TM
5-811-1/AFJMAN
32-1080
even in areas having a low lightning incidence.
addition to the required equipment grounding
Except for riser poles supplying critical facilities,
conductor. Possibility of mechanical damage, corro-
the configuration for placement of surge arresters
sion, and other conditions which can degrade the
(i.e., at the cable termination or ahead of the fuse
continuity of a grounding system make such
cutout) will follow local utility practice. For criti-
multiple-grounding points necessary.
cal facilities, one set of arresters will be placed at
the cable termination and another set ahead of the
tems will be grounded in accordance with NFPA
fuse cutout. Figure 9-4 illustrates a medium-
70. Because of the low-frequency nature of instru-
voltage riser pole with arresters placed ahead of
mentation systems, single-point grounding will be
the fuse cutout to prevent lightning current from
specified in accordance with MIL-HDBK-419A
flowing through the fuse. Arresters are sometimes
and FIPS Pub 94. For widely-separated installa-
placed at the cable termination to reduce the
tions, where it becomes impractical to implement
length of the grounding conductor (and thus the
single-point grounding, fiber-optic cable systems
voltage drop). However, this configuration allows
should be used for data transmission. Where fiber-
the lightning current to flow through the fuse.
optic cable is not practicable, follow grounding
d. Miscellaneous. Conductive elements such as
recommendations in MIL-HDBK-419A. Where
metal poles or reinforced concrete will be provided
transducers and associated devices are installed as
with an individual ground electrode connection in
an integral part of a facility, the instrumentation
US ArmY Corps of Engineers
Figure 9-4. Provision of Surge Arresters at a Medium-Voltage Riser Pole.
9-9
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