The NEC does not explicitly define a "basement". It references basements in various sections but relies on the general understanding of what constitutes a basement. However, it does define "basement" in one specific context: Article 550 - Mobile Homes, Manufactured Homes, and Mobile Home Parks: In this article, 550.2 defines a basement as: "The portion of a building that is partly or completely below grade."General Understanding & Considerations

The common understanding of a basement is a story of a building that is partially or entirely underground.

Ranch House & First Floor

Based on the information you provided: No, the first floor of a ranch-style house, that opens directly to the outside, is generally NOT considered a basement.* A basement is either entirely or partially below grade (ground level). If the floor you're describing opens directly to the outside, it's at grade level and therefore is not a basement. It would be considered the main living level or ground floor.

In Summary

The NEC doesn't have a universal definition of a "basement" for all applications. The general understanding is a story below grade, and a ranch house's first floor that opens directly to the outside is typically NOT a basement. If a ranch house has a portion of the structure below grade it may have a basement. The NEC Article 550 has a definition of "Basement". Flag for review