What is the primary focus of Article 551 in the National Electrical Code?

The primary focus of Article 551 in the National Electrical Code is indeed on Recreational Vehicles and Recreational Vehicle Parks. This article establishes the specific requirements for the safe installation and use of electrical systems within recreational vehicles, ensuring that they meet safety standards for both the vehicles themselves and the various parks where they may be stationed.

By detailing the appropriate methods for wiring, grounding, and overall electrical system design within these contexts, the article helps to promote the safety and efficacy of electrical installations in these mobile living environments. This is crucial given the unique challenges posed by transportable structures, including the need for compliance with varying local regulations and safety protocols.

Understanding the context of the other options highlights the specificity of Article 551. While park trailers, floating buildings, and electric signs may each have their respective sections within the NEC, they fall under different articles that address their unique requirements. This distinction underscores why Article 551 is particularly centered on recreational vehicles and their associated parks, thus validating the correctness of the provided answer.