UNITED STATES DEPARTMENT OF AGRICULTURE

Rural Utilities Service

**BULLETIN 1751F-643**

**SUBJECT: [Underground Plant Design]{.underline}**

**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-643,
"Underground Plant Design," 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 design
and construction of underground plant facilities. This bulletin also
provides information on the design of poured-in-place underground cable
vaults.

[Roberta D. Purcell]{.underline} [8/28/02]{.underline}

Roberta D. Purcell Date

Assistant Administrator

Telecommunications Program

**TABLE OF CONTENTS**

Abbreviations \...\...\...\...\...\...\...\...\...\...\...\...\...\....
4

Definitions \...\...\...\...\...\...\...\...\...\...\...\...\...\...\...
4

1\. General
\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.... 7

2\. Application
\...\...\...\...\...\...\...\...\...\...\...\...\...\...\... 8

3\. Construction Materials \...\...\...\...\...\...\...\...\...\...\...
11

4\. Conduit Types and Usage \...\...\...\...\...\...\...\...\...\.....
11

5\. Conduit Formations and Curves \...\...\...\...\...\...\...\..... 13

6\. Conduit Section Lengths \...\...\...\...\...\...\...\...\...\.....
14

7\. Conduit Protection \...\...\...\...\...\...\...\...\...\...\...\....
15

8\. UCV Types
\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.... 15

9\. Cable Racks, Rack Supports, and Pulling Irons \...\...\.... 22

10\. UCV and Conduit Locations \...\...\...\...\...\...\...\...\...\...
24

11\. Determination of Installation Length and Pulling

Tension of Filled Copper Cables \...\...\...\...\...\...\...\... 25

12\. Determination of Installation Length and Pulling

Tension of Filled Fiber Optic Cables \...\...\...\...\...\.... 28

13\. Design Considerations \...\...\...\...\...\...\...\...\...\...\....
29

# TABLES & FIGURES

Table 1 Conduit Formations \...\...\...\...\...\...\...\...\...\...\...
14

Table 2 Minimum Headroom - Poured-In-Place UCVs \...\...\...\... 16

Table 3 Floor Thicknesses and Reinforcing Rod Spacings

Rectangular Poured-In-Place UCVs in Fluid Soils \.... 17

Table 4 Floor Thicknesses and Reinforcing Rod Spacings

Type UM-V Poured-In-Place UCVs in Fluid Soils \...\... 17

Table 5 Wall Construction -- Poured-In-Place UCVs

in Firm Soils \...\...\...\...\...\...\...\...\...\...\...\..... 19

Table 6 Wall Construction -- Poured-In-Place UCVs

in Fluid Soils \...\...\...\...\...\...\...\...\...\...\...\.... 20

Table 7 Roof Thicknesses and Reinforcing Rod Diameters

Rectangular Poured-In-Place UCVs \...\...\...\...\...\.... 21

Table 8 Roof Thicknesses and Reinforcing Rod Diameters

Type UM-V Poured-In-Place UCVs \...\...\...\...\...\...\... 21

Table 9 UCV Opening Forms for UCV Frame Types and Sizes

Poured-In-Place UCVs \...\...\...\...\...\...\...\...\...\.... 21

Table 10 Number and Size of Cable Racks Versus Headroom

##  Poured-In-Place UCVs \...\...\...\...\...\...\...\...\...\.... 23

Table 11 Coefficient of Friction

Conduit Versus Cable Jacket Material \...\...\...\...\... 25

**TABLES & FIGURES - Continued**

Table 12 Cross-sectional Area of Copper Conductors \...\..... 27

Figure 1 Overall Design Layout -- Poured-In-Place UCVs \..... 31

Figure 2 Floor Construction

Poured-In-Place UCVs In Fluid Soils \...\...\...\..... 32

Figure 3 Sump and Drain Construction

Poured-In-Place UCVs \...\...\...\...\...\...\...\...\..... 33

Figure 4 Wall Construction -- Poured-In-Place UCVs \...\...\... 34

Figure 5 Roof Construction -- Poured-In-Place UCVs \...\...\... 35

Figure 6 Conduit Entrances and Recesses

Poured-In-Place UCVs \...\...\...\...\...\...\...\...\..... 36

Figure 7 Frame and Cover Types -- Poured-In-Place UCVs \..... 37

Figure 8 Brick Collar Construction -- Poured-In-Place UCVs . 38

Figure 9 Typical Installation of Cable Racks

Poured-In-Place UCVs \...\...\...\...\...\...\...\...\..... 39

Figure 10 Arrangement and Installation of Pulling-In Irons

Poured-In-Place UCVs \...\...\...\...\...\...\...\...\..... 40

Figure 11 Example of Underground Cable Vault and Conduit

Route Construction Drawing \...\...\...\...\...\...\..... 41

Figure 12 Underground Plant Construction Abbreviations

and Symbols \...\...\...\...\...\...\...\...\...\...\...\..... 42

Figure 12A Underground Plant Construction Abbreviations

and Symbols (Continued) \...\...\...\...\...\...\...\..... 43

Figure 12B Underground Plant Construction Abbreviations

and Symbols (Continued) \...\...\...\...\...\...\...\..... 44

Figure 12C Underground Plant Construction Abbreviations

and Symbols (Continued) \...\...\...\...\...\...\...\..... 45

Figure 13 Example of Underground Filled Copper Cable

Installation in a Conduit and UCV System

Containing Multiple Bends \...\...\...\...\...\...\...\... 46

Figure 13A Example of Underground Filled Copper Cable

Installation in a Conduit and UCV System

Containing Multiple Bends (Continued) \...\...\...\... 47

**TABLES & FIGURES - Continued**

Figure 13B Example of Underground Filled Copper Cable

Installation in a Conduit and UCV System

Containing Multiple Bends (Continued) \...\...\...\... 48

Figure 14 Example of Determining the Cable Sidewall Pressure

at Conduit Bends in a Conduit and UCV System \..... 49

Figure 14A Example of Determining the Cable Sidewall Pressure

at Conduit Bends in a Conduit and UCV System

(Continued) \...\...\...\...\...\...\...\...\...\...\...\..... 50

**INDEX**:

##  Outside Plant

Design, Underground

Telecommunications

**ABBREVIATIONS**

AWG American Wire Gauge

CFR Code of Federal Regulations

cm Centimeters

ft Foot or Feet

in. Inches

kgs Kilograms

kgs/m Kilograms per meter

kgs/mm^2^ Kilograms per square millimeter

lbs Pounds

lbs/ft Pounds per foot

LD Loan Design

m Meter

mm Millimeters

mm^2^ Square Millimeters

R/W Rights-of-way

RUS Rural Utilities Service

SAVE Serving Area Value Engineering

TE&CM Telecommunications Engineering and Construction Manual

UCV Underground Cable Vault

UCVS Underground Cable Vaults

UM Underground Manhole

**DEFINITIONS**

**[Cable Rack]{.underline}:** A device usually secured to the wall of an
underground cable vault, cable raceway, or building to provide support
for cables.

**[Conduit]{.underline}:** A tubular raceway for holding wires or
cables, which is designed expressly for, and used solely for, this
purpose.

**DEFINITIONS - Continued**

**[Construction Drawings]{.underline}:** The drawings developed through
the staking process and used to guide the construction of outside plant
facilities.

**[Eligible Country]{.underline}:** 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 United States Trade
Representative.

**[Loan Design]{.underline}:** A comprehensive engineering plan for the
project supporting a loan application to RUS.

**[Underground Cable Vault (UCV)]{.underline}:** 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.

**[Underground Cable Vault (UCV) Cover]{.underline}:** A removable lid
which closes the opening to an underground cable vault or similar
subsurface enclosure.

**[Underground Cable Vault (UCV) Frame]{.underline}:** A structure that
caps the roof opening of the underground cable vault at ground level and
supports the cover.

**[Pulling Iron]{.underline}:** An anchor secured in the wall, ceiling,
or floor of an underground cable vault to attach rigging used to pull
cable.

**[Resident]{.underline}:** The qualified representative of the Engineer
who is delegated full time \"on site\" Construction Administration
responsibilities of the Engineer.

**[Right-of-way]{.underline}:** The strip of land over which facilities
such as highways, railroads, power lines, other utilities, or
telecommunication lines are constructed.

