| Design
of Aerial Plant
UNITED STATES DEPARTMENT OF
AGRICULTURE
Rural Utilities Service
BULLETIN 1751F-630
SUBJECT: Design of Aerial Plant
TO: All Telecommunications Borrowers
RUS Telecommunications Staff
EFFECTIVE DATE: Date of Approval
EXPIRATION DATE: Seven years from effective
date
OFFICE OF PRIMARY INTEREST: Outside Plant
Branch, Telecommunications Standards Division
PREVIOUS INSTRUCTIONS: This bulletin replaces
RUS Telecommunications Engineering & Construction Manual
(TE&CM) Sections 630, Design of Aerial Plant, Issue 3,
dated March 1962; Addenda 2 and 3, dated October 1966 and
January 1979, respectively; and 611, Design of Pole Lines,
Issue 3, dated March 1960; Addendum 3, dated October 1996.
FILING INSTRUCTIONS: Discard RUS TE&CM
Sections 630, Design of Aerial Plant, Issue 3, dated March
1962; Addenda 2 and 3, dated October 1966 and January 1979,
respectively; and 611, Design of Pole Lines, Issue 3, dated
March 1960; Addendum 3, dated
October 1996, and replace it with this bulletin.
File with 7 CFR Part 1751 and is available to RUS staff on
RUSNET.
PURPOSE: This bulletin provides RUS borrowers,
consulting engineers, contractors and other interested parties
with information on the design of aerial plant facilities.
Wally Beyer 1-19-96
______________________________ __________________________
Administrator Date
TABLE OF CONTENTS
Abbreviations ...........................................
3
Definitions .............................................
3
1. General .................................................
6
2. Design Considerations ...................................
7
3. Economic Considerations .................................
8
4. Construction Materials ..................................
9
5. Pole Line Design ........................................
9
6. Pole Class Selection ...................................
10
7. Suspension Strand Selection ............................
12
8. Span Lengths ...........................................
12
9. Pole Guying ............................................
18
10. Sag ....................................................
18
TABLES & FIGURES
Table 1 Transverse Breaking Loads ........................
10
Table 2 Cable Weights - Filled Copper Cables
-
Solid Insulation .................................
13
Table 3 Cable Weights - Filled Copper Cables
-
Expanded Insulation ..............................
14
Table 4 Cable Weights - Nonarmored Filled
Fiber Optic
Cables - Multiple Loose Tube Core ................
14
Table 5 Cable Weights - Armored Filled Fiber
Optic
Cables - Multiple Loose Tube Core ................
15
Table 6 Cable Weights - Nonarmored Filled
Fiber Optic
Cables - Central Core Tube .......................
15
Table 7 Cable Weights - Armored Filled Fiber
Optic
Cables - Central Core Tube .......................
15
Table 8 Cable Weights - Self-Supporting, Filled
Fiber
Optic Cables - Multiple Loose Tube Core ..........
17
Table 9 Cable Weights - Self-Supporting, Filled
Fiber
Optic Cables - Central Core Tube .................
17
Figure 1 Poles per Mile versus Span Length
................ 19
Figure 2 Final Unloaded Sag at 60°F -
Heavy Loading
District - 6M Strand .............................
20
Figure 3 Final Unloaded Sag at 60°F -
Medium Loading
District - 6M Strand .............................
21
Figure 4 Final Unloaded Sag at 60°F -
Light Loading
District - 6M Strand .............................
22
Figure 5 Final Unloaded Sag at 60°F -
Heavy Loading
District - 10M Strand ............................
23
Figure 6 Final Unloaded Sag at 60°F -
Medium Loading
District - 10M Strand ............................
24
Figure 7 Final Unloaded Sag at 60°F -
Light Loading
District - 10M Strand ............................
25
Figure 8 Final Unloaded Sag at 60°F -
Heavy Loading
District - 16M Strand ............................
26
Figure 9 Final Unloaded Sag at 60°F -
Medium Loading
District - 16M Strand ............................
27
Figure 10 Final Unloaded Sag at 60°F -
Light Loading
District - 16M Strand ............................
28
Figure 11 Catenary Suspension Strand Construction
General Features .................................
29
Figure 12 Slack Span Construction Example
.................. 30
Figure 13 Determination of Maximum Sag Point
............... 31
Figure 14 Catenary Curve for Determining the
Sag at Any
Point in a Level Span ............................
