UNITED STATES DEPARTMENT OF AGRICULTURE

Rural Utilities Service

BULLETIN 1751F-644

RD-GD-2002-47

SUBJECT: Underground Plant Construction

TO: All Telecommunications Borrowers

 RUS Telecommunications Staff

EFFECTIVE DATE: August 28, 2002

OFFICE OF PRIMARY INTEREST: Outside Plant Branch,

Telecommunications Standards Division

INSTRUCTIONS: This bulletin supersedes RUS Bulletin 1751F-644,

“Underground Plant Construction,” issued May 14, 1998.

AVAILABILITY: This bulletin is available on the Internet at

http://www.usda.gov/rus/telecom/publications/bulletins.htm

PURPOSE: This bulletin provides RUS borrowers, consulting

engineers, contractors and other interested parties with

information on the construction of underground plant facilities.

This bulletin also provides information on the construction of

poured-in-place underground cable vaults.

 Roberta D. Purcell 8/28/02

Roberta D. Purcell Date

Assistant Administrator

Telecommunications Program

Disclaimer: The contents of this guidance document does not have the 

force and effect of law and is not meant to bind the public in any way. 

This document is intended only to provide clarity to the public regarding 

existing requirements under the law or agency policies.
Bulletin 1751F-644

Page 2

TABLE OF CONTENTS

 Abbreviations ............................................ 3

 Definitions .............................................. 4

 1. General .................................................. 6

 2. Inspection of Construction ............................... 7

 3. UCV Excavating and Grading .............................. 11

 4. Conduit Excavating, Grading, and Laying ................. 14

 5. Backfilling of Conduit Trenches and Conduit Sealing ..... 18

 6. Subsidiary Conduit Installation ......................... 19

 7. Concrete and Aggregate for Poured-In-Place UCVs and

 for Conduit Protection and Encasement ................... 20

 8. Conduit Rodding and Cleaning ............................ 25

 9. Cable Location and Conduit Selection .................... 25

10. Cable Reel and Apparatus Set-Up ......................... 26

11. Pulling Lines and Attachments ........................... 26

12. Cable Feeding and Pulling ............................... 27

13. Pulling Cables into Subsidiary Conduits ................. 28

14. Safety Precautions ...................................... 29

15. Handling and Care of Materials During Construction ...... 30

16. Repair of Cables Damaged During Construction ............ 31

17. Preparation for Splicing or Termination ................. 31

18. Installation Procedures for Filled Cables

 in Cold Weather ......................................... 31

19. Assembly Units and Acceptance Testing ................... 32

TABLES & FIGURES

Table 1 Poured-In-Place UCV Excavations - Minimum Lengths

 and Widths - Without Sheeting Materials ............ 12

Table 2 Poured-In-Place UCV Excavations - Minimum Lengths

 and Widths - With Sheeting Materials ............... 12

Table 3 Poured-In-Place UCV Excavations - Bracing and

 Shoring - Firm or Hard Soils ....................... 13

Table 4 Poured-In-Place UCV Excavations - Bracing and

 Shoring - Cracking or Crumbling Soils .............. 14

Table 5 Poured-In-Place UCV Excavations - Bracing and

 Shoring - Soft Sands or Loose Soils ................ 14

Table 6 Conduit Trench Excavations - Bracing and Sheet

 Piling - All Trench Widths - Soft, Sandy, or

 Loose Soils ........................................ 15

Table 7 Conduit Trench Excavations - Bracing and Sheet

 Piling - Trench Widths of 4 ft (1.2 m) or Less - 

 Cracking or Crumbling Soils ........................ 15
Bulletin 1751F-644

Page 3

TABLES & FIGURES - Continued

Table 8 Conduit Trench Excavations - Bracing and Sheet

 Piling - Trench Widths Greater than 4 ft (1.2 m) 

 Cracking or Crumbling Soils ........................ 16

Table 9 Trial Mixes for Cubic Yard of Concrete ............. 22

Table 10 Fine Aggregate Grading ............................. 24

Table 11 Coarse Aggregates - Usage, Sieve Sizes, and

 Aggregate Sizes .................................... 24

Figure 1 Example of Construction Details – 

 Poured-In-Place UCV Types A, L, T, J, X, and Y ..... 33

Figure 2 Example of Construction Details –

 Poured-In-Place UCV Type V ......................... 34

Figure 3 Subsidiary Conduit Installation - 

 Riser Pole Example ................................. 35

Figure 4 UCV Underground Cable and Splice Case

 Racking Diagram Example ............................ 36

Figure 5 Pulling Line Attachment Examples ................... 37

INDEX:

Outside Plant

Construction, Underground

Telecommunications

ABBREVIATIONS

°C Degrees Celsius

cm Centimeter

CT Construction Truck

°F Degrees Fahrenheit

ft Foot or feet

ft/min Feet per minute

kg Kilograms

lbs Pounds

in. Inches

m Meter

m3 Cubic Meters

m/min Meters per minute

mm Millimeter

MPa Megapascals

psi Pounds per square inch

NESC National Electrical Safety Code
Bulletin 1751F-644

Page 4

ABBREVIATIONS - Continued

R/W Right-of-way

RUS Rural Utilities Service

TE&CM Telecommunications Engineering and Construction Manual

UCV Underground Cable Vault

UCVs Underground Cable Vaults

DEFINITIONS

Aggregate: The mineral materials such as sand or stone used in

making concrete.

Backfill: Materials such as sand, crushed stone, or soil, which

are used to refill a trench after conduits or cables have been

laid therein.

Cable Rack: A device usually secured to the wall of an

underground cable vault (UCV), cable raceway, or building to

provide support for cables.

Conduit: A tubular raceway for holding wires or cables, which is

designed expressly for, and used solely for, this purpose.

Conduit Run: An arrangement of conduit providing one or more

continuous conduits between two points.

Construction Drawings: The drawings developed through the

staking process and used to guide the construction of outside

plant facilities.

Eligible Country: Any country that applies with respect to the

United States an agreement ensuring reciprocal access for United

States products and services and United States suppliers to the

market of that country, as determined by the Unites States Trade

Representative.

Resident: The competent representative of the Engineer who is

delegated full time “on site” Construction Administration

responsibilities of the Engineer.

Right-of-Way: The strip of land over which facilities such as

highways, railroads, power lines, other utilities, or

telecommunication lines are constructed.

Rodding: A device that can be either pulled or pushed through a

conduit that cleans the conduit of stones, rubble, etc. and

prepares the conduit to receive the cable.
Bulletin 1751F-644

Page 5

DEFINITIONS - Continued

RUS Accepted (Material and Equipment): Equipment which RUS has

reviewed and determined that:

a. Final assembly or manufacture of the equipment is

completed in the United States, its territories and

possessions, or in an eligible country;

b. The cost of components within the material or equipment

manufactured in the United States, its territories and

possessions, or in an eligible country is more than 50

percent of the total cost of all components used in the

material or equipment; and

c. The material or equipment is suitable for use on

systems of RUS telecommunications borrowers.

RUS Technically Accepted (Material and Equipment): Equipment

which RUS has reviewed and determined that the material or

equipment is suitable for use on systems of RUS

telecommunications borrowers but the material or equipment does

not satisfy both paragraph (a) and (b) of this definition:

a. Final assembly or manufacture of the equipment is

not completed in the United States, its territories and

possessions, or in an eligible country; and

b. The cost of components within the material or equipment

manufactured in the United States, its territories and

possessions, or in an eligible country is 50 percent or

less than the total cost of all components used in the

material or equipment.

