Photovoltaic (PV) System Design Flashcards

Under NEC 2017/2020 rapid shutdown rules (690.12), controlled conductors outside the array boundary must be limited to what level within 30 seconds of initiation?

Answer: 30 V

Conductors more than 1 ft outside the array boundary must drop to 30 V or less within 30 seconds.

A home has a 200 A busbar and a 200 A main breaker. Using the NEC 705.12 120% rule with the breaker at the opposite end, what is the largest PV backfeed breaker allowed?

Answer: 40 A

120% of 200 A is 240 A, and 240 A minus the 200 A main leaves 40 A for the PV breaker.

What happens to voltage and current when identical PV modules are wired in series?

Answer: Voltages add while current stays the same

Series connections add voltage, and the current is the same through every module in the string.

Overcurrent protection for PV source circuits is generally not required when how many strings are connected in parallel?

Answer: Two or fewer

With no more than two parallel strings, fault current from the other string usually cannot exceed the module's series fuse rating.

What is the main design advantage of microinverters compared with a single string inverter?

Answer: Module-level MPPT that reduces mismatch and shading losses

Each microinverter tracks the maximum power point of its own module, so one shaded module does not drag down the others.

Which standard certifies that a grid-tied inverter has anti-islanding protection and meets utility interconnection requirements?

Answer: UL 1741

UL 1741 (including SA/SB, which reference IEEE 1547) covers inverter interconnection safety, including anti-islanding.

Designers commonly limit DC circuit voltage drop to about what level to keep losses low?

Answer: 2%

Keeping DC voltage drop to about 2% (within an overall budget of 2–3%) is common practice, even though the NEC does not require it.