Approved Grounds
encased ground, or a ground ring. If these grounds are not available, the water pipe ground can be supplemented by one of the following types of grounds:
■Other local metal underground systems or structures — Local underground structures such as tanks and piping systems
■Rod and pipe electrodes — A 5/8 inch (1.6 cm) (solid rod) or 3/4 inch (1.9 cm) (conduit or pipe) electrode driven to a minimum depth of 8 feet (2.5 meters)
■Plate electrodes — Must have a m inimum of 2 square feet (0.6 sq. meter) of metallic surface exposed to the exterior soil
Concrete Encased Ground. — An electrode encased by at least 2 inches (5 cm) of concrete and located within and near the bottom of a concrete foundation or footing in direct contact with the earth. The electrode must be at least 20 feet (6 meters) of one or more steel reinforcing bars or rods 1/2 inch (1.3 cm) in diameter, or at least 20 feet (6 meters) of bare, solid copper,
4 AWG wire.
Ground Ring. — A buried ground that encircles a buil ding or structure at a depth of at least
Approved Floor Grounds
Approved floor grounds are those grounds on the floor of each
■Building steel
■The grounding conductor for the secondary side of the power transformer feeding the floor
■Metallic water pipes
■Power feed metallic conduit supplying panel boards on the floor
■A grounding point specifically provided in the building for the purpose
!WARNING:
If the approved ground or approved floor ground can only be accessed inside a dedicated power equipment room, then connections to this ground should be made by a licensed electrician.
NOTE:
All protective grounds must be electrically connected together to form a single grounding electrode system.
