Selection of the Correct Optical Cable Outer Jacket for

Application Notes
Selection of the Correct
Optical Cable Outer Jacket for
the Application
Issued
December 2012
Abstract
The cable jacket provides the first line of defense against the surrounding environment. It resists
water entry while remaining inert to gases and liquids that the cable may be exposed to during
its service life. It provides a smooth, low friction surface for cable placement. The jacket must be
made of a material that will allow the cable to remain flexible and serviceable at all of the
temperatures it will experience during its lifetime.
Keywords
Jacket materials, single jacket versus dual jacket, armored versus unarmored, and
metallic versus dielectric armoring.
Introduction
This Cable Jacket Selection Note is intended to provide the reader with an organized selection
methodology when selecting the optimum optical cable for a specific application. Sheath
issues discussed: single jacket versus dual jacket, armored versus unarmored, and metallic
versus dielectric armoring.
The following issues will play a role in the cable selection process:
1. Surface loading and depth of cover.
2. Area being served: urban, suburban, rural. Existing
3. plant infrastructure presently serving intended
4. area. Climate (wind and ice loading). Access to
5. right-of way.
6. Access to roads, traffic, and public.
7. Rodent damage potential.
8. Lightening issues.
This note will address those issues that directly influence the jacket or sheath selection process.
Jacket materials
The cable jacket provides the first line of defense against the surrounding environment. It
resists water entry while remaining inert to gases and liquids that the cable may be exposed to
during its service life. It provides a smooth, low friction surface for cable placement. The jacket
must be made of a material that will allow the cable to remain flexible and serviceable at all of
the temperatures it will experience during its lifetime.
It must resist abrasion during installation. It must provide, along with the cable's strength
members, the mechanical strength required to survive its environment and installation forces.
For indoor cables, the jacket also provides the fire retardance required by building codes.
Many different materials are available for cable jacketing making it possible to match the jacket
material to the end user application requirements. The table below provides a listing of some of
the more popular jacketing materials used for optical cables.
Table 1- Summary of Popular Cable Jacketing Materials
Sheath Material
Features
PE 1
Polyethylene
MDPE – medium density PE
HDPE – high density PE
Primary outside jacket material.
Good resistance to UV (sun light) due to carbon black. Good
flexibility over wide range of temperatures. Good abrasion
and crack resistance.
Anti-tracking PE
Use in all dielectric self-supporting cable in high voltage aerial
fields exceeding 12 kV, but not exceeding 50 kV applications. The
anti-tracking jacket withstands a condition known as dry arcing.
PVC Polyvinyl chloride
Provides good mechanical protection.
Flexible at normal installation temperatures.
Flame retardant. (typical riser material)
Used for many indoor applications.
Can be protected against sunlight with various UV inhibitors.
LSZH - Low smoke, zero halogen
Flame Retardant with low smoke and no halogenated materials
For use in unventilated areas exposed to public, e.g., subways and
tunnels. Good mechanical performance.
PVDF - Polyvinyl difluoride
Flame retardant. (typical plenum material)
It produces low smoke and low flame propogation.
Most Outside Plant optical cables are made from medium density or high density polyethylene
with carbon black for UV stabilization. In North America the National Electric Code dictates that
this type of a cable jacket cannot penetrate any building by more than 50 feet. A fire retardant,
listed cable must be used for indoor applications. Often a riser rated PVC jacket is used for
indoor/outdoor cables that must penetrate the building more than 50 feet.
Armored Versus Non-armored Cable
Armoring increases the strength and robustness of a cable relative to its surroundings. The
armoring is placed either just under the outside plastic jacket for single jacket cables or
between two layers of jacket material for dual jacket cables. The armoring layer is typically
corrugated metallic tape, but tightly wound steel wires, or dielectric fiber layer are options for
specialty applications. Double jacket, double steel tape armor is occasionally used for
increased protection in direct buried, high rodent infested areas. Rip cords are placed under
the armor layer(s) to enable jacket removal during cable preparation for termination.
Non-armored cables are also available that provide suitable service in underground conduit
systems or aerial pole lines. Their light weight causes placing tensions to be somewhat
reduced. Non-armored cables provide an easier cable to prepare for splicing. Non-armored
cable will not have the extra crush resistance, impact strength, or rodent resistance of armored
cable.
1Various polyethylene plastics should meet Table 5.4.2 of ANSI/ICEA S-87-640.
