£18,000 rail theft appeal at Gwersyllt near Wrexham
Thieves made off with £18,000 worth of rail equipment in Wrexham, say British Transport Police.
They say the equipment, from a trackside storage unit near Gwersyllt railway station, is valueless outside the industry.
But police said the cost of replacing it was high.
The thieves were disturbed and made off across a field backing onto a housing estate.
The theft took place between 20:00 and 22:00 GMT on 29 January.
Investigating officer Pc Kirk Smith said: "The irony is that the stolen items are of no real value to anyone outside the railway industry, yet the cost to replace them is extremely high.
"In fact, the thieves will struggle to get any money at all as dealers are highly unlikely to accept them."
Officers want to trace a man walking an Alsatian dog around 22:00 GMT near the storage unit, who may be a witness.
British Transport Police asked anyone with any information to call on 0800 40 50 40 quoting background log B2/WQA of 05/02/2013, or call Crimestoppers anonymously on 0800 555 111.