TM
5-811-1/AFJMAN
32-1080
soon begin to sag, degrading the reliability of the
spool insulators for low-voltage circuits; and strain
line as well as creating as unsightly installation
insulators for insulating guy wires. In crossarm
and increased maintenance.
construction, pin insulators may be used as a
a. Components. A guy installation consists of
designer's option, but line-post insulators are supe-
rior in operation to corresponding pin types since
various components as follows:
line-post units are stronger, more resistant to
(1) Guy wire (strand). The strength of a guy
vandalism, and inherently more radio-interference-
installation is a function of the guy wire, the
free.
anchor, and the soil type. The rated breaking
b. Classes. Selection of the class used is depen-
strength of the guy wire determines the require-
dent upon operating voltage, strength require-
ments for all other components. Wire of either
ments, and the degree of atmospheric pollution.
three or seven strands will be used. Each strand
Long periods without rain to wash off insulator
consists of a steel core having a protective coating
contamination tend to aggravate the pollutant
of zinc, copper, or aluminum. Zinc coatings are
buildup problem. Selection of suitable insulator
available in standard ASTM coating weights. A
ratings will be based on local practice. Where lines
Class A coating weight is half of a Class B coating
are to be constructed on existing Government
weight and a third of a Class C coating weight.
installations, that installation's experience or that
The coating weight used is dependent upon atmo-
of the serving utility will determine the insulation
spheric corrosion with Class A used in dry or
level used.
desert areas with little industrial contamination,
c. Dimensions. Figure 6-6 indicates dimensional
Class C used in salt-laden or foggy areas or
r a n g e s of insulators used. ANSI suspension
heavily contaminated locations, and Class B used
Classes 52-3 and 52-4 have the same electrical,
elsewhere. Rated breaking strength used will be
mechanical, and overall dimensions; but Class
not less than 6,000 (6M) pounds. No more than two
52-3 has a ball-and-socket connection and Class
strengths of guys should be used for any one
52-4 has a clevis eye connection. Selection of the
project. All guys will be sized for the maximum
type of connection provided is a matter of designer
loading tension of the line.
preference. Line-post insulators shown are either
(2) Grounded guys. Conductive poles such as
tie-top or clamp-top. The only difference between
steel or concrete, poles with overhead grounding
Class 57-1 and Class 57-11 is that Class 57-1
conductors, and poles with guys connected to pri-
denotes a tie-top and Class 57-11 denotes a clamp-
mary neutrals are considered grounded, since in-
top. Tie-tops can be used for angles up to two
sertion of guy strain insulators does not isolate
degrees and clamp-tops are necessary for angles
any portion of the pole from the ground.
greater than fifteen degrees. For angles of three
(a) Connection to primary neutrals. For some
degrees to fifteen degrees, choice will be dependent
installations, connection of primary neutrals to
upon mounting and loading requirements. Tie-top
guys can improve secondary equipment protection.
units are less expensive in cost, but a clamp-top
A detailed discussion of why this improvement is
eliminates both material and labor costs for the tie
effected is given in REA Bulletin 83-1 which also
wire thus providing ease of installation. Where
covers the influence of such grounding on anchor
horizontal mounting is required there is, at
rod corrosion. For other installations, such a con-
present, no ANSI class; specifications therefore
nection may not meet local code requirements or
will indicate electrical, mechanical, and overall
will not be possible when the installation does not
dimensions are the same as for the appropriate 57
have a primary neutral system.
subclass. Insulators with short studs (S) are used
(b) Anchor corrosion. Corrosion can be a
on armless configurations; those with long studs
problem in systems that have primary neutrals
(L) are used on wood crossarm configurations.
interconnected with grounded guys when such
d. Colors. Insulator colors available are brown
systems are installed in areas having a low soil
resistivity and a low ratio of buried steel to buried
and light gray. Light gray insulators will be used;
copper. In such cases, anchor rods and grounding
however, in wooded areas or where lines are seen
electrodes will be of the same composition, either
principally against hillside or tree-covered back-
both of galvanized steel or both of copper-clad
grounds, the brown glaze may provide a more
steel. The first installation is less expensive, but
acceptable appearance.
also provides more resistance. Choice of the anchor
6-7. Guying.
composition will be based on soil composition,
resistivity, and corrosion properties. In highly
Particular care will be taken to ensure that all
corrosive soil conditions, anchor life has been
points of strain in the pole lines are adequately
extended by installing guy strain insulators in the
guyed. Improperly or inadequately guyed lines
6-12
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