**DEFINITIONS - Continued**

**[RUS Accepted (Material and Equipment)]{.underline}:** 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)]{.underline}:**
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.

**1. GENERAL**

**1.1** This bulletin discusses in particular the design of underground
plant using filled copper or fiber optic cables. This bulletin also
provides information on the design and construction of poured-in-place
underground cable vaults (UCVS). The information and recommendations in
this bulletin are advisory.

**1.2** Underground plant consists of a conduit and an underground cable
vault (UCV) system and the telecommunications copper or fiber optic
cables installed in the conduit and UCV system.

**1.3** Additional information for the use in the design and
construction of underground plant facilities can be found in the
following Rural Utilities Service (RUS) documents:

a\. Telecommunications Engineering and Construction Manual

(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 230, General Principles of Feeder-

Distribution Cable Engineering \[Serving Area Value

Engineering (SAVE)\];

g\. TE&CM Section 231, Design Techniques of Feeder-

Distribution Cable Engineering (SAVE);

h\. TE&CM Section 232, Transmission Design and Costs

Considerations of Feeder-Distribution Cable

Engineering (SAVE);

i\. TE&CM Section 628, Plastic-Insulated Cable Plant Layout;

j\. TE&CM Section 629, Cable Plant Layout - Serving Area

Value Concept for Rural Systems;

k\. RUS Bulletin 344-3, \"Buy American\" Requirement, as

amended by the Notice published in the Federal Register,

Volume 66, Number 222, dated November 16, 2001;

l\. RUS Bulletin 1751F-644, Underground Plant Construction;

m\. RUS Bulletin 1751F-670, Outside Plant Corrosion

Considerations;

n\. RUS Bulletin 1751F-801, Electrical Protection

Fundamentals;

o\. RUS Bulletin 1751F-815, Electrical Protection of Outside

Plant;

p\. RUS Bulletin 1751H-601, Lightwave Fundamentals, Systems,

and Application;

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

Construction of Underground Plant, Form 515b;

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

Filled Telephone Cables;

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

Filled Telephone Cables with Expanded Insulation;

t\. RUS Bulletin 1753F-402(PC-2), RUS Standard for Splicing

Copper and Fiber Optic Cables;

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

Filled Fiber Optic Cables;

v\. 7 Code of Federal Regulations (CFR) § 1753.6,

> Standards, specifications, and general requirements.

**2. APPLICATION**

**2.1** Underground plant facilities should be considered for the
following conditions:

a\. In urban or suburban areas;

b\. Where public authorities object to aerial plant

construction;

c\. Where direct buried plant is inadvisable;

d\. Where alternative aerial or buried routes are not

practicable;

e\. Where the appearance of an aerial entrance cable to a

central office building would be objectionable; or

f\. Where department of transportation officials prohibit

aerial crossings over roads, streets, highways, etc.

**2.2** Since underground plant facilities are usually exposed to less
physical damage than aerial or buried facilities, fewer cable faults
should be associated with underground plant facilities. This lower fault
rate should result in long periods of maintenance-free operation and
greater subscriber satisfaction. Underground plant facilities could be
used in areas susceptible to frequent ice storms and/or high wind
velocities.

**2.3** Permission from appropriate authorities needs to be obtained
before installing underground plant facilities, which include conduits,
UCVs, and copper or fiber optic cables, in public rights-of-way (R/W) or
travel lanes of roadways, streets, etc. In most circumstances
cooperation with appropriate authorities can be obtained when
underground plant construction techniques are fully explained. A
comprehensive investigation of the public R/W or travel portions of
roadways, streets, etc. should be made as to possible roadway, street,
etc. improvements, such as widening or changing grade elevations, before
the installation of underground plant facilities to eliminate costly
future rearrangements and rerouting. When installing underground plant
facilities at railroad crossings, on bridges, and the crossing of
facilities owned by other utilities, the need for permits should be
thoroughly investigated.

**2.4** In urban and suburban areas, other buried or underground
facilities such as water lines, gas lines, sewer lines, Community
Antenna Television lines, electric and/or telecommunications lines
present obstacles to the installation of the conduit and UCV components
of underground plant facilities. When the above buried or underground
obstacles are anticipated, detailed information should be obtained from
the other utilities on present and proposed buried or underground
facilities locations. Where it is known that buried or underground
obstacles will be encountered during construction of the conduit and UCV
components of underground plant facilities, those areas should be
identified separately in the Loan Design (LD).

**2.5** The physical location of the conduit and UCV components of the
underground plant facilities should be determined in conjunction with
federal, state, county, and local authorities, as applicable. Special
attention should also be given to the type and size of equipment that
will be required to perform the conduit, UCV, and cable installation of
underground plant facilities.

**2.6** Some of the considerations that can affect the physical
locations of the conduit and UCV components of underground plant
facilities are:

a\. Width of road shoulders;

b\. Type of road and road surface;

c\. Easements;

d\. Required number of conduits and UCVs;

e\. Public R/W;

f\. Railroad crossings;

g\. Bridge crossings;

h\. Buried or underground obstacles of other utilities; and

i\. Environmentally sensitive areas.

**2.7** When conduit and UCV components of underground plant facilities
are to be installed in public R/W or travel lanes of roadways, streets,
etc. discussions with department of transportation authorities should be
held to inform the authorities as to locations and depths of conduits
and UCVs in the R/W or travel lanes of roadways, streets, etc.

**2.8** The same procedure as outlined in paragraph 2.7 of this section
should be followed in coordination with town and development areas where
conduit and UCV components of underground plant facilities are to be
installed. Assistance should be given to town planning authorities,
land, industrial, and commercial developers by either identifying on
existing construction drawings or in the preparation of new construction
drawings, the locations and depths of all conduits and UCVs. Here again,
these organizations should be informed that the borrower will provide
identification and location of its existing underground plant facilities
when requested.

**2.9** Proposed underground plant construction activities should be
coordinated with other utilities. This coordination is necessary to
properly develop a working relationship among the various utilities on
future planning of all utility plant. Construction drawings of
underground plant to be constructed should be provided to each of the
utility companies whose plant is, or may be placed, within the area of
the borrower\'s underground plant facilities.

**2.10** RUS Bulletin 1753F-151, Specifications and Drawings for
Construction of Underground Plant, RUS Form 515b, provides assistance to
either the resident, consulting engineer, or borrower's engineering
staff in the design and construction of underground plant facilities.
The resident, consulting engineer, or borrower's engineering staff
should check with Federal, State, county, and local authorities in
regard to any existing and proposed land development programs which
would require special design considerations to be taken into account in
the design and construction of underground plant facilities.

**2.11** In the design of conduit and UCV systems of underground plant
facilities, more conduits than initially needed should be provided to
eliminate the added expense of reopening trenches and adding additional
conduits to existing conduit systems.

**2.12** The resident, consulting engineer, or borrower's engineering
staff should keep in mind during the design of underground filled copper
or fiber optic cable components of underground plant facilities that
flexibility of underground cable components depend to a great extent on
the physical arrangement of the cables and associated equipment in the
conduit and UCV systems of underground plant facilities. Correct
assignments and arrangements of underground copper or fiber optic cables
should provide economical advantages by decreasing the cost of future
rearrangements.

**2.13** Prior to the design layout of the underground filled copper or
fiber optic cables, the resident, consulting engineer, or borrower's
engineering staff should make an on-site field survey of all UCVs, riser
poles, building conduits, etc.

**2.14** Where underground filled copper or fiber optic cables are
pulled through UCVs without splicing, duct selections should be the same
at both ends of UCVs. Changes in duct selections, especially in
elevations, should be considered carefully to avoid damage to
underground cable sheaths and to keep the pulling tensions as low as
possible.

**3.** **CONSTRUCTION MATERIALS**

**3.1** For all underground plant construction projects financed with
RUS loan funds, RUS regulation 7 CFR 1753.6 requires that only RUS
accepted materials be used.

**3.2** RUS technically accepted, nondomestic manufactured materials,
may also be used on underground plant construction projects. Before
technically accepted materials can be used on underground 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 are at least 6 percent less than the cost
of the RUS accepted materials, as specified in RUS Bulletin 344-3, \"Buy
American\" Requirement, as amended by the Notice published in the
Federal Register, Volume 66, Number 222, dated November 16, 2001.

