TM 5-811-3/AFM 889, Chap. 3
corrosive soils is impracticable, use of stainless steel
magnetic shielding not suitable for complete lightning
rods and magnesium-anode protection will be consid-
protection system. However, exterior protection
ered. Driving stud bolts will be used for driving, and
grounding system will be bonded to static electricity
couplings will be used for sectional rods. Where
exterior grounding system.
buried metal pipes enter a building, the nearest
b. Ground rods. Ground rods will be not less than
ground rod will be connected thereto.
10 feet in length, nor less than -inch diameter pipe
c. Earth electrode subsystem. Each earth electrode
or equivalent solid rod. Ground rods will be located
subsystem or counterpoise will consist of one or more
clear of paved surfaces, walkways, and roadways.
closed loops or grid arrangement of No. 1/0 AWG
Rods will be driven so that tops are at least six
bare copper conductors installed around facility pe-
inches below finished grade, and three to eight feet
rimeter not less than 2 feet below earth surface.
beyond perimeter of building foundation. Where
Larger conductors should be used when installed in
ground rods are used with a counterpoise, tops will
highly corrosive soils. A second loop, if used, should
be driven to same elevation as counterpoise below
not be less than 10 feet beyond the first and inner
finished grade. Exact location of rods must give pref-
loop. At least 2 ground rods should be provided at
erence to use of moist earth. Contact with chemically
each corner of each counterpoise loop where earth-
injurious waste water or other corrosive soils wiIl be
seeking current tend to concentrate. Counterpoise
avoided. Where avoidance of chemically injurious or
ROOF RIDGE
LOCK NUTS OR
COUPLING
R
s
P
CONDUCTOR
US Army Corps of Engineers
Figure 22. Typical air terminal assembly using steel, framing as
protective system conductor
2-4
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