For a start your ticket i.e contract of sale is between you and IE (CIE board actually)
In this case the cable was outside the IE boundary and was not an IE cable, in fact had no connection to IE at all as the only connection to the system is at Heuston. The signalling installation in Heuston is brand new and has an emergency generator as do all signalling equipment rooms. The spec for the Kildare Route Project includes UPS devices so power surges, power cuts etc are not going to effect the system I'd bet money Heuston has this given its recent installation
In this case a safety critical system shutdown, if it had been a real power surge there would have been quite significant damage, don't hear of any businesses complaining
The onus is on IE to prove that this was out of there hands
http://www.platform11.org/passenger_info/refunds.php
Despite that the law in this case would indicate libility on the part of IE for failure to provide service. Its not an act of god its reasonable to expect power cuts and the surge that follows a reset