Tuesday, October 5, 2021


What is the Optical Fiber Cable and its Fittings?

This section of the specification covers optical fibre suitable for incorporation into the non-metallic underground fibre optic cable.

Design Guide of a Fiber Cable

Fiber Optic Cable Sectional Diagram
Fig: Fiber Optic Cable Sectional Diagram 

The overall system design of the fibre optic system shall meet the following minimum requirements:

The product reliability is to be ensured through rigorous quality testing of each product family. Both initial and periodic quality testing is to be performed to assure the cable performance and durability in the field environment.

Increase in optical system transmission attenuation due to accumulated ageing and other effects at the end of five years not more than 0.05 dB/km.

 What Would be Optical Fibre for Cable Construction?

Optical fibres shall be single-mode fibre. The fibres shall be coded for ready identification at each end. Single-mode fibres shall conform to CCITT G652 or to IEC 793-B1 and Appendix 8.A2.

The optical fibre coating material shall be mechanically strippable. The optical fibres shall be capable of being joined by fusion splicing techniques.

The optical fibres shall not be subjected to any critical stresses when the cable is at its maximum system loading reference Appendix.

The fibre optic cable shall be circular in cross-section and shall be designed so that any cable strain is not directly imported on the optical fibres. The cables shall not include any metallic components to prevent high induced voltage when used by the side of the power cable.

What Would be Major Constructional Features of Optical Fiber Cable?

Optical fibres shall be single-mode constructional features of the optical fibre cable have to be in line with the date given below:

·    Optical fibre               
·    Loose buffer tube   
·   Cable                         
·   Colour code              

Required drawings for the construction of the optical fibre construction of loose buffer tube constructional feature of the optical fibre cable as a whole and specifications of the optical fibre are to be attached with the offer of the Bidders separately and standard of specifications are to be mentioned in the offer of the bidder. 

Detailed data about similar projects (as a minimum three (3)) of compatible volume have to be provided with the offer. After finalisation of the drum lengths, the contractor/supplier shall submit calculations for the expected overall attenuation and dispersion. 

This is a Hold point. This will be compared with the actual values measured after the completion of the installation.

Characteristic of FOC

For details on optical fibres please see

Optical properties of the optical fibre.

Sheath Printing of Fibre-optic Cable

The following marks shall be printed on the cable sheath in one-meter intervals:

  1. Symbol of FOC
  2. Manufacturer Name
  3. Year of manufacturer
  4. Length marking
  5. Warning tape shall be used as per standard.

The box shall be supplied complete with internal spice cassettes to accommodate the required number of splices. Glands shall be fitted to accommodate the underground fibre poetic cable.

Required drawings and specifications are to be supplied along with the document and the standard of the specification is to be referred to.

What Would Be the Packing Drum?

The cable will be delivered in the length required on a wooden drum.

Cable end Identification

Both ends of the cable shall be fitted with a suitable cap to protect the FOC from the penetration of water or dirt.

Optical joint boxes shall be provided to protect the splice joints when individual lengths of fibre optic cables are jointed. The optical joint Boxes shall protect the splice from both mechanical and environmental damage.

What Would be the Characteristics of Fiber Optic Cable Joint Boxes?

The joint boxes shall consist of a high impact plastic ABS box to IEC 529 IP54.

The external housing shall be designed so that rainwater is directed away from the door, and there shall be no water ingress when the door is opened.

The door of the box shall be fitted with captive hinges and shall be fastened shut by screw fixings.

The bottom of the box shall be fitted with a gland plate with four entry points suitable for a certain number of different FOC diameters. The joint boxes shall be supplied complete with all fittings to satire and seal the cable in the gland plates or blank the unused spigots. 

Cable cleats to settle the fibre optic underground cable shall be fitted inside the box. The cleats shall not have a detrimental effect on the performance of the optical fibres when tightened to the recommended torque.

The top and bottom of the joint box shall be vented and the vents provided with vermin shields.

The box shall be supplied complete with internal splice cassettes to accommodate the required number of splices. Glands shall be fitted to accommodate the underground fibre optic cable.

Required drawings and specifications are to be supplied along with the document and the standard of the specification are to be referred to.

What Would be Fiber Optic Enclosure Feature?

At both ends of a FOC line fibre optic termination equipment (FOTE) is to be installed where the FOC shall be terminated spare length and pigtails are safely fixed. 

The FOTE should provide easy access to the FOC for maintenance and operating purposes. The interior of the FOTE has to contain cable trays to allow safe store of fibres and splices in accordance with the FOC specification.

The drawing and specifications of the FOTE are to be supplied with the offer and standard specification is to be referred to. The enclosure shall perform the following functions:

FOTE shall support organise and protect the optical fibres and the fibre splices whilst ensuring that the optical fibre minimum bending radius is not exceeded.

The splice tray shall not have any sharp edges or protrusions that may damage the optical fibre cable.

FOTE shall provide entry for FOC up to 48 fibres

Number tags for tube and fibre identification are to be included.

FOTE shall provide mounting positions for the bulkhead FC/PC type connectors on which the cable will be terminated.

FOTE shall allow patching of fibres

FOTE shall consist of two (2) separate, lockable compartments one to connect the FOC with pigtails to the couplings and store the spare length of the FOC/ pigtails accurately and a second compartment which provide access to the other site of the coupling only.

This type of enclosure shall be mounted on the wall at a conveniently accessible height.

What is the Fiber Optic Cable Pigtails?

Where a termination enclosure has been installed all fibres of all cables are to be terminated on pigtails with a minimum length of 1m.

