Which NEC rule type is indicated by the words 'shall' or 'shall not'?

• A. Mandatory Rules
• B. Permissive Rules
• C. Advisory Rules
• D. Interpretive Rules

Answer: (A)

In the NEC, the words “shall” and “shall not” signal a binding requirement. When the code says something shall be done, that action is required; when it says something shall not be done, that action is prohibited. This makes the rule mandatory and enforceable, guiding safe and compliant installations.

Other language like “may” or “permitted” indicates permission to do something, not a mandate, while terms such as “should” or “advisory” suggest a recommended practice rather than a strict requirement. Interpretive language is used to clarify how to apply existing rules, not to impose a new mandatory action.

So the best choice is the one that describes these as mandatory rules.