32
INDEX:
Outside Plant
Design
Telecommunications
ABBREVIATIONS
AWG American Wire Gauge
°C Degrees Celsius
CFR Code of Federal Regulations
cm Centimeters
°F Degrees Fahrenheit
ft Feet
in. Inches
kg/m Kilograms per meter
lb/ft Pounds per foot
LD Loan Design
NAFTA North American Free Trade Agreement
NEC National Electrical Code
NESC National Electrical Safety Code
m Meter
mm Millimeters
RUS Rural Utilities Service
TE&CM Telecommunications Engineering and
Construction Manual
DEFINITIONS
Anchor: A device that serves as a reliable
support to hold an object firmly in place. The term anchor
is normally associated with cone, plate, screw, or concrete
anchors, but the terms snub, deadman and anchor log are usually
associated with pole stubs or logs set or buried in the ground
to serve as temporary anchors. The latter are often used at
pull and tension sites.
Anchor Guy: The buried element of a guy assembly
that provides holding strength or resistance to guy wire pull.
Ground Clearance: The minimum separation between
cables and the ground.
Guy: A tension member having one end secured
to a fixed object and the other end attached to a pole or
other structural part that it supports.
Heavy Loading District: Horizontal wind pressure,
at a right angle to the line, of 4 pounds per square foot
(190 Pascals) upon the projected area of the cylindrical surfaces
of all supported wires (including suspension strand and cables)
when coated with a radial thickness of 0.50 in. (12.5 mm)
of ice at a temperature of 0°F (-20°C).
Lashed Aerial Cable: Cable that is attached
to the separate suspension strand by lashing wire to support
the cable.
Light Loading District: Horizontal wind pressure,
at a right angle to the line, of 9 pounds per square foot
(430 Pascals) upon the projected area of the cylindrical surfaces
of all supported wires (including suspension strand and cables)
at a temperature of 30°F (-1°C).
Loan Design: A comprehensive engineering plan
for the project used to support a loan application to RUS.
Medium Loading District: Horizontal wind pressure,
at a right angle to the line, of 4 pounds per square foot
(190 Pascals) upon the projected area of the cylindrical surfaces
of all supported wires (including suspension strand and cables)
when coated with a radial thickness of 0.25 in. (6.5 mm) of
ice at a temperature of 15°F (-10°C).
Pole: A column of wood supporting overhead
cables usually by means of brackets.
Pole Line: A series of poles arranged to support
cables above the surface of the ground: and the structures
and cables supported thereon.
Push Brace: A supporting member, usually of
timber, placed between a pole or other structural part of
a line and the ground or a fixed object.
RUS Accepted (Material and Equipment): Material
and equipment which RUS has reviewed and determined that:
a. Final assembly is conducted within the
United States, Mexico, or Canada, or any of their respective
territories and the cost of United States, Mexican, or Canadian,
manufactured components, in any combination, is more than
50 percent of the total cost of all components utilized in
the material or equipment, and
b. The material or equipment complies with
pertinent RUS or industry standards and field experience has
demonstrated that the material or equipment is suitable for
use on systems of RUS telecommunications borrowers.
RUS Technically Accepted (Material and Equipment):
Material and equipment which RUS has reviewed and determined
that:
a. Final assembly is not conducted within
the United States, Mexico, or Canada, or any of their territories,
or the cost of components within the material or equipment
which are manufactured within the United States, Mexico, or
Canada, or any of their territories, cost 50 percent or less
than the total cost of all components utilized in the material
or equipment, and
b. The material or equipment complies with
pertinent RUS or industry standards and field experience has
demonstrated that the material or equipment is suitable for
use on systems of RUS telecommunications borrowers.
Sag: The distance measured vertically from
a cable to the straight line joining its two points of support.
Unless otherwise stated in the NESC, the sag referred to is
the sag at the midpoint of the span.
Self-Supporting Aerial Fiber Optic Cable:
A cable consisting of one or more buffered optical fibers
factory assembled with a messenger that supports the cable.
Span Length: The horizontal distance between
two adjacent supporting points of a cable.
Suspension Strand: A stranded group of wires
supported above the ground at intervals by poles or other
structures and employed to furnish within these intervals
frequent points of support for cables.
