AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 69

Introduction
For most surge occurrences, the following standard grounding requirements
provide adequate lightning and power surge protection:
Properly wired/grounded/bonded outside line protectors
Properly wired/grounded AC outlet
Properly grounded single-point ground bar
Properly wired connection between single-point ground and power
supplies
Additional Power Surge Protection
The 391A1 power supply has built-in AC line protection. This built-in protection
handles almost all situations.
occasionally, additional protection may be needed if the customer is located in
a heavy lightning area. A 147A surge protector can be connected to the
system to limit surges from the AC lines and outside lines. One 147A protector
provides protection for four outside lines. Up to three 146A protectors can be
added to the 147A to provide protection for a maximum of 16 outside lines. For
more than sixteen lines, additional 147A protectors are required.
Concrete-encased ground--must be an electrode, consisting of
one of the following:
— At least 20 feet (6.1 meters) of one or more steel
reinforcing rods, each being at least 1/2-inch (1.27 cm) in
diameter
— 20 feet (6.1 meters) of bare copper conductor not smaller
than #4 AWG, encased in 2 inches (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---consists of at least 20 feet (6. 1 meters) 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 feet (77 cm)
below the earth's surface.
WARNING:
Do not use metal underground gas piping system—this
is a safety risk.
System Capacities and Requirements 1-41