text: Gaps in the third rail at complex pointwork or level crossings mean that a short electric locomotive such as Class 73 is liable to momentarily lose power when passing over. This results in noticeable arcing if the driver does not shut off power. However, this rarely affects the locomotives, except to burn out the carbon brush pick-up shoes more quickly. The issue of arcing only became a problem when some of these locomotives were altered to work "Gatwick Express" services using modified Mark 2 coaching stock and 500 hp Gatwick Luggage Vans (GLVs), as 750V power jumpers between locos or units were banned on BR designs (the last EMUs to have such jumpers were the Bulleid designed 4SUBs). The Class 73s therefore could not benefit from the pick-up shoes at the opposite end of the train on the GLV. As a result of removing the last bank of resistance on the Class 73 locos to make these trains accelerate more quickly, arcing increased. Therefore, to reduce damage to other electrical equipment from the increased arcing, these particular locomotives had "flash guards" fitted on their bogies around the shoes. Stories of Class 73s catching fire were greatly exaggerated.
  The Class 73 locomotives were very versatile, with dual cab controls; three brake systems (vacuum, air and EPB) as detailed below; a well-designed cab with good sighting that aided shunting; the ability to work fitted freight (fully braked) and unfitted freight (no train brakes) as well as locomotive-hauled coaching stock; the ability to work in multiple with blue star coded diesel locomotives; and the ability to operate in multiple with the Southern's diesel electric multiple unit fleet (Class 73/0) or its electric multiple unit fleet (Class 73/1).
  Power supply
  Unlike the previous Southern Region Class 70 and Class 71 electric locomotives, these did not have a booster to maintain traction power over gaps in the conductor rail. However, they could move forward onto an electrified section under diesel power.
  Diesel engine and generator
  The  English Electric 4SRKT Mk II diesel engine was less powerful, but more reliable than the  Paxman 6YJXL fitted to the later
  Class 74 electro-diesel locomotives.