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© Panduit Corp. 201 4
Buried Cable Installation
Table of Contents
1.0 General ........................................................................................................................... 3
2.0 Precautions ..................................................................................................................... 3
3.0 Pre-survey ...................................................................................................................... 4
4.0 Location and Depth ........................................................................................................ 4
5.0 Plowing versus Trenching............................................................................................... 5
6.0 Plowing ........................................................................................................................... 5
7.0 Trenching ........................................................................................................................ 9
List of Illustrations and Tables
Figure 1Tractor and Plow ..................................................................................................... 6
Figure 2 Splice Van .............................................................................................................. 7
Figure 3 Figure-eighting Cable ............................................................................................. 7
Figure 4 Pulling the Cable .................................................................................................... 8
Figure 5 Using a Figure-eight Machine ................................................................................. 8
Figure 6 Pulling Using a Figure-eight Machine ..................................................................... 8
Figure 7 Cutaway View of a Buried Cable ............................................................................ 9
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DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES
The practices containe d herein are designed as a guide for use by persons h aving technical skill at the ir own
discretion and risk. The rec ommended practices are based on average cond itions. Panduit does not guarantee
any favorable results or assume any liability in connection with this document.
In addition, the materials a nd hardware referenced herein appear as examples, but in no way reflect the only
tools and materials available to perform thes e ins ta llati ons .
Local, State, Federal and Industry Codes and Regulations, as well as manufacturers requirements, must be
consulted before proceeding with any project. Panduit makes no representations of, nor assumes any
responsibility for, the ac c urac y or c omplete nes s of t his doc ume nt. Panduit disclaims any liab i lity ar ising from an y
information contained herein or for the absence of same.
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1.0 GENERAL
1.01 This best practices procedure provides genera l information for the installation of fiber optic cables in
direct buried applications. The methods described are intended for guideline use only, as it is impossible
to cover all the various con ditions that m ay arise durin g an installati on. Individua l com pany practices for
placing fiber optic cable should supersede any conflicting instructions in this document when they do not
exceed the cable’s optical and mechanical performance specifications.
1.02 Placement methods f or direct buried f iber optic cable ar e essentia ll y the same as those used for placing
direct buried copper cable. However it must be kept in mind that fiber optic cable is a high capacit y
transmission medium which can have its transmission characteristics degraded when subjected to
excessive pulling for ce, sharp bends, or c rushing forces. These loss es may not be revealed for up to
two years after insta llation. For these r easons, extra care must be taken during the entire installati on
procedure.
1.03 Fiber optic cables are usually ordered in specific lengths as calculated by an OSP (Outside Plant)
Engineer. The lengths are determined by m easuring between splice locations then adding the am ount
required to reach the splicing vehicle (truck or trailer) and some minimum of excess cable.
1.04 It is assumed in this document that the reader is familiar with the direct burial procedure used for copper
cable. Direct buried fiber optic cable installation practices are essentially the same as those used for
placing copper cable. The following methods of direct burial of fiber optic cables will be addressed:
plowing and trenching.
2.0 PRECAUTIONS
2.01 The following are s ome suggested precauti ons that should be observed when working with fiber optic
cables. Before starting any buried cable installation, all personnel must be thoroughly familiar with
Occupational Safet y and Hazard Act (OSHA) reg ulations. Also, company safet y precautions for direct
buried cable operations should be reviewed before work begins and practiced during the entire
installation process.
2.02 Before cable installation begins, the cable reels should be carefully inspected for any imperfections such
as nails, broken flang es, cable crossovers or anythin g which might cause damage to the ca ble as it is
paid out. Precautions sho uld be tak en to protect store d reels fr om possible dam age by vanda ls or other
sources when left unattended. The thermal protective covering provided with each reel of fiber optic
cable should always remain in place when storing cable reels.
2.03 Whenever cable from the reel is placed on pavement or other surfaces, it should be protected with
barricades or cones to prevent possible vehicular or pedestrian traffic damage. A “figure-eight”
configuration should be used when the cable is removed from the reel and piled on the ground. This
prevents kinking and t wisting of the cable wh ich could cause damage. Fiber optic cable should not be
coiled in a continuous direction except for lengths of 30 meters (100 ft) or less. T he preferred sized for
the “figure-eight” is about 4. 5 meters (15 f t) in lengt h with each loop 1.5 me ters ( 5 ft) to 2.4 meters (8 ft)
in diameter.
