Development of Optical Fiber-Power Composite Cables
by Masanori Hattori *, Yuichi Sekii *2, Takeshi Maki *3, Toyomitsu Asakura *4,
Masashi Akita *5, Yuji Minamitani *6 and Masahiro Sugimoto *6

Two types of optical fiber-power composite cables have been developed asunder floor wiring cable, which is indispensable for realizing FTTD (Fiber To The
Desk). VVR (round) and VVF (flat) types of ordinary 600-V polyvinyl insulated and sheathedcable have been adopted in the development. With VVR, an optical fiber unit is sheathed together with power lines; and with VVF, the cable structure is such that a hollow pipe is sheathed withpower lines, into which an optical fiber unit is to be air-blown after cable installation, thereby comprising an optical fiber-power composite cable. The developed cables are expected to improve
cable congestion under the floor, facilitating the construction of transmission lines for FTTD.

ABSTRACT1.

INTRODUCTION

The number of Internet users in Japan is estimated tohave reached 27 million at the end of 1999 (a 59.7%
increase over the previous year), rising to 77 million at theend of 2005. In terms of diffusion rate, Internet users
account for 19.1% of every household, 31.8% of enterprises with 5 employees or over and 88.6% of enterprises
with 300 employees or over 1).
It is anticipated that data communications continue rapid
expansion, thereby promoting a transition of wiring configuration for office LANs from the conventional ones basedon twisted pairs to a new one that uses optical fibers.
Thus, optical access cables have to be upgraded in termsof performance and cost in order to enable economical
and rapid expansion of optical access networks.
In this paper, the design and development of new optical fiber-power composite cables is reported. The cables
are to be used, approaching nearer to the users side thanaccess cables, for wiring within office buildings and especially under the floor, and for connection between officecabinet and outlet so as to realize FTTD.

2.

NECESSITY FOR OPTICAL FIBERPOWER COMPOSITE CABLES

Telecommunications trunk cables led into an office building are connected to on-premises trunk cables, which run
longitudinally to be connected to floor cables at the endfloor cabinet, while a required number of optical fibers are
branched at each intermediate floor. On the other hand,
longitudinal power cables are branched at each floor in asimilar manner. Thus, in the conventional wiring, opticalfiber cables and power cables are installed individually,
resulting in the increase of wiring work hour and cablecongestion under the floor.
In order to solve such a problem of congested wiring, itis necessary to develop an optical fiber-power composite
cable including accessories so that the wiring work is
improved in terms of working hour and cable congestion.
Figure 1 shows the typical cable configuration in officebuildings illustrating both the conventional wiring method
and the new method based on composite cables.

Case 2:Composite cable
is used between
distribution panel
and outlet
Optical-powercomposite panel

Optical-power
Optical-powercomposite cable composite outlet

Optical floor cable
Optical termination cable
Case 1:
Conventional
wiring method

PC
Optical outlet* Development Sec., Engineering Dept., Opto-Comm Div.
*2 1st Sec., Engineering Dept., Opto-Comm Div.
*3 Production Engineering Sec., Chiba Production Dept., OptoComm Div.
*4 3rd Sec., Engineering Dept., Opto-Comm Div.
*5 Kansai Engineering Sec., Engineering Dept., Opto-CommDiv.
*6 Kinden Corporation

Optical fiber cable fortelecommunications
trunk line

Power line
Power distribution panel
Optical distribution patch panel

Power outlet

Power cable for trunk line

Optical cable for LAN trunk line

Server, etc.

Figure 1

Typical cable configuration in office buildings.

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3.

REQUIREMENTS FOR OPTICAL FIBERPOWER COMPOSITE CABLESVVR (round) and VVF (flat) types of 600-V polyvinyl insulated and sheathed cable are widely used for under floor
wiring since they are low in cost due to large-volume production. We have designed and developed the opticalfiber-power composite cable based on these cables.
Requirements for the cable design are as follows:
1) Since the cable is cut and worked for termination at
the site, the optical fiber has to be easily accessed fortermination work.
2) The power line of the cable complies with JIS C3342"600-V polyvinyl insulated and sheathed cable", sothat the cable structure certified according to theElectrical Appliance and Material Control Law should
not be changed.
The cables were designed to meet these requirements.

