Where a building is supplied by an ungrounded system, what must the feeder include?

In an ungrounded system, the feeder must include either an equipment grounding conductor or a supply-side bonding jumper to ensure safety and functionality in the electrical system. This requirement is essential because ungrounded systems do not have a direct path to ground, which can create potential safety hazards if ground fault conditions occur. By incorporating an equipment grounding conductor or a supply-side bonding jumper, it ensures a reliable way to facilitate fault currents safely to ground, ultimately protecting equipment and personnel.

Equipment grounding conductors provide a low-resistance path back to ground, which helps mitigate the risk of electric shock and unintended electrical currents, while supply-side bonding jumpers can help in maintaining a low-impedance path for fault currents to operate circuit protection devices effectively. Thus, the correct answer underscores the necessity of including either of these components in an ungrounded system to adhere to safety standards and provide proper protection in the electrical installation.