1. GENERAL
1.1 This bulletin discusses in particular
the design of aerial plant using filled copper cables and
filled fiber optic cables. The information and recommendations
in this bulletin are advisory.
1.2 Aerial plant refers to telecommunication
copper cables and fiber optic cables that are attached to
utility poles at varying span lengths by lashing cables to
separate suspension strands. Filled fiber optic cables may
also be attached to utility poles using cables containing
an integrated suspension strand. Filled fiber optic aerial
cables containing integrated suspension strands are referred
to as a self-supporting fiber optic cables.
1.3 Additional information for the use in
the design of aerial plant facilities can be found in following
RUS documents:
a. TE&CM Section 116, Plant Engineering
and Record System;
b. TE&CM Section 204, Telephone System
Design;
c. TE&CM Section 210, Telephone System
Design - Sizing
Criteria;
d. TE&CM Section 218, Plant Annual Cost
Data for System
Design Purposes;
e. TE&CM Section 219, Present Worth of
Annual Charge
Studies for System Design;
f. TE&CM Section 424, Design Guideline
for
Telecommunications Subscriber Loop Plant;
g. TE&CM Section 628, Plastic Insulated
Cable Plant Layout;
h. TE&CM Section 635, Construction of
Aerial Plant;
i. TE&CM Section 650, Guy and Anchors
on Wire and Cable
Lines;
j. RUS Bulletin 345-153, Specifications and
Drawings for
Construction of Pole Lines, Aerial Cables
and Wires
(RUS Form 515f);
k. RUS Bulletin 344-3, "Buy American"
Requirement, as
amended by the NAFTA;
l. RUS Bulletin 1728F-700, RUS Specification
for Wood
Poles, Stubs and Anchor Logs;
m. RUS Bulletin 1751F-626, Staking of Aerial
Plant;
n. RUS Bulletin 1751F-670, Outside Plant Corrosion
Considerations;
o. RUS Bulletin 1751F-801, Electrical Protection
Fundamentals;
p. RUS Bulletin 1751F-815, Electrical Protection
of Outside
Plant;
q. RUS Bulletin 1751H-601, Lightwave Fundamentals,
Systems,
and Application;
r. RUS Bulletin 1753F-401(PC-2), RUS Standard
for Splicing
Copper and Fiber Optic Cables (codified under
7 CFR Part 1755.200);
s. 7 CFR Part 1751, Subpart B, State Telecommunications
Modernization Plan; and
t. 7 CFR Part 1753.6, Standards, Specifications,
and
General Requirements.
2. DESIGN CONSIDERATIONS
2.1 Aerial plant construction should be the
method of construction when the initial construction cost
is lower than the initial construction cost of buried plant
construction and when the annual cost of the aerial plant
facilities are lower than the annual cost of buried plant
facilities. Aerial plant construction should also be the method
of construction when rock conditions are encountered that
economically restrict the use of direct buried plant.
2.2 Aerial plant construction involving the
use of joint occupancy utility poles should only be considered
when required by local, State, or Federal ordinances or regulations.
When joint occupancy of aerial electric and telecommunications
cables is considered, the design and construction of the joint
occupancy facilities should performed in accordance with the
latest editions of the NEC, NESC, local or State regulations,
or Federal regulations. When the local, State, or Federal
regulations are more stringent than the NEC or NESC codes,
the more stringent requirements should be observed.
2.3 For outside plant aerial facilities using
copper cables, circuit requirements should be thoroughly evaluated
to provide sufficient margin in the sizing of both aerial
distribution and feeder cables. The sizing of the copper cables
should be based on the recommendations listed in RUS TE&CM
Section 210, Telephone System Design - Sizing Criteria. The
assigning of cable pairs should be based on the recommendations
listed in RUS TE&CM Section 628, Plastic Insulated Cable
Plant Layout.
2.4 For outside plant aerial facilities using
fiber optic cables, circuit requirements should be thoroughly
evaluated to provide sufficient margin in the sizing of the
cables. The sizing of the fiber optic cables should be based
on the fiber pair requirements of the approved LD plus the
number of fiber pairs needed for future growth.
2.5 Serving additional subscribers not anticipated
at the time of construction may become a problem in aerial
plant design. Therefore thorough planning is of utmost importance.