Note: An alternative t o the m anual figure-eight is the “figure-eight” machine. T his equ ipment will “figure-
eight” cable much faster than manual methods saving time and manpower. The machine winds any
cable remaining on t he reel on to the machine’s drum . Once the inside cable end is accessible, the
machine is reversed and th e cable is pulled from the m achine’s drum through the duct. T he machine’s
drum and rollers ar e d es ig n ed t o keep the cable at a b end radius greater tha n the minimum bend r ad ius
of the cable.
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2.04 Standard fiber optic cable has a maximum recommended pulling tension of 600 lbs. The maximum
pulling tension is not to b e exceeded . Please co nsult Panduit’s Best Pr actices f or the prop er installat ion
and use of pulling grips. Cables may be ordered from the factory with pulling eyes already installed.
2.05 Fiber optic cables are more susceptible to performance degradation due to tight bending than are
copper cables. The m inimum bend radius of each cable is relative to the cable’s diameter. A g eneral
guideline is that a cable under tension should not be exposed to a bend radius less than 20
times the cable diameter and a cable with no tension should not be exposed to a bend radius
less than 10 times the cable diameter.
3.0 PRE-SURVEY
3.01 A pre-survey of th e fiber cable route is very importan t in planning for a dir ect buried optical fiber cable
project. Each section of the route from splice location to splice location must be prepared properly
before cable installatio n begins. It is very important to identify all conflicts and obstructions along the
route before installat ion is under way. Co nflicts an d obstr uctions wil l influenc e the prelim inary se lection
of splice locations and will have a direct effect on the overall trans mission design of the route. Splic es
cases should not be loc ated where t he s plicing veh icle will h ave t o be park ed in a ha zardous area. T his
would include: over a hil l to p, around a sharp curve, near an in ters ec tio n, to o c lose to the r oa d, a h id den
area in an unsafe neighbor hood, or anywhere the spli cing vehicle cannot get saf ely and completely off
the highway.
3.02 One of the objectives of the pre-survey is to determine where each reel of fiber optic cable is to be
placed. Slack locations and cable storage requirements must also be considered along with splice
locations. The pre-surve y will verify construction methods, s pecial tools required, or possibl y require a
revision of preliminary splice locations.
3.03 The characteristic of the ground along the route needs to be investigated. If a subsurf ace investigation
seems to be required, it should be conducted. This will clear up any concerns about underground
conditions that may be encountered during plowing or trenching.
3.04 All road crossings, creek crossings, etc. need to be addressed so that preparatory work can begin
before plowing or trench ing. This will identif y what casing is needed and what type of preparator y work
will be required to negotiate these crossing points.
3.05 A good pre-survey and proper planning will preclude reel ends falling too close to roads, creeks, or any
other undesirable locations.
4.0 LOCATION AND DEPTH
4.01 Buried fiber optic cabl e route locati ons are selecte d by the Outside Plant Engin eering group. T he cable
route location should be on e t ha t is the le as t l ik el y to b e d is turbed and that will ha ve t he le ast number of
obstructions.
4.02 When burying fiber opt ic cables that must cross ditches, avoi d crossing locations that might interfer e
with natural drainage. Also, avoid areas subject to surface drainage that may result in subsequent
washing away of soil and exposing of the fiber optic cable.
4.03 Pipe or conduits are used at highway and railroad crossing.
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4.04 The depth at which fiber optic cable can be buried will vary with local conditions according to freeze
lines (depth to which the gr ound freezes in the wint er). Under all cond itions, the cabl e should be buried
at a depth that will provid e adequate protection. The depth m ay vary as conditions vary. In croplan ds
and pastures, a ca ble depth of 36” is the minimum depth. The c a bl e n eeds t o be buried 12” deep er th an
the maximum depth reached by agricultural equipment.
5.0 PLOWING VERSUS TRENCHING
5.01 In general, the most desirable and economical method of cable placement in open or rural areas is
plowing. Here there will be fewer obstacles to impede the progress of the plowing equipment.
Advantages of Plowing:
Speed of installation in open areas
Less ground disturbance than may be caused by trenching
Disadvantages of Plowing:
Large size and high cost of equipment
Requires skilled equipment operators, quality supervision, and equipment in good condition
Can not be used for all soil and terrain conditions
Possibility of damaging cables or underground utilities
5.02 In urban or suburban areas w here there can be m any obstac les such as undergr ound ut iliti es, s idewa lk
and paved road crossings, trenching has advantages.
Advantages of Trenching:
Lower cost of equipment
Digging operation is separate from cable placement
Better depth control
Less risk of damaging underground utilities
Provides the opportunity to place conduit at the same time
Disadvantages of Trenching:
Slower rate of cable placement than with plow
Not suitable for all soil and terrain conditions
6.0 PLOWING
6.01 It is important to not ify all other ut ilities that m ay occup y the same rig ht-of-way ( ROW) that a f iber optic
cable will be placed. If there is a “1-call-center” or a local utility location and coordination committee
active in the area, they shoul d be notified 72 hours before plo wing operations begin. This will provide
them with enough advance notice to locate and mark their route along the ROW prior to construction.