Sieve: A wire mesh or closely perforated metal used for

straining, sifting, or ricing.

Stringer: A long, heavy horizontal timber used for any of

several connective or supportive purposes.

Subsidiary Conduit: A minor or spur conduit route leading from

an underground cable vault or jointing chamber to a building or

distribution point.

Underground Cable Vault (UCV): A subsurface chamber, large

enough for a person to enter for the purpose of installing cables

and other devices, and for making connections and tests.
Bulletin 1751F-644

Page 6

1. GENERAL

1.1 This bulletin discusses construction of underground plant

facilities using filled copper or fiber optic cables. The

information and recommendations in this bulletin are advisory.

1.2 Some of the work items associated with underground plant

construction are as follows:

a. Pre-installation inspection of copper cables and fiber

optic cables;

b. Pre-installation inspection of precast underground cable

vaults (UCVs) and conduits;

c. Trenching and installation of conduit runs;

d. Excavation of precast or poured-in-place underground

cable vault (UCV) pits;

e. Installation and inspection of bracing for precast or

poured-in-place UCV pits;

f. Installation of precast UCVs;

g. Construction of poured-in-place UCVs;

h. The installation of filled copper or fiber optic cables

in conduits and UCVs;

i. Installation of underground filled splice cases for

copper or fiber optic cables;

j. Splicing of copper cables and connection of shield

bonds and related grounding;

k. Splicing of fiber optic cables;

l. Connection of armor bonds and related grounding for

underground, armored, fiber optic cables;

m. Conducting acceptance tests.

1.3 Information for the design, splicing, acceptance testing,

and construction of underground plant facilities can be found in

the following Rural Utilities Service (RUS) documents:

a. RUS Form 515 RUS Telecommunications System Construction

Contract (Labor and Materials);

b. RUS Bulletin 1751F-643, Underground Plant Design;
Bulletin 1751F-644

Page 7

c. RUS Bulletin 1753F-151, Specifications and Drawings for

Construction of Underground Plant, RUS Form 515b;

d. RUS Bulletin 1753F-201(PC-4), RUS Standard for

Acceptance Tests and Measurements of Telecommunications

Plant;

e. RUS Bulletin 1753F-205(PE-39), RUS Specification for

Filled Telephone Cables;

f. RUS Bulletin 1753F-208(PE-89), RUS Specification for

Filled Telephone Cables with Expanded Insulation;

g. RUS Bulletin 1753F-401(PC-2), RUS Standard for Splicing

Copper and Fiber Optic Cables;

h. RUS Bulletin 1753F-601(PE-90), RUS Specification for

Filled Fiber Optic Cables; and

i. Latest edition of the National Electrical Safety

Code (NESC).

2. INSPECTION OF CONSTRUCTION

2.1 The construction of underground plant facilities should be

inspected. This inspection should be accomplished by having the

resident or resident’s assigned inspector present at all times

during the underground plant construction operation. The

resident or resident’s assigned inspector also should ensure that

correct conduit sizes and number of conduits; correct UCV sizes;

correct pair sizes, gauges, and types of copper cables; and the

correct number of optical fibers, types of optical fibers, and

types of fiber optic cables are installed and free of damage

during the underground plant construction operations.

2.2 When more than one underground plant construction operation

is being performed at the same time, each operation should be

inspected. During the installation of the conduit and UCV

system, construction may be stopped pending the resident’s

decision concerning proposed changes in the construction route

from that shown on the construction drawings. Undue delays in

making such decisions are costly to the borrower and should be

avoided.

2.3 All reels of filled copper or fiber optic cables; conduit

sections; and precast UCVs should be inspected before

installation for visual signs of damage. In addition, filled

copper or fiber optic cable ends should be sealed to prevent

moisture entry into the cores of copper or fiber optic cables

during transportation, in storage, and during placement.
Bulletin 1751F-644

Page 8

2.4 The underground plant construction route should be inspected

before beginning construction. When selecting the underground

plant construction route, the convenience and ease of

installation should be considered providing the quality of

construction is not decreased and construction costs to the

borrower are not substantially increased, which would affect

future operation and maintenance of the telecommunications

system.

2.5 Cables, conduit runs, UCVs, etc., as well as, the equipment

and procedures should be continuously inspected during the

installation to prevent damage to the cables, conduits, UCVs,

etc., and to ensure that proper depths of conduit runs and UCVs

are maintained at all times. Conduit runs should be checked for

damage at severe changes in grade and corner angles. The

resident should make certain that conduit runs are properly

installed in open trenches, that trenches are properly

backfilled, and that ground surfaces are restored to their

previous conditions. The resident should also make certain that

UCVs are properly installed in open vault pits, that vault pits

are properly backfilled, and ground surfaces are restored to

their previous conditions.

2.6 Sequential markings on the outer jackets of cables are

provided to facilitate the inventory of cable units. The

resident and the contractor should agree on the inventory of

underground plant units as they are installed. Construction

drawings should be appropriately marked so they can be used as

permanent records of all plant items.

2.7 Road and ground surfaces should be inspected to determine if

the surfaces have been damaged by the trenching and cable

placement equipment. If surfaces have been damaged, surfaces

should be repaired and reinspected. If repairs are necessary,

repairs should be performed in accordance with Federal, State, or

local codes, as set forth in, the RUS Telecommunications System

Construction Contract (RUS Form 515).

2.8 Conduit runs should be inspected during construction to

determine that:

a. Conduits have been properly installed in trenches;

b. Multi-duct conduit formations have the proper vertical

and horizontal spacings in trenches;

c. Conduit sections have been properly jointed;

d. Proper bend radii of curved conduit sections have

been maintained;

e. Required slope and depth of conduits have been

maintained;
Bulletin 1751F-644

Page 9

f. Concrete encasements have been properly installed,

when required;

g. Concrete bases have been properly installed,

when required; and

h. Top protection has been properly installed,

when required.

2.9 Precast and poured-in-place UCVs should be inspected during

construction to determine that:

a. UCVs have been properly installed in vault pits;

b. UCV collars, frames, and covers have been properly

installed;

c. Cable racks and their associated spacings have been

properly installed on UCV walls;

d. Underground filled copper or fiber optic splice cases

are supported on racks;

e. Underground filled copper or fiber optic cables are

supported on cable racks;

f. Vacant conduit ends are sealed; and

g. Cable tags have been marked with the proper information

per RUS Bulletin 1753F-401(PC-2),RUS Standard for

Splicing Copper and Fiber Optic Cables.

2.10 Underground splices and cases should be inspected during

construction to ensure that:

a. Cable jackets have been properly prepared;

b. Copper cable conductors have been properly spliced;

c. Optical fibers have been properly spliced;

d. Buffer tubes containing the optical fibers have a

sufficient amount of slack;

e. Shields of copper cables have been bonded

and grounded;

f. Armors of armored, filled, fiber optic cables have been

bonded and grounded;
Bulletin 1751F-644

Page 10

g. Encapsulating compounds have been properly mixed and

applied; and

h. Underground filled splice cases have been

properly installed.

