How high must a warning ribbon be placed above the ungrounded installation for direct-buried conductors that are buried 18 inches or more below grade?

The requirement for placing a warning ribbon above direct-buried conductors is established to ensure safety and alert anyone digging in the area to the presence of electrical installations below. According to the National Electrical Code (NEC), when conductors are buried at a depth of 18 inches or more, a warning ribbon must be placed above them, specifically at a height of 12 inches from the top of the buried conductors.

This 12-inch placement serves as a clear indication to notify individuals of the potentially hazardous wiring below, thereby decreasing the risk of accidental damage during excavation or landscaping activities. The height is designed to balance visibility and practicality, allowing for easy identification while not being too far above the ground, which could reduce its effectiveness.

In contrast to this correct answer, other heights do not comply with the safety measures recommended for electrical installations. For instance, placing the warning ribbon at 6, 10, or 18 inches would not meet the NEC guidelines and could potentially lead to accidents or damage to the buried electrical systems, as these heights either fall short of the required standard or exceed practical visibility guidelines.