Long range subscriber estimates by grade of service should
be made prior to the preparation of the LD. The estimate should
take into account the upgrading of existing services and the
addition of new subscribers.
2.6 For copper aerial plant, the design should
provide for the optimum use of fine gauge cable (22 and 24
gauge conductors). Care should be exercised in the design
to ensure that transmission requirements are met and that
high lightning areas are considered.
2.7 For copper aerial plant, the choice of
the proper gauge conductors should depend on the transmission
and signaling requirements. Care should be exercised in selecting
the cables since initial cost differentials between the various
cable types, sizes, and conductor gauges can be appreciable.
Where economic costs consistent with the State Telecommunications
Modernization Plan (7 CFR Part 1751, Subpart B) indicate the
use of digital carrier and other types of electronic equipment
over physical circuits, the electronic equipment should be
installed.
2.8. For optical fiber aerial plant, the design
should provide for the use of either dispersion-unshifted
single mode fibers (operates at both the 1310 and 1550 nanometer
windows) or dispersion-shifted single mode fibers (operates
at the 1550 nanometer window). The choice as to which single
mode fiber to use should depend on the optical system's length
and the transmission and signaling requirements.
2.9 For lightwave systems, the design should
be prepared in accordance with the recommendations listed
in RUS Bulletin
1751H-601, Lightwave Fundamentals, Systems,
and Application.
3. ECONOMIC CONSIDERATIONS
3.1 The decision to construct the project
area using aerial plant facilities should be based on an economic
analysis using the recommendations referenced in RUS TE&CM
Sections 218, Plant Annual Cost Data for System Design Purposes
and 219, Present Worth of Annual Charge Studies for System
Design.
3.2 If the economic analysis indicates that
the project area should be constructed using aerial plant
facilities, a decision should then be made regarding the design
of the project area using either an all copper design or a
combination copper/fiber design.
3.3 Selection of either the all copper design
or the combination copper/fiber design should be based on
a long-term economic plan, good engineering judgement, and
the individual State Telecommunications Modernization Plan
(7 CFR Part 1751,
Subpart B). The initial and annual cost data
should be used as economic guidelines to supplement and support
the engineering judgement and decision. The objective is to
choose the most suitable elements of the new plant facilities.
In general, the design with the lowest annual cost should
be selected. However, other considerations such as reliability
and quality of service, connecting company arrangements, flexibility
for meeting potential new market opportunities, or other effects
on system operation may outweigh annual cost considerations.
3.4 Local characteristics of the project area
should be known before comparative cost studies are commenced.
It should also be determined if special types of equipment
or cable are required so that the added expense can be evaluated.
4. CONSTRUCTION MATERIALS
4.1 For all aerial plant construction projects
financed with RUS loan funds, RUS regulation 7 CFR Part 1753.6
requires that only RUS accepted materials be used.
4.2 RUS technically accepted, nondomestic
manufactured materials, may also be used on aerial plant construction
projects. Before technically accepted materials can be used
on aerial plant construction projects, permission is required
from the RUS borrower. In addition, borrower's are required
to ensure that the cost of the technically accepted materials
comply with RUS Bulletin 344-3, "Buy American" Requirement,
as amended by NAFTA.
4.3 RUS Bulletin 1728F-700, RUS Specification
for Wood Poles, Stubs and Anchor Logs, lists the requirements
for wood poles that should be used by RUS borrowers in aerial
plant construction.
5. POLE LINE DESIGN
5.1 Pole lines for aerial plant construction
should be designed based on the pole's class and length. The
class of pole selected should be determined by the pole's
strength and transverse load requirements. The length of the
pole should be determined by ground clearances, sags. etc.
5.2 Pole lines for the majority of aerial
plant construction performed by RUS borrowers should be designed
for Grade C construction which is defined in Section 24, Grades
of Construction, of the latest edition of the NESC.
5.3 Pole lines for aerial plant construction
involving the crossing of railroads, limited-access highways,
and other special situations should be designed for Grade
B construction which is defined in Section 24 of the latest
edition of the NESC.
5.4 To assist RUS borrowers in the design
of the pole line for aerial plant construction, Figure 1 provides
information on the number of poles per mile versus the span
length.