2.11 Construction drawings should be accurately marked to

indicate the following:

a. Routing of conduit and UCV system;

b. Locations of UCVs, buildings, and/or pole risers in

relation to streets, roads, buildings, poles, or other

obstructions;

c. Distances between UCVs (wall-to-wall measurements),

UCVs to pole risers (wall-to-pole measurements) and UCVs

to buildings (wall-to-building measurements);

d. Conduit configurations, sizes and types between UCVs,

UCVs to pole risers, and UCVs to buildings;

e. Locations of existing and proposed cables and conduits

in which cables either exist or are to be installed;

f. UCV, cable vault, and building cable racking diagrams

indicating the positions of all existing and proposed

cables and cable stubs;

g. Conduit configurations indicating particular cable

assignments;

h. Exact cable (splice-to-splice) cut lengths for all

proposed cables to be installed in conduits;

i. Pole and building risers indicating splice locations,

supporting structures, cable attachment methods, and

physical protection, when required;

j. Lengths, pair sizes, gauges, and types of copper cables;

k. Lengths, number and types of optical fibers, and types

of fiber optic cables;

l. Locations of underground filled splice cases; and

m. Locations of other underground utilities and obstacles.
Bulletin 1751F-644

Page 11

2.12 Special care should be exercised to avoid damage to fences,

trees, lawns, and shrubs during installations of conduit and UCV

systems. Damages to fences, trees, lawns, and shrubs should be

repaired in accordance with RUS Bulletin 1753F-151,

Specifications and Drawings for Construction of Underground

Plant, RUS Form 515b.

2.13 Trenching operations of conduit and UCV systems within

areas of subsurface structures should be carried out in a manner

that will avoid accidental contact of the digging tools with such

structures. The equipment, which is used for such operations,

should be operated only by qualified personnel. When foreign

subsurface structures are encountered such as power cables,

Community Antenna Television cables, gas lines, etc.,

installations of conduit and UCV systems should be performed in

accordance with the requirements of the latest edition of the

NESC or Federal, State, or local codes. Where Federal, State, or

local codes are more stringent than the NESC, installations of

conduit and UCV systems should be performed in accordance with

the more stringent codes.

3. UCV EXCAVATING AND GRADING

3.1 Lengths, widths, depths, bracing, and sheeting, if required,

of excavations for precast UCVs should be in accordance with

precast UCV manufacturers’ recommendations

3.2 Lengths and widths of excavations for poured-in-place UCVs

should be constructed with interior dimensions as specified on

construction drawings and with walls of necessary thicknesses at

points of minimum dimensions. Figures 1 and 2 of this bulletin

provide examples of the construction details containing the above

mentioned interior dimensions of the UCVs. Where sheeting is

required to prevent cave-ins, poured-in-place UCV excavations

should be enlarged accordingly to account for sheeting materials.

Table 1 of this section may be used for determining minimum

lengths and widths of poured-in-place UCV excavations without

sheeting materials. Table 2 of this section may be used for

determining minimum lengths and depths of poured-in-place UCV

excavations with sheeting materials.
Bulletin 1751F-644

Page 12

TABLE 1

Poured-In-Place UCV Excavations

Minimum Lengths and Widths

Without Sheeting Materials

UCV Wall Thicknesses 

Inches (in.) [millimeters (mm)]

6 (152) 7 (178) 8 (203) 9 (229)

Inside Lengths or

Widths of UCVs

in. [Centimeters (cm)]

Lengths or Widths of Excavations

in. (cm)

42 (107) 54 (137) 56 (142) 58 (147) 60 (152)

48 (122) 60 (152) 62 (157) 64 (163) 66 (167)

54 (137) 66 (167) 68 (173) 70 (178) 72 (183)

60 (152) 72 (183) 74 (188) 76 (193) 78 (183)

66 (167) 78 (198) 80 (203) 82 (208) 84 (213)

72 (183) 84 (213) 86 (218) 88 (223) 90 (229)

78 (198) 90 (229) 92 (234) 94 (239) 96 (244)

84 (213) 96 (244) 98 (249) 100 (254) 102 (259)

90 (229) 102 (259) 104 (264) 106 (269) 108 (274)

96 (244) 108 (274) 110 (279) 112 (284) 114 (289)

102 (259) 114 (289) 116 (295) 118 (300) 120 (305) 

TABLE 2

Poured-In-Place UCV Excavations

Minimum Lengths and Widths

With Sheeting Materials

UCV Wall Thicknesses 

in. (mm)

6 (152) 7 (178) 8 (203) 9 (229)

Inside Lengths or

Widths of UCVs

in. (cm)]

Lengths or Widths of Excavations

in. (cm)

42 (107) 58 (147) 60 (152) 62 (157) 64 (163)

48 (122) 64 (163) 66 (168) 68 (173) 70 (178)

54 (137) 70 (178) 72 (183) 74 (188) 76 (193)

60 (152) 76 (193) 78 (198) 80 (203) 82 (208)

66 (167) 82 (208) 84 (213) 86 (218) 88 (223)

72 (183) 88 (223) 90 (229) 92 (234) 94 (239)

78 (198) 94 (239) 96 (244) 98 (249) 100 (254)

84 (213) 100 (254) 102 (259) 104 (264) 106 (269)

90 (229) 106 (269) 108 (274) 110 (279) 112 (284)

96 (244) 112 (284) 114 (289) 116 (295) 118 (300)

102 (259) 118 (300) 120 (305) 122 (310) 124 (315) 
Bulletin 1751F-644

Page 13

3.3 Depths of poured-in-place UCV excavations should be

determined using the following measurements:

a. UCV frame depths;

b. Depths of brick or concrete collars for UCV frames;

c. UCV roof thicknesses;

d. UCV headroom; and

e. UCV floor thicknesses.

If poured-in-place UCV excavations are constructed in wet

locations, 4 in. (102 mm) layers of crushed stone should be added

to the above measurements to determine poured-in-place UCV

excavation depths. The crushed stone layers should provide for

drainage of water during construction.

3.4 Types and amounts of sheeting and bracing required for

poured-in-place UCV excavations vary with soil stability and

excavation depths. Poured-in-place UCV excavations in soils that

are considered firm or hard should be shored and braced as

indicated in Table 3 of this section. For poured-in-place UCV

excavations in soils likely to either crack or crumble,

excavations should be shored and braced as indicated in Table 4

of this section. For poured-in-place UCV excavations in either

soft sands or loose soils, excavations should be shored and

braced as indicated in Table 5 of this section.

TABLE 3

Poured-In-Place UCV Excavations

Bracing and Shoring

Firm or Hard Soils

Sheet Piling Stringers Cross Bracing

Depth of 

Exacavations

Feet (ft)

[Meter(m)]

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

5 to 10

(1.5 to

3.0)

2 x 6

(51 x

152)

6

(1.8)

4 x 6

(102 x

152)

4

(1.2)

4 x 6

(102 x

152)

6

(1.8)

10 to 20

(3.0 to

6.1)

2 x 6

(51 x

152)

Tight

6 x 6

(152 x

152)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)
Bulletin 1751F-644

Page 14

TABLE 4

Poured-In-Place UCV Excavations

Bracing and Shoring

Cracking or Crumbling Soils

Sheet Piling Stringers Cross Bracing

Depth of 

Exacavations

ft (m)

Size

in.

(mm)

Horizontal

Spacing

Ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

5 to 10

(1.5 to

3.0)

2 x 6

(51 x

152)

3

(1.0)

4 x 6

(102 x

152)

4

(1.2)

4 x 6

(102 x

152)

6

(1.8)

10 to 20

(3.0 to

6.1)

2 x 6

(51 x

152)

Tight

6 x 6

(152 x

152)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)

TABLE 5

Poured-In-Place UCV Excavations

Bracing and Shoring

Soft Sands or Loose Soils

Sheet Piling Stringers Cross Bracing

Depth of 

Exacavations

ft (m)

Size

in.

