Large-Scale Photovoltaic Electric Supply Stations

Article 691 was created because utility-scale PV had outgrown the rooftop-oriented rules of Article 690. A giant solar station is a power plant with restricted public access, professional operators, and engineered documentation. So 691 lets certain provisions be handled through engineering supervision and stamped studies rather than prescriptive one-size rules, while still ensuring the interconnection and safety fundamentals hold.

I find this article exciting because it treats big solar as the serious generation it has become. On these sites the documentation, the fault studies, and the qualified-person requirements do the heavy lifting, and my field work has to line up exactly with the engineered package instead of improvising like on a small residential array.

When it applies

Article 691 is for utility-scale PV generating stations, the big engineered plants pushing serious power onto the grid. It recognizes that a plant designed, built, and maintained by qualified people under engineering supervision can follow certain performance-based rules instead of the prescriptive residential and commercial requirements.

Common mistakes

• Trying to apply Article 691 to a rooftop or small commercial array. It is written for large stations meeting specific size and access criteria.
• Assuming engineering supervision replaces documentation. The stamped studies and load calcs are the whole basis for the alternative rules.
• Overlooking that public access restrictions are part of what makes the relaxed approach acceptable.

In the field

On a large ground-mount project the design leaned on engineered studies for things like available fault current and rapid shutdown that a small system would handle prescriptively. What makes that legitimate is the whole package: qualified operators, restricted access, and stamped engineering behind every decision. If you cannot produce that documentation, you are not in 691 territory, you are back in the standard PV rules.