2004 Point CT

[PJW]

Thanks for your detailed explanation. I am glad to communicate with you all here. It is truely a useful forum~

But in Mod3 2004, Signal 121,123, 125, 127 must not be the same type... Is 123 a control signal?Emm... I am waiting for further information, maybe from another Peter~ Still thank you~

Beware that there are different signalling practices in use at different localities and indeed periods; that is why a candidate should always declare the practices to which they are working

203 Item 1
136 is a shunt signal- modern practice on NR is to give shunt signals overlaps, but that has not traditionally been the case and hence only a minority of the installations in the UK feature this. Therefore many are familiar with signalling they have worked upon and adopt these within IRSE exam. Indeed I would generally advise that the IRSE examiners are in fact more familiar with the practices of some years ago and that generally I'd advise working to a practice that doesn't give shunt routes overlaps (simpler and easier, also demonstrates more "difference" between the various classes of routes), but it is the candidate's choice. Sometimes the layout given suggests that shunts should be given overlaps, sometimes there is no hint, but in this one there are no overlap joints beyond 115, 129, 136 so certainly indicative that NOT expecting this practice. If they showed an overlap but it was your practice not to provide then state that as an assumption; conversely if they didn't show and you needed to have one then declare that as an assumption.
So if you are providing overlaps then you are right that 203 would be trailing points beyond 116/118 (or facing / conditional trailing points in swinging overlap beyond 114) and you would need to show relevant locking.
There are overlap symbols (certainly relevant for M/W moves up to 114) at the joints BF/BH and EB/EC and so I would assume that there are two possibilities for full overlap, though there is also a potential third possibility via 203R and 201R- there is I some little advantage in providing such (allows 142A(W) for example) but "bath-tub" swinging overlaps are complex for locking and in the limited time available in IRSE Exam it makes it desirable to ignore as on a "marks per minute" basis it is simply not worth it unless you are a genius and very quick and would otherwise finish the paper with time remaining!
Indeed unless a candidate is reasonably strong then I wouldn't advise attempting much for swinging overlaps at all- certainly where there are other weaknesses in people's attempts I concentrate on feedback re these rather than distract/ confuse / demoralise; hence don't assume that even a commented CT example is "perfect". The better the quality of the submitted work, the deeper the level of my comments.

203 Item 2
As above, yes it is.
To NR practice, facing points in the simplest swinging overlaps are not called, not are they locked.
However in almost all cases there are more track circuits to be included in the aspect of the signal if the points are in one lie rather than the other; hence in 142A(M) there will be an entries such as: (BH or 203N) and (EC or 203R). In the first case BH itself deadlocks 203 so there is no problem; if 203 started R then 203 would be locked if BH were occupied. However in the other case there would be problem: if 203 started R and EC were occupied then we would not want 203 to be able to go N or else 142 would be replaced to danger, yet EC would not normally lock 203. In these circumstances we need to ensure that it DOES lock 203 and therefore we have to provide a special