Electrical metallic tubing must be constructed from which of the following materials?

Electrical metallic tubing (EMT) is specifically designed for electrical installations and is used for routing and protecting electrical conductors. The correct material for EMT is steel, which provides the necessary strength, durability, and conductivity required for this type of application.

Steel EMT is recognized for its excellent resistance to impact and corrosion when properly coated, making it suitable for both indoor and outdoor environments. Additionally, its magnetic properties often help in grounding installations.

Other materials mentioned in the options, while used in various electrical applications, do not meet the specifications for EMT. For example, red brass and aluminum are not typically utilized for EMT due to factors like cost, weight, and material properties that do not align with the robustness required in metal conduit applications. Plastic is also not suitable for EMT, as it lacks the mechanical strength and grounding capabilities of steel, which is critical for safety in electrical installations. Thus, steel is the appropriate choice and is widely accepted in electrical code regulations governing the use of metallic tubing.