specifications (25kV AC at 50Hz), the EF class could not be used on Auckland's network due to that network requiring higher fault current tolerances than the NIMT. In order to run on Auckland's network, the EF class would require upgraded rectifiers. Only heavy repairs are undertaken at the main Hutt Workshops near Wellington which, due to the non-electrified section between Palmerston North and Waikanae (and Wellington's electrification being DC rather than AC), the locomotives must be towed by a diesel engine to access the workshops. All other work is carried out in Palmerston North. From June 2006, the locomotives have been fitted with AAR couplers, each weighing over , to allow them to pull heavier trains. In July 2010, EF 30065 and EF 30128 were assessed for a return to service, having been held in open storage (along with EF 30186) for many years at Palmerston North as surplus to operational requirements. It is hoped that reinstating the locomotives will help to ease pressure on the working fleet, especially as locomotives are currently regularly out of service for maintenance, modification and re-branding. EF 30065 was placed on second-hand bogies and moved to Hutt Workshops in August 2010 to begin the assessment, followed by EF 30186 in September. EF 30128 followed to Wellington in April 2011. It is anticipated that one of the locomotives will serve as a parts source to return the other two to service and the remaining hulk scrapped. All EFs went through a minor upgrade to ensure reliability before a full overhaul is carried out. The upgrade included replacing the obsolete Locolog event recorder and vigilance system with the latest generation system known as Tranzlog. This system also includes fault recording. EF 30013 was fitted with a replacement air compressor as a trial during 2012, which all locomotives will now receive. The original compressor has become uneconomic to rebuild and is becoming increasingly difficult to keep functioning. These locomotives can be recognised by a new louver being fitted to 2B side of the locomotive. Withdrawal and disposal Seven EF class locomotives have been withdrawn from service: EFs 30036 and 30088 were withdrawn from service following a derailment caused by a washout at Oio (north of Raurimu) on 7 August 1991 that also killed the locomotive engineer. After recovery from the site, the two heavily damaged locomotives were stored at Hutt Workshops until the decision was made that