What type of wire must be accessible within a plumbing system according to regulations?

Tracer wire must be accessible within a plumbing system according to regulations because it plays a crucial role in the identification and locating of underground utility lines. Tracer wire is specifically designed to aid in detecting the position of non-metallic piping, such as PVC or polyethylene, which does not have inherent metallic properties that would allow for traditional locating methods. It ensures that any underground plumbing systems can be accurately mapped and located, preventing accidental damage during excavation or construction activities. This is particularly important for safety and compliance with local and national regulations regarding utility line management. The accessibility of tracer wire allows for easy connection to locating devices, facilitating maintenance and ensuring that plumbers can adhere to best practices in the field.