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Figure 1 – Tractor and Plow
6.02 The ROW should be stak ed in advance of plowing. T he locations of all under ground struc tures such as
culverts, water lines, and other utilities should clearly be marked for the plowing crew. If necessary,
obstructions should be uncovered prior to plowing.
6.03 Cable plows are generally of two types: static and vibr ator y. Eit her type may be used to install f iber op tic
cable. Steerable plows, which can be offset to place the cable away from the centerline of the cable
plow prime mover, are available in both types.
6.04 Successful and econom ical plowing of cable depends primarily on having equipment powerf ul enough
for terrain conditions. Local soil conditions and c able depth are the two prim ary determining factors in
the correct size of tractor necessary for plowing. Too much horsepower is better than too little
horsepower.
6.05 A crawler tractor is most suitable for static buried cable plowing. A tractor equipped with a torque
converter drive should be u sed whenever it is a vailable. T his will permit sm oother plowing perf ormance
by absorbing the shock loads encountered in the plowing operations.
6.06 The drawbar force f or soil penetration by a static plo w may reach a magnitude of tens of thousands of
pounds. Heavy and l arge equipment is nee ded to generate a dra wbar force of this m agnitude. A plow
that vibrates substant ially reduces the drawbar f orce required t o plow-in cab le when com pared with the
force necessary to move a static plow of the same size. With drawbar force reduced, the equipment size
required for the plow is also reduced.
6.07 The reel carrier should allow for easy installation of the reel using such features as hydraulic lift
assistance and shou ld accommodate a r eel or reels of adequat e size for the int ended installation. T he
cable feed system inc ludes all the components mounted on the tractor which supports and guides the
cable as it is fed into the plow chute. T ypically, it includes a reel carrier, rollers and/or guide tubes. Us e
of capstan drive units is recommended. Capstan dri ve units, which provide pulling f orce of up to 250
pounds can help prevent excessive pulling, tension at the cable feed tube entry and exits.
6.08 All rollers or guides in the cable feed system whic h cause a change in the direction of the cable pa th
must conform to the m inimum bend radius of the c able being placed. Sm all diameter rollers (fairleads)
can be used to guide the cable over the tractor cab, if the feed chute guide and cable reel are positioned
so that the cable cannot b e tensioned ov er the smaller rollers. Fairleads should be designe d to prevent
the cable from becoming wedged between the vertical and horizontal rollers.
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Figure 2 – Splice Van
Figure 3 – “Figure-eighting” of the Cable
6.09 The cable path inside the feed chute must be clean and free of burrs, sharp edges, stiffeners, or
roughness. Welds must be smooth. Gussets on the divider gate in multiple chute designs must not
interfere with the sm ooth passage of the cable. The cabl e must feed smoothly through the chute and
must not exceed the minimum bending radius of the cable.
6.10 Before plowing begins, a means of communications must be established between the equipment
operator and the superviso r monitoring the cable placement and r oute. The communications lin k mus t
be able to override the equipment noise.
6.11 The starting point for the reel be ing plo wed shou ld be a splice pi t or hole exc avat ed to the pro per depth.
Sufficient slack should b e reeled off at this point to reach a spl ice vehicle or splice locati on. The plow
should start at the required depth from the splice pit.
6.12 A figure-eight operation is necessary whenever the cable must be pulled through a pipe or conduit. This
often occurs at road, river, bridge, or railroad crossings. A figure-eight operation requires that the cable
be removed from the reel.
6.13 With the plow stoppe d, remove the cable from the plow’s chute. Do not rais e the plow to the surfac e
when the plow is not movi ng. Never back up the plo w with a cable still in the chute. The cable to the
rear of the feed chute m ust be excavated and slack pull ed to prevent kinking the cable over the exit
chute before raising the plow.
6.14 The cable remaining on th e reel must be laid out in a large figur e-eight configuration cl ose to the pullthru location. Ke ep t he c a bl e as c le an of de br is as p os sible by not figure-eighti ng t he c ab le ont o sand or
dirt which might adhere to the cable. Sand or dirt clinging to the cable can cause increased pulling
tensions. Spreading ou t a sheet of po lyethylene bef ore begin ning to figure-e ight is one m ethod that will
help keep the cable reason abl y clean. Figur e-ei ghtin g onto clean p avem ent or grass will also h elp lo wer
the possibility of a dirty cable.