6. POLE CLASS SELECTION
6.1 Grade C construction of the NESC specifies
specific overload capacity factors of poles use in aerial
plant construction. To ensure that poles have adequate strength
to support aerial plant construction, poles should be designed
to meet the overload capacity factors specified in NESC Rule
261 for Grade C construction.
6.2 Poles are divided into nine classes based
on their rated breaking loads. The classes are numbered 1
through 10, with class 8 being omitted. The rated breaking
loads are applied transversely 24 in. (60.9 cm) from the top
of the pole. Table 1 lists the transverse breaking loads for
each pole class:
TABLE 1
Transverse Breaking Loads
Pole Class Pounds-Force (Newtons)
1 4500 (20,017)
2 3700 (16,458)
3 3000 (13,345)
4 2400 (10,676)
5 1900 (8,452)
6 1500 (6,672)
7 1200 (5,338)
9 740 (3,292)
10 370 (1,646)
The values in the table for a given pole class
are the same for all species of pole timber. For classes 1
to 7, the strength of any class is approximately 25 percent
greater than the next weaker class.
6.3 The pole class selected is assumed to
have the required strength to support the vertical loads.
Vertical loads to which poles are subjected to are as follows:
a. Weight of the suspension strand;
b. Weight of the cable; and
c. The increase in weight when the suspension
strand and
cable are coated with ice.
6.4 Poles are also subjected to a transverse
load. The transverse load is the load applied when the wind
pressure occurs at a right angle to the direction of the pole
line. Transverse loading on poles should be calculated using
the storm loading assumptions for the three loading districts
established in Section 25, Loading for Grades B, C, and D,
of the latest edition of the NESC.
6.5 In addition to the transverse wind pressure
load on the suspension strand and cable, the pole itself and
attachments should also withstand the transverse wind pressure
load. This additional load will vary due to differences in
dimensions and length in any given pole class and type of
attachments made on the pole. RUS has adopted as an approximation
for this purpose 50 pounds-force (222 newtons) in the heavy
and medium storm loading districts and 75 pounds-force (334
newtons) in the light storm loading district, applied 24 in.
(60.9 cm) from the pole top.
6.6 The pole class for lashed filled copper
and fiber optic cable should be selected based on the calculated
transverse wind loading using the storm loading assumptions
for the three loading districts established in Section 25
of the latest edition of the NESC and the average span length.
6.7 The pole class for self-supporting filled
fiber optic cable should be selected based on the calculated
transverse wind loading using the storm loading assumptions
for the three loading districts established in Section 25
of the latest edition of the NESC and the average span length.
6.8 Poles used as push braces should be of
the same class as the poles they brace.
6.9 Poles used as stubs for overhead and anchor
guys should be of the same class as the poles to which they
are associated.
7. SUSPENSION STRAND SELECTION
7.1 Suspension strands are available in utilities
and extra high strength grades. Both the utilities and extra
high strength grades come in 6M, 10M, and 16M sizes. The suspension
strand size for cable in RUS borrowers' systems usually will
be either 6M or 10M strand. The rated breaking strength (minimum
breaking strength) of the 6M and 10M strands are 6,000 pounds-force
(26,689 newtons) and 11,500 pounds-force (51,154 newtons),
respectively. Aerial cable plant design is based on not exceeding
60 percent of the rated breaking strength of the suspension
strand when the cable and strand are loaded as calculated
according to assumptions of wind, ice, and temperature specified
in accordance with the storm loading districts specified in
Section 25 of the latest edition of the NESC. The 16M strand
will permit longer spans than the 10M strand but it is a rather
large size as compared to the cable diameters usually installed
in RUS borrowers' telecommunications systems and is about
30 percent more costly than 10M strand. The 16M strand has
a rated breaking strength of 18,000 pounds-force (80,067 newtons).
The 16M strand is not recommended for use with cables weighing
less than 1.5 lb/ft (2.2 kg/m).
7.2 Both the utilities and extra high strength
grade suspension strands are available in three zinc coating
weights referred to as Class A, Class B, and Class C coatings.
The Class A coated strand has lowest zinc coating weight while
Class C coated strand has the highest zinc coating weight.
The Class A coated strand is the preferred suspension strand
installed in RUS borrower telecommunications systems. The
Class C coated suspension strand should be used in aerial
plant construction where the Class A coated strand is subjected
to excessive corrosion. RUS Bulletin 1751F-670, Outside Plant
Corrosion Consideration, should be referenced to determine
if the corrosion could be a problem in the construction area.