(mm)

Horizontal

Spacing

Ft (m)

Size

In.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

5 to 10

(1.5 to

3.0)

2 x 6

(51 x

152)

Tight

6 x 6

(152 x

152)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)

10 to 20

(3.0 to

6.1)

2 x 6

(51 x

152)

Tight

8 x 8

(203 x

203)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)

4. CONDUIT EXCAVATING, GRADING, AND LAYING

4.1 Conduit trenches excavated in firm soils should be shored

using 2 in. by 6 in. (51 mm by 152 mm) or larger planks. Planks

should be vertically spaced along both sides of trenches and

braced using either jacks or 2 in. by 6 in. (51 mm by 152 mm)

braces that are either cleated or rigidly wedged.

4.2 Conduit trenches excavated in soils that are susceptible to

cave-ins such as soft, sandy, or loose soils, trenches should be

shored and braced as indicated in Table 6 of this section. For

conduit trenches having widths of 4 ft (1.2 m) or less and
Bulletin 1751F-644

Page 15

excavated in soils likely to either crack or crumble, trenches

should be shored and braced as indicated in Table 7 of this

section. For conduit trenches having widths greater than 4 ft

(1.2 m) and excavated in soils likely to either crack or crumble,

trenches should be shored and braced as indicated in Table 8 of

this section.

TABLE 6

Conduit Trench Excavations

Bracing and Sheet Piling

All Trench Widths

Soft, Sandy, or Loose Soils

Sheet Piling Stringers Cross Bracing

Depth of 

Trench

ft (m)

Size

in.

(mm)

Horizontal

Spacing

Ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

5 to 10

(1.5 to

3.0)

2 x 6

(51 x

152)

Tight

6 x 6

(152 x

152)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)

10 to 20

(3.0 to

6.1)

2 x 6

(51 x

152)

Tight

8 x 8

(203 x

203)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)

TABLE 7

Conduit Trench Excavations

Bracing and Sheet Piling 

Trench Widths of 4 ft (1.2 m) or Less

Cracking or Crumbling Soils

Sheet Piling Stringers Cross Bracing

Depth of 

Trench

ft (m)

Size

in.

(mm)

Horizontal

Spacing

Ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

5 to 10

(1.5 to

3.0)

2 x 6

(51 x

152)

3

(1)

4 x 6

(102 x

152)

5

(1.5)

4 x 6

(102 x

152)

5

(1.5)

10 to 15

(3.0 to

4.6)

2 x 6

(51 x

152)

2

(0.6)

4 x 6

(102 x

152)

4

(1.2)

4 x 6

(102 x

152)

4

(1.2)
Bulletin 1751F-644

Page 16

TABLE 8

Conduit Trench Excavations

Bracing and Sheet Piling 

Trench Widths Greater Than 4 ft (1.2 m)

Cracking or Crumbling Soils

Sheet Piling Stringers Cross Bracing

Depth of 

Trench

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

Size

in.

(mm)

Horizontal

Spacing

ft (m)

5 to 10

(1.5 to

3.0)

2 x 6

(51 x

152)

3

(1)

4 x 6

(102 x

152)

4

(1.2)

4 x 6

(102 x

152)

6

(1.8)

10 to 20

(3.0 to

6.1)

2 x 6

(51 x

152)

Tight

6 x 6

(152 x

152)

4

(1.2)

6 x 6

(152 x

152)

6

(1.8)

4.3 When excessive water is present in conduit trenches, tongue

and groove sheeting should be considered for use to reduce

pumping requirements.

4.4 When removing braces from trenches, lower braces should be

removed first. Upper braces should be removed last to provide

protection for construction personnel.

4.5 When foreign structures are encountered in trenches, it may

be necessary to go to greater depths than would otherwise be

required in order to obtain suitable clearances for conduits.

Where this is impracticable or undesirable, foreign structures

may be moved or trench lines shifted to obtain the required

clearances. If foreign structures must be moved to obtain

clearances, companies owning the foreign structures should be

contacted about performing the work.

4.6 Conduit trenches should cross under gas, steam, or water

lines rather than above them provided, however, that depths of

trenches would not be excessively increased. Conduit trenches

paralleling either above or below gas, steam, or water lines

should be avoided, as far as practicable.

4.7 Gas and oil lines should be given special attention and

precaution should be taken to guard against fire hazards they

present. Excavations in public streets should always be checked

for gas leaks, even though gas or sewer lines may not be directly

encountered. Open flames of any sort should not be permitted

around excavations when gas odors are detected. Construction

personnel should not be allowed to smoke and precautions should

be taken to prevent pedestrians from throwing lighted products

into such excavations. When excavations involving foreign
Bulletin 1751F-644

Page 17

structures are undertaken, owners of foreign structures should be

notified so that representatives of foreign structures may be

present at excavations if desired.

4.8 The minimum separation between electric power conduits and

telecommunications conduits should be as indicated in the latest

edition of the NESC. The minimum separation between foreign

pipes such as gas, water, oil, etc. and telecommunications

conduits should be at least 6 in. (152 mm) when crossing such

pipes and at least 12 in. (305 mm) when paralleling such pipes

measured from the nearest part of the conduit structure.

4.9 Foreign pipes diagonally crossing trenches should be

supported when necessary. Foreign pipes paralleling trenches and

either extending partially into trenches or located within 12 in.

(305 mm) of trenches should be laterally braced by shoring,

except when sheeting materials used to support trench walls

provide adequate bracing for pipes.

4.10 Trench beds should be leveled to provide even bases before

installing conduits. In some cases, sand or screened earth may

be required to be placed in trench beds to provide conduits with

stable bases. In other cases, concrete may be required to be

placed in trench beds to provide conduits with stable bases. The

types of bases to be placed in trench beds to provide adequate

conduit support should be based on the plans and specifications.

4.11 When trenches containing large volumes of water will not

permit installation or jointing of conduits, water in those

trenches should be disposed of by placing layers of crushed stone

in trench beds to allow the water to drain to sumps while

conduits are being installed. Layers of earth or sand over stone

should be applied prior to installation of conduits. Where

conditions exist that water in trenches can not be adequately

removed, systems of well-points paralleling trenches to lower

levels of ground water to levels below bottoms of excavations may

have to be employed.

4.12 Conduit entrances at opposite ends of UCVs should be at the

same levels and in the same positions with respect to side walls

to facilitate conduit rodding, cable placing, and splicing.

Conduit trenches should be graded to conduit entrances of UCVs.

Locations at which trench grades to UCV entrances should begin to

change will depend on the following:

a. Types of conduit configurations;

b. Usage of mitered conduits; or

c. Employment of splayed conduits.
Bulletin 1751F-644

Page 18

4.13 Conduit trenches should be graded in areas where

subfreezing ground conditions are expected to penetrate to

conduit installation depths. In those areas, trench grades

should fall 3 in. (76 mm) in 100 ft (30 m) for conduits toward

lower UCVs or from high points in conduit sections toward both

UCVs.

4.14 Installation of conduits; spacer supports; jointing of

conduits with associated fittings for bends, sweeps, bell ends,

adapters for jointing different types of conduits; and

terminations should be performed in accordance with conduit

manufacturers’ installation practices.

