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 MIL-HDBK-232A
60. Grounding, bonding, and shielding (GBS). Grounding of transportable
facilities is dependent on the type of operation and the terrain. Short-term
operation and rapid deployment or frequent relocations may require the use of
a single earth electrode. Operation in one area for more than 1 or 2 hours,
however, would permit the use of a more extensive and effective ground
system. All transportable shelters should have at least two ground terminals
at diagonal corners of the shelter. Systems operated in the same geographic
area should have an EESS and should be connected to the EESS of other
shelters so long as the length of the interconnecting ground conductor is 12
feet (3.6 m) or less. Longer conductors should not be used as this would
increase the vulnerability to lightning or EMP/HEMP. Various ground systems
may be used for transportable systems.
60.1 Metal shelters. Shelters constructed of metal material should use the
inner and outer skin as an equipotential ground plane. This requires all
seams to be continuously welded so that the resistance of the seam is not
more than the resistance of the conductive panel. This will create a
circumferential, low impedance, conductive path to ground. Multiple ground
terminals should be welded to the outer skin so that multiple ground
conductors may be connected between the shelter and the EESS. When
installing the ground terminals, all paint or other protective substances
should be removed prior to installation to provide a good mechanical and
electrical bond. Welds should be circumferential to assure proper and
effective bonding. Internal grounds should consist of threaded terminals of
1 inch (25 mm) by 0.25 inch (6 mm) copper ground bus, welded or brazed to the
skin. Prior to installation, the skin should be free of any insulating
materials that may increase resistance in the ground network. Then, the
ground terminal should be circumferentially welded. The inner and outer
skins should be bonded to the shelter frame at multiple points to provide
electrical continuity. All welds should he treated with a conductive,
protective coating to prevent corrosion and deterioration. The skin of the
shelter should be bonded to the transporting frame (if the shelter is
permanently affixed to the frame) by welding ground conductors (solid strap
with a stress bend) to the skin and frame at multiple points to assure that a
difference in potential does not exist.
60.2 Nonconductive shelters. Shelters constructed of nonconductive material
should have a copper mesh screen installed between the inner and outer skin
to form an equipotential ground plane. The screen should be installed in the
floor, ceiling, and all walls of the shelter and should cover all surfaces
except apertures for air-conditioners and cable entrance plates.
Air-conditioner mounts and cases should be bonded to the screen. Cable
entrance plates should be circumferentially welded to the screen and
connected to the EESS using a No. 2 AWG stranded copper wire. Since the
-screen in the door must be detached from the rest of the screen to permit
the door to open and close, multiple flexible conductors should be bonded
to-the door and main screens.
60.3 Earth electrode subsystem (EESS). An effective method of providing the
earth ground is to use a circumferential EESS that consists of multiple
copper-clad steel rods installed around the shelter. The rods should be 5
feet (1.5 m) long and 0.75 inch (19 mm) in diameter. At least two ground
rods should be installed at diagonal corners of the shelter. Additional rods
may be installed if the shelter size permits. It is important, however, that
a minimum distance of one rod length and a maximum distance of two rod
lengths is maintained between rods (see figure A-3). For shelters which are
too small to permit proper spacing when using rods at each corner, one rod
will be installed at the front corner and another rod at the diagonal rear
corner. The purpose of using multiple rods is to provide more than one
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