**4. CONDUIT TYPES AND USAGE**

**4.1** Conduit types most frequently used in underground plant
facilities are as follows:

a\. Multi-duct concrete;

b\. Multi-duct plastic;

c\. Fiberglass/epoxy;

d\. Plastic;

e\. Flexible plastic; and

f\. Plastic fiber optic cable duct.

**4.2** Multi-duct concrete conduits are available in 3.5 inch (in.)
\[89 millimeters (mm)\] and 4 in. (102 mm) bore sizes and two design
types. The first design consists of a bell and spigot with joint seals
utilizing rubber gaskets and/or joint sealing compound. The second
design utilizes a polyethylene sleeve with dowel pins for alignment.
Conduits are available in 4-way, 6-way, and 9-way configurations. Short
joints, miters, split conduits, and special adapters; such as
concrete-to-steel, concrete-to-concrete, and concrete-to-plastic, are
standard stock items for both designs which are available from
manufacturers.

**4.3** Multi-duct plastic conduits are available in bore sizes of

4 in. (102 mm) in bell and spigot designs. Joint seals are made using
rubber gaskets and spring clips. Conduits are available in 4-way, 6-way,
and 9-way configurations supplied in 42 in.

\[107 centimeters (cm)\] sections. Miters, double bells, spigots, etc.
are standard stock items available from manufacturers. Short joint
sections can be made in the field by cutting conduits with a hacksaw.

**4.4** Fiberglass/epoxy conduits are available in 2 in. (51 mm),

3 in. (76 mm), 4 in. (102 mm), and 6 in. (152 mm) bore sizes and three
design types. The first design is a bell and spigot with joint seals
utilizing joint sealing compound. The second design is a bell and spigot
with joint seals utilizing joint sealing compound and a mechanical
thread to ensure proper make up. The last design uses threaded
mechanical connectors to ensure positive joint seals. Sweeps, elbows,
bends, expansion joints, etc. are standard stock items available from
manufacturers.

**4.5** Plastic conduits are available in bore sizes of 2 in.

(51 mm), 3 in. (76 mm), 4 in. (102 mm), and 6 in. (152 mm) and five
design types. The five design types are B, C, D, EB, and DB. Design
types B and EB are used for concrete encasement. Types C and DB are used
for direct burial. Type D is used for exposed installations, such as on
bridges, viaducts, etc. Jointing is accomplished with plastic couplings
and solvent cements. Sweeps, elbows, adapters, plugs, bell ends, etc.
are standard stock items available from manufacturers. Conduits can be
cut with a hacksaw in the field to provide short joint sections. Plastic
spacers are available for building conduit formations. The conduits are
usually supplied in 20 foot (ft)

\[6 meter (m)\] lengths. Because plastic conduits are somewhat flexible,
gradual changes in widths and heights of conduit banks can be made
without special miter fittings. Plastic conduits also have low
coefficients of friction which allow longer conduit runs.

**4.6** Flexible plastic conduits are available in bore sizes of

2 in. (51 mm), 3 in. (76 mm), 3.5 in. (89 mm), 4 in. (102 mm), and 6 in.
(152 mm) and two design types. The first type is a smooth wall finish.
The second design is a corrugated wall finish. Jointing is accomplished
by heat fusion with caps, ells, etc. which are standard stock items from
manufacturers. The conduits are usually supplied in 500 ft (152 m)
coiled lengths. Because of the conduit's flexibility, the conduit may be
bent in radii as sharp as 4 ft (1.2 m) without kinking. Special fittings
necessary to make turns, dips, and bends are not usually needed with
flexible plastic conduits. Flexible plastic conduits can be installed
either by trenching or plowing. Smooth wall flexible conduits may be
installed in multiple configurations. Corrugated wall flexible conduits
should only be used on subsidiary conduit routes. Corrugated wall
flexible conduits should only be placed on horizontal planes (side by
side).

**4.7** Plastic fiber optic cable ducts are small diameter flexible
plastic conduits available in bore sizes of 0.5 in. (13 mm),

1 in. (25 mm), and 1.5 in. (38 mm). These type ducts are available in
either smooth or corrugated wall finishes. The ducts can be supplied in
1650 ft (502 m) coiled lengths. The primary usage of this type duct is
for installation in existing conduits. This duct may also be used for
direct burial. Placement of filled fiber optic cables in these type
ducts provide clean, low friction, low hazard environment for fiber
optic cable installations.

**4.8** Steel pipes may be used as conduits where special conditions
prohibit the use of conduit types listed in paragraph 4.1 of this
section. Such conditions may include locations where trenching could not
be performed or where pipe pushes are required. Steel pipes are
available in all commercial sizes and can be obtained with threaded ends
and couplings or with plain ends.

**4.9** Sewer tiles, which are available in all commercial sizes, should
be used as drains or sumps for poured-in-place UCVs.

**5. CONDUIT FORMATIONS AND CURVES**

**5.1** Conduit formations consisting of four or more ducts should not
be less than two, nor greater than four, ducts wide. Table 1 of this
section lists various conduit formations based on trench sizes and UCV
vault racking diagrams.

TABLE 1

Conduit Formations

  ----------------------------------- -----------------------------------
  Number of Ducts                     Duct Width

  4, 6, 8, and 10 ducts               2 wide

  9, 12, 15, and 18 ducts             3 wide
  ----------------------------------- -----------------------------------

**5.2** Conduit sections containing curves should be avoided whenever
possible. When curves are required in conduit sections, angles of curves
should be less than 90 degrees. Curves with angles greater than 90
degrees or curves with extremely small radii should not be used because
of possible damage to conduits or cables.

**6. CONDUIT SECTION LENGTHS**

**6.1** Conduit section lengths should depend on diameters and types of
conduits and types of filled copper or fiber optic cables to be
installed in conduits. Conduit sections should be as long as practicable
to reduce the number of UCVs, splices, and set-ups for cable pulling.

**6.2** Conduit sections should not exceed 1500 ft (457 m). Typical
conduit sections range from 600 to 1,000 ft (183 to 305 m). Achieving
the 600 to 1,000 ft (183 to 305 m) distance may be restricted by
junction points, offsets, or degrees of curvature in conduit sections.
An offset is defined as the displacement of one portion of a straight
conduit section run relative to the remainder of the conduit run.
Displacements (offsets) may occur in any plane. If offset distances are
5 ft (1.5 m) or less, offsets may be disregarded in determining maximum
section lengths. If offsets in otherwise straight conduit sections are
greater than 5 ft (1.5 m) or radii of sweeps in offsets are less than
1200 ft (366 m), conduit section lengths should be shortened
proportionately (up to one-third for extreme conditions). Conduit
sections containing offsets should normally not exceed 600 ft (183 m).

**6.3** Bends, twists, or curves in conduit runs should be used to
change the general direction of conduit runs at street corners or to
avoid underground obstructions. For conduit sections containing bends or
curves, maximum conduit section lengths should be determined by angles
between straight conduit runs on each side of curves and radii of
curves.

**6.4** Actual lengths of conduit runs should be obtained and verified
from existing conduit system records to ensure that cable lengths will
be correct. Distances, such as UCV wall-to-wall, UCV-to-riser pole, or
UCV-to-building, should be measured and added to the length of cable
required in each UCV for pulling-in, setting-up, splicing, and testing.
The sum of the distance measurements mentioned above and the cable
lengths for pulling-in, setting-up, splicing, and testing is known as
the cable "cut lengths." Cable "cut lengths" should be indicated on
construction drawings. The excess length of copper cable normally
required for splicing, testing, and pulling usually amounts to 3 ft (one
meter) per cable or 6 ft (2 m) per section. The excess length of fiber
optic cable normally required for splicing, testing, and pulling should
be based on the LD.

**7. CONDUIT PROTECTION**

**7.1** Conduits should be protected against mechanical damage due to
settlement of the ducts, excavating equipment, etc. by use of either
treated wood planks or concrete. Protection may consist of top
protection only, base only, top and sides only, or complete encasement.
The type of protection should depend on the particular circumstances of
the project. Where no hazards are likely to be encountered, protection
of conduits should not be required.