5. BACKFILLING OF CONDUIT TRENCHES AND CONDUIT SEALING

5.1 Backfilling material installed next to conduits should be

free of stones and other materials, which could damage either

conduits or conduit joints. Backfilling material should not

contain large boulders. Tamping of backfill at sides of conduits

should be performed with extreme care to avoid either damage to

joints or shifting of conduit configurations. The use of spacer

supports placed at distances recommended by the conduit

manufacturer in conduit configurations should aid in the

prevention of shifting conduit configurations during tamping

operations. Backfilling and tamping alongside conduits should be

performed in 2 in. (51 mm) thick layers until level with top of

conduit configurations. Backfilling around conduits jointed with

mortar bandages should proceed as soon as joints are completed.

Troweled joints should be allowed to set-up for 24 hours before

backfilling. Conduit trenches with concrete top protection or

encasement should be backfilled as soon as possible.

5.2 Backfill above conduits should be thoroughly tamped in 6 in.

(152 mm) layers. In most cases mechanically tamped backfill will

provide better compaction than hand-tamped backfill. Where large

amounts of backfilling and tamping are to be performed,

backfilling and tamping machines should be used. To avoid damage

to conduits, mechanical tampers should not be used until conduit

configurations have been covered with at least 12 in. (305 mm) of

hand-tamped backfill. In sandy soils, water may be used to

provide satisfactory compaction when backfill is installed in

6 in. (152 mm) layers and flooded. Where cinders form part of

the soil, clean earth should be used as backfill adjacent to

conduits and soils containing the cinders should not be replaced

until conduits have been covered with at least 6 in. (152 mm) of

cinder-free soil. In cases where soils are composed of mainly

cinders, concrete encasement of conduits should be considered.

5.3 Test mandrels which are 0.25 in (6 mm) smaller in diameters

than the inside diameters of conduits should be pulled through

all single conduits and through two diagonally opposite conduits

in multi-conduit configurations to ensure proper alignments. The
Bulletin 1751F-644

Page 19

pulling of the test mandrels through the conduits should be

performed after backfilling but prior to the replacement of any

grass, sod, repaving, etc. In addition, all conduits should be

cleaned of loose materials such as concrete, mud, dirt, stones,

etc.

5.4 Paving or temporary repaving over conduit trenches should be

performed in accordance with local, county and/or state

regulations. The local, county and/or state regulations

regarding paving or repaving should be included as of part of the

RUS Telecommunications System Construction Contract

(RUS Form 515).

5.5 All surplus matter excavated in conjunction with backfilling

operations should be removed so as not to obstruct traffic.

Where space is restricted, surplus matter should be removed at

the time of excavating. If possible, small quantities of

excavated materials should remain at construction sites to be

used later for filling in temporarily repaved trenches where

settlement occurs.

5.6 On public rights-of-way (R/W) or lands where construction of

conduit trenches require removal of sod or top soil, trench

surfaces should be restored to their original appearances by

resurfacing trenches with the original sod or top soil removed

during construction operations.

5.7 When the construction projects have been completed, all

surplus materials and debris should be removed from construction

sites.

5.8 Conduit ends should be sealed to prevent the entrance of

foreign matter and to prevent the entrance of water or gas into

UCVs or buildings. Conduits should be sealed in accordance with

conduit manufacturer’s recommendations. All conduits entering

central offices or other buildings should be sealed at all times

except when placing cables. If construction work extends over

several days, conduits should be temporarily sealed at night, but

permanently sealed upon completion of construction.

6. SUBSIDIARY CONDUIT INSTALLATION

6.1 The term “subsidiary conduits” is commonly used to define

any conduits branching off from main conduit runs. Subsidiary

conduits should be installed using the same construction and

installation practices as defined for main line conduits.

6.2 Figure 3 of this bulletin indicates the typical installation

procedures for subsidiary conduits when used as pole riser

conduits.
Bulletin 1751F-644

Page 20

6.3 Subsidiary conduits entering buildings should be placed

before buildings are erected if possible. In this situation,

suitable sleeves or stub outs can be inserted in building walls

or floors at the time of construction. If subsidiary conduits

are placed after building construction, entrances should be

installed through building walls or floors at points not vital to

support the buildings.

7. CONCRETE AND AGGREGATE FOR POURED-IN-PLACE UCVS AND FOR

 CONDUIT PROTECTION AND ENCASEMENT

7.1 Concrete mixtures containing Portland cement should be used

in the construction of all poured-in-place UCVs. Concrete

mixtures containing Portland cement should also be used for

either top protection, base stability, or encasement of conduits

when required.

7.2 Basically there are three types of Portland cement, which

may be used, in concrete construction of underground plant. The

three types are as follows:

a. Normal;

b. High early strength; and

c. Sulfate-resisting.

7.3 Normal Portland cement should be used for all concrete

construction unless otherwise indicated on the construction

drawings by the resident. High early strength Portland cement

should be used for concrete construction when it is necessary to

remove forms and open structures to traffic at earlier dates

after concrete has been placed. High early strength Portland

cement may also be used for concrete construction during low

temperatures. Sulfate-resisting Portland cement has the

characteristics to withstand exposure to severe alkali conditions

and has the same setting characteristics as normal Portland

cement. Therefore, sulfate-resisting Portland cement should only

be used for concrete construction when designated by the

resident.

7.4 There are eight classes of concrete that may be used in

underground plant construction. The eight concrete classes and

their suggested usage for underground plant concrete construction

are listed below:

a. Class 1A - For poured-in-place UCVs where concrete is

compacted by hand tamping;
Bulletin 1751F-644

Page 21

b. Class 1B - For poured-in-place UCVs where concrete is

compacted by mechanical vibration, for replacing

concrete pavements, and for poured-in-place UCV floors

where compaction is performed by hand tamping;

c. Class 1C - For poured-in-place UCVs where concrete is

compacted by hand tamping and where high early strength

Portland cement is required and for low temperature

construction;

d. Class 1D - For poured-in-place UCVs where concrete is

compacted by mechanical vibration and where high early

strength Portland cement is required, for concrete

pavement replacement where high early strength Portland

strength is required, and for poured-in-place UCV

floors where compaction is performed by hand tamping and

where high early strength Portland cement is required;

e. Class 2A - For conduit base or top protection;

f. Class 2B - For conduit encasement, particularly where it

is necessary to work the concrete between and around

closely spaced units of various types of single conduit;

g. Class 2C - For replacement of concrete bases for

asphalt, brick, or granite pavements; and

h. Class 2D - As a substitute for Class 2C concrete where

high early strength Portland cement is required or for

low temperature construction.

7.5 Bags of cement should be kept dry at all times to prevent

deterioration of the cement. Bags should be stored in either

buildings or on raised platforms that are covered with tarps.

7.6 Cement containing lumps that can not be pulverized by hand

should not be used in concrete construction operations. The

presence of such lumps indicates that the cement has absorbed

moisture, which is an indication that the cement has

deteriorated.

7.7 All Class 1 grades of concrete should have compressive

strengths equal to or greater than 3600 pounds per square inch

(psi) [25 megapascals (MPa)] at 28 days when made with normal or

sulfate-resisting Portland cement and at 7 days when made with

high early strength Portland cement.

7.8 All Class 2 grades of concrete should have compressive

strengths equal to or greater than 2500 psi (17 MPa) at 28 days

when made with normal or sulfate-resisting Portland cement and at

7 days when made with high early strength Portland cement.
Bulletin 1751F-644

Page 22

7.9 Water contained in aggregates should be considered as part

of the water used in mixing the concrete. Therefore, the

quantity of water added to the concrete mixture should be

adjusted so that the total quantity of water in the concrete

would not exceed the quantities shown in Table 9 of this section.

