National Electrical Code (NEC) Article 690 Practice Test

The maximum DC voltage for a photovoltaic (PV) source circuit is calculated by considering the effects of the lowest expected ambient temperature. This is important because as the temperature decreases, the voltage output of the PV modules can increase due to the negative temperature coefficient of the materials used in solar cells.

When assessing the maximum voltage, it's essential to take into account this potential rise in voltage during colder conditions, as it can affect the system's safety and performance. The calculation ensures that the system components, like inverters, breakers, and wiring, can handle these higher voltages without risk of failure or fire.

While the voltage ratings of the modules and manufacturer guidelines provide useful information, they do not directly address the effects of temperature on voltage output. The average voltage rating does not accurately reflect the maximum voltage that can occur during extreme temperature conditions, which is why the correct approach is to adjust for these ambient temperature conditions. This consideration helps ensure that installations comply with safety standards and operate effectively under varying weather conditions.