**7.2** Top protection should be provided where conduits are to be
installed under roadways which may be paved at later dates. Concrete
bases should be used whenever the ground is spongy or yielding, such as
swamps or marshlands, or where bases are desirable as leveling mediums
under conditions where sand base trenches are subjected to washing out.
Conduits within railroad R/W should be protected if required by
regulations.

**7.3** Concrete encasement of conduits should be considered for the
following conditions:

a\. Road or street crossings having earth covers that are

equal to or less than 30 in. (76 cm);

b\. Railroad crossings;

c\. Earth covers parallel to and within street, highway, or

road travel areas that are less than 30 in. (76 cm);

d\. Stream crossings, storm canals, ditches, etc.; and

e\. Bend angles of 20 or greater in conduit lengths equal

to or greater than 550 ft (168 m).

**8. UCV TYPES**

**8.1** Precast and poured-in-place UCVs should be designed to provide
sufficient and suitable space for installation of cables and associated
equipment. Precast and poured-in-place UCV types and sizes that are
normally used within the RUS program are shown in the construction guide
drawings of RUS Bulletin 1753F-151, Specifications and Drawings for
Construction of Underground Plant, Form 515b, listed below:

a\. Guide drawing Underground Manhole (UM) UM-A,-L,-T,-J;

b\. Guide drawing UM-V; and

c\. Guide drawing UM-X,-Y.

**8.2** Headroom, floor, wall, and roof thicknesses, openings, wall
recesses, frames, covers, collars, sumps, or drains of precast UCVs
should be designed in accordance with the manufacturers'
recommendations.

**8.3** Headroom, floor, wall, and roof thicknesses, openings, wall
recesses, frames, covers, collars, sumps, or drains of poured-in-place
UCVs should be designed in accordance with the engineer's
specifications. Figure 1 of this bulletin provides an example of the
poured-in-place UCV overall design layout.

**8.4** Sufficient headroom should be provided in poured-in-place UCVs
to allow for racking of cables plus a clear space of 12 in. (305 mm)
just above the floor and below the UCV roof. Table 2 of this section
indicates the minimum headroom recommended for the various types of
poured-in-place UCVs.

TABLE 2

Minimum Headroom

Poured-In-Place UCVs

+-----------------------------------+-----------------------------------+
| UCV Types                         | Minimum Headroom                  |
|                                   |                                   |
|                                   | in. (cm)                          |
+-----------------------------------+-----------------------------------+
| UM-X                              | 42 (107)                          |
+-----------------------------------+-----------------------------------+
| UM-Y                              | 48 (122)                          |
+-----------------------------------+-----------------------------------+
| UM-A                              | 66 (168)                          |
+-----------------------------------+-----------------------------------+
| UM-L                              | 66 (168)                          |
+-----------------------------------+-----------------------------------+
| UM-T                              | 66 (168)                          |
+-----------------------------------+-----------------------------------+
| UM-V                              | 66 (168)                          |
+-----------------------------------+-----------------------------------+
| UM-J                              | 66 (168)                          |
+-----------------------------------+-----------------------------------+

**8.5** Unreinforced concrete should be used for floors of
poured-in-place UCVs that are to be constructed in firm soils. Floor
thicknesses should be 4 in. (102 mm) for poured-in-place UCVs with
unreinforced concrete walls. For poured-in-place UCVs with reinforced
concrete walls, floors should be 6 in. (152 mm) thick.

**8.6** Reinforced concrete should be used for floors of poured-in-place
UCVs that are to be constructed in fluid soils. The reinforcing members
should be 5/8 in. (16 mm) diameter deformed bars. Table 3 of this
section and Figure 2 of this bulletin provide design information on the
floor thicknesses and reinforcing bar spacings of all rectangular
poured-in-place UCVs in fluid soils. Floor thicknesses of UM-V type
poured-in-place UCVs vary with depths of finished floors below grade.
Table 4 of this section and Figure 2 of this bulletin provide design
information on the floor thicknesses and reinforcing bar spacings of
UM-V type UCVs in fluid soil.

TABLE 3

Floor Thicknesses and Reinforcing Rod Spacings

Rectangular Poured-In-Place UCVs in Fluid Soils

+-----------------------+-----------------------+-----------------------+
| Depth of UCV Floor    | Floor Thickness       | Spacing of            |
| Below Grade           |                       | Reinforcing Rods      |
|                       | In. (mm)              |                       |
| Ft (m)                |                       | in. (mm)^(See\ Note)^ |
+-----------------------+-----------------------+-----------------------+
| 8 (2.4)               | 6 (152)               | 8 (203)               |
+-----------------------+-----------------------+-----------------------+
| 9 (2.7)               | 6 (152)               | 8 (203)               |
+-----------------------+-----------------------+-----------------------+
| 10 (3.0)              | 6 (152)               | 8 (203)               |
+-----------------------+-----------------------+-----------------------+
| 11 (3.4)              | 6 (152)               | 8 (203)               |
+-----------------------+-----------------------+-----------------------+
| 12 (3.7)              | 6 (152)               | 8 (203)               |
+-----------------------+-----------------------+-----------------------+
| 13 (4.0)              | 6 (152)               | 8 (203)               |
+-----------------------+-----------------------+-----------------------+
| 14 (4.3)              | 6 (152)               | 7 (178)               |
+-----------------------+-----------------------+-----------------------+
| 15 (4.6)              | 6 (152)               | 6.5 (165)             |
+-----------------------+-----------------------+-----------------------+
| 16 (4.9)              | 6 (152)               | 6.5 (165)             |
+-----------------------+-----------------------+-----------------------+

TABLE 4

Floor Thicknesses and Reinforcing Rod Spacings

Type UM-V Poured-In-Place UCVs in Fluid Soils

+--------------------+---------------+----------+----------+----------+
| Depth of UCV       | Floor         | Spacing  |          |          |
|                    | Thickness     | of       |          |          |
| Floor Below Grade  |               | Rei      |          |          |
|                    |               | nforcing |          |          |
|                    |               | Rods     |          |          |
|                    |               |          |          |          |
|                    |               | In.      |          |          |
|                    |               | (        |          |          |
|                    |               | mm)^(See |          |          |
|                    |               | \ Note)^ |          |          |
+--------------------+---------------+----------+----------+----------+
| ft (m)             | in. (mm)      | Spacing  | Spacing  | Spacing  |
|                    |               | A        | B        | C        |
+--------------------+---------------+----------+----------+----------+
| 8 (2.4)            | 6 (152)       | 8 (203)  | 9 (229)  | 11 (279) |
+--------------------+---------------+----------+----------+----------+
| 9 (2.7)            | 6 (152)       | 8 (203)  | 9 (229)  | 11 (279) |
+--------------------+---------------+----------+----------+----------+
| 10 (3.0)           | 6 (152)       | 8 (203)  | 9 (229)  | 11 (279) |
+--------------------+---------------+----------+----------+----------+
| 11 (3.4)           | 6 (152)       | 8 (203)  | 9 (229)  | 11 (279) |
+--------------------+---------------+----------+----------+----------+
| 12 (3.7)           | 6 (152)       | 8 (203)  | 9 (229)  | 11 (279) |
+--------------------+---------------+----------+----------+----------+
| 13 (4.0)           | 6 (152)       | 8 (203)  | 9 (229)  | 11 (279) |
+--------------------+---------------+----------+----------+----------+
| 14 (4.3)           | 6.5 (165)     | 7 (178)  | 8 (203)  | 10 (254) |
+--------------------+---------------+----------+----------+----------+
| 15 (4.6)           | 7 (178)       | 6.5      | 8 (203)  | 10 (254) |
|                    |               | (165)    |          |          |
+--------------------+---------------+----------+----------+----------+
| 16 (4.9)           | 7 (178)       | 6.5      | 8 (203)  | 10 (254) |
|                    |               | (165)    |          |          |
+--------------------+---------------+----------+----------+----------+

Note: See Figure 2 of this bulletin for diagrams of reinforcing

rod spacings.

**8.7** Sumps or drains for poured-in-place UCVs should be located
directly under UCV covers and at depths such that finished floor
surfaces should be graded toward the sumps or drains. Sumps or drains
should be at least 8 in. (203 mm) in diameter or 8 in. (203 mm) square.
Sumps or drains should be constructed using

12 in. (305 mm) lengths of 8 in. (203 mm) sewer tiles. Figure 3 of this
bulletin provides information on two types of sump or drain designs.