TABLE 9

Trial Mixes for Cubic Yards of Concrete

Concrete Class 1A 1B 1C 1D 2A 2B 2C 2D

Cement Type N or S* N or S* HES** HES** N or S* N or S* N or S* HES**

Tamping Requirement Hand Mech. Hand Mech. Hand Hand Hand Hand

Slump Range in. 4 – 6 2 – 4 4 – 6 2 – 4 1.5 – 3 6 – 8 2 – 4 2 – 4

Cement

(Sacks) 6.5 6.25 6.5 6.25 4.75 5.5 4.5 4.5

Water

Gallons 30.5 28.5 30.5 28.5 26.5 32 25.75 25.75

With

Gravel

Sand

Pounds

(lbs)

Fine

Aggregate

1420 1440 1420 1440 1510 1440 1290 1290

Sand Cubic

Yards Fine

Aggregate

0.59 0.60 0.59 0.60 0.63 0.60 0.54 0.54

Gravel

lbs Coarse

Aggregate

1750 1780 1750 1780 1860 1770 2130 2130

Gravel

Cubic

Yards

Coarse

Aggregate

0.65 0.67 0.65 0.67 0.70 0.66 0.80 0.80

Cement

(Sacks) 7 6.75 7 6.75 5.25 6 5 5

Water

Gallons 33.25 31 33.25 31 29.5 35 28 28

With

Stone

Sand lbs

Fine

Aggregate

1510 1570 1510 1570 1620 1540 1420 1420

Sand

Cubic

Yards Fine

Aggregate

0.63 0.65 0.63 0.65 0.68 0.64 0.59 0.59

Gravel

lbs Coarse

Aggregate

1530 1560 1530 1560 1640 1560 1910 1910

Gravel

Cubic

Yards

Coarse

Aggregate

0.57 0.58 0.57 0.58 0.61 0.58 0.71 0.71
Bulletin 1751F-644

Page 23

Notes:

1. *N – Normal or S – Sulfate Resisting Cement.

2. **HES – High Early Strength Cement.

3. To convert inches (in.) to millimeters (mm)

multiply by 25.4.

4. To convert gallons to cubic meters (m3)

multiply by 0.003785.

5. To convert pounds (lbs) to kilograms (kg)

 multiply by 0.4535.

6. To convert cubic yards to cubic meters

 multiply by 0.7645.

7.10 Watertight concrete uses aggregates that are completely

coated with cement paste that resists passage of water. Water

leakage through concrete is usually through the cement paste.

Water leakage may be prevented by having a sufficient quantity of

cement paste to coat all aggregate particles and to fill all

voids between aggregate particles. Class 1 grades of concrete

have water-cement ratios that should produce watertight concrete.

To ensure that concrete would be watertight, water should be

prevented from flowing through or over freshly placed concrete to

eliminate the washing away of the cement paste. Concrete

mixtures using additives to produce watertight concrete should

not be used in underground plant construction. The use of

watertight concrete for underground plant construction should be

indicated on the construction drawings by the resident.

7.11 Aggregates used in the preparation of concrete have an

important bearing on the quality of finished concrete. Fine

aggregates should consist of either natural sand, sand prepared

from stone, blast furnace slag, or gravel. Coarse aggregates

should consist of crushed stone, gravel, blast furnace slag, or

other inert materials of similar characteristics, or combinations

of the above materials having hard, strong, durable pieces and

free from adherent coatings. Aggregates used in concrete should

not contain cinders.

7.12 Fine aggregates for concrete should be graded from coarse

to fine by means of sieves as indicated in Table 10 of this

section. In coarse aggregates, the amounts of foreign substances

such as soft fragments, coal, clay, shale, or other materials

detrimental to the concrete quality should not exceed 5 percent

of the total weight of coarse aggregates. Table 11 of this

section indicates the sizes, grading sieves, and intended usage

of coarse aggregates that should be used in concrete construction

operations of underground plant.
Bulletin 1751F-644

Page 24

TABLE 10

Fine Aggregate Grading

Sieve Sizes

Grading

Percent By Weight

Passing a 3/8 in. (9.5 mm) 100

Passing a No. 4 95 to 100

Passing a No. 16 45 to 80

Passing a No. 50 5 to 30

Passing a No. 100 0 to 8

TABLE 11

Coarse Aggregates

Usage, Sieve Sizes, and Aggregate Sizes

Intended Use Concrete Class

Sieve Size

Minimum

Aggregate Size

Maximum

in. (mm)

Conduit

Protection 2A No. 4 0.75 (19)

Conduit

Encasement 2B No. 4 0.5 (13)

Pavement

Replacement 2C and 2D No. 4 1.5 (38)

7.13 Aggregates should be stored separately to prevent mixture

with other types of aggregates until aggregates are used and to

prevent inclusion of foreign materials.

7.14 Concrete construction during cold weather may be performed

where suitable precautions are observed. In early winter, when

freezing temperatures occur only at night, finished concrete

should be protected against freezing. When freezing temperatures

constantly persist, it may be necessary to heat the water and

aggregates during concrete mixing operation in addition to

protecting the finished concrete from freezing. With approval of

the resident, concrete construction may be performed at

temperatures below 20°F (-6.7°C) when the above mentioned

precautions are observed and high early strength Portland cement

is substituted for normal Portland cement in the concrete

mixture. Earth surrounding the conduit installation also serves

to protect the concrete from freezing. Therefore, conduit

trenches constructed during cold weather should be immediately

backfilled with material that is not frozen after conduit

installations. Concrete, which has been damaged by freezing

temperatures, should be replaced with freshly mixed concrete.

7.15 In localities where ready-mix concrete is available, the

use of ready-mix concrete should be considered for the concrete

construction operation because ready-mix concrete affords

convenience of delivery and uniform concrete quality at

reasonable costs.
Bulletin 1751F-644

Page 25

8. CONDUIT RODDING AND CLEANING

8.1 Before installation of underground cables, conduits should

be rodded to determine if conduits are free of foreign

obstructions, which may prevent placement of cables in conduits.

Rodding consists of pulling a test mandrel through the conduit

section between UCVs to remove the obstruction. The diameter of

the test mandrel should be equal to or slightly larger than the

diameter of either the cable or the pulling eye, whichever is

larger.

8.2 Conduits suspected or found to contain particles of earth,

sand, gravel, etc. should be cleaned by pulling a stiff bristled

wire brush through the conduits.

8.3 Conduits suspected or found to be obstructed with foreign

materials which can not be removed by rodding or cleaning should

be immediately reported to the resident. The resident should

then determine what appropriate action should be taken to

alleviate the obstructions.

9. CABLE LOCATION AND CONDUIT SELECTION

9.1 Filled copper cables should be placed relative to cable

numbers, pair counts, cable sizes, cutting lengths, and conductor

gauges in accordance with construction drawings. Filled fiber

optic cables should be placed relative to cable numbers, fiber

counts, cable sizes, cutting lengths, and optical fiber types in

accordance with construction drawings.

9.2 Records of copper or fiber optic cable footage installed and

footage of copper or fiber optic cables remaining on reels after

cutting lengths have been removed should be maintained for each

reel of underground copper or fiber optic cable used on the

construction project.

9.3 Each copper or fiber optic cable reel should have a tag

fixed to the outside of each flange indicating the copper or

fiber optic cable footage remaining on the reel. The tag should

be updated immediately after a cut length is removed from the

reel.