7.3 The integral support messenger of a self-supporting,
filled, aerial fiber optic cable is a 0.25 in. (6.35 mm) diameter,
7 wire, extra high strength grade, Class A
galvanized steel strand coated with a corrosion protective
floodant.
8. SPAN LENGTHS
8.1 Span lengths for lashed, filled copper
and fiber optic cables should be determined using the following
factors:
a. Cable weight per ft (m);
b. Strand size;
c. Coating class;
d. Pole length;
e. Pole setting depth;
f. Maximum permissible sag;
g. Maximum span for 14 ft (9.1 m) clearance;
h. Poles per mile (kilometer);
i. Pole class;
j. Terrain;
k. Subscriber distribution;
l. Strand cost per mile (kilometer);
m. Pole cost per mile (kilometer) in place;
and
n. Pole and strand cost per mile (kilometer).
8.2 Cable weights of filled copper cables
by pair size, gauge, and insulation type which should be used
for the cable weight factor in determining span lengths for
copper cables in aerial plant construction projects are given
in Tables 2 and 3.
TABLE 2
Cable Weights
Filled Copper Cables - Solid Insulation
Cable Weights lb/ft (kg/m)
Pair Size 19 AWG 22 AWG 24 AWG 26 AWG
6 0.2 (0.30) 0.1 (0.15) 0.1 (0.15) -
12 0.3 (0.45) 0.2 (0.30) 0.1 (0.15) -
18 0.4 (0.60) 0.2 (0.30) 0.1 (0.15) -
25 0.5 (0.74) 0.3 (0.45) 0.2 (0.30) 0.1 (0.15)
50 0.9 (1.34) 0.5 (0.74) 0.3 (0.45) 0.2 (0.30)
75 1.3 (1.93) 0.7 (1.04) 0.5 (0.74) 0.3 (0.45)
100 1.8 (2.68) 0.9 (1.34) 0.6 (0.89) 0.4 (0.60)
150 2.6 (3.87) 1.3 (1.93) 0.8 (1.19) 0.6 (0.89)
200 3.3 (4.91) 1.7 (2.53) 1.1 (1.64) 0.7 (1.04)
300 4.9 (7.29) 2.4 (3.57) 1.6 (2.38) 1.0 (1.49)
400 6.4 (9.52) 3.2 (4.76) 2.1 (3.12) 1.3 (1.93)
600 - 4.7 (6.99) 3.1 (4.61) 2.0 (2.98)
900 - 6.9 (10.3) 4.5 (6.70) 2.9 (4.31)
1200 - - 5.9 (8.78) 3.7 (5.50)
1500 - - 7.3 (10.9) 4.7 (6.99)
1800 - - 8.7 (12.9) 5.5 (8.18)
2100 - - 10.0 (14.9) 6.4 (9.52)
2400 - - - 7.2 (10.7)
TABLE 3
Cable Weights
Filled Copper Cables - Expanded Insulation
Cable Weights lb/ft (kg/m)
Pair Size 19 AWG 22 AWG 24 AWG 26 AWG
6 0.1 (0.15) 0.1 (0.15) 0.1 (0.15) -
12 0.2 (0.30) 0.1 (0.15) 0.1 (0.15) -
18 0.3 (0.45) 0.2 (0.30) 0.1 (0.15) -
25 0.4 (0.60) 0.2 (0.30) 0.2 (0.30) 0.1 (0.15)
50 0.7 (1.04) 0.4 (0.60) 0.3 (0.45) 0.2 (0.30)
75 1.0 (1.49) 0.6 (0.89) 0.4 (0.60) 0.3 (0.45)
100 1.4 (2.08) 0.7 (1.04) 0.5 (0.74) 0.3 (0.45)
150 2.0 (2.98) 1.0 (1.49) 0.7 (1.04) 0.5 (0.74)
200 2.6 (3.87) 1.4 (2.08) 1.0 (1.49) 0.6 (0.89)
300 3.8 (5.65) 2.0 (2.98) 1.3 (1.93) 0.9 (1.34)
400 5.1 (7.59) 2.6 (3.87) 1.7 (2.53) 1.1 (1.64)
600 7.5 (11.2) 3.8 (5.65) 2.5 (3.72) 1.7 (2.53)
900 - 5.7 (8.48) 3.7 (5.50) 2.4 (3.57)
1200 - 7.5 (11.2) 5.0 (7.44) 3.2 (4.76)
1500 - 9.2 (13.7) 6.1 (9.08) 4.0 (5.95)
1800 - - 7.3 (10.9) 4.8 (7.14)
2100 - - 8.4 (12.5) 5.5 (8.18)
2400 - - 9.5 (14.1) 6.2 (9.23)
2700 - - - 6.7 (9.97)
3000 - - - 7.7 (11.5)
3300 - - - 8.4 (12.5)
3600 - - - 9.1 (13.5)
8.3 Cable weights of filled fiber optic cables
by fiber size, strength member type, core type, and cable
construction which should be used for the cable weight factor
in determining span lengths for fiber optic cables in aerial
plant construction projects are given in Tables 4 through
7.
