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MIL-HDBK-419A
2.4 GROUNDING CONSIDERATIONS FOR CLASSIFIED INFORMATION PROCESSORS (RED/BLACK
EQUIPMENTS) INSTALLED PRIOR TO THIS HANDBOOK.
2.4.1 Introduction. Previous chapters of this handbook provide grounding, bonding, and shielding practices for
unclassified (BLACK) portions of the facilities or systems, and although the BLACK facility ground subsystem
constitutes the basic ground for the whole facility, special additional grounding considerations must be designed
into those facilities which process classified (RED) information. This section will cover those requirements
which are necessary for the RED/BLACK grounding subsystem.
2.4.2 Existing Facilities. In the past, communication facilities have been designed and installed with separate
RED and BLACK ground systems isolated from each other as shown in Figure 2-17. Each of these systems was
generally installed as single-point or tree-type grounding networks. While these systems generally do not meet
the current requirements of MIL-STD-188-124A, they continue to be in use at existing facilities. Descriptions
of these systems are therefore included for maintenance purposes only. Single-point signal ground systems
(either RED or BLACK) will not be installed in new or upgraded facilities processing classified information.
Any major building or facility rehabilitation should include upgrading the signal reference subsystem to include
use of the equipotential plane.  All additions to existing buildings shall include an equipotential plane in
accordance with MIL-STD-188-124A.
2.4.3 Protection Grounds. The methods of providing a ground for the signal reference subsystem are variable,
and dependent on system equipment type, configuration, level of signaling, number of equipments, and location
of the facility. These methods were intended to provide general parameters and outline the basic concept of a
grounding system which would ensure an adequate signal-to-noise ratio in signaling circuits while affording
requisite system security. The prime purpose of this guidance is to reduce or eliminate the number of points in
the limited exclusion area (LEA) at which the RED equipment area nonferrous shield or signal ground makes
contact with the distribution facilities or components of the ac fault protection subsystem in the LEA (including
the equipment cases, duct, conduit, frames, panels) at other than intended points. Such isolation was intended
to help reduce the probability of compromising emanations on the ac fault protection subsystem in the LEA.
The physical makeup of many equipments in the government inventory however precludes complete separation
of the ac fault protection subsystem from the signal reference subsystem. The ac fault protection subsystem
was made up of several components for which the prime purpose is to safeguard life and equipment throughout
the facility and is generally based on requirements defined in MIL-STD-188-124A. (Also See Figure 1-69.) The
following comprise the fault protection ground subsystem:
AC Metal. The ac metallic distribution subsystem (part of the fault protection subsystem) of a
a.
facility includes all equipment cases, cabinet racks, duct, conduit (rigid, EMT, flexible) metallic cellular
flooring, technical power panels, main power panels, and distribution frames, connected or interconnected in
such a manner that the components are electrically common and connected to the ac protection ground or earth
electrode subsystem. (See Figure 1-69.) Electrical continuity of the system is accomplished via metal-to-metal
contact.
Grounding (Green) Wire. The ac power required to operate equipment in the facility has the hazard
b.
integrity doubly insured by the inclusion of an unbroken green grounding conductor within the normal ac
metallic distribution or the fault protection subsystem of the facility. This green grounding conductor is
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