NCCER Electrical Level 2 Practice Exam

Non-metallic sheathing is the correct insulation used in NM (non-metallic) cable. NM cable, often referred to as Romex, is widely utilized in residential wiring due to its cost-effectiveness and ease of installation. The non-metallic sheathing is designed to protect the insulated conductors inside from moisture and mechanical damage while also providing a lightweight and flexible solution.

This type of insulation allows for safe usage in dry locations, which is typical for much of residential wiring. The sheathing is made from thermoplastic materials that provide adequate insulation and are non-conductive, ensuring electrical safety. In addition, non-metallic sheathing adds to the overall durability of the cable while also resisting many environmental factors that could impact performance over time.

The other types of insulation mentioned do not apply to NM cable for various reasons. For instance, metallic coating is not used in NM cable because this type of cable is designed to be lightweight and flexible without the added weight and rigidity of metal. Rubber insulation is typically associated with other types of wiring or flexible cords, while polyethylene insulation is more common in specialized applications like outdoor or high-temperature environments rather than standard residential wiring.