Which type of cable must be secured at specific intervals according to electrical code?

Nonmetallic-sheathed cable is the correct answer because it is specifically addressed in electrical codes that require it to be secured at regular intervals to ensure safety and prevent physical damage. This type of cable, commonly recognized by its plastic sheath, must be fastened in place to maintain its integrity and to minimize hazards such as excessive movement or potential abrasion against surfaces.

The requirement for securing nonmetallic-sheathed cable applies within the guidelines outlined in the National Electrical Code (NEC), which helps to standardize electrical installations for safety. Regular securing not only helps to protect the wire insulation but also contributes to the overall safety of the electrical system by preventing unintentional movement that could lead to wear or accidental contact with other materials.

In contrast, other types of cables such as metal conduit and armored cable are usually less prone to physical damage due to their construction and therefore may not have the same stringent securing requirements, although they must still comply with relevant code provisions. Flexible cables typically may not need to be secured as frequently due to their intended use in movable applications, where flexibility is a key characteristic.