TM 5-811-3/AFM 889, Chap. 3
2-5. Nonreinforced concrete or wood frame
will extend not less than 3 feet nor more than 8 feet
buildings. Lightning protection will be provided on
beyond the perimeter of building walls or footings.
outside of exterior surfaces without reliance upon
Conductor ends, connections to down conductors,
components of building for conductors. Fasteners for
tops of ground rodsj and crossovers will reconnected
conductors will be other than aluminum on concrete,
for electrical continuity. Figure 2-3 illustrates a be-
and will be selected for attachment to building con-
low grade weapons system facility counterpoise. Pat-
crete or wood.
tern will be as required in this manual or as required
by using service.
26. Reinforced concrete buildings. Reinforce-
d. Radials. A radial system of grounding consists
of one or more No. 1/0 AWG copper conductors not
ment steel may be used for down conductors in con-
less than 12 feet long, extending away from each
formance with NFPA No. 78 and if approved by the
using agency. Joints should be made in no fewer than
ground rod or grounding connection. The use of mul-
tiple radials is an effective form of grounding, offer-
every fifth reinforcement rod and at corners of build-
ing substantially lower reactance to the high fre-
ing. Joints will be made electrically conductive and
will be connected top and bottom for connections to
quency of lightning current wave fronts than do
roof conductors and to grounding electrodes, respec-
single straight conductors. Installation of grounding
radials will take advantage of crags and cracks in
tively. Grounding pigtails from bottoms of reinforce-
ment fabric will be connected to exterior grounding
surface rock formations in obtaining maximum avail-
system at same or lower elevation as that where pig-
able earth cover. Connections of radials to down con-
tails leave walls and footings.
ductors will be made so as to insure electrical
FINISHED
GRADE
2-5
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