For underground service conductors only [not for feeders or branch circuits] up to 600 volts when not encased in concrete and buried 18 inches or more below grade, are required to have their location identified by a "warning ribbon" that is placed in the trench at least 12 inches above the underground installation. 300.5(D)(3)
No ribbon is required for feeders and branch circuits because they contain short-circuit and overload protection.
Table 300.50 for over 600 volts ......
Exception No. 3: The minimum cover requirements do not apply to conduits or other raceways that are located under a building or exterior concrete slab not less than 4 inches in thickness that extends not less than 6 inches beyond the underground installation.
A warning ribbon "or other effective means suitable for the conditions" must be placed above the underground installation.
[This message has been edited by Joe Tedesco (edited 10-20-2002).]
