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 MIL-HDBK-419A
1.3.2.2 Grounding Conductors. Provide each air terminal with a two-way path to earth through the
installation of roof and down conductors conforming to Table 1-2 for structures not greater than 75 feet in
height and conforming to Table 1-3 for structures greater than 75 feet in height. An exception is that air
terminals located on prominent dormers extending less than 16 feet from the main structure need have only one
connecting path from the terminal to the main down conductor as shown in Figure 1-22. Additional information
on copper wires is contained in Table 1-4.
1.3.2.2.1 Roof Conductors.
Roof conductors should be routed along ridges of gable, gambrel, and hip roofs, and around the
a.
perimeter of flat and gently sloping roofs.
Roof grounding conductors routed throughout decks, flat surfaces, and flat roofs should be
b.
interconnected to form closed loops to insure that all air terminals have at least two paths to earth.
Ridge conductors may drop from a higher to a lower roof level without installing an extra down lead
c.
at the point of intersection of the two roof levels if there are not more than two air terminals on the lower roof
level.
On roofs that exceed 50 feet in width, additional conductors are to be provided to interconnect
the
d.
air terminals required to protect large flat areas (see Figure 1-18). One additional conductor for each 50
feet
in width is necessary. For example, on roofs 50 to 100 feet wide, add one additional run; on roofs 100 to
150
feet wide, add two additional runs, etc. These additional runs must be interconnected together and to
the
perimeter conductor at 150-foot intervals with cross conductors as illustrated in Figure 1-18.
1-33
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