I guess you are now referring to 148 points which I haven't looked at before, but yes it is certainly usual to provide flank protection for overlaps as well. There are circumstances when we don't but in this case setting and locking 148N for 494 routed to 484 would not be in anyway restrictive, so I would do it. Proving 148 detection though isn't so clear cut as a point detection failure would necessitate handsignalling from 494 and I think the modern view is that could be the greater risk. However in this particular case it isn't just flank- it is also trapping from shunting moves, so in this scenario I'd certainly detect, though this could perhaps be "at time of clearance only".
When you are talking about the route release for 494 what I understand you to mean is the "maintained locking after 484 used"; the route release would occur by EG clear after EG, EH occ provided that the route had been cancelled and aspect relay proved de-energised.
I am not quite sure whether you mean the locking imposed on
a) the points or
b) opposing routes (as not exactly the same).
I'll assume the former.
There is no value in listing any tracks beyond 484 as the tracks ought to be dead locked by EK anyway. Even with SSI there is no track bob protection for overlaps so including overlap route locking gives nothing extra over the dead track locking. The only time that you'd list is where there is a track beyond the signal that does not deadlock because the point end is in the second or subsequent track.
If you were thinking about the application of locking to an opposing move (not that there is one here as the Up Branch is uni directional), then yes you would list all the tracks within the overlap. However you wouldn't list both lies of the points in the overlap since any opposing route would require those points either the one way or the other; obviously only need to worry about the opposing move for the lie of the points which is compatible with the route. I suppose one could envisage a very odd layout where two routes opposite direction routes shared overlaps that had two parallel facing crossovers that acted as swinging overlaps for both; in that case one would have to put the opposing route locking entry in twice, once coupled with one lie of the swinging overlap points and the other overlap tracks listed in conjunction with the opposite point availability- I would really hope that this sort of thing wouldn't feature in the IRSE Exam (and suggest best avoided in real life too).
When you are talking about the route release for 494 what I understand you to mean is the "maintained locking after 484 used"; the route release would occur by EG clear after EG, EH occ provided that the route had been cancelled and aspect relay proved de-energised.
I am not quite sure whether you mean the locking imposed on
a) the points or
b) opposing routes (as not exactly the same).
I'll assume the former.
There is no value in listing any tracks beyond 484 as the tracks ought to be dead locked by EK anyway. Even with SSI there is no track bob protection for overlaps so including overlap route locking gives nothing extra over the dead track locking. The only time that you'd list is where there is a track beyond the signal that does not deadlock because the point end is in the second or subsequent track.
If you were thinking about the application of locking to an opposing move (not that there is one here as the Up Branch is uni directional), then yes you would list all the tracks within the overlap. However you wouldn't list both lies of the points in the overlap since any opposing route would require those points either the one way or the other; obviously only need to worry about the opposing move for the lie of the points which is compatible with the route. I suppose one could envisage a very odd layout where two routes opposite direction routes shared overlaps that had two parallel facing crossovers that acted as swinging overlaps for both; in that case one would have to put the opposing route locking entry in twice, once coupled with one lie of the swinging overlap points and the other overlap tracks listed in conjunction with the opposite point availability- I would really hope that this sort of thing wouldn't feature in the IRSE Exam (and suggest best avoided in real life too).
(01-09-2011, 12:58 PM)Tony Soprano Wrote: [The overlap for 484 goes beyond the crossing between 148A and 148B, so by the same logic that you have included the routes from 484, you also need to include the route from 494 up to 484 which requires the overlap.]
When an overlap extends through a set of points like 148 do you have to include these extra tracks as part of the route release for 494 signal i.e. EL track circuit?
So ignoring the swinging overlap
Route-----Tc's clear-------------Occ---t
494A(M) - EK, EL, (EG, EH, EJ..... EJ....20s)
Any secondly if we encounter a swinging O/L do we have to condition this into the release (something like)
Route-----Tc's clear-------------------------------------Occ---t
494A(M) - EK, {(EL or 146R),(CJ or 146N)}, (EG, EH, EJ..... EJ....20s)
Doesn't look right (as it probably isn't) but there doesn't seem to be any real benefit in including TC's (EL or CJ) passed the dead locking tracks. Could we not just release all point locking associated with 494 once EL becomes clear after having been occupied (which would presumably only happen after a SPAD?)
Think I've lost the plot on this a bit.
Cheers
PJW