Which of the following is permitted to be used as an equipment grounding conductor?

The correct answer is that all of the listed options can be used as an equipment grounding conductor. Each choice represents an accepted method of grounding in electrical installations.

The armor of Type AC cable is specifically designed to provide a path for grounding faults. In this case, the metallic armor can serve effectively as a grounding conductor, ensuring that any fault current can safely flow back to the ground, helping to minimize the risk of electric shock or fire.

Building steel, which includes structural steel members, can also serve as a grounding conductor. This is particularly useful in large buildings where the steel framing provides a reliable conductive path to ground. This method of grounding is commonly employed as it provides a robust grounding system.

Similarly, the steel sheath of Type MI cable is designed to be conductive and can be used for grounding. It provides not only physical protection for the conductors inside but also acts as a grounding conductor, effectively serving the same purpose as the armor of AC cable.

Given that each of these components can fulfill the role of an equipment grounding conductor, it confirms that all listed options are permissible, reinforcing the importance of proper grounding practices for safety and equipment protection in electrical systems.