WCA MAY 2015

Using this criterion, the example given in Table 1 can be simplified as follows: • 0.69 GPa fibre at 20 per cent long-term load will provide reliable performance • 0.69 GPa fibre at 40 per cent long-term load will not provide reliable performance • 1.38 GPa fibre at 20 per cent long-term load will not provide reliable performance Though it is apparent that proof-testing at higher levels greatly improves the performance of the cables, the value commonly used in cabling standards – 20 per cent of the proof test level – can lead to false expectations about the long-term reliability of the optical cables. 6 Recommendations The information described in this document indicates that, though 20 per cent of the proof-test load for a long-term load on optical fibre may be a reasonable criterion for optical fibre proof-tested at 0.69 GPa or less, it may produce optimistic estimations for optical fibre proof-tested at higher levels. Currently, most major optical fibre standards, including those in ITU-T, IEC, and TIA, require the fibre to be proof-tested at 0.69 GPa. Cable standards in IEC, ICEA and IEEE should align with this criterion. It is thus recommended that the documents be modified to simply require maximum long-term load of 0.14 GPa (20 kpsi) on the cabled optical fibre after deployment, regardless of the proof-test level. A note could be added to the requirement stating that when optical fibre with proof-test levels higher than 0.69 GPa is deployed, higher strains on the optical fibre will affect reliability and should be agreed to by the cable supplier and end user, and that more precise fibre reliability models should be considered. 7 Conclusions This paper has shown that modern cable designs are pushing the design limits for allowable long-term strain in optical cables. Under these new boundary conditions, the old rule of thumb allowing up to 20 per cent of the proof-test level as a long-term strain may no longer be appropriate. A new recommendation requiring the long-term load be limited to 0.14 GPa is proposed as an alternative criterion. This new criterion should be included in upcoming revisions of fibre cable standards. Particularly critical designs are high-strain cable types such as drop cable, and overhead cables including OPGW and ADSS cables. 8 Acknowledgments Special thanks to Peter Hasløv (OFS), Hiroshi Nakamura (Furukawa) and Peter Pondillo (Corning) for their helpful discussions on fibre lifetime. 9 References [1] Steven R Schmid, et. al, ‘Development and Characterisation of a Superior Class of Micro bend Resistant Coatings for Today’s Networks’, Proceedings of the 58 th IWCS, (2009), 72-78

[2] Glaesemann, G S, and Gulati, S T, ‘Design Methodology for the mechanical reliability of optical fibre’, Optical Engineering, June 1991, Vol 30 No 6, 709-715 [3] Castilone, Glaesemann G S, and Hanson, T, NFOEC-2000, 1-9 (August 2000) [4] IEC TR 62048 Power Law Reliability Paper courtesy of the 62 nd International Wire and Cable Symposium, North Carolina, USA, 10 th to 13 th November 2013.

OFS 2000 Northeast Expressway Norcross, Georgia USA Tel : +1 508 637 1114 Email : dmazzarese@ofsoptics.com Website : www.ofsoptics.com

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Wire & Cable ASIA – May/June 2015