control to reduce fall hazards during rooftop PV installation?
- Providing workers with fall-arrest harnesses
- Installing temporary guardrails along roof edges before workers begin installation (Correct answer)
- Conducting a safety briefing before work begins
- Posting warning signs on the ground below the work area
Correct answer: Installing temporary guardrails along roof edges before workers begin installation
Engineering controls such as temporary guardrails physically prevent falls by creating a barrier, and are preferred over administrative controls or PPE in the hierarchy of controls.
Question 5: What is the function of a ground fault protection device (GFPD) in a PV system?
- It limits the maximum current output of the array
- It detects unintended current flow to ground and disconnects the faulted circuit to prevent fire (Correct answer)
- It protects the inverter from over-voltage surges
- It monitors the system's grounding electrode resistance
Correct answer: It detects unintended current flow to ground and disconnects the faulted circuit to prevent fire
A GFPD monitors for current flowing outside its intended path to ground, and when detected, disconnects the circuit to prevent fires caused by arcing at the fault point.
Question 6: According to OSHA, what is the required minimum illumination level for general construction work areas?
- 3 foot-candles
- 5 foot-candles (Correct answer)
- 10 foot-candles
- 30 foot-candles
Correct answer: 5 foot-candles
OSHA 1926.56 requires a minimum of 5 foot-candles of illumination for general construction areas, warehouses, corridors, hallways, and exitways.
Question 7: What is the primary purpose of bonding all metal parts of a PV array racking system together?
- To improve the efficiency of the modules by reducing stray currents
- To establish a low-impedance fault path so overcurrent devices operate quickly during a ground fault (Correct answer)
- To prevent corrosion between dissimilar metals
- To meet aesthetic requirements for grounding conductor visibility
Correct answer: To establish a low-impedance fault path so overcurrent devices operate quickly during a ground fault
Equipment bonding creates a low-impedance path back to the source so that a ground fault produces enough current to trip the overcurrent protective device and clear the fault safely.
NABCEP Installation & Safety 5
When torquing module mounting hardware, why is it important to follow the manufacturer's specified torque values?