Instruction manual

AC Power and Grounding
2-14
Installation, SPM, Maintenance, and Troubleshooting Supplement
WARNING:
An improper ground can cause equipment failures, service outages, and
electrical shock. Verify that the AC power uses an approved ground for its
primary ground, that all voltage-limiting devices are grounded to an
approved ground, and that the ground is one of the approved grounds
listed below.
Approved Grounds 2
Approved grounds are listed below, in order of preference:
■ Most preferred ground:
It must be a metal, not plastic or vinyl, underground water pipe at least
1/2 inch (1.27 cm) in diameter, and in direct contact with the earth for at
least 10 feet (3 m).
It must be electrically continuous so that the protector ground is
uninterrupted. (Check for insulated joints, plastic pipe, and plastic water
meters that might interrupt electrical continuity.)
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 grounds:
— Other local metal underground systems or structures, such as tanks
and piping systems, but not gas pipes.
— Rod and pipe electrodes, a 5/8 inch (1.58 cm) solid rod or ¼ inch
(0.63 cm) conduit or pipe electrode driven to a minimum depth of 8 feet
(244 cm).
— Plate electrode, a minimum of 2 square feet (61 square cm) of metallic
surface exposed to the exterior soil.
■ Next preferred ground:
It must be an electrode consisting of one of the following:
— At least 20 feet (6.1 m) of one or more steel reinforcing rods, each at
least 1/2 inch (1.27 cm) in diameter