Class 303s, general questions.?

Question

How did the jumper cables work?

If one unit broke down, could it be kept in service by joining it to another 303?

If a 303 broke down and there was a 314/318 or a 320 behind it, how does the driver of the following train know what signals or platform position of the train he is pushing?

Why was the 3 or 4.the maximum nuber of units that could be run as one set?

Answer 1

The Jumper cables on Cl303 multiple unit's work in the same way as the jumper cables between each coach (in a 3 car set), The jumpers that are visible on the front of the unit are just "Plug in" versions of the hard wired connections between the coaches in the formation of a unit.

If a 303 did fail, then yes, it could be kept in service by coupling it in "Multiple" to another 303, but only if the fault on the failed unit was not a "Safety Critical Defect" i.e. a brake fault or door interlocking etc.

303's cannot be coupled to 314/318 or 320 EMU's as there draw gear (Buffers and hooks) are incompatible as 314/318 and 320's do not carry hooks or buffers. Also there electrical control systems are incompatible, so it is fair to say that none of these units could assist a 303.

If you are in the position of having to propel (Push) a failed unit, if the control systems are compatible then you may still drive from the leading cab, but, if the train to be pushed is a total failure, then it can be pushed at a reduced speed (5mph) only as far as the next place where it can be left clear of the mainline. If this happened then there would have to be a driver in the leading cab of the failed train to relay signalling information back to the driver of the propelling train. In this situation it is more likely that the train would be towed rather than pushed.

Last one now. Unit's are limited to how many can work together by the controls in there cabs for controls such as door opening, as there cannot be an infinate number of "Door open" switches etc...........

Answer 2

The 314/318 or a 320 all have 'tightlock' autocouplers where the air and electrical connections are made though the coupler (electric connections are under a movable cover below the mechanism - air is though the block above the mechanism with sealing O-rings) - 303s have manual 'buckeye' couplers, with the jumper cables used to make electrical connections and air pipes mounted on the buffer beam for brake connections

Answer 3

I think the maximum number of units allowed to run as one set has something to do with the current limit index.  It's all about how much power each unit draws from the electric supply be it overhead lines or 3rd rail.  In my neck of the woods, our network of rail permits a maximum CLI of 16.  Each unit of our local trains has a CLI of 4, so the maximum length of a train would be 4 units (or 16 coaches).  If for any reason more than the maximum number of units have to travel as a set, then some of the traction motors have to be isolated.

Answer 4

I really MUST say what a treat it is to see some interesting and intelligent answers to an equally interesting question (and NO, I'm not just writing this for a couple of meaningless points!). The BEST part of it is that there are no large chunks of rubbish which have been cut and pasted from a certain dubious source on the pretext of being "answers".

Oh if only ALL answers were of the same quality!