Bank Holiday Weekend

Quite simply, 'Plate Racks' are the changeover links used to switch between two different circuit configurations - though this is a real simplification of what is happening this weekend.

Within 4LM the process is known as the ‘cut-in’ commissioning (because Thales ‘cut in’ to the existing circuits), and even that’s simplifying it. This is a possession to commission signalling enabling works ready for eventual CBTC.
At the moment the points are controlled from the signal cabin or Interlocking Machine Room for the area, either driving the points directly or via a trackside kiosk. This is all very well, but we need to be able to control them from the new CBTC system. To do this, the point controls (the request for the points to move, the control of the locking valves on the points themselves, and the detection) has to be relocated from the existing equipment room to the new. There are a couple of ways to do this.

One involves changing over lots of cables every time there’s a testing session - but this is time consuming.
The other method, which is being used here, is to provide new point circuits, from the new equipment room, with some additional changeover circuitry in the room so that they can still be controlled from the old equipment room.

Plate racks are a set of changeover terminals which enable switching from one system to the other. They’ll be in the new equipment room, and when the time comes to start doing CTBC testing the links get moved from one position (the A-B position) to the other (the B-C). Once that shift’s testing is done, they get moved back to the A-B position. On the night of CBTC commissioning, they get ‘overed’ but don’t get ‘backed’.

However this needs a lot more than a few wires. All the points have to be completely re-cabled from the new equipment room, and the temporary circuits have to be provided to allow the old room to link to the new.

In some cases on the electric (Surelock) points, the existing control relays have to be changed to a new type, which means that the base the relay plugs into also needs to be changed. It’s not unusual for several hundred wire ends to be changed over in the closure. (For comparison purposes, this is about as many as we changed over when King’s Cross was resignalled in 2015, and we had a week to do that job!)
As you might imagine, this takes a lot of people and time. A recent commissioning at Northwood took 22 staff four hours, multiply that by the number of points at both Rickmansworth and