Recent overhead power problems in Hertfordshire and Cambridgeshire which led to rail chaos were caused by "component failures", Network Rail has said.
The company said it had identified exactly which components failed at Radlett in Hertfordshire and at St Neots in Cambridgeshire.
Network Rail has apologised to travellers who were caught up in the delays.
"We are carrying out further work to establish the reasons so that we can minimise the chance of repeat failures in the future," said a company spokesman.
More top news
Becoming drier by this evening with the chance of a late sunny spell.
The Chief Executive of Southend United has told ITV News Anglia that his players deserved to win promotion to League One at Wembley.
Some sunny intervals are possible initially this morning but cloud and patchy rain will gradually sweep in as the day goes on.