9.4 Conduit assignments for each individual copper or fiber

optic cable for any conduit section should be in accordance with

the construction drawings. Copper or fiber optic cables should

be racked in UCVs or buildings in accordance with the

construction drawings. Figure 4 of this bulletin provides an

example of racking underground cable and splice cases in UCVs.
Bulletin 1751F-644

Page 26

10. CABLE REEL AND APPARATUS SET-UP

10.1 Cable reels should be inspected for flange protrusions,

which could damage cable sheaths. Construction areas should be

inspected to determine if any obstructions are present that could

interfere with unwinding of cables.

10.2 When cable reels are required to be moved to different

locations, cable reels should be rolled in the direction

indicated by the arrows painted on the reel flanges. Cable reels

should not be permitted to tilt. Where uneven ground conditions

exist that may cause reels to tilt, heavy planks or equivalent

materials should be used as runways for moving reels to avoid

tilting of reels. Where it is necessary to move cable reels with

construction trucks, construction truck (CT) slings or

equivalents should be used.

10.3 In conduit sections containing curves, cable reels should

be set-up at UCVs near the curves unless not permitted by traffic

or other conditions.

10.4 Cable reels should be set-up on the same sides of UCVs as

conduit sections in which cables are to be placed. Reels should

be leveled and aligned with conduit sections to prevent twisting

of cables during installation into conduits. Cables should be

pulled into conduits from tops of reels in long smooth bends.

Cables should not be pulled into conduits from bottoms of reels.

10.5 Cables should be removed from reels by manually rotating

the reels. To eliminate cable binding during removal from reels,

adjacent cable layers on reels should not be allowed to adhere to

one another.

11. PULLING LINES AND ATTACHMENTS

11.1 Pulling lines used in cable placing operations should be in

good condition.

11.2 Markers should be placed on pulling lines 20 ft (6.0 m)

from cable ends to indicate when cables are about to enter UCVs.

11.3 Pulling lines should be attached to factory installed

pulling eyes as shown in Sketch A of Figure 5 of this bulletin.

Pulling lines should be attached to cable grips as shown in

Sketch B of Figure 5 of this bulletin. Rings to prevent grips

from slipping should not be beaten into cable sheaths. Swivels

selected for use should be able to withstand maximum pulling

tensions and still allow pivoting about their axis.
Bulletin 1751F-644

Page 27

12. CABLE FEEDING AND PULLING

12.1 Cable feed guides of suitable dimensions should be used

between cable reels and conduit faces to protect cables and guide

cables into conduits as cables are payed-off reels. Bend radii

of feed guides for filled copper cables should not be less than

10 times the outside diameters of cables. Bend radii of feed

guides for filled fiber optic cables should be in accordance with

fiber optic cable manufacturers’ recommendations.

12.2 Before cable placing operations begin, equipment should be

checked to ensure that equipment is properly set-up to ensure

that cables can be placed in conduit sections between UCVs in one

operation without interruptions. Tension should be applied to

both cable reels and pulling lines at the start of cable placing

operations. Excessive slack and twisting of pulling lines should

be held to a minimum at the start of cable placing operations to

avoid the possibility of connecting links twisting and catching

in conduits. As far as possible, cables should be placed without

stopping until the required cable amounts have been installed in

UCVs. Pulling speeds for filled copper cable installations

should not exceed 80 to 100 ft/minute (ft/min) (24 to 30 m/min).

Pulling speeds for filled fiber optic cables should be in

accordance with cable manufacturers’ recommendations.

12.3 Mechanical stresses applied to cables during installations

should be held to absolute minimums to avoid excessive twisting,

stretching, or flexing of cables. Excessive twisting,

stretching, or flexing of cables during installations can result

in either physical damage to cable sheaths or deterioration of

electrical or optical properties of filled copper or fiber optic

cables, respectively. Therefore mechanical stresses applied to

cables during installations should not exceed cable

manufacturers’ recommendations.

12.4 Cables should be lubricated with lubricants that are

compatible with cable jacket materials as cables are payed-off

reels into cable feed tubes. Cable lubricators (funnels) should

be placed around cables in front of cable feed tubes to

facilitate proper lubrication of cables. Lubricants used in

cable placing operations should be in accordance with cable

manufacturer’s recommendations. Soap lubricants or lubricants

containing soap should not be used.

12.5 The quantities of cable lubricants that should be used in

cable placing operations should be in accordance with cable

manufacturers’ recommendations. Lubrication of cables should not

be necessary for conduit sections that are less than or equal to

300 ft (90 m) provided conduit sections are free of sharp bends.

12.6 After cables have been installed and before leaving UCVs,

exposed cables in UCVs should be cleaned of lubricants using dry

rags.
Bulletin 1751F-644

Page 28

12.7 Careful attention should be paid to signals from

installation crews as cables are being placed so that placing may

be stopped instantly to avoid damage to cables. When placing

operations are stopped between UCVs, operators should not release

tension on winches unless directed by the resident. In

restarting placing operations, inertia of cables should be

overcome by gradually increasing the tension in steps a few

seconds apart until cables are again in full motion.

12.8 Leading ends of cables at intermediate UCVs should be

guided into conduits and feeder tubes placed around cables to

prevent cables from rubbing on conduit edges. To ensure that

pressure is maintained on sealing gaskets of factory installed

pulling eyes at intermediate UCVs, pulling eye nuts should be

retightened at each intermediate UCV.

12.9 Sufficient lengths of cables should be left in each UCV to

properly rack and splice cables in accordance with construction

drawings. The amount of cable slack left in each UCV should be

indicated on the construction drawings.

12.10 After cables have been installed in UCVs, cable ends in

all UCVs should be temporarily secured to cable racks to prevent

damage. Bending of cables in UCVs should be accomplished in a

manner to avoid damage to cables. Cable slack left in UCVs

should be looped around UCVs in long sweeping bends and tied

securely in locations where cables would not obstruct UCV working

areas. Cable ends should be placed near UCV roofs.

12.11 After cables have been installed, copper cables should be

identified on ends of splices with tags indicating cable numbers,

pair counts, sizes, gauges, and cut lengths. Fiber optic cables

should be identified on ends of splices with tags indicating

cable numbers, number of fibers, fiber types, and cut lengths.

13. PULLING CABLES INTO SUBSIDIARY CONDUITS

13.1 When installing cables in subsidiary conduits extending

from UCVs, service UCVs or vaults to pole risers, or buildings,

cable reels should be located at the ends of the conduits nearest

the bends. Cables should be fed in long smooth curves rather

than pulled upward around the bends from the opposite ends.

13.2 Due to the number of bends usually encountered in

subsidiary conduits, cable lubricants should be used to

facilitate placement of cables regardless of conduit lengths.

13.3 Sufficient lengths of cables should left at ends of

conduits to permit setting-up and splicing operations. Cables

should be lashed temporarily to poles or walls to insure that

cables do not interfere with other activities, become safety
Bulletin 1751F-644

Page 29

hazards in work areas, or come in contact with electrical power

services.

14. SAFETY PRECAUTIONS

14.1 Open UCVs should be guarded at all times with either UCV

guards or barricades. These and other warning devices should be

set up at UCVs before removal of UCV covers.

14.2 During construction of underground plant, warning lights

should be placed between sunset and sunrise and when vision is

impaired by fog, haze, etc. Warning lights should be placed in

accordance with local, State, and/or Federal ordinances.

14.3 Flames, torches, lit tobacco products, etc. should not be

brought near open UCVS, into covers or tents over UCV openings,

or into UCVs until tests for combustible gases indicate that no

such gases are present in the UCVs.

14.4 When lighting and heating equipment are to be used in UCVs,

only lighting and heating equipment designated for use in UCVs

should be used. Connection and disconnection of lighting and

heating equipment should be performed outside of UCVs.