Table 2- Comparison of Outside Plant Applications Provided by Armored/Non-armored
Armor
Steel Tape
Aerial Plant
Armor
Double Jacket &
Single Jacket
Non- Armor
Fig 8, Single jacket,
Double jacket, ADSS
Buried Plant
Underground
Plant
Micro-Cables
Single Jacket
No
In duct
In microduct
Double Jacket &
Single Jacket
No
DJ – Dual Jacket, SJ – Single Jacket, Fig 8 – Figure 8, self-supporting
Single Jacket Versus Dual Jacket Armor Cable
A dual jacket is characterized by two extruded plastic jackets separated by a layer of armoring.
If a second layer of armoring is used, it will be below the inner plastic jacket, just above the cable
core.
A dual jacket with dual armoring will amplify the positive effects of increased
robustness, i.e.,provide best crush and impact resistance as compared to a single
jacketed cable. A dual jacket with dual armoring sheath will also amplify the negative issues,
i.e., it is heavier, stiffer, and more labor intensive to prepare for splicing than a single jacket
cable.
The table that follows summarizes most of the key considerations in deciding between single
and dual jacketed cables.
Table 4- Comparison between Single and Dual Jacketed Cable armor cable
Single Jacket
Suitable for direct burial and underground applications.
Cable is lighter and easier to install.
Cable is more flexible, easier to prepare.
Metallic armoring requires the cable to be properly
bonded and grounded.
Dual Jacket
·Suitable for direct burial and underground applications.
Extra protection for direct buried applications.
Cable is somewhat heavier than single jacket cable.
Most robust design, good crush and impact resistance.
Metallic armoring requires the cable to be properly
bonded and grounded.
Extra weight makes cable more difficult to place.
Requires more time and is more difficult to prepare for
splicing.
Single jacket single armor cable is used for most applications because the dual layer
version does not provide sufficient benefits to support the additional cost and time
associated with dual layer designs.
Steel Tape Armor Requires Bonding And Grounding
Bonding and grounding of all metallic elements is required for all outside plant equipment
including optical cables. If lightening occurs or an accident takes down a power line, it is
possible for unwanted current to be coupled into the metallic components of the outside plant
cable. Dangerous current can potentially be coupled into any metallic cable components or into
the messenger supporting strand in the case of aerial cables. If any conductor at the ground
potential comes in contact with the metallic member carrying the coupled current, any
unbalanced current will flow through the conductor to ground.
Improperly grounded metallic armoring in fiber cables can cause voltage potential levels to be
different from the ground potential for long stretches of cable, through intermediate manholes or
hand holes and even into buildings, hence the requirement for metallic element bonding and
grounding at regular intervals along the cable length.
Bonding is the connection of all metallic components in the cable sheath together (metallic
armor and metallic central strength members) to keep them at the same potential and ensure
electrical continuity with sufficient capacity to safely conduct any imposed current to ground.
Grounding is defined in the National Electric Code (NEC) as, “A conducting connection,
whether intentional or unintentional, between electrical circuits or equipment and the earth, or
some conducting body that serves in place of the earth.”
Normally, metallic members in armored fiber optic cables are bonded at splice closures
through bonding clamps at the cable entrance to the closure and a conductive strap or wire
within the closure to connect the mating cables to a common bond for all cables entering the
closure. The grounding within the closure also connects all metallic components entering the
closure to a low-resistance ground to earth at each splice manhole, hand hole, pedestal, or at
building entrance; where ever splices are located. As a result, all metallic items at the
grounding manholes, hand holes, pedestals, or building entrances are bonded together and
connected to a common ground.
The messenger strand in aerial plant is grounded at each support structure. Aerial splices of
metallic armored fiber cables are bonded at their splice closures to their adjacent cable mate
and to the messenger strand.
If all-dielectric fiber optic cables are used, they are made without any conductive paths, and as
a result, do not need to be bonded or connected to existing grounds at intermediate ground
locations. It is imperative that all national, local, and industry codes covering bonding and
grounding be followed.
Summary
Except for the most severe Outside Plant conditions, a single jacket, either metallic or dielectric
armored cable will likely provide sufficient protection to the cable required for it to provide
satisfactory performance under nearly all conditions.
The cable sheath which provides the optimal balance between robustness and economics for
the OSP service to be provided and environment to be encountered is the sheath design that
will ultimately determine the optimal cable design.
If there are questions concerning any of this information please contact Sterlite at:
Additional Information
If there are additional questions on this topic or other fiber optic issues, please contact:
Contact Information
telecom.sales@sterlite.com
www.sterlitetechnologies.com
Copyright© 2017 Sterlite Technologies Limited. All rights reserved. The word and design marks set
forth herein are trademarks and/or registered trademarks of Sterlite Technologies and/or related
affiliates and subsidiaries. All other trademarks listed herein are the property of their respective
owners.
www.sterlitetech.com
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