Locating faults in submarine cable systems was a pressing topic of discussion at Submarine Networks Europe and was keenly debated during the roundtable session.

Fault location in subsea cable systems

Fortunately, faults on Undersea Cable Systems are relatively few and far between.  A system operator may see one every couple of years or if they are very lucky it may be much longer before they see any failure.  However, when faults do occur, it is a very costly exercise to perform a repair in the submerged plant.  Sadly, companies tend not to consider how they will deal with these problems until they occur.

In the past most of the cable systems have been owned and operated by a consortium of well-known operators (BT, Cable & Wireless, France Telecom, Deutsch Telekom, etc).  Because these companies were part owners in multiple cables they built expertise in fault finding as, on average, they could see one or two faults per year.  However, even these organisations have downsized and reduced their personnel and investment in systems so now have limited experience in these techniques.
Today there are many new operators entering the industry and it is unlikely they will have the in-house expertise to enable failures to be accurately determined and located.  It should be noted however, that any error in a location can result in hundreds of thousands of Dollars of additional costs, so it is vital that every effort is made to “get it right first time”.

Tools for identifying faults

Currently there are limited tools to assist with this work.  There is a single supplier for the machine used for locating optical faults on an amplified system (Anritsu COTDR).  Some system suppliers are beginning to incorporate such a device within their equipment design but this is by no means standard currently.  Interpreting the results from these tools is also not straight forward.  An inexperienced operator can easily be misled.
Electrical faults (Shunt faults) can be even more difficult to locate.  There are some tools (Tinsley products) available to assist with this but the traditional method is to use the Power Feeding Equipment readings.  These can lead to very confusing results and considerable inaccuracies in the locations given to the repair ship operator.  An error of just 1 volt equates to at least 1 Km of cable and there are many variables that need to be considered.  So, getting an accurate location using these dc tools is even more difficult and, if the cable is not broken, this may be the only option available.

The solution

The time may be right for the industry to consider investment in improved tools and/or training of personnel to enable them to utilise these existing tools effectively.  Or, given the current trend, where staff frequently do not to stay with a company for many years, it may be more cost effective to employ a specialist independent company to assist with localising these underwater failures.  Any such company would need to be employed on a long-term basis to enable them to keep up-to-date with any changes that are occurring during the lifetime of the system.  It would not be possible for any external organisation to simply arrive on-site and accurately identify a failure without some in-depth knowledge of the system design and its performance trends.  However, the use of an independent company may well be the optimal way forward for the industry.


Adrian Hilton, Owner and Technical Director at Subsea 123, was a speaker at Submarine Networks Europe 2018 in London. The event, organised by Total Telecom, will be back in 2019, find out more at