**8.8** Table 5 of this section and Figure 4 of this bulletin provide
design information on wall thicknesses and vertical reinforcement
spacings, if any, for concrete walls of poured-in-place UCVs in firm
soils. Table 6 of this section and Figure 4 of this bulletin provide
design information on wall thicknesses and vertical reinforcement
spacings, if any, for concrete walls of poured-in-place UCVs in fluid
soils. It should be noted in Tables 5 and 6 of this section that the
variations in concrete wall thickness and the quantity of vertical
reinforcement required varies only with the depths of the
poured-in-place UCV walls. Vertical reinforcing bars should be of
sufficient lengths to extend 1 in. (25 mm) from the bottoms of concrete
floors to within 1 in. (25 mm) of the tops of UCV roofs. In addition to
vertical reinforcement, UCV walls should also contain horizontal
reinforcement. For UCV walls that are 12 in. (305 mm) or less in
thickness, horizontal reinforcement should consist of 3/8 in.

(10 mm) or larger diameter round bars spaced 12 in. (305 mm) on centers.
UCV walls that are greater than 12 in. (305 mm) thick should be
horizontally reinforced using 5/8 in. (16 mm) or larger diameter round
bars spaced 12 in (305 mm) on centers. Horizontal reinforcing bars
should be of sufficient lengths to extend within 1 in. (25.4 mm) of
outside surfaces of the two adjacent walls.

TABLE 5

Wall Construction

Poured-In-Place UCVs in Firm Soils

<table>
<colgroup>
<col style="width: 0%" />
<col style="width: 14%" />
<col style="width: 12%" />
<col style="width: 0%" />
<col style="width: 14%" />
<col style="width: 0%" />
<col style="width: 12%" />
<col style="width: 1%" />
<col style="width: 12%" />
<col style="width: 13%" />
<col style="width: 13%" />
<col style="width: 0%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="5"></td>
<td colspan="6">Reinforced Walls</td>
<td></td>
</tr>
<tr class="even">
<td colspan="3"></td>
<td colspan="2">Plain Walls</td>
<td colspan="2"></td>
<td colspan="4">Vertical Reinforcement Using Deformed Bars</td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>Category</td>
<td colspan="2"><p>Depth of UCV Floor Below Surface of Street</p>
<p>in. (cm)</p></td>
<td colspan="2"><p>Wall Thickness</p>
<p>in. (mm)</p></td>
<td colspan="2"><p>Wall Thickness</p>
<p>in. (mm)</p></td>
<td><p>Size</p>
<p>In. (mm)</p></td>
<td>Deformed Bar Types</td>
<td colspan="2"><p>Spacing On Center</p>
<p>in. (mm)</p></td>
</tr>
<tr class="even">
<td></td>
<td>8.0</td>
<td colspan="2">96 (244) or less</td>
<td colspan="2">6 (152)</td>
<td colspan="2">6 (152)</td>
<td>None</td>
<td>None</td>
<td colspan="2">None</td>
</tr>
<tr class="odd">
<td></td>
<td>8.5</td>
<td colspan="2">102 (259)</td>
<td colspan="2">7 (178)</td>
<td colspan="2">6 (152)</td>
<td><p>3/8 (10)</p>
<p>½ (13)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>8 (203)</p>
<p>12 (305)</p></td>
</tr>
<tr class="even">
<td></td>
<td>9.0</td>
<td colspan="2">108 (274)</td>
<td colspan="2">7.5 (190)</td>
<td colspan="2">6 (152)</td>
<td><p>3/8 (10)</p>
<p>½ (13)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>6 (152)</p>
<p>10 (254)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>9.5</td>
<td colspan="2">114 (289)</td>
<td colspan="2">8 (203)</td>
<td colspan="2">6 (152)</td>
<td><p>3/8 (10)</p>
<p>½ (13)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>5.5 (140)</p>
<p>9 (229)</p></td>
</tr>
<tr class="even">
<td></td>
<td>10.0</td>
<td colspan="2">120 (305)</td>
<td colspan="2">8.5 (216)</td>
<td colspan="2">6 (152)</td>
<td><p>3/8 (10)</p>
<p>½ (13)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4 (102)</p>
<p>8 (203)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>10.5</td>
<td colspan="2">126 (320)</td>
<td colspan="2">9 (229)</td>
<td colspan="2">6 (152)</td>
<td><p>3/8 (10)</p>
<p>½ (13)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4 (102)</p>
<p>7 (178)</p></td>
</tr>
<tr class="even">
<td></td>
<td>11.0</td>
<td colspan="2">132 (335)</td>
<td colspan="2">10 (254)</td>
<td colspan="2">6 (152)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">6 (152)</td>
</tr>
<tr class="odd">
<td></td>
<td>11.5</td>
<td colspan="2">138 (350)</td>
<td colspan="2">10.5 (267)</td>
<td colspan="2">6 (152)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">5 (127)</td>
</tr>
<tr class="even">
<td></td>
<td>12.0</td>
<td colspan="2">144 (366)</td>
<td colspan="2">11 (279)</td>
<td colspan="2">6.5 (165)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">5 (127)</td>
</tr>
<tr class="odd">
<td></td>
<td>12.5</td>
<td colspan="2">150 (381)</td>
<td colspan="2">12 (305)</td>
<td colspan="2">6.5 (165)</td>
<td><p>½ (13)</p>
<p>5/8 (16)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4.5 (114)</p>
<p>7 (178)</p></td>
</tr>
<tr class="even">
<td></td>
<td>13.0</td>
<td colspan="2">156 (396)</td>
<td colspan="2">12.5 (317)</td>
<td colspan="2">7 (178)</td>
<td><p>½ (13)</p>
<p>5/8 (16)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4.5 (114)</p>
<p>7 (178)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>13.5</td>
<td colspan="2">162 (411)</td>
<td colspan="2">13 (330)</td>
<td colspan="2">7 (178)</td>
<td>5/8 (16)</td>
<td>Round</td>
<td colspan="2">6.5 (165)</td>
</tr>
<tr class="even">
<td></td>
<td>14.0</td>
<td colspan="2">168 (427)</td>
<td colspan="2">14 (356)</td>
<td colspan="2">7.5 (190)</td>
<td>5/8 (16)</td>
<td>Round</td>
<td colspan="2">6.5 (165)</td>
</tr>
<tr class="odd">
<td></td>
<td>14.5</td>
<td colspan="2">174 (442)</td>
<td colspan="2">14.5 (368)</td>
<td colspan="2">7.5 (190)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>5.5 (140)</p>
<p>8 (203)</p></td>
</tr>
<tr class="even">
<td></td>
<td>15.0</td>
<td colspan="2">180 (457)</td>
<td colspan="2">15 (381)</td>
<td colspan="2">8 (203)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>5.5 (140)</p>
<p>8 (203)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>16.0</td>
<td colspan="2">192 (488)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">9 (229)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>5.5 (140)</p>
<p>7.5 (190)</p></td>
</tr>
<tr class="even">
<td></td>
<td>17.0</td>
<td colspan="2">204 (518)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">9.5 (241)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4.5 (114)</p>
<p>7 (178)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>18.0</td>
<td colspan="2">216 (549)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">10 (254)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4 (102)</p>
<p>6 (152)</p></td>
</tr>
<tr class="even">
<td></td>
<td>19.0</td>
<td colspan="2">228 (579)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">11 (279)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4 (102)</p>
<p>5.5 (140)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>20.0</td>
<td colspan="2">240 (610)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">11.5 (292)</td>
<td><p>5/8 (10)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>3.5 (89)</p>
<p>5.5 (140)</p></td>
</tr>
</tbody>
</table>