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Figure 4 – Pulling the Cable
Figure 5 – Using a Figure-eight Machine
6.15 With all the cabl e of f the r e el and laying on the grou nd in a f igure-eight, attach the pu lling l in e t o th e end
of the cable. Begin the pul l just as before b y hand pulling the ca ble out of the figur e-eight an d feeding it
into the pipe or cond uit plac ed under th e obstacle . Once t he cable en d has ent ered th e pipe or condu it,
the cable should be carefully guided from the figure-eight by hand. Radio communications must be
maintained to ensure the p ull can be quick ly stopped if trouble develops with feedin g the cable fr om the
figure-eight.
6.16 An alternative to manually f igure-eighting the cable off the reel bef ore continuing the pull, is to us e a
figure-eight machine s hown in Figure 5 below. Instead of pulling th e cable f rom the ree l and laying it on
the ground, the cable is looped o ver the barrel of the figure-eigh t machine. Guided by a revolvin g arm
and a series of rollers, the cable can be rapidly removed from the reel as it is wound around the
machine’s drum.
6.17 Once the inside end of the cable is freed, it is connected to the pull line and the figure-eight machine
reversed. The cable is now removed from the figure-eight machine’s drum as the end winch or capstan
pulls the cable through the duct
.
Figure 6 –Pulling Using a Figure-eight Machine
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Figure 7 –Cutaway View of Buried Cable
6.18 Company practices m ay prescribe a ripp ing pass to the depth of the cable burial along the entire route
prior to plowing in operat ions to ensure the r oute is clear bet ween start and stop locations. The rippi ng
pass is made in the same direction as the c able plowing operation. T he ripping pass ensur es the route
is clear before the fiber optic cable is loaded for plowing.
6.19 When plowing in fiber optic cable a war ning tape is placed 12” belo w the surface of the ground direc tly
above the cable. Both the cable and the warning tape are normally plowed in at the same time
.
6.20 The plow movement should be started s lowly and its speed gra dual ly increas ed af ter all cable slac k has
been taken up from the delivery system. Plow attitude and depth should be changed gradually.
Changes should be made onl y with the plow under way. Never raise the plow to the surface if the plow
is not moving. The ca ble to the rear of the feed chu te must be excavated and slack pulled to prevent
kinking the cable over th e exit c hute befor e rais ing the plo w. Never back up the p lo w with a cable s till in
the chute.
6.21 Each section, after it is plowed in, should be checked with an OTDR for possible increases in
attenuation due to pressure or breaks.
6.22 Any cable ends left f or future splic ing shoul d have the ir protecti ve caps r einstalled and sealed with tape
prior to burial.
7.0 TRENCHING
7.01 Trenching may be chose n to bury fiber optic cable in urban a nd sub urban ar eas where th e high num ber
of obstacles (sidewalk and street crossings) makes plowing impractical.
7.02 The choice of location for trenching in fiber optic cable follows the same set of rules as for plowing.
Buried cable should be loc ated w here ther e is the lea st pos sibilit y of it being d ist urbed. Al ong roads , the
cable should be located s o that future surfacing and widening op erations will not extend over it. Care
should be taken that the route selected will not interfere with the natural drainage of the area and so that
the natural drainage does not result in the depth of cable coverage being affected.
7.03 Trenching is norm ally conducted by using m achinery. In some ar eas however, it m ay be necessary to
hand-dig the trench. For m aximum speed, hand digging s hould be held to a minimum. For maximum
trenching speed, ne ver dig a deeper or wider trenc h than required. H owever, it i s recommended that a
4” wide trench be considered the minimum practical width.
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7.04 The backfilling material m us t conf orm to local regu lati ons. Clean bac k fill should b e placed f rom 9” to 12”
from the bottom of the trench to provide protection for the c able. On private right-of-way (ROW ), the
earth should be mounded over the trench to compensate f or future settling. The bac kfilled trench may,
in some cases, be sat isf actoril y pack ed do wn by runn ing th e trac tor or wheel of a truck along t he tre nch
line on top of the bac kfill. W hen possible the t op should be filled with top soil. Roc ks and debris sh ould
never be left in the bottom of the trench. Surface compression could cause cable damage in the future.
7.05 All permanent pavem ent and sid ewalk s must be r estored to the s atisf action of pr oper author ities . When
shrubs or other local veget ation must be disturbed it s hould be set aside and replace d when possible.
Where lawn has been removed, it should be replaced or re-s eeded.
7.06 Following the installation of the cable, each section should be checked with an OTDR for possible
increases in attenuation due to pressure or breaks.
7.07 Any cable ends left for future splicing should have their protective caps reinstalled and sealed with tape
prior to burial
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