TM 5-811-3/AFM 88-9, Chap. 3
ring to become set below apron surface. The recessed
grounding conductors of the static electricity protec-
cavity will be wide enough to permit static grounding
tion systems, when required, will be bonded to these
temporary connections to metal tie-down ring. Re-
other protective systems at convenient locations be-
sistance to ground of each tie down ring connected to
low finished grade. Separate static electricity protec-
the reinforcing steel can be anticipated to be less
tion is not required for static producing units such as
than 10,000 ohms. In hydrant refueling areas one
doors, fixed or movable equipment, electric motors,
static grounding tie-down ring will be installed be-
and storage containers, when these items are bonded
tween each refueling hydrant and electrical cable
electrically to other grounding type of protection sys-
control box. Tie-down ring grounding electrode inter-
tem. When question arises whether static electricity
connections between hydrant and cable housing will
generating sources may be controlled, these units
not be required. Static grounds are not designed for
will be bonded to a grounding system to assure
aircraft lightning protection.
safety of personnel and prevent malfunction and
breakdown of weapons system tactical control func-
3-12. Airplane hangar floors. Grounding devices
tions. Weapons system support facilities provisions
installed in floors are intended to serve for airplane
for static electricity protection will conform to above
static and equipment grounding. A static grounding
general requirements.
system conforming to NFPA No. 77 is suitable for
3-9. Classified communications buildings.
dissipation of any aircraft static electricity to ground.
Classified communications cannot risk being compro-
However, inasmuch as NFPA No. 70 requires a max-
mised and endangered by permitting ungrounded
imum of 25 ohms resistance to ground for equipment
static electricity discharges. Static electricity
grounding, the 25-ohms requirement will govern for
generating equipment used in classified communica-
this dual-purpose grounding system. Floor grounding
tions operations will be bonded to a grounding sys-
systems electrodes will be interconnected below con-
tem separate from other grounding systems in ac-
crete, and interconnection also will be made to han-
and
with
MIL-HDBK-419
cordance
gar electrical service grounding system. Interconnec-
MIL-STD-188-124. This is required to insure com-
tions will be of not less than No. 4 AWG bare copper.
plete invulnerability to intelligence countermeasures
Each floor receptacle will consist essentially of a
from any possible potential static electricity dis-
housing, grounding connection stud, housing cover,
charge, No fewer than two shielded grounding buses
and ground rod as illustrated in figure 3-1. Floor lay-
will be provided within each classified room or area.
outs for receptacles will be essentially as follows:
Not more than two such grounding buses will be con-
a. Where hangars will be used for a specific num-
nected by shielded conductor to one electrode below
ber and type of aircraft, one grounding electrode will
finished grade, Grounding buses will be arranged
be provided for each aircraft space approximately 10
with a number of shielding one-wire grounding recep-
feet from the centerline of the aircraft space in the
tacles to provide a plug-in grounding jack (telephone
vicinity of one of the main landing gears.
type) connection for each classified unit of equip-
b. For general purpose hangars, electrodes will be
ment, Grounding of other than classified equipment
provided for each aircraft space approximately 10
to these grounding buses will be permitted. Ground
feet from centerline of the aircraft space, and will be
rods will be driven into earth so that tops and con-
installed at 50-foot intervals. Spacing of electrodes
nections thereto will be not less than 2 feet below fin-
from wall lines or columns will not exceed 50 feet.
ished grade.
3-13. Conductive flooring. Where conductive
3-10. Corrugated steel arch type igloos for
flooring is provided in an area of a room, it is not nec-
s t o r a g e of MB-1, GAM-87 and GAR cased
essary to provide separate grounds for metal frames
p r o p e l l a n t type weapons. Static electricity
of nonelectric equipment located on that flooring.
grounding of case will be bonded to the lightning pro-
Conductive floors are provided essentially to protect
tection grounding electrodes. This arrangment will
operating and maintenance personnel from hazards of
permit no space between cased weapons and storage
shock where personnel may otherwise become ex-
racks for possibility of any static spark.
posed to low resistances to ground (less than 25,000
ohms), at voltages of electrical distribution system,
3-11. Airplane parking aprons. Static electricity
or other hazardous area system, The following guide
grounding in new construction for airplane parking-
may be used in identifying hazardous conditions and
hydrant refueling areas will be accomplished with a
materials requiring conductive flooring for protection
closed metal tie-down ring, 1% inch inside diameter,
of personnel from static electricity:
welded to the reinforcing steel in the concrete, Park-
a. Areas containing units of operating equipment
ing apron will be provided with a recess cavity at
hazardous to operating and maintenance personnel.
each ground rod location, permitting top of tie-down
3-4
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