Which material can not be used with nonmetallic boxes?

The correct answer is that metal conduits cannot be used with nonmetallic boxes. This limitation stems from the differing properties of metal and nonmetallic materials. Nonmetallic boxes are typically designed to accommodate nonmetallic wiring methods, which provide benefits like resistance to corrosion and reduced weight.

When metal conduits are introduced, they can create potential grounding issues and may not be compatible with the installation methods intended for nonmetallic boxes. These boxes rely on methods that do not require the grounding and bonding that metal conduits would necessitate, which could lead to safety concerns and violations of electrical codes.

In contrast, flexible cords, nonmetallic raceways, and nonmetallic sheaths are designed to be used together safely, allowing for a consistent and compliant installation that addresses the characteristics of nonmetallic materials effectively. Hence, the incompatibility of metal conduits with nonmetallic boxes makes this the correct choice.