TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
position is correct and will remain in position even
breaking of strands due to vibration; the wearing of
under the most severe conditions. Use of a takeoff
the conductor at its point of support; and the burn-
clip permits the tap to be removed as easily as it
ing of the conductor from flashover or tap contact.
was installed, using the same application tool.
Armor rods are sometimes used as a repair for bro-
ken or damaged strands. If damaged armor rods are
4-43. Overhead line armor rods.
found, replacement is recommended. Armor rods
Armor rods are required for all aluminum and
should be installed in accordance with manufactur-
ACSR cable supports except at dead ends. The rods
provide threefold protection by preventing the
Section XII - POLE-LINE INSULATORS
4-44. Pole-line insulator related material.
lines. They are available for secondary lines, but
should only be used if the secondary line is mounted
Insulator use, inspection, repair, and cleaning are
on crossarm construction. Conductors are fastened
discussed in chapter 3, section IV, which also ap-
to pin insulators with wire ties.
plies to pole-line insulators. Apparatus insulators
b. Post insulators. Armless construction using
used on substation equipment and to support buses
post insulators is the preferable construction if
are much heavier and more expensive than pole-
practicable, as it is clean-looking and requires less
line insulators. It may be more economical to re-
space. Post insulators can also be used on crossarm
place pole-line insulators than to repair them. In
construction. Line posts are stronger, more resis-
many instances it is possible to wash energized
tant to vandalism, and inherently more radio-
pole-line insulators, as covered in section XV
interference free than pin insulators. Post insula-
tors can be provided with clamp tops or tie tops. Tie
4-45. Insulator operating performance.
tops cannot be used for angles of more than 15
Operating performance of aerial lines is dependent
degrees. For some mountings and loadings they can
upon the quality of the line insulators. Pole-line
only be used for angles up to 2 degrees. Tie tops are
inspection should reveal damage, even if visible co-
less expensive, but clamp tops eliminate both tie
rona or recognizable interference voltages have not
wire material and labor costs, resulting in an easier
already indicated some impairment.
a. Damaging conditions. Most pole-line insulator
c. Suspension insulators. Suspension insulators
damage results from gun shots, lightning or con-
(dead-end bells) are used for primary lines, where
tamination flashovers, and wind damage.
pin or post insulators do not provide the required
b. Understanding insulator provisions. Insula-
strength. They may also be referred to as strain
tors provide mechanical and electrical performance
insulators where lines are dead-ended at corners,
values to meet requirements imposed by different
where there are sharp curves or extra long spans,
applications. Mechanical performance dictates to a
and at other places where a pull must be carried as
certain extent the type of insulator most suitable for
well as insulation provided.
the line being supported. Electrical performance re-
d. Spool insulators. Spool insulators are used on
quirements are mainly based on operating voltage
secondary racks or clevises, as required to support
and the degree to which area conditions affect the
secondary cables, and require tie wires. Knob insu-
lators should not be used, as they are not covered by
an ANSI insulator standard and are manufactured
4-46. Types of pole-line insulators.
for indoor installation.
Insulators used are the pin, post, and suspension
e. Tie wires. Prefabricated ties are recommended
type for primary lines; the spool, pin, and knob type
for maintenance installation. They can be installed
for secondary lines; and the guy strain type for
on energized line circuits, with proper protective
guys, as covered in section XIII. Figure 4-17 shows
equipment placed to insulate the tie from grounded
the different types normally used on facilities cov-
equipment or other energized phase conductors. Hot
ered by this manual.
line tools or rubber gloves and rubber sleeves are
a. Pin insulators. This insulator gets its name
used, depending on the voltage of the conductor. Tie
from the fact it is supported on a pin. The pin is
wire sizes should be in accordance with table 4-3.
usually attached to a wood crossarm. Steel pins
The wires should hold the line conductor tightly at
should always be used, as wood pins deteriorate
all times to prevent chafing at the point of support.
rapidly from the leakage currents through the insu-
Never reuse a tie wire, as the kinks from the first
lator. Where crossarm construction is being phased
use will prevent a satisfactory tie. A bare tie wire, of
out, pin insulators are used less often on primary
the same metal, should always be used on a bare