TABLE 6

Wall Construction

Poured-In-Place UCVs in Fluid Soils

<table style="width:100%;">
<colgroup>
<col style="width: 0%" />
<col style="width: 13%" />
<col style="width: 12%" />
<col style="width: 0%" />
<col style="width: 14%" />
<col style="width: 0%" />
<col style="width: 13%" />
<col style="width: 0%" />
<col style="width: 13%" />
<col style="width: 13%" />
<col style="width: 13%" />
<col style="width: 0%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="5"></td>
<td colspan="6">Reinforced Walls</td>
<td></td>
</tr>
<tr class="even">
<td colspan="3"></td>
<td colspan="2">Plain Walls</td>
<td colspan="2"></td>
<td colspan="4">Vertical Reinforcement Using Deformed Bars</td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td>Category</td>
<td colspan="2"><p>Depth of UCV Floor Below Surface of Street</p>
<p>In. (cm)</p></td>
<td colspan="2"><p>Wall Thickness</p>
<p>in. (mm)</p></td>
<td colspan="2"><p>Wall Thickness</p>
<p>In. (mm)</p></td>
<td><p>Size</p>
<p>In. (mm)</p></td>
<td>Deformed Bar Types</td>
<td colspan="2"><p>Spacing On Center</p>
<p>in. (mm)</p></td>
</tr>
<tr class="even">
<td></td>
<td>8.0A</td>
<td colspan="2">96 (244) or less</td>
<td colspan="2">9 (229)</td>
<td colspan="2">6 (152)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">6 (152)</td>
</tr>
<tr class="odd">
<td></td>
<td>8.5A</td>
<td colspan="2">102 (259)</td>
<td colspan="2">10 (254)</td>
<td colspan="2">6.5 (165)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">6 (152)</td>
</tr>
<tr class="even">
<td></td>
<td>9.0A</td>
<td colspan="2">108 (274)</td>
<td colspan="2">11 (279)</td>
<td colspan="2">7 (178)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">5.5 (140)</td>
</tr>
<tr class="odd">
<td></td>
<td>9.5A</td>
<td colspan="2">114 (289)</td>
<td colspan="2">12 (305)</td>
<td colspan="2">7.5 (190)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">5 (127)</td>
</tr>
<tr class="even">
<td></td>
<td>10.0A</td>
<td colspan="2">120 (305)</td>
<td colspan="2">13 (330)</td>
<td colspan="2">8 (203)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">4.5 (114)</td>
</tr>
<tr class="odd">
<td></td>
<td>10.5A</td>
<td colspan="2">126 (320)</td>
<td colspan="2">14 (356)</td>
<td colspan="2">8.5 (216)</td>
<td>½ (13)</td>
<td>Round</td>
<td colspan="2">4 (102)</td>
</tr>
<tr class="even">
<td></td>
<td>11.0A</td>
<td colspan="2">132 (335)</td>
<td colspan="2">15 (381)</td>
<td colspan="2">9 (229)</td>
<td>5/8 (10)</td>
<td>Round</td>
<td colspan="2">6 (152)</td>
</tr>
<tr class="odd">
<td></td>
<td>11.5A</td>
<td colspan="2">138 (350)</td>
<td colspan="2">16 (406)</td>
<td colspan="2">9.5 (241)</td>
<td>5/8 (16)</td>
<td>Round</td>
<td colspan="2">5.5 (140)</td>
</tr>
<tr class="even">
<td></td>
<td>12.0A</td>
<td colspan="2">144 (366)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">10 (254)</td>
<td>5/8 (16)</td>
<td>Round</td>
<td colspan="2">5.5 (140)</td>
</tr>
<tr class="odd">
<td></td>
<td>12.5A</td>
<td colspan="2">150 (381)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">10.5 (267)</td>
<td>5/8 (16)</td>
<td>Round</td>
<td colspan="2">5 (127)</td>
</tr>
<tr class="even">
<td></td>
<td>13.0A</td>
<td colspan="2">156 (396)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">11 (279)</td>
<td><p>5/8 (16)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4.5 (114)</p>
<p>6 (152)</p></td>
</tr>
<tr class="odd">
<td></td>
<td>13.5A</td>
<td colspan="2">162 (411)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">11.5 (292)</td>
<td><p>5/8 (16)</p>
<p>¾ (19)</p></td>
<td><p>Round</p>
<p>Round</p></td>
<td colspan="2"><p>4 (102)</p>
<p>6.5 (165)</p></td>
</tr>
<tr class="even">
<td></td>
<td>14.0A</td>
<td colspan="2">168 (427)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">12 (305)</td>
<td>¾ (19)</td>
<td>Round</td>
<td colspan="2">5.5 (140)</td>
</tr>
<tr class="odd">
<td></td>
<td>14.5A</td>
<td colspan="2">174 (442)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">12.5 (317)</td>
<td>¾ (13)</td>
<td>Round</td>
<td colspan="2">5.5 (140)</td>
</tr>
<tr class="even">
<td></td>
<td>15.0A</td>
<td colspan="2">180 (457)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">13 (330)</td>
<td>¾ (13)</td>
<td>Round</td>
<td colspan="2">5 (127)</td>
</tr>
<tr class="odd">
<td></td>
<td>16.0A</td>
<td colspan="2">192 (488)</td>
<td colspan="2">Reinforcement Required</td>
<td colspan="2">14 (356)</td>
<td>¾ (13)</td>
<td>Round</td>
<td colspan="2">4.5 (114)</td>
</tr>
</tbody>
</table>

**8.9** Roofs of poured-in-place UCVs should be designed using
reinforced concrete. Table 7 of this section provides design information
on UCV roofs regarding thicknesses and reinforcing rod diameters for all
rectangular poured-in-place UCVs. Table 8 of this section provides
design information on UCV roofs regarding thicknesses and reinforcing
rod diameters for UM-V type poured-in-place UCVs. Figure 5 of this
bulletin provides design information on center-to-center spacings of
reinforcing rods for both rectangular and UM-V type poured-in-place UCV
roofs.

TABLE 7

Roof Thicknesses and Reinforcing Rod Diameters

Rectangular Poured-In-Place UCVs

+-----------------------+-----------------------+-----------------------+
| Inside Width of UCV   | Roof Thickness        | Reinforcing           |
|                       |                       |                       |
| in. (cm)              | In. (mm)              | Rod Diameter          |
|                       |                       |                       |
|                       |                       | in. (mm)              |
+-----------------------+-----------------------+-----------------------+
| 36 (91)               | 6 (152)               | 1/2 (13)              |
+-----------------------+-----------------------+-----------------------+
| 42 (107)              | 6 (152)               | 1/2 (13)              |
+-----------------------+-----------------------+-----------------------+
| 48 (122)              | 7 (178)               | 1/2 (13)              |
+-----------------------+-----------------------+-----------------------+
| 54 (137)              | 7.5 (190)             | 1/2 (13)              |
+-----------------------+-----------------------+-----------------------+

TABLE 8

Roof Thicknesses and Reinforcing Rod Diameters

Type UM-V Poured-In-Place UCVs

+-----------------------+-----------------------+-----------------------+
| Inside Width or       | Roof Thickness        | Reinforcing           |
|                       |                       |                       |
| Length of UCV         | In. (mm)              | Rod Diameter          |
|                       |                       |                       |
| Whichever is Greater  |                       | in. (mm)              |
|                       |                       |                       |
| ft (m)                |                       |                       |
+-----------------------+-----------------------+-----------------------+
| 8 (2.4)               | 11 (279)              | 3/4 (19)              |
+-----------------------+-----------------------+-----------------------+
| 9 (2.7)               | 11.5 (292)            | 3/4 (19)              |
+-----------------------+-----------------------+-----------------------+
| 10 (3.0)              | 12 (305)              | 3/4 (19)              |
+-----------------------+-----------------------+-----------------------+
| 11 (3.3)              | 12.5 (317)            | 3/4 (19)              |
+-----------------------+-----------------------+-----------------------+
| 12 (3.7)              | 13 (330)              | 3/4 (19)              |
+-----------------------+-----------------------+-----------------------+

**8.10** Openings of poured-in-place UCVs should be determined by the
types and sizes of UCV frames. Diameters of frame openings at bases of
frames should be equal to diameters of UCV roof openings. Table 9 of
this section provides design information on the sizes of UCV opening
forms to be used with various types and sizes of UCV frames.

