Instruction manual

POWER AND GROUNDING
Grounding
An approved ground for the cabinets used in the equipment room is essential. A typical
approved ground is one of the following:
Grounded Building Steel —The metal frame of the building where effectively grounded
by one of the following grounds: acceptable metallic water pipe, concrete-encased
ground, or a ground ring.
Acceptable Water Pipe —A metal underground water pipe, at least 1/2-inch in diameter,
in direct contact with the earth for at least 10 feet. The pipe must be electrically continu-
ous (or made electrically continuous by bonding around insulated joints, plastic pipe, or
plastic meters) to the point where the protector ground wire is connected. A metallic
underground water pipe must be supplemented by the metal frame of the building, a
concrete-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 ground:
— Metal underground gas piping system—An electrically continuous metal under-
ground gas piping system that is uninterrupted with insulating sections or joints
and without an outer nonconductive coating
— Other local metal underground systems or structures—local underground struc-
tures such as tanks and piping systems
— Rod and pipe electrodes—A 5/8-inch (solid rod) or 3/4-inch (conduit or pipe)
electrode driven to a minimum depth of 8 feet
— Plate electrodes—Expose a minimum of 2 square feet of metallic surface to the
exterior soil
Concrete-Encased Ground —An electrode encased by at least 2 inches 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 of one or more steel reinforcing
bars or rods, not less than 1/2 inch in diameter, or at least 20 feet of bare, solid copper
wire not smaller than 4 AWG.
Ground Ring —A buried ground that encircles a building or structure at a depth of a least
2-1/2 feet below the earth’s surface. The ring must consist of at least 20 feet of bare
copper conductor not smaller than 2 AWG.
All approved grounds used must be bonded together to form a single grounding electrode system
as required in Section 250-81 of the National Electrical Code.
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