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EuroWire – January 2008
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few fibre splice and connection
points, it is cost efficient to joint ducts
and it also needs less skilled labour.
Furthermore, a more reliable solution is
achieved compared to a solution with
optical connectors.
The solution is exemplified by the following
scenario, shown in
Figure 1
. This is a typical
residential area consisting of detached
houses. In this scenario, only one fibre joint
closure on every 5
th
pole is required. From
this small closure, 20-24 homes are served.
The network connecting the joint closures
towards the splicing cabinet (with splitters)
is referred to as the main distribution
cabling. The drop cabling from the end
user is carried out by installing single drop
ducts connected to the main duct, see
Figure 2
. One simple duct joint, see
3.3
,
typically serves four subscribers from the
closest pole. Note that no fibre splicing is
done in the duct joint.
As described, this design enables a single
duct assembly for feeding a long distance
of poles. The number of fibre splices will be
kept to a minimum since splicing between
air-blown fibre and air-blown micro cable
is only required on each 5
th
pole.
To reach all customers in the described
scenario the distribution cable needs to be
installed up to 1,000 metres and the drop
•
cable only up to 200 metres. The blowing
installation distances are further discussed
under section 4.4.
3. Products
3.1 Duct assemblies
The duct assemblies are made in different
configurations, see examples in
Figures
3
and
4
. The ducts are self supporting,
either as figure-8 or with an under-sheath
integrated strength member.
By combining both 10mm ducts for micro
cable (distribution cable) and 5mm ducts
for air-blown fibre (drop) in the same
assembly, an installation of an access
network with only one duct assembly
between poles is possible.
3.2 Fibre joint closure
A fibre joint closure for this application is
unique in many aspects. It must be able
to handle several different features, such
as ducts (both for blown fibre units and
for micro cables), fibre management and
splices, mid-span storage of micro cable
fibre units and storage of blown fibre units.
It should be pole mounted (and in some
cases span-mounted).
Finally, all of this has to be squeezed into
a small package, see
Figure 5
. Aesthetics
are very important. The closure must be
visually discreet. In principle, the closure
does not exceed the width of the pole and
as such is visually hidden from most views
of the pole. The length of the closure is
also important.
3.3 Duct joint
A duct joint is needed to branch out single
ducts from the principle duct assembly to
any premises requiring service. The duct
joint is of a span-mounted design.
It typically enables four ducts to be
accessed at every pole span, enabling
access to the four premises serviced from
that particular pole. The duct joint that
provides for this distribution from the main
duct assembly is a key design feature.
3.4 Fittings
The aerial duct support fittings are of the
wedge clamp type and very easy to install,
Figure 3
: Example of an aerial multi-duct assembly
with 8 x 5mm ducts for air-blown fibre and 2 x 10mm
ducts for micro cable
▼
Figure 4
: Example of a self supporting drop duct
with 1 x 5mm inner duct
▼
Figure 5
:
Example of fibre joint closure with two
main duct assemblies terminated
▲
Figure 6
:
Example of duct joint with four single duct
assemblies jointed to one multi-duct assembly
▲
Figure 7
:
Tension clamp for multi-duct assembly
▲
Figure 8
:
Four-fibre EPFU (Enhanced Performance
Fibre Unit)
▲
Figure 2
: Installation example – Aerial installation of FTTH network with air-blown fibre and cable
▼