Electrical & Mechanical Concepts Flashcards

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?

Answer: 38–40 V

Vmp is typically about 80% of Voc, placing it around 38–40 V for a 48 V Voc array.

Which NEC article governs the installation of photovoltaic systems?

Answer: Article 690

NEC Article 690 specifically covers solar photovoltaic systems.

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?

Answer: 252 W

ΔT = 40°C, derating = 0.4% × 40 = 16%, 300 W × 0.84 = 252 W.

What is the purpose of a fused disconnect on the DC side of a PV system?

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.

In a series-connected PV string, if one module is shaded, what happens to the string current?

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.

What does a bypass diode do in a PV module?

Answer: Allows current to flow around shaded cells

Bypass diodes allow string current to route around shaded or defective cell groups, reducing power loss.

What is the correct formula for calculating conductor ampacity derating when ambient temperature exceeds 30°C?

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.