14.5 UCVs opened for the first time during the day or reopened

after having been closed for any length of time should be tested

for the presence of combustible gases. Additional tests should

be performed at the start of each work shift change and at

intervals not to exceed two hours during work shifts. UCVs

covered with tents or tarpaulins should be tested for combustible

gases at intervals not to exceed one hour. UCVs should also be

tested for combustible gases after removal of conduit plugs,

which could possibly have permitted the flow of gases into UCVs.

Where gases are detected or suspected, UCVs should be ventilated

using forced fresh air equipment in accordance with the

manufacturer’s instructions.

14.6 Adequate communications should be established between cable

feeding locations and other pulling equipment locations prior to

starting of pulling operations.

14.7 Construction materials and tools should be arranged in such

manners to avoid the possibility of such materials and tools

falling into UCVs or unnecessarily interfering with pedestrian or

vehicular traffic.

14.8 Caution should be exercised when entering or exiting UCVs,

particularly UCVs located on traveled thoroughfares. Ladders

should be for entering and exiting UCVs. Entering and exiting

UCVs should be performed facing oncoming traffic. Hands should

be kept free of materials or tools when ascending or descending

ladders.
Bulletin 1751F-644

Page 30

15. HANDLING AND CARE OF MATERIALS DURING CONSTRUCTION

15.1 Extreme care should be exercised in handling materials

during the construction process. Underground cable pulling

operations should be inspected at all times to ensure that

maximum cable pulling tensions are not exceeded. Under no

circumstances should maximum pulling tensions be allowed to

develop in the cables during pulling operations. Exceeding

maximum cable pulling tensions could result in damages to cables.

Whenever pulling operations are stopped, cables should remain

under tension. When restarting pulling operations, tensions on

cables should be gradually increased in steps of a few seconds

apart until cables are once again in motion.

15.2 Cable reels delivered to work locations but not set up

immediately for pulling operations should be securely blocked or

secured to substantial supports to prevent rolling or movement of

reels. Cable reels used in pulling operations should not be left

on grades or in traffic lanes. When reels are required to be

left on grades, reels should be turned against curbs and blocked

to prevent rolling of reels.

15.3 Cable reels stored overnight on streets or highways should

be marked in accordance with local, State, or Federal

regulations. If no local, State, or Federal marking regulations

exist for storing reels overnight on streets or highways, reels

should be barricaded and lit with flashing lights or red lanterns

not later than one-half hour before sunset.

15.4 Care should be exercised to prevent damage to exposed

cables during the construction period. Construction work should

be scheduled to keep such exposure to a minimum. Cables left

exposed are susceptible to damage. Cables left exposed are also

considered hazards to vehicles, pedestrians, or animals.

15.5 Copper and fiber optic cables in UCVs should be racked in

accordance with the construction drawings and spliced in

underground filled splice cases as soon as practicable. The

installation work should be completed within one week after the

cables have been installed.

15.6 Underground plant connections using dissimilar metals

should be avoided to eliminate the possibility of galvanic

corrosion. Therefore underground plant connections should be

made using only tinned coated metals.

15.7 When working in UCVs care should be exercised to prevent

damage to cables in setting up pulling apparatus or while using

tools of any kind. Cables, splice cases, etc. should not be used

as steps for entering or exiting UCVs.
Bulletin 1751F-644

Page 31

16 REPAIR OF CABLES DAMAGED DURING CONSTRUCTION

16.1 Minor damage to the outer jackets, where the shields or

armors of the cables have not been bent, abraded, or penetrated

should be repaired in accordance with Bulletin 1753F-401(PC-2),

RUS Standard for Splicing Copper and Fiber Optic Cables.

16.2 Cables found to be damaged after installation should be

repaired. If the damage is considered minor, the damage should

be repaired in accordance with Bulletin 1753F-401(PC-2), RUS

Standard for Splicing Copper and Fiber Optic Cables. If the

damage is considered major, the damage should be repaired either

by replacing the damaged sections with new cables spliced to the

undamaged sections of the cable or repaired in accordance with

the method specified in the contract.

17. PREPARATION FOR SPLICING OR TERMINATION

17.1 Underground filled copper cables should be spliced in

accordance with Bulletin 1753F-401(PC-2), RUS Standard for

Splicing Copper and Fiber Optic Cables, and enclosed in RUS

accepted or technically accepted underground filled splice cases.

17.2 Underground filled fiber optic cables should be spliced in

accordance with Bulletin 1753F-401(PC-2), RUS Standard for

Splicing Copper and Fiber Optic Cables, and enclosed in RUS

accepted or technically accepted filled fiber optic splice cases.

18. INSTALLATION PROCEDURES FOR FILLED CABLES IN COLD WEATHER

18.1 Flexibility of filled copper and fiber optic cables should

not be a problem at normal operating temperatures. However,

flexibility may be affected when cables are exposed to lower

temperatures. The flexibility of filled copper and fiber optic

cables could be sharply reduced at temperatures below 40°F

(4.4°C). At temperatures below 40°F (4.4°C), almost twice the

force may be needed to bend the filled copper and fiber optic

cables. Filled copper and fiber optic cables should be inspected

each morning to determine if the cables are flexible enough for

underground placement when night time temperatures drop below

30°F (-1.1°C). When filled copper or fiber optic cables have

been stored outdoors and subjected to cold nights, considerable

time may be lost each morning waiting for the cables to warm up

even though the day time temperature may be above 40°F (4.4°C).

During the spring and fall of the year, filled copper or fiber

optic cables may be stored in heated warehouses prior to

placement in underground conduits. This storage in heated

warehouses allows the filled copper or fiber optic cables to be

transported to the project site as needed and installed while the

cables are still flexible.
Bulletin 1751F-644

Page 32

18.2 Some filling compounds used in the cores of filled copper

cables may be stiff as the temperature decreases making it

difficult to separate the cable pairs. In general, filled copper

cables installations below 40°F (4.4°C) could be slow, difficult,

and possibly even halted unless special precautions are taken to

offset the effects of the lower temperatures.

18.3 Filling compounds used in loose tube buffers of filled

fiber optic cables should not become stiff as the temperature

decreases. This should allow the optical fibers to be easily

separated at low temperatures.

18.4 As mentioned in paragraph 18.2 of this section, the copper

pairs may be difficult to separate as the temperature decreases.

At temperatures as low as 20°F (-6.7°C), copper pairs may be

separated by flexing the free ends of the cable cores and

separating a few pairs at a time. It is also interesting to note

that filling compounds at a temperature of 20°F (-6.7°C) are more

user friendly to work with than at elevated temperatures.

Consequently, the copper cable pairs may be spliced without

wiping the pairs free of filling compound.

19. ASSEMBLY UNITS AND ACCEPTANCE TESTS

19.1 Detailed descriptions of all standard underground plant

assembly units are given in RUS Bulletin 1753F-151,

Specifications and Drawings for Construction of Underground

Plant, RUS Form 515b.

19.2 Where standard underground plant assembly units are

insufficient to provide for unique underground plant construction

requirements, detailed “nonstandard assembly units” should be

created to meet those requirements. The underground plant

nonstandard assembly units should be approved by RUS prior to the

bidding of the project.

19.3 After installation, underground copper and fiber optic

cables should be tested in accordance with RUS Bulletin 1753F201(PC-4), RUS Standard for Acceptance Tests and Measurements of

Telecommunications Plant, and the RUS Form 515 Contract.