In the NEC, what word or words indicate a mandatory requirement?

In the National Electrical Code (NEC), the terms that indicate a mandatory requirement are "shall" or "shall not." The use of "shall" conveys an imperative duty, indicating that compliance is not optional. This language is critical in technical standards like the NEC, as it ensures that specific safety, performance, and construction standards are met in electrical installations.

Using "must" can imply a similar requirement in some contexts, but in the NEC, "shall" is more firmly entrenched in the legal and compliance vernacular. This precision in language helps avoid any ambiguity regarding what is required for safety and functionality in electrical systems, thus ensuring that all professionals in the field can rely on a clear and uniform interpretation of the regulations.