NABCEP Electrical & Mechanical Concepts 2 — Questions and Answers
Question 1: A PV array produces 48 V open-circuit and 8 A short-circuit current. What is the maximum power point voltage most likely to be?
- 48 V
- 38–40 V (Correct answer)
- 8 V
- 24 V
Correct answer: 38–40 V
Vmp is typically about 80% of Voc, placing it around 38–40 V for a 48 V Voc array.
Question 2: Which NEC article governs the installation of photovoltaic systems?
- Article 230
- Article 690 (Correct answer)
- Article 705
- Article 700
Correct answer: Article 690
NEC Article 690 specifically covers solar photovoltaic systems.
Question 3: A solar module has a temperature coefficient of power of -0.4%/°C and is rated at 300 W at STC (25°C). What is its power output at 65°C?
- 252 W (Correct answer)
- 300 W
- 348 W
- 288 W
Correct answer: 252 W
ΔT = 40°C, derating = 0.4% × 40 = 16%, 300 W × 0.84 = 252 W.
Question 4: What is the purpose of a fused disconnect on the DC side of a PV system?
- Boost voltage to inverter
- Allow safe isolation of PV source circuits (Correct answer)
- Regulate battery charge
- Convert AC to DC
Correct answer: Allow safe isolation of PV source circuits
A fused DC disconnect allows the array to be safely isolated from the inverter for maintenance or emergencies.
Question 5: In a series-connected PV string, if one module is shaded, what happens to the string current?
- Current increases to compensate
- Current is limited to the shaded module's reduced output (Correct answer)
- Voltage drops but current stays the same
- Other modules bypass the shaded module automatically
Correct answer: Current is limited to the shaded module's reduced output
In a series string, current is limited by the weakest (most shaded) module, reducing total output.
Question 6: What does a bypass diode do in a PV module?
- Increases module voltage
- Prevents reverse current flow during nighttime
- Allows current to flow around shaded cells (Correct answer)
- Measures module temperature
Correct answer: Allows current to flow around shaded cells
Bypass diodes allow string current to route around shaded or defective cell groups, reducing power loss.
Question 7: What is the correct formula for calculating conductor ampacity derating when ambient temperature exceeds 30°C?
- Ampacity × (1 + correction factor)
- Ampacity × temperature correction factor (Correct answer)
- Ampacity ÷ temperature correction factor
- Ampacity × number of conductors
Correct answer: Ampacity × temperature correction factor
NEC tables provide temperature correction factors that are multiplied by the base ampacity to derate conductors in elevated ambient temperatures.
NABCEP Electrical & Mechanical Concepts 2
A PV array produces 48 V open-circuit and 8 A short-circuit current.
What is the maximum power point voltage most likely to be?