The pigtail shall be a kevlar® (or aramid) reinforced and plastic coated optical fibre conforming to ITU-T Recommendation G.652. 

For terminating and connecting the FOC FC/PC type connectors shall be provided. The connector shall be inserted on the cable side of the bulkhead (feed through) connector in the termination enclosure.

All connectors shall be supplied with a removable cap to be protected against moisture and dust ingress when not connected to a coupling.

Required drawings and specifications are to be supplied with the offer and the standard of speciation is to be mentioned.

Protective Treatment of Optical Fibre Cable

Where two layers of wire strands are provided over the optical sub-unit, the external surface of the optical sub-unit and the inner strand flayer shall be greased, using approved conductor grease.

Ingress of moisture
The cable shall be capped before shipment to prevent the ingress of water.

Optical Fibre Cable Installation Guides

The manufacturer of the optical fibre cable will be responsible for the supervision of installation by the Contractor to ensure that overall system reliability requirements are met. 

To ensure that this is undertaken, the manufacturer will provide the services of a suitably qualified/experienced installation supervisor, who shall supervise the installation of the works and shall advise the Engineer and contractor in matters of methods procedures and precautions to be followed and will be responsible for all matters pertaining to the quality of the installation. 

The manufacturer’s installation supervisor shall make at least four visits of 2(two) weeks each during the progress of optical fibre cable installation work for the purpose.

The contractor shall provide the Engineer with a method statement giving sequential details of the stripping procedure and the optical fibre jointing (splicing) procedure. 

The method statement shall take full cognizance of the manufacturer’s installation instructions. 

The underground optical fibre cable shall be installed through an HKPE duct throughout the length of the cable. 

The permissible bending radius of the FOC has to be considered in the design of the cable route. The HDPE duct has to be sealed on end to avoid animals e.g. rates cannot get in and eat the FOC.

The cable should be installed at least 6 inches below the level of the power cable following the drawing attached herewith.

The overall attenuation of the installed cable shall not exceed that calculated using the attenuation and splice loss values specified in Appendix.

The contractor shall give the Engineer the requisite period of notice prior to commencing the tests. This is a Notification point. Details of the test results shall be submitted to the Engineer.

The manufacturer of the FOC is requested to co-operate with the fibre optic terminal equipment manufacturer (if this is under a separate contract) and shall supply all technical data requested.

The manufacturer shall be submitted to the Engineer for acceptance with the requisite period prior to optical fibre jointing commences. 

The following tests shall be undertaken by the contractor:
Prior to installation, the fibre optic cable shall be tested with an OTDR on each fibre to ensure that no physical damage has occurred to the fibre during, delivery and shall be compared with the results prior to dispatch.

After installation, the above test shall be repeated to ensure that no damage has occurred to the fibre during installation.
An end to end attenuation measurement shall be taken in each direction on each fibre using an optical source and optical meter.

The overall attenuation of the installed cable shall not exceed that calculated using the attenuation and splice loss values specified in Appendix 8.A2. The tests records have to be submitted to the Engineer for approval.

The contractor shall ensure that the fibre optic cables are not strained or damaged either mechanically or optically during layin gout and paying out of cable and jointing. 

If necessary the contractor shall demonstrate the suitability of his proposed method, including the choice of running blocks prior to the commencement of laying out and paying out operations.

What Would be the Optical fibre joints Feature?

Optical fibre joints between non-metallic underground fibre optic cables shall be housed in optical joint boxes.

 Construction of the optical fibre


Fibre Type
Matched Clad type single-mode ITU-T optical fibre The    optical fibre are   compliance   with recommendation G.652.B
Doped silica


125 + 1 µm

Primary Coating
Inner layer
UV curable acrylate

Outer layer
UV curable acrylate

245 ± 10 µm

Core / cladding concentricity €
Max. 0.8 µm

Cladding non-circularity
Max. 1 %

Mode field diameter
9.0 µm ± 0.5 urn at 1310 nm

Color coating

Proof test level
Equivalent to 1% strain, 1 sec.

              Construction of loose buffer tube

Optical fiber
The same as Table 1
Max. 6
Thixotropic Jelly Compound
PBT or equivalent with colour coding
Nom. Outer Dia. (mm)
Colour Code
Table 4

 Construction of cable

Loose buffer tube
The same as Table 2.


Central strength member
FRP (Fiber reinforced with plastic) rod

Dia. (mm)
Plastic rod, coloured natural

Dia. (mm)

Nylon Yarn(s)
Flooding Compound
Water Resistant Compound
Strength Element
Aramid Yarn(s)
Ripcord 1 Inner sheath
Material Material
Plastic thread High-Density Polyethylene, coloured black

Thickness (mm)
1.0 ± 0.15
Ripcord 2
Aramid Thread
Armor Flooding
Water Resistant Compound
Outer Sheath
Material Thickness (mm)
High-Density Polyethylene, coloured black 1.310.2
Nylon Sheath
Polyamide, coloured black

Thickness (mm)
Cable dimension
Approx. (mm)
Cable weight '
Approx. (kg/km)
Fig. 4

Colour code of Fibre Optic Cable

(1) Color code for the fiber in a tube
  Fiber No.
Colour of fiber
(2)  Color code for the tube
   Tube No.
Colour of tube

Mechanical Properties of Cable

Maximum tensile strength
2700 N
Bending radius of the cable
  • at no load
  • at half max. design tensile load
  • at max. design tensile load
Min. 10D mm Min. 20D
mm (D: Overall cable diameter (mm))
Temperature range
Operation Installation
-10o to 70T –
10o to 70oC


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