All rail lines blocked between Eastbourne and Bexhill due to electricity supply failure between two stations
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Southern said Network Rail response staff investigated the issue overnight, and have since found the section of cable that has been damaged.
Specialist equipment is needed to repair the fault and this is in the process of being taken to site, fitted and tested, Southern added.
A Southern spokesperson added: “A power surge has damaged the signalling system overnight, and this means that all lines will remain closed until repairs are completed.
“Southern have requested rail replacement buses but these will be extremely limited. Stagecoach route 99 runs between Eastbourne and Bexhill, but please note you will need to buy a ticket to travel on these services at your own cost.
“You can check if your journey will be affected using Southern's live route map here.”