TABLE 4
Cable Weights
Nonarmored Filled Fiber Optic Cables
Multiple Loose Tube Core
Cable Weights lb/ft (kg/m)
Fiber Sizes Nonmetallic Strength Member Metallic
Strength Member
2 - 36 0.07 (0.10) 0.08 (0.12)
38 - 72 0.09 (0.13) 0.10 (0.15)
74 - 84 0.10 (0.15) 0.11 (0.16)
86 - 96 0.11 (0.16) 0.12 (0.18)
98 - 108 0.13 (0.19) 0.14 (0.21)
110 - 120 0.15 (0.22) 0.16 (0.24)
122 - 132 0.16 (0.24) 0.17 (0.25)
134 - 216 0.18 (0.27) 0.19 (0.28)
218 - 264 0.20 (0.30) 0.21 (0.31)
TABLE 5
Cable Weights
Armored Filled Fiber Optic Cables
Multiple Loose Tube Core
Cable Weights lb/ft (kg/m)
Fiber Sizes Nonmetallic Strength Member Metallic
Strength Member
2 - 36 0.11 (0.16) 0.13 (0.19)
38 - 72 0.14 (0.21) 0.15 (0.22)
74 - 84 0.16 (0.24) 0.17 (0.25)
86 - 96 0.18 (0.27) 0.19 (0.28)
98 - 108 0.20 (0.30) 0.21 (0.31)
110 - 120 0.22 (0.33) 0.23 (0.34)
122 - 132 0.24 (0.36) 0.25 (0.37)
134 - 216 0.27 (0.40) 0.28 (0.42)
218 - 264 0.28 (0.42) 0.29 (0.43)
TABLE 6
Cable Weights
Nonarmored Filled Fiber Optic Cables
Central Core Tube
Cable Weights lb/ft (kg/m)
Fiber Sizes Nonmetallic Strength Member Metallic
Strength Member
6 - 60 0.08 (0.12) 0.10 (0.15)
62 - 96 0.11 (0.16) 0.15 (0.22)
TABLE 7
Cable Weights
Armored Filled Fiber Optic Cables
Central Core Tube
Cable Weights lb/ft (kg/m)
Fiber Sizes Nonmetallic Strength Member Metallic
Strength Member
6 - 60 0.11 (0.16) 0.13 (0.19)
62 - 96 0.14 (0.21) 0.18 (0.27)
8.4 For lashed, filled copper cables, Figures
2 through 10 indicate the span length limits for poles of
various lengths on level ground which will provide 14 ft (4.3
m) of final unloaded ground clearance at 60°F (15.6°C)
for cables of various weights on the 6M, 10M, and 16M strands
in the three storm loading districts referenced in Section
25 of the latest edition of NESC. Cost studies indicate that
30 ft (9.1 m) Class 7 poles are strong enough to provide the
spans at the lowest cost. The 30 ft
(9.1 m) poles have an advantage over 25 ft
(7.6 m) poles in providing greater height for aerial service
wire road crossings.
8.5 For lashed, filled fiber optic cables,
recommended span length limits for poles of various lengths
on level ground which will provide 14 ft (4.3 m) of final
unloaded ground clearance at 60°F (15.6°C) for cables
of various weights on the 6M strands in the three storm loading
districts referenced in Section 25 of the latest edition of
NESC should be obtained from fiber optic cable manufacturers.
