New tube for London stock

Traction voltage bus lines have an interesting history... I would recommend reading the Southern Railway rule book appendix for Electric trains c.1940s.

So we have a multiple unit, this will have a number of shoe beam pick ups and a number of motor cars. If we connect all the shoe beams together with a bus we make it easy to get power to the motors... This then creates a problem say we have a four car EMU, the outer shoe beams will be 4 cars apart. If we can join several EMUs together to create a 12 COR, the outer shoe beams are even further apart.

So an electrified line will have different supplies with dead sections between them, with a 4 car unit with a continuous traction bus we would need a long dead section. Now things get very dangerous, what happens if our EMU bridges between two different electrified sections? What happens if one section has been turned off due to an accident? The EMU bus line can then end up carrying and enormous current as several trains on the dead section could still be trying to draw current and all this current is having to go through the EMU bus. This has been the cause of some major fires as the bus wire ends up carrying far more current that it is designed to and gets very hot and sets fire to the wooden framed EMU!

We have another safety aspect, those that have a LU depot pass will have been told all about the depot jumpers... Having a plug carrying 420V / 630V, 650V or 750V is rather dangerous. We need to have a safe method of working to attach and detach jumpers between cars. This of course can be done in the depot, but in the past this could be done when units were split or joined while in service. The latter was banned because of safety rules, but if a safe (automatic) method is devised perhaps as part of an automatic coupler the problem is solved.