Instruction manual

ENVIRONMENTAL REQUIREMENTS
Grounding
Connection of an approved ground to the system cabinets is essential. An approved ground
may consist of any of the following:
● Grounded Building Steel
—The metal frame of the building.
● Water Pipe—
A continuous metal water pipe, not less than 1/2 inch diameter, that is
connected to an underground metal water pipe that is in direct contact with earth for
10 feet or more.
● Concrete-Encased Ground—
An electrode encased by at least 2 inches of concrete
and located within and near the bottom of a concrete foundation or footing in direct
contact with the earth. The foundation must consist of at least 20 feet of one or
more steel reinforcing bars or rods of not less than 1/2 inch diameter, or at least 20
feet of bare, solid copper wire no smaller than No. 4 gauge.
● Ground Ring
—A ring that encircles a building or structure in direct contact with earth
at a depth of at least 2-1/2 feet.
The ring must consist of at least 20 feet of bare
copper conductor no smaller than No. 2 gauge.
Lightning Protection
The System 25 lightning protections plan requires five distinct but interdependent items at
each installation:
● Primary protection in the form of voltage limiters (typically carbon blocks or gas
tubes). These devices bypass surges to approved building ground and limit potential
differences between T/R pairs and building ground to less than 1500 volts.
● A single-point ground (SPG) system that connects green wire ground, System 25
system ground, and telephone company (TelCo) ground together and to approved
building ground (Figure 6-3).
● Coupled bonding conductor (CBC) connected between the TelCo ground at the
building entrance and System 25’s SPG.
CBC is tie-wrapped to all trunks to provide lightning protection; it can be a 16-gauge
ground wire or continuous cable sheath. The CBC should also be run from the
TelCo-provided network interface to the ground block of cabinet 1 (see Figure 3-4 in
the “Functional Description”
section). If the TelCo has not extended the CBC from
the facility entrance to the network interface, the installer should run the CBC along
the same route as the incoming facilities where feasible.
● Secondary protection provided within TN742 and all trunk CPs; such ports can
withstand 800 volt metallic (differential) and 1500 volt longitudinal (common mode)
surges.
6-10