Underground service conductors that are buried 18 in. or more below grade shall have their location identified by a warning ribbon placed at least ________ above the underground installation.

The requirement for placing a warning ribbon above underground service conductors buried at least 18 inches below grade is designed to ensure safety during excavation activities. By placing the ribbon 12 inches above the installation, it provides a clear visual marker for anyone digging in the area to be aware of the presence of these conductors. This helps prevent accidental damage to the underground wiring, which can pose serious safety hazards.

The specified height of 12 inches is a standard practice that balances visibility with practical excavation considerations, allowing for enough space above the conductors for the ribbon to be easily seen while still keeping in mind the depth of the buried conductors. This measure is part of compliance with safety regulations that aim to protect workers and the infrastructure itself from potential hazards associated with unintentional contact with electrical lines.