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Technical article
November 2012
74
www.read-eurowire.comthe other elements of the cable design
are driven by the mechanical and optical
requirements based on the installation
and operating conditions.
For the dielectric version, over the central
ceramifiable inner tube an intermediate
flame retardant sheath is applied rein-
forced by two glass rods longitudinally
embedded into the wall of the jacket; the
glass rods withstand both tensile load and
low temperature shrinkage. Then some fire
resistant tapes are applied together with
the outer LSZH sheath. The cross section
of the all-dielectric version developed is
shown in
Figure 1
.
For the metallic armoured version, the
corrugated steel tape is applied over the
ceramifiable tube followed by an outer
HFFR sheath reinforced by two glass rods
with the same function described above.
The cross section of the armoured version
developed is shown in
Figure 2
.
2.3 Cable trials and production
Cables in all dielectric and metallic
versions have been developed from 48
to 144 optical fibres. Many experimental
trials have been carried out before the
production of the final versions; then
the cables have been fully characterised
for optical, mechanical and thermal
performances, together with the fire
behaviour as reported in the following. In
Picture 1
two cable samples are shown.
2.4 Cable characterisation
The two cable designs have been
manufactured with three different types
of optical fibres, ie SM-R, NZD and MM. The
cables have been tested according to the
main international fire tests, IEC 60331-25
and EN50200. In
Pictures 2
and
3
the fire
tests performed on the cables are shown.
Each type of fibre has been closed in loop
and connected with a Led-Power meter,
measuring the increase of attenuation at
1,310 and 1,550 nm in the circuit with SMR
fibres, at 1,550 nm with NZD fibres and at
1,300 nm with MM fibres.
The fire lasted 90 or 180 minutes and the
recording of the attenuation values has
been extended up to 15 or 30 minutes
later. Examples of some test results are
collected in
Figures 3 to 5
.
All the results are positive with very
limited attenuation increase (less than
0.2 dB/fibre) for any of the fibre types
tested. This really confirms that the
ceramifiable protection, in combination
with an appropriate cable design, is able
to preserve the fibre performance from fire
load also in cable solutions with high fibre
density.
3 Conclusion
The cable family developed with a
special protective layer to preserve the
fibres transmission performances from
fire action is particularly effective when
the application of flame is turned off
and the material contractions start. The
cables have been developed in metallic
armoured and all dielectric version
with the optical fibres organised in
micromodules up to 144 fibres with a very
compact design, and are now available on
the market.
n
4 Acknowledgements
The authors would like to thank their many
colleagues within Prysmian who have
contributed to this work, and in particular
Paolo Marelli and Gianluigi Radaelli for the
helpful support.
Prysmian SpA
Viale Sarca 222
20126 Milan, Italy
Tel:
+39 026 44 91
Website
:
www.prysmian.com:
info@prysmian.com▲
▲
Figure 4
:
Fire resistant test of all dielectric versions according to EN50200
▲
▲
Figure 5
:
Fire resistant test of the armoured version according to EN50200
Fire resistant test EN 50200
All dielectric micromodules cable
180 min fire + 30 min cooling
Attentuation [dB/fibre]
Attentuation [dB/fibre]
Time (minutes)
Time (minutes)
Fire resistant test EN 50200
Armoured micromodules cable
180 min flame + 30 min cooling