4.

DEVELOPMENT OF OPTICAL FIBERPOWER COMPOSITE VVR CABLE

4.1 VVR Cable
The structure of VVR cable is stipulated in detail in JIS
C3342 "600-V polyvinyl insulated and sheathed cable",
where "V" stands for "vinyl" and "R" for "round". Table 1
shows excerpts from JIS C3342.
As can be seen, single- to 4-insulated wire cables witheach wire consisting of vinyl-insulated single conductor or
stranded conductor are stipulated. Multiple wires are to be
S stranded with the specified conditions.
4.2 Investigation on Composite Cable Structure
The cable structure investigated for optical fiber incorporation is a round 3-insulated wire type, and the conductor

Table 1size was selected as 2 mm2 --the smallest nominal crosssectional area among the stranded conductors. Figure 2
and Table 2 show the cross section and the dimensions of
the VVR cable studied, respectively.
In terms of optical fiber incorporation into this cablestructure, it was considered that the optical fiber would be
most advantageously combined without changing thebasic cable structure and dimensions when the space atthe shoulder of the three power lines was used for accommodation.
4.2.1 Investigation on Optical Fiber Unit Structure
In view of LAN configuration using this composite cable,
the number of optical fiber to be incorporated in the cable
was determined as eight --2 fibers for 4 bi-directional
channels. The cross section of the optical fiber unit isshown in Figure 3, where 8 fibers are stranded around acentral tension member, then covered with thermoplastic
resin.
The outer diameter of the unit should be appropriately
designed so as not to interfere with the binding layer ofthe cable, because excessive diameter may degrade its
lateral pressure performance. Accordingly, UV coatedfiber of 0.25 mmφ was used for the unit, and GI fiber of
50/125 cross section was selected in view of application
for LAN environments.
During cable manufacturing, the optical fiber unit isstranded simultaneously with the power lines in the same
stranding pitch. The stranding pitch is stipulated by JIS as"30 times or less of the center diameter of the insulated
wire layer", or about 117 mm or less in this case.
Consideration has to be given whether the strain on fiber
remain under the allowable limit when the optical unit containing the fibers are stranded in this pitch and subsequently wound on a reel. We have calculated the minimum bending radius to be imposed on the fiber, taking

Table 2

Excerpts from JIS C3342.

Dimensions of VVR cable.

Discrimination ofSingle insulated wire Black

Structure

Dimension

cable core

2-insulated wire

Black, White

Conductor

2 mm2 in nominal, 7/0.6 strand

3- insulated wire

Black, White, Red

4- insulated wire

Black, White, Red, Green

Stranding pitch of

30 times or less of the center diameter ofcable core

the insulated wire layer for nominal

Insulation thickness

0.8 mmSheath thickness

1.5 mmOuter diameter11.0 mmconductor cross section of 100 mm2 or lessSheathBlack

0.25 mm φ colored fiber
GI 50/125

Figure 3
Figure 2

23

Cross-sectional view of VVR cable.

Cross section of optical fiber-power composite VVR
cable.

Furukawa Review, No. 21

2002such factors as the stranding pitch of the fiber in the optical unit and that of the unit in the cable together with thebending radius of the cable, and it was confirmed that theradius was more than the allowable limit for fiber.

45

0.5

40

0.4

35

0.3

30

0.2
Temperature

25

Loss
0.1

Current loading off

Loss increase (dB / 24 m)

Temperature in cable (°C)

4.2.2 Temperature Rise during Current Loading
Temperature rise during current loading has to be considered for such an optical fiber-power composite cable.
Accordingly, we have experimentally evaluated the temperature rises during both short-circuited operation andcurrent loading of nominal current, based on the allowablecurrent of the cable.
The allowable current is 15 A, so that the short-circuitedcurrent at which the circuit breaker operates is calculated
to be 234 A. Figure 4 shows the temperature rise in thecable and the loss increase of the fiber when the cable
was subjected to the short-circuited current, and Figure 5
shows these characteristics when the cable continued tocarry the allowable current. Table 3 summarizes theresults of the measurements.
In the short-circuit experiment, although a circuit breaker operates in 0.2 second, the duration time was set to 1
second so as to keep on the safe side. It is seen that thetemperature rise is below about 14°C, while it is about
10°C when the cable continued to carry the allowable current, and that no deterioration is seen for the cable characteristics. Thus, it may be concluded that the cable with-

