Scrap metal dealers across south Wales are being urged to look out for cables stolen from railway lines as part of a police crackdown on the problem.
Police held a national day of action to target metal theft
Transport police have been visiting dealers to highlight the fact that accepting stolen cable and other metals is a criminal offence.
Last year, 85 people were arrested in the Wales and western England in connection with cable thefts.
Officers urged dealers to report any suspicious looking metal to police.
Det Insp Dave Goddard, from British Transport Police in Cardiff, said: "We are encouraging scrap metal dealers in Cardiff, Newport, Pontypridd and Swansea to be particularly vigilant and if they suspect metals to have been stolen, to report it to police.
"Accepting stolen cable and other metals is a criminal offence."
Police said 14 people were arrested in Wales in 2007 in connection with the theft or handling of stolen goods.
Officers from Cardiff and Bristol carried out visits across south Wales to local scrap metal dealers and metal recycling facilities on Monday to ensure they are aware of what to look for in identifying cable stolen from the rail network.
It was part of a national day of action to target metal theft
Det Sgt Kaz Pitham, from British Transport Police, said metal theft is a "major crime".
"It is certainly not a victimless crime," he added.
"On the rail system, it is extremely dangerous to those involved.
"It can also cause hours of delay to the thousands of passengers who rely on the rail network.
"Those who steal cable are not just risking a prison sentence, they are risking their lives."