AT&T MERLIN LEGEND Release 3.0 Installation Manual page 43

AC Power and Grounding
WARNING:
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
Approved grounds are listed below, in order of preference:
Building Steel. The most preferred ground.
Acceptable Water Pipe. Must be a metal, not plastic or vinyl,
underground water pipe at least ½ in. (1.27 cm) in diameter, and in
direct contact with the earth for at least 10 ft. (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-in. (1.58-cm) solid rod or ¼-in.
(0.63-cm) conduit or pipe electrode driven to a minimum depth of 8
ft. (244 cm)
— Plate electrode, a minimum of 2 square ft. (61 square cm) of
metallic surface exposed to the exterior soil
2-12 Installing the Control Unit