4.3 Cable Characteristics
Table 4 summarizes the results of the evaluation of cablecharacteristics. As can be seen, the cable satisfies thecharacteristics required for general optical fiber cables.

5.

DEVELOPMENT OF OPTICAL FIBERPOWER COMPOSITE VVF CABLE

5.1 VVF Cable
The structure of VVF cable is stipulated in detail in JIS
C3342 "600-V polyvinyl insulated and sheathed cable",
where "V" stands for "vinyl" and "F" for "flat". The VVF
cable is most extensively used in office building wiring for
power supply, permitting easy installation under the floor
due to its flat cross section. Figure 6 shows the structureof the VVF cable.
5.2 Problems with VVF Cable Structure
In the case of the VVR cable, as described in Chapter 4,
the optical unit that contains fiber is assembled by strand-

Table 3Temperature rise and loss increase of cable during
current loading experiments.
Short-circuit test

Allowable current test

Initial value

30°C

28°C

After current loading

44°C

38°C

0 dB / 24 m

0 dB / 24 m

Temperature

Loss increas

Table 4

Optical and mechanical characteristics of opticalfiber-power composite VVR cable.

0

20
0

10

20

30

40

50

Test item

Time (sec)Figure 4

stands the intended application as an optical fiber-powercomposite cable.

Results

Optical characteristics ( λ =1.30 µm)

Temperature rise and loss increase of VVR composite cable subjected to a short-circuited current of 237
A x 1 sec.

Average transmission loss

0.80 dB/km

Temperature dependence at -10°C~+60°C Loss change: 0.05 dB/km or less
Mechanical characteristics (λ =1.30 µm)
Tension (400 N)

0.5

45
Loss

0.4

35

0.3

30

0.2

25

0.1

Current loading with 15 A

20

0

50

100

Loss increase (dB / 24 m)

Temperature in cable (°C)

Temperature

40

Bending (R = 55 mm)

Loss change: 0.01 dB/km or less

Twist (±90°C/1 m)

Residual: None

Lateral pressure (1200 N/25 mm)
Impact (7 kg, 60 mm)
Fiber accessibility

Good

0

Time (min)Figure 5

Temperature rise and loss increase of VVR composite cable subjected to an allowable current of 15 A.

Figure 6

Cross-sectional view of VVF cable.

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Table 5

Dimensions of VVF cable.

Structure
Conductor

R60 mmDimension
2 mmφ in diameter

Insulation thickness+= 60 m

0.8 mmSheath thickness

1.5 mmOuter dimension

6.6 mm × 14.0 mm, approx.

R40 mmCable 10 m in length

Pipe bundle 50 m in length

Figure 8

Test line configuration for blowing-in experiment.

Table 6

Optical characteristics of optical fiber-power composite VVF cable after blowing-in test.
Test item

Test results

Averaged transmission loss (λ =1.30 µm)

0.80 dB/km

Example: 8-fiber round unit
Power line: 3.6 mm φ in outer diameter
Pipe: 2.5 / 4.0 mm φ
Applicable optical unit: 1-, 2-, 4-, 6-, 8-fiber unit,
1.5 mm or less in outer diameter

Figure 7

Cross section of pipe-composite VVF cable.

