AT&T MERLIN LEGEND Release 3.0 Installation Manual page 44

AC Power and Grounding
Concrete-Encased Ground. Must be an electrode, consisting of one
of the following:
At least 20 ft. (6.1 m) of one or more steel reinforcing rods, each at
least ½ in. (1.27 cm) in diameter
20 ft. (6.1 m) of bare copper conductor not smaller than
encased in 2 in, (5 cm) of concrete
This electrode must be located within and near the bottom of a
concrete foundation or footing that is in direct contact with the
earth.
Ground ring, consisting of at least 20 ft. (6.1 m) of bare copper
conductor (not smaller than #2 AWG) encircling the building. The
ground ring must be in direct contact with the earth and buried at
least 2.5 ft. (77 cm) below the earth's surface.
WARNING:
Do not use a metal underground gas piping system—this is a safety
risk.
Central Office Trunk Protection
The telephone company is responsible for providing the following protection
of central office (co) trunks at the entrance to the site:
Carbon blocks or gas discharge tubes connected to an approved
ground
Adequate bonding of the central office trunk protector ground and the
power company ground
CAUTION:
Check these requirements with a simple, visual inspection. If you cannot
verify that the central office grounding requirements are met, contact the
central office. Do not connect the control unit to the central office trunks
until you are certain that these requirements are met.
Installing the Control Unit 2-13
AWG,
#4