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

An equipment grounding conductor (EGC) serves to create a low-resistance path to the ground for electrical faults, enhancing safety by helping to prevent shock hazards and ensuring that overcurrent protective devices operate effectively. The essential requirement for an EGC is that it must have the capability to safely carry fault current until the circuit overcurrent protective device operates.

The first option highlights that a bare conductor included within a listed cable assembly can serve as an EGC because it is designed for this function and meets the necessary standards for grounding.

The second option discusses a metallic cable sheath or armor, which can also serve as an EGC. Such sheathing provides a grounded path back to the electrical service for fault currents, thereby helping to protect both the equipment and individuals.

The third option indicates that a metallic water piping system is permitted to act as an EGC. In this case, it must be effectively bonded to the grounding system and is often used in installations where it is practical.

Therefore, since each of these elements has been recognized and set forth in electrical standards as capable of functioning safely and effectively as grounding conductors, the correct answer encompasses all of them.