NABCEP Electrical & Mechanical Concepts 5 — Questions and Answers
Question 1: What is the purpose of equipotential bonding in a PV array?
- Improve module efficiency
- Connect all metallic parts to the same electrical potential to prevent shock (Correct answer)
- Increase system voltage
- Protect against lightning directly
Correct answer: Connect all metallic parts to the same electrical potential to prevent shock
Equipotential bonding ensures all metal racking, frames, and enclosures are at the same voltage, eliminating dangerous potential differences.
Question 2: In a transformer, if the primary has 240 turns and the secondary has 60 turns, what is the turns ratio and secondary voltage for a 120 V primary?
- 4:1, 30 V (Correct answer)
- 1:4, 480 V
- 4:1, 480 V
- 1:4, 30 V
Correct answer: 4:1, 30 V
Turns ratio = 240/60 = 4:1, so secondary voltage = 120 V ÷ 4 = 30 V.
Question 3: What type of load calculation must be performed before designing a rooftop PV mounting system?
- Electrical load calculation
- Structural load analysis including dead, live, wind, and seismic loads (Correct answer)
- Thermal load calculation
- Hydraulic load calculation
Correct answer: Structural load analysis including dead, live, wind, and seismic loads
A structural load analysis evaluates the roof's ability to support the array's weight plus environmental forces such as wind and snow.
Question 4: What does a negative temperature coefficient of Isc mean for a crystalline silicon PV module?
- Isc decreases as temperature rises
- Isc increases slightly as temperature rises (Correct answer)
- Isc is unaffected by temperature
- Isc doubles every 10°C
Correct answer: Isc increases slightly as temperature rises
Crystalline silicon modules have a slightly positive Isc temperature coefficient, meaning current increases marginally with temperature.
Question 5: A 240 V AC, single-phase circuit carries 20 A. What is the apparent power in VA?
- 240 VA
- 20 VA
- 4,800 VA (Correct answer)
- 960 VA
Correct answer: 4,800 VA
Apparent power (VA) = Voltage × Current = 240 V × 20 A = 4,800 VA.
Question 6: What standard torque specification concern applies when installing PV module mounting hardware on racking?
- Over-torquing is never an issue with stainless steel fasteners
- Under-torquing or over-torquing can cause frame damage or loose connections (Correct answer)
- All fasteners should be hand-tightened only
- Torque specifications only apply to electrical connections
Correct answer: Under-torquing or over-torquing can cause frame damage or loose connections
Module frames can crack if over-torqued, while under-torqued connections can loosen under wind and thermal cycling.
Question 7: Which NABCEP competency area requires understanding of wire sizing based on both ampacity and voltage drop?
- Site Assessment
- System Design (Correct answer)
- Commissioning
- Operations & Maintenance
Correct answer: System Design
System Design requires selecting conductors that meet both ampacity requirements and allowable voltage drop limits for optimal performance.
NABCEP Electrical & Mechanical Concepts 5
What is the purpose of equipotential bonding in a PV array?