AT&T 3.0 manual Approved Grounds

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

2-12Installing the Control Unit