Which of the following is NOT a permissible material for electrical metallic tubing?

The correct answer is red brass, which is not a permissible material for electrical metallic tubing (EMT). EMT is specifically designed to be constructed from certain materials that ensure its effectiveness in an electrical installation. The primary materials acceptable for EMT are steel, aluminum, and certain other metal alloys that provide the necessary strength, durability, and conductivity.

Steel is commonly used in EMT because it is strong and provides good protection against physical damage. Aluminum is also used due to its lightweight properties and resistance to corrosion, making it suitable for various environmental conditions. Copper, while not typically used in EMT, is often found in other types of electrical conduits, such as flexible or rigid conduits.

Red brass, while it does have some electrical applications due to its excellent conductivity and corrosion resistance, does not meet the standards for EMT as it lacks the structural properties required for this specific application. EMT needs to provide reliable protection and support for electrical wiring, and red brass does not fulfill these criteria. Thus, it is not an acceptable material for electrical metallic tubing.