What is the name for a raceway of circular cross-section made of helically wound, formed, interlocked metal strips?

The correct answer is Flexible Metal Conduit. This type of conduit is specifically designed to be flexible while providing protection for electrical wiring. The helically wound structure, formed from interlocked metal strips, allows it to bend and flex around obstacles, which is crucial for applications where the layout requires adaptability. This flexibility makes it particularly useful in areas where traditional rigid conduits would be too cumbersome to install or would not provide the necessary flexibility for movement or changes in direction.

Flexible Metal Conduit also offers mechanical protection and is often used in environments where robust construction is required. Its design allows for easy installation and is suitable for use in both exposed and concealed applications. In comparison, flexible plastic conduit does not offer the same level of mechanical strength and is primarily used in less demanding installations. Rigid metal conduit is not flexible at all, making it unsuitable for applications needing bending. Non-metallic conduits, while lightweight and resistant to corrosion, do not possess the same mechanical integrity as Flexible Metal Conduit, especially in environments that may involve physical stress.