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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
Aeolian vibration, galloping, sway oscillation, un-
line will not be too tight in the cold of winter or too
slack in summer heat. If the sag is insufficient, the
balanced loading, lightning discharges, and short-
tension will be too great and the conductor will
circuit effects can be damaging to conductors in
stretch and might break. If the sag is too great,
service. Poor connections cannot only cause dam-
vertical clearances may be compromised and con-
age, but are also possible sources of radio or televi-
ductors may then blow together. Before adjusting
sion interference. An infrared scanning system is
the sag, check for a broken guy or pole, a tree limb
recommended over visual inspection. Equipment
lying on the wires, or twisted or leaning poles. All
can be operated from the air or from the ground
wires in any span should be sagged the same or
using aircraft or aerial equipment or vehicular-
with greater sag in the lower wires than in any
mounted or hand-held devices.
above. This is important in maintaining midspan
a. Damage signs. The following signs indicate
clearances.
that the conductor is probably being damaged.
a. Sag tables. Tables providing initial tension sag
for most open wire conductors may be obtained from
your local utility company. Line conductor manufac-
SIGHTING M
t u r e r s may a l s o p r o v i d e t h i s d a t a . T M
A
R
K
E
R
S
-
,
5-811-l/AFJMAN 32-1080 provides information on
sag determination. As-built drawings, if available,
may provide the initial tension sag at the time of
construction. Resagging requirements should allow
for the normal increase in sag caused by the un-
loaded weight of the conductors.
b. Measuring existing sag. Measuring existing
sag can be done by following these instructions.
Showing
position
of
sighting
markers.
Note that in both cases the line of sight is parallel to
a line joining points of wire support. This may not
be horizontal.
(1) Line conductors. See figure 4-10 for pri-
A TOP Of SIGHTING
mary and secondary line conductor sag measure-
TOP Of SIGHTING MARKER
C CONDUCTOR'S LOWERMOST POINT
ments.
Of EXISTING SAG
E AMOUNT OF EXISTING SAC
(a) Estimate approximate sag in section and
hold marker on each pole.
mode.
Showing how meosurement is
(b) Adjust marker equally on each support
until A, B, and C shown in figure 4-10 are in line.
Figure
Measuring sag on line conductors
(c) Measure distances D and E shown in fig-
ure 4-10. If markers were adjusted properly, D and
E will be the same, which is the amount of existing
sag.
(2) Service drop conductors. See figure 4-11 for
secondary service-drop procedures.
(a) Estimate approximate sag in service-drop
conductors and hold marker on pole and building.
(b) Adjust markers equally at pole and build-
ing until A, B, and C are in line.
(c) Measure distances D and E. These dis-
a.
the markers.
tances should be equal. This is the amount of exist-
ing sag.
c. Clearances. Minimum clearances that should
be maintained between conductors and other ob-
jects are contained in the NESC.
OF
MARKER
TOP OF
C CONDUCTOR'S
POINT
4-36. Overhead conductor damage.
0 AMOUNT OF
SAC
AMOUNT OF
Conductors can be damaged in many ways, and
Showing how measurement is made.
what appears initially to be superficial damage may
b.
in time cause a failure. Carelessness in installation
may kink, nick, abrade, or overstress the conductor.
Figure 4-11. Measuring sag on service drop conductors
4-17
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