01.03.15
Protecting rail cables from the rat pack
Source: Rail Technology Magazine Feb/March 2015
Mark Fletcher, national sales manager – rail at PMA UK, spoke to RTM’s David Stevenson about the problem of vermin attacks on rail cables.
There is an urban myth in the UK that you are never more than six feet away from a rat. What isn’t a myth, though, is the disruption that rats and other vermin can cause to the rail industry by chewing through cables.
In April, rats caused a fire on the Melbourne Metro that disrupted services for days, while in July, a high-speed TGV was struck from behind by a regional train in south-west France because of a vermin attack.
An SNCF investigation found the regional train had passed a signal wrongly set on green because of a malfunction caused by rodents gnawing at trackside signal cables.
The accident at Pau prompted the French national railway to carry out an urgent check on 10,000 signals to prevent what it says was an incident that was “exceptional and unprecedented”.
But Mark Fletcher of PMA UK, a company working in cable protection systems, said the problem is not all that exceptional, and in fact is a “massive problem” in the UK and worldwide.
Territorial
He told us that wild rats often make their nests in concrete troughs along the lineside. “Rats are territorial creatures that use urine as a way to mark their territory,” he said. “If and when they smell the urine of another rat on their marked territory, they gnaw the affected material away – removing the offending rat’s scent.”
Fletcher added that there has been a move to introducing nylon conduits to protect lineside cables, as the nylon is too tough for rats to chew through and, when wet, the scent is easily washed away.
Five years ago there were two rat attacks within the space of two weeks that significantly disrupted the West Coast Main Line. They also led to Network Rail rolling out its rail “strengthening” programme. In the first instance, rodents chewed through cables crippling services between Preston and Lancaster with more than 107 trains cancelled. The second event, in Cheshire, saw rats chew through a high-voltage power cable leading to 20 trains being cancelled.
Network Rail announced a two-year programme to strengthen the rail system’s defences by laying steel armoured replacement cables.
“Traditionally, in the UK, we have used steel wired armoured cable to protect control cables, wi-fi and, especially, signalling cables,” said Fletcher. “But there is a desire to reduce the metal content associated with cables, especially because of cable theft. There is a push to move to smaller, less armoured control cables. So, you then really need to put them in a protection method, such as conduit, that is tough and reliable.”
Long-term safeguard
RTM asked Fletcher about Network Rail’s rail “strengthening” programme, and was told: “I believe Network Rail are continually replacing steel armoured cables on various projects around the country, however this will never eliminate the underlying problem. Rats and mice chew and nibble at the outer layers of PVC or rubber, thus exposing the inner layers to corrosion from the elements. So, as you can imagine, this will be an ongoing problem for Network Rail and installers.
“We are offering a solution more for control cabling, where smaller unarmoured cables can be used and rely on the nylon conduits to offer protection. We are aligned with the Plug and Play installation with the modular revolution.
“We are encouraging Network Rail to embrace new ways of cabling to solve problems of the past.”
Conduit on the continent
Discussing the potential application of a nylon conduit, Fletcher noted that Deutsche Bahn in Germany and SNCF in France have started going down this route, but the UK is “a bit behind the curve with the adoption of this type of system”.
“In the UK there is very little nylon conduit used at present for applications trackside,” he said. “But I suppose it mirrors the situation with regards to rail vehicles. Years ago they used to use lots of metalised conduit and heavy conduit on trains, but 99% of conduit applications on trains these days are nylon-based cable protection.”
Dr Jeremy Hodge, chief executive of the British Approvals Service for Cables (BASEC), recently noted that the threat from rodents and others to cabling and the systems they carry is always with us and presents serious challenges to specifiers, installers and end-users.
Three lines of defence
Hodge said there were three lines of defence against rats attacking cabling: building in physical barriers or deterrence, including routing cable to avoid spaces where rodents live; selecting the most suitable cabling for use where vermin might be present (steel wire armoured or steel braided cable offers some protection, though the sheathing itself may be attacked); and possibly using bad-tasting ‘deterrent additives’ in the sheathing material of some cables. This last method has limited effect with mice or rats, and is instead mainly used overseas where damage from insects, including termites, is the bigger issue.
Hodge said: “We receive many enquiries about how to protect cables against rats, mice, squirrels, pigeons and even insects – with the first three the most pernicious and determined.
“Cables gnawed through by vermin can result in electrical short circuits and fires and, as in the case of the Pau train collision, are significant threats to life and safety. It is unlikely we are going to declare victory over rats, mice and squirrels soon but by remaining vigilant and adopting sensible preventive measures we can help guard our vital systems and infrastructure against their attacks.”
Fletcher added that the final decision on tackling vermin attacks comes down to the rail organisations in the various countries.
“Deutsche Bahn and SNCF tend to specify or allow nylon conduit products to be used in certain locations and give contractors and installers options as to which sort of method they prefer to use,” he said. “I presume that Network Rail will go down a similar route.”
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