TABLE 9

UCV Opening Forms

for UCV Frame Types and Sizes

Poured-In-Place UCVs

+-----------------------+-----------------------+-----------------------+
| Frame Types           | Frame Sizes           | UCV Opening           |
|                       |                       |                       |
|                       | In. (cm)              | Form Sizes            |
|                       |                       |                       |
|                       |                       | in. (cm)              |
+-----------------------+-----------------------+-----------------------+
| B                     | 24 (61)               | 35 (89)               |
+-----------------------+-----------------------+-----------------------+
| B                     | 27 (69)               | 38 (96)               |
+-----------------------+-----------------------+-----------------------+
| B                     | 30 (76)               | 41 (104)              |
+-----------------------+-----------------------+-----------------------+
| R                     | 27 (69)               | 28 (71)               |
+-----------------------+-----------------------+-----------------------+
| R                     | 30 (76)               | 31 (79)               |
+-----------------------+-----------------------+-----------------------+

**8.11** When poured-in-place UCVs require wall recesses at conduit
entrances, concrete should be placed between the faces of the recesses
and the excavation walls to provide watertight bonds. Concrete
thicknesses should be equal to at least one-half of UCV wall
thicknesses. Figure 6 of this bulletin provides additional design
information concerning wall recesses. When conduits entering UCVs are
splayed, recessing of conduit banks should not be required.

**8.12** Type B frames should be used with poured-in-place UCVs
installed in areas subjected to vehicular traffic. Type R frames should
be used with poured-in-place UCVs that are installed in areas not
subjected to vehicular traffic such as sidewalks, median strips. etc.
Figure 7 of this bulletin provides additional design information on
Types B and R frames. Thirty inch (30 in.) (76 cm) frames should be used
in areas subjected to vehicular traffic. Twenty-seven inch (27 in.) (69
cm) frames should be used in areas not subjected to vehicular traffic.
Poured-in-place UM-X and UM-Y type UCVs normally use 24 in.

(61 cm) frames.

**8.13** Frames of poured-in-place UCVs should be supported with either
brick or concrete collars. Brick or concrete collars should be of
sufficient heights to bring UCV covers flush with grades of travel
surfaces. Figure 8 of this bulletin provides additional design
information on brick collars.

**8.14** Solid covers should be used with all types of poured-in-place
UCVs except when light and ventilation of UCVs are required. Heavy duty
covers should be used on all types of poured-in-place UCVs that are
subjected to vehicular traffic.

**9. CABLE RACKS, RACK SUPPORTS, and PULLING IRONS**

**9.1** The number of cable racks and rack supports, spacing of cable
racks, and placement of pulling irons for precast UCVs should be
designed in accordance with manufacturers' recommendations.

**9.2** For poured-in-place UCVs, the number and size of vertical cable
racks should be based on headroom within UCVs as shown in Table 10 of
this section. Additional design information that may be used to assist
in the installation of cable racks within poured-in-place UCVs may be
found in Figure 9 of this bulletin.

TABLE 10

Number and Size of Cable Racks Versus Headroom

Poured-In-Place UCVs

+----------------+-----------------+-----------------+-----------------+
|                | Number of Racks |                 |                 |
+----------------+-----------------+-----------------+-----------------+
| Headroom       | 14 Hole         | 18 Hole         | 37 Hole         |
|                |                 |                 |                 |
| In. (cm)       | Rack Size       | Rack Size       | Rack Size       |
+----------------+-----------------+-----------------+-----------------+
| 60 (152)^(1)^  | 1               | 1               | 1               |
+----------------+-----------------+-----------------+-----------------+
| 66 (168)^(2)^  | \-              | 2               | 1               |
+----------------+-----------------+-----------------+-----------------+
| 72 (183)^(2)^  | \-              | 2               | 1               |
+----------------+-----------------+-----------------+-----------------+
| 78 (198)       | 3               | \-              | \-              |
+----------------+-----------------+-----------------+-----------------+
| 84 (213)       | 2               | 1               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 90 (229)       | 1               | 2               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 96 (244)       | \-              | 3               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 102 (259)      | 4               | \-              | \-              |
+----------------+-----------------+-----------------+-----------------+
| 108 (274)      | 3               | 1               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 114 (290)      | 2               | 2               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 120 (305)      | 1               | 3               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 126 (320)      | 4               | 1               | \-              |
+----------------+-----------------+-----------------+-----------------+
| 132 (335)      | 4               | 1               | \-              |
+----------------+-----------------+-----------------+-----------------+

Note (1): UCVs may contain either one 14 and one 18 hole rack or

one 14 and one 37 hole rack

Note (2): UCVs may contain either two 18 hole racks or one 37

hole rack.

**9.3** UCV racking diagrams for poured-in-place UCVs should include all
hardware items needed for supporting cables within UCVs along with all
additional work such as drilling holes, etc.

**9.4** The spacing of cable racks within poured-in-place UCVs should be
specified on the construction drawings.

**9.5** Cable racking diagrams should be made for central office vaults,
cable troughs, and central office building walls showing locations of
all existing cables, stubs, load coil cases, if any, and ducts in use.
Using this information vacant ducts should be selected that would allow
new cables to be installed without crossing over existing cables or
blocking other vacant ducts. Trunk and special cables, which require
protection, should be assigned lower conduits because these type cables
usually do not require replacement. Cable duct assignments should be the
same in each UCV, whenever possible. However, each duct should be chosen
section-by-section, since the same relative position in each UCV may not
always provide the best cable arrangement.

**9.6** Cables and stubs should be arranged in UCVs to allow
accessibility to cable splices. The number of branch cables from ends of
mainline splices should be limited to two. Stub cables may be necessary
to maintain this arrangement. At locations requiring cable stubs,
racking of main cables should be based on pair counts, gauge sizes, and
intended use stub cables. Where stub cables are used to connect branch
feeder or distribution cables entering UCVs from branch circuits,
terminal ends of stub cables should be racked on UCV walls opposite
branch conduits.

**9.7** For pull-through UCVs (no splice), cable lengths necessary for
racking should be added to wall-to-wall lengths of conduit sections on
both sides of UCVs.

**9.8** Figure 10 of this bulletin should be used in the design of
pulling irons for poured-in-place UCVs.

**10. UCV AND CONDUIT LOCATIONS**

**10.1** Locations of UCVs and conduit routes between UCVs should be
indicated on construction drawings. An example of a construction drawing
indicating UCV locations and conduit routes is shown in Figure 11 of
this bulletin. The construction symbols and abbreviations used in
preparing construction drawings are shown in Figures 12 through 12C of
this bulletin. Poured-in-place or precast UCVs should be located to
avoid unnecessary hazards and to ensure that future work in UCVs will
cause minimum interference with the normal flow of vehicular traffic.
Poured-in-place or precast UCVs should be located in public R/W wherever
possible. When poured-in-place or precast UCVs are located in the travel
portion of roads, streets, etc., intersection locations should be avoid
wherever possible. In congested areas where the possibility of
undisclosed subsurface conditions exist, test holes may be required to
verify that construction can be carried out as planned to avoid useless
excavation. Test holes should be dug 12 in. (305 mm) deeper than the
depth of the proposed UCV excavation. If foreign pipes or other
structures are encountered in the test holes, steps should be taken to
determine ownership of the foreign structures. If the structures can not
be readily removed, a decision should be made as to the practicability
of either shifting the UCV, arranging with the owning company for a
change in the route of their plant, or include the structure in the UCV.
Penalties or costs associated with each of the above mentioned
alternatives should be carefully considered before reaching a decision.
Poured-in-place or precast UCVs should not be located near springs or
underground streams.

**10.2** Main conduits entering poured-in-place or precast UCVs should
be located equidistant between the floors and roofs and centered between
end walls. For UM-L, UM-J, and UM-T poured-in-place or precast UCVs,
conduits entering side walls should be located 4 in. (102 mm) from end
walls which are located farthest from central offices. Clearances of 12
in. (305 mm) should be maintained between main conduit formations and
roofs or floors of UCVs. Unless indicated on the construction drawings,
wall

recesses should be provided at conduit entrances. Subsidiary conduits
entering UCVs should be located to provide clearances of 4 in. (102 mm)
from roofs and adjacent walls.

**11. DETERMINATION OF INSTALLATION LENGTH AND PULLING TENSION**

**OF FILLED COPPER CABLES**

**11.1** Mechanical stresses placed on copper cables during
installations should be held to absolute minimums to avoid excessive
twisting, stretching, or flexing of cables. Therefore to avoid excessive
twisting , stretching, or flexing of copper cables during installations,
maximum pulling tensions for copper cables should be calculated to
ensure that copper cables can be placed in conduit and UCV systems
without damage.