8.6 For lashed, filled copper and fiber optic
cables, an occasional span that is shorter than adjacent spans
should not be a concern except from the standpoint of the
effect of short spans on the average spans and, therefore,
the number of poles needed. However, when an individual span
occurs which is appreciably longer than the average span in
its section of line, consideration should be given to the
question of proper limits for such spans before employing
special construction methods. Special long span construction
is recommended for such occasional spans when the length of
the span in question is more than 50 percent than the average
of five adjacent spans in either direction.
8.7 Long span construction for lashed, filled
copper and fiber optic cables may be necessary in the aerial
plant because of terrain (such as river crossings, etc.) that
make construction of normal span lengths impracticable. When
long span construction is contemplated, the long span construction
should be designed for the particular situation.
8.8 One method of long span construction could
be the use of catenary suspension strands to avoid excessive
sags on spans. When catenary suspension strand construction
is contemplated, the following factors should be consider:
a. Selection of a cable suspension strand
which would be
strong enough to support the cable without
the catenary
strand;
b. Selection of a catenary strand as strong
or stronger
than the cable suspension strand;
c. Selection of suitable heights and classes
of poles;
d. Pole setting depths and their footings;
and
e. Side and head guy requirements.
8.9 When catenary suspension strand construction
is employed, the cable suspension strand should be fastened
to long span poles at heights which will conform to the required
ground clearances. The cable suspension strand should also
be supported at one or more points in the span by the catenary
suspension strand. The catenary suspension strand should be
attached to the long span poles at locations above the cable
suspension strand. The separation between the cable suspension
strand and the catenary suspension strand at poles should
be such as to allow span attachments to the catenary and support
points to be in horizontal alignment. The catenary suspension
strand is usually attached to the cable suspension strand
by means of cable suspension hooks. Figure 11 shows the general
features of catenary suspension strand construction.
8.10 When circumstances indicate the use of
slack span construction, Figure 12 depicts such construction.
8.11 Cable weights of self-supporting, filled,
fiber optic cables by fiber size, core type, and cable construction
which should be used for the cable weight factor in determining
span lengths for self-supporting fiber optic cables in aerial
plant construction projects are given in Tables 8 and 9.
TABLE 8
Cable Weights
Self-Supporting, Filled Fiber Optic Cables
Multiple Loose Tube Core
Cable Weights lb/ft (kg/m)
Fiber Sizes Nonarmored Armored
2 - 72 0.25 (0.37) 0.32 (0.48)
74 - 84 0.27 (0.40) 0.34 (0.51)
86 - 96 0.28 (0.42) 0.36 (0.54)
98 - 108 0.30 (0.45) 0.38 (0.57)
110 - 120 0.31 (0.46) 0.40 (0.60)
122 - 132 0.33 (0.49) 0.42 (0.62)
134 - 144 0.35 (0.52) 0.45 (0.67)
TABLE 9
Cable Weights
Self-Supporting, Filled Fiber Optic Cables
Central Core Tube
Cable Weights lb/ft (kg/m)
Fiber Sizes Nonarmored Armored
2 - 48 0.08 (0.12) 0.12 (0.18)
50 - 96 0.13 (0.19) 0.18 (0.27)
8.12 For self-supporting, filled, fiber optic
cables, recommended span length limits for poles of various
lengths on level ground which will provide 14 ft (4.3 m) of
final unloaded ground clearance at 60°F (15.6°C) for
cables in the three storm loading districts referenced in
Section 25 of the latest edition of NESC should be obtained
from fiber optic cable manufacturers.
9. POLE GUYING
9.1 Guying of poles may be necessary in certain
situations to provide additional strength to the pole to sustain
the longitudinal load from the wind pressure, the weight of
the cable, and the weight of the suspension strand, etc.
9.2 RUS TE&CM Section 650, Guy and Anchors
on Wire and Cable Lines, should be consulted when guying of
poles is required.
10. SAG
10.1 Locations and amounts of sag at low points
in hillside situations and river crossings where support points
are at different elevations should be determined in accordance
with Figure 13.
10.2 Sag values in percent of midspan sag
of level spans at points along a span should be determined
from Figure 14. The information in Figure 14 may also be useful
in determining separations in a span involving clearances.
Figures 1 thru 14 are graphs and drawings.
Reference hard copy.
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