ing it in the same pitch as the power line, forming a composite cable structure. With the VVF cable, on the other
hand, the following problems about optical unit assemblyarise due to its simple structure of flat cross section:1) Large strains will be generated on the optical unit
when the cable is bent in the plane of cable width.
2) Large stresses will be imposed on the fibers because
the optical unit is of tight structure.
These problems were investigated to find a solution.
5.2.1 Investigation on Cable Structure
The VVF cable investigated for optical fiber incorporation
is a 3-insulated wire type, as is the case with VVR, and asolid conductor with a diameter of 2 mm was selected.
Table 5 shows the dimensions of the VVF cable. The
number of fiber is eight, the same as for VVR.
If the optical unit is sheathed jointly with the insulated
conductors for power line coated with talc thus forming aflat cross section, strain on the fiber together with protrusion of cores present problems. Solid structure of opticalunit seemed unsuitable to deal with this problem, so thatloose structure was studied once. However, since fibers
are encapsulated in the optical unit that is bulk sheathedwith insulated conductors, it was feared that severe bending during cable installation might adversely influence thefibers.
It was decided, therefore, to make a pipe composite
VVF structure by bulk sheathing a polyethylene pipe with
the insulated conductors, into which an optical unit was tobe air-blown after cable installation using compressed air,
thereby comprising an optical fiber-composite power cable 2).
This cable structure eliminates those problems of fiber
strain during cable installation as well as lateral pressure
on the fiber. Figure 7 shows the cross section of a pipecomposite VVF cable.

25

The pipe, 2.5 mm in inner diameter and 4.0 mm in outer
diameter, is made of polyethylene. The outer diameter ofthe pipe is nearly equal to that of the insulated conductor--3.6 mmφ, thereby suppressing increase in cable thickness and enabling to achieve the same pattern of bending
behavior. The optical unit is also shown in Figure 7.
5.2.2 Blowing-in Characteristics
A pipe-composite VVF cable was installed and tested forblowing-in characteristics of optical units using a test line
shown in Figure 8. As shown, a 10 m piece of the pipecomposite VVF cable was installed with two 180° turns 60
mm in radius and three 180° turns 40 mm in radius, and a
50 m long pipe having a cross section of 2.5/4.0 mm inloose bundle was connected to the cable making the total
pipe line 60 m in length. Subsequently, an 8-fiber roundunit was air-blown into the test line.
Blowing-in experiments were carried out from the bothends alternatively, and it was confirmed that the entire
length of fiber unit was successfully blown-in within 1 min
20 sec to 1 min 30 sec. Moreover, the unit was checked
for optical characteristics after blowing-in, and no problems were found. Table 6 shows the transmission loss ofthe optical unit measured after blowing-in.

6.

SUMMARY

Two types of 600-V polyvinyl insulated and sheathedcables that are in extensive use for power supply wiring
have been incorporated with 8-fiber optical fiber unit, comprising optical fiber-power composite cables applicable to
FTTD.
VVR: A cable structure has been developed in which an
optical unit is placed at the shoulder of the three powerlines, and all of them are stranded in the same pitch. This
enables to offer an optical fiber-power composite cablewithout changing the outer diameter of the original VVR
cable.
VVF: A cable structure incorporating a hollow pipe has
been developed, into which a fiber unit can be blown-in

Furukawa Review, No. 21

2002when the need arises. Moreover, the number and the typeof fiber can be selected by appropriate selection of the
optical unit.
These composite cables are fully provided with thecharacteristics generally required for both power cables
and optical cables. Furthermore, the cables enable reduction in the number of cables to be installed, thereby
improving cable installation work as well as cable congestion.

7.

IN CONCLUSION

The development of new optical fiber-power composite
cables capable of coping with implementation of FTTD
has been reported. It is anticipated that optical fiber installation approaches nearer to the users side during thecourse of FTTD and FTTH implementation. We plan tocontinue developing high-performance, low-cost cables
required for FTTD and FTTH.
The optical fiber-power composite VVR cable reported
here is an achievement of the joint study by Kinden
Corporation and Furukawa Electric, and the product has
been in practical use since July 2000, under the tradename of "GIGA-POWER" cable.

REFERENCES
1) Ministry of Posts and Telecommunications; White Paper on Infocommunications in Japan, 2000 (in Japanese).
2) I. Kobayashi et al.; Innovative Optical Fiber Cables in Support of
FTTH Implementation, Furukawa Review No. 17, August 1998,
p53.

Manuscript received on July 1, 2001.

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