What does "listed" refer to in terms of equipment?

The term "listed" in the context of equipment refers to items that have been evaluated and approved by a recognized testing laboratory or organization, ensuring that they meet specific standards for safety and performance. When equipment is "listed," it signifies that it has undergone rigorous testing and has met the criteria set forth by standards organizations, which is vital for ensuring compliance with safety regulations.

Listed equipment is typically included in a published document or database provided by the testing organization, allowing professionals to verify that the equipment is of suitable quality and safety. This is particularly important in industries such as gas installation, where the integrity and reliability of equipment are crucial to preventing accidents and ensuring safe operation. The listing serves as a mark of assurance for consumers and professionals alike.

Other options do not correctly capture the essence of what "listed" means within this context. Equipment being less expensive than labeled items does not imply any safety or quality standards; aesthetic approval alone does not ensure performance; and the notion that listed equipment does not require periodic inspections oversimplifies the ongoing obligation to ensure safety standards are met continually.