**11.2** One of the factors to consider in determining copper cable
pulling tensions is the coefficient of friction between various conduit
and cable jacket materials. Table 11 of this section provides both dry
and lubricated coefficient of friction values between various conduit
and cable jacket materials which may be used in determining pulling
tensions of cables. The information in Table 11 of this section is based
on conduit interior surfaces being free of dirt, gravel, etc. Interior
conduit surfaces that are considered dirty, could result in increased
coefficient of friction values. Therefore interior conduit surfaces
should be cleaned before installation of cables.

TABLE 11

Coefficient of Friction

Conduit Versus Cable Jacket Materials

  ---------------------- -------------- ------------ -------------- -------------
                         Coefficient of                             
                         Friction                                   
                         (Sliding)                                  

                         High Density                Low Density    
                         Polyethylene                Polyethylene   

  Conduit Material       Dry            Lubricated   Dry            Lubricated

  Polyvinyl Chloride     0.31           0.13         0.36           0.16

  Concrete               0.48           0.37         0.57           0.41

  Corrugated Plastic     0.22           0.13         0.40           0.13
  ---------------------- -------------- ------------ -------------- -------------

As the table indicates lubricated coefficient of friction values are
generally one-half or less of the dry coefficient of friction values.
The lower lubricated coefficient of friction values should allow for
lower cable pulling tensions which in turn would allow the installation
of longer cable lengths in conduit and UCV systems. For purposes of
safety, maximum pulling tension calculations for copper cables should be
computed using the dry coefficient of friction values. The effectiveness
of lubricants is dependent to a large extent on the thoroughness of its
application to copper cables. In addition, conduit surface conditions
can contribute significantly to the actual coefficient of friction.

**11.3** The factors that should be used in determining the lengths of
copper cables that may be safely installed in conduit systems are as
follows:

a\. Cable size and conductor gauge;

b\. Maximum pulling strain allowed on conductors;

c\. Cable pulling method (pulling eye or basket weave grip);

d\. Number of bends in conduit system;

e\. Bend radii;

f\. Bend angles;

g\. Coefficient of friction; and

h\. Cables pulled dry or lubricated.

**11.4** Equation #1 of this section listed below should be used for
calculating maximum pulling tensions of copper cables equipped with
factory installed pulling eyes:

T = ANK (Equation #1)

Where:

T = Maximum allowable pulling tension in pounds

(lbs) \[kilograms (kgs)\].

A = Cross-sectional area of copper conductors in

circular mils \[square millimeters (mm^2^)\].

N = Number of conductors terminated in factory

installed pulling eyes. Typical all conductors

in cables are terminated in factory installed

pulling eyes.

K = 0.008 lbs/circular mils (7.2 kgs/mm^2^)

for copper.

The cross-sectional areas of copper conductors designated by the letter
"A" in equation #1 of this section are listed in Table 12 of this
section:

TABLE 12

Cross-sectional Area of Copper Conductors

  ----------------------------------- -----------------------------------
  Conductor Size                      Cross-sectional Area

  American Wire Gauge (AWG)           Circular Mils (mm^2^)

  19                                  1290 (0.653)

  22                                  642 (0.324)

  24                                  404 (0.205)

  26                                  254 (0.128)
  ----------------------------------- -----------------------------------

**11.5** After calculating maximum pulling tensions of copper cables,
maximum allowable pulling lengths of cables should be calculated using
equation #2 of this section listed below:

L = T/Wf (Equation #2)

Where:

L = Maximum allowable pulling length in ft (m).

T = Maximum allowable pulling tension in lbs (kgs).

W = Cable weight in lbs/ft (kgs/m).

f = Coefficient of friction for type of conduit

used in installation.

**11.6** Another factor that should be considered in calculating cable
pulling tensions is the number and effects of bends in conduit systems.
For conduit systems containing bends, pulling tensions of copper cables
should be calculated on cumulative basis using equations #3 and #4 of
this section listed below:

  ----------------------------------- -----------------------------------
  T = LWf (Equation #3)               T = T~1~e^fa^ (Equation #4)

  ----------------------------------- -----------------------------------

Where:

T = Pulling tension in lbs (kgs).

L = Cable length in ft (m).

W = Cable weight in lbs/ft (kgs/m).

T~1~ = Accumulated tension to start of bend

in lbs (kgs).

e = Naperian logarithm equal to 2.718.

f = Coefficient of friction for type of conduit

used in installation.

a = Bend angle in radians (1 radian = 57.3 degrees).

**11.7** Another factor that should be considered is the maximum
allowable sidewall pressure. Sidewall pressures are radial forces
exerted on cable sheaths at bend points when cables are under tension.
Sidewall pressures at bend points should be calculated using equation #5
of this section listed below:

P = T/R (Equation #5)

Where:

P = Sidewall Pressure in lbs/ft (kgs/m).

T = Pulling tension in lbs (kgs).

R = Bend radius in ft (m).

The maximum allowable sidewall pressure for copper cables should not
exceed 100 lbs/ft (149 kgs/m). In conduit systems containing multiple
bends, the last bend in the system would develop the greatest sidewall
pressure on the cable. Therefore during the design of conduit systems,
bends with the severest radii should be installed at the start of
conduit systems.

**11.8** Figures 13 through 13B of this bulletin provide an example of
an underground filled copper cable installation that may be used for
calculating maximum cable pulling tensions for conduit and UCV systems
containing multiple conduit bends. Figures 14 and 14A of this bulletin
provide an example of an underground filled copper cable installation
that may be used for calculating the maximum sidewall pressures for
conduit and UCV systems containing multiple conduit bends.

**12. DETERMINATION OF INSTALLATION LENGTH AND PULLING TENSION**

**OF FILLED FIBER OPTIC CABLES**

**12.1** Factors that should be considered in determining the
installation lengths and pulling tensions of fiber optic cables to
ensure that fiber optic cables can be placed in conduit and UCV systems
without damage are listed below:

a\. Maximum allowable pulling tension;

a\. Minimum allowable bending radius during installation;

b\. Minimum allowable bending radius after installation;

c\. Construction and dimensions of pulling end;

d\. Cable weight and diameter;

e\. Supply length of cable; and

f\. Excess cable length at each splice location.

**12.2** Fiber optic cable manufacturers should be contacted to
determine the appropriate values for the items listed in paragraph 12.1
of this section to ensure that fiber optic cables can be placed in
conduit and UCV systems without damage.

**12.3** In addition to the factors listed in paragraph 12.1 of this
section, fiber optic cable manufacturers should also be contacted to
determine the maximum allowable sidewall pressure that may be exerted on
fiber optic cable sheaths at bend points when cables are under tension.

**13. DESIGN CONSIDERATIONS**

**13.1** For outside plant underground facilities using copper cables,
circuit requirements should be thoroughly evaluated to provide
sufficient margin in the sizing of underground 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 included
in RUS TE&CM Section 629, Cable Plant Layout - Serving Area Value
Engineering for Rural Systems.

**13.2** For outside plant underground 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 circuit requirements of the LD plus the
number of circuits needed for future growth.

**13.3** Local characteristics of the project area should be thoroughly
studied to determine whether normal or extraordinary construction
conditions exist before making comparative cost studies. In addition,
the determination should be made as to whether or not protection of
conduits would be required so that the increase in the incremental cost
associated with the protection of the conduits can be evaluated.

**13.4** For copper underground plant, the design should provide for the
optimum use of fine gauge cable (22 and 24 American Wire Gauge (AWG)
conductors). Care should be exercised in the design to ensure that
transmission requirements will be met.

**13.5** For copper underground 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 indicate the use of
digital carrier and other types of electronic equipment over physical
circuits, the electronic equipment should be designed.

**13.6** For optical fiber underground plant, the design should provide
for the use of either dispersion-unshifted single mode fibers (operate
at both the 1310 and 1550 nanometer windows) or dispersion-shifted
single mode fibers (operate 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.

**13.7** The optical fiber design should be prepared in accordance with
the recommendations in RUS Bulletin 1751H-601, Lightwave Fundamentals,
Systems, and Application.