What is a requirement for ENT material according to NEC standards?

The requirement that ENT (Electrical Nonmetallic Tubing) material must be moisture and chemical resistant aligns with the standards set by the National Electrical Code (NEC). This characteristic is crucial because ENT is often used in environments where exposure to moisture or various chemicals could occur, such as in basements or commercial settings. The moisture and chemical resistance ensures that the tubing maintains its integrity and does not degrade over time, which would compromise electrical safety and system reliability.

The other attributes mentioned in the incorrect options do not align with the NEC standards for ENT. For instance, ENT does not need to be filled with electrical insulation, as it is designed to provide a pathway for electrical conductors without such filling. It is also not required to be made of metal; ENT is specifically a nonmetallic type of conduit. While flexibility can be an advantage in certain applications, the NEC does not mandate that ENT be inflexible; it can actually be somewhat flexible to accommodate different installation scenarios. Therefore, the requirement for moisture and chemical resistance is the key aspect highlighted in the NEC specifications for ENT material.