AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 68

Introduction
The telephone company is responsible for providing protection of outside
lines/trunks at the entrance to the site. The protection should consist of the
following:
Carbon blocks or gas discharge tubes connected to an approved
ground
Adequate bonding of the outside line/trunk protector ground and the
power company ground
The following is a list of approved grounds, starting with the most
preferred:
1-40 System Capacities and Requirements
WARNING:
An improper ground can result in equipment failures and
service outages. 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 below.
Building steel
Acceptable water pipe-must be a metal, underground water
pipe at least 1/2-inch (30.4 cm) in diameter, and in direct contact
with the earth for at least 10 feet (3 meters).
It must be electrically continuous so that the protector ground is
connected. (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—
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 (244 cm)
—
Plate electrode—a minimum of 2 square feet
(61 square cm) of metallic surface exposed to the exterior
soil