which would cause damage to the train as the pantograph ran off the end of the overhead line and struck the tunnel portal. On journeys from Moorgate traction power is maintained into Drayton Park for the rising gradient. Once the train is at a stand the driver selects AC traction and raises the pantograph. There is no system forcing the driver to change traction supplies beyond the customary 'PANS UP' sign at the end of the platform. If the driver forgets to change to AC no damage will occur to the train or any infrastructure; there will simply be a loss of power as the train runs out of third rail. Great Northern 313s were electrically limited to in DC mode, the maximum line speed on the Northern City Line. 313134 was named "City of London" at Moorgate on 9 December 2010 by Michael Bear, the Lord Mayor of London. The final Class 313 service on Great Northern was the 23:33 Hertford North to Moorgate on 30 September 2019. A final railtour, operating from London King's Cross to Royston (via Welwyn Garden City) and back (via Hertford North and Moorgate) was held on 23 October 2019 with units 313134 and 313064; the DMSO vehicle of 313064 was repainted in Network SouthEast livery. Departmental use Network Rail leased Beacon Rail-owned unit 313121 as a test vehicle for the European Rail Traffic Management System (ERTMS) installation on the Hertford Loop. The unit was repainted into Network Rail's yellow house colours and internally refurbished at Alstom's Wembley Intercity Depot, to include a new driving desk, technician's workstation, kitchen and toilet facilities, and the necessary ERTMS equipment. The work was completed in June 2013 and the unit was tested for the first time on Friday 5 July 2013 between Wembley and . It commenced testing on the Hertford Loop later that month. Following conclusion of the Hertford Loop works, it was placed in store at Eastleigh Works in May 2018. It will be returned to service when ERTMS is ready for testing on the Great Western Main Line. Replacement The Great Northern fleet has been replaced by new six-carriage Class 717s. The transition commenced on 25 March 2019, with the first two 717s entering service. The first of the Great Northern fleet withdrawn was 313026 in February 2019. It was the first dispatched for scrapping in April 2019. All 44 of the Great Northern