AT&T MERLIN LEGEND Installation & Maintenance Manual page 104

Preparation
Each power supply module in the CU must be connected to the
single-point ground bar by a #12 AWG or a #14 AWG solid
copper wire. The wire run should not exceed 25 feet. (See
"Provide Proper Grounding" in Chapter 3, "Installation.")
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 below.
Approved grounds (listed from most to least preferred) are
building steel
acceptable water pipe-must be a metal, underground water
pipe at least 1/2 inch in diameter, in direct contact with the
earth for at least 10 feet. It must be electrically continuous (or
made electrically continuous by bonding around insulated
joints, plastic pipe, or plastic water meters) to the point where
the protector ground 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 grounds:
metal underground gas piping system—an electrically
continuous metal underground 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 structures such as tanks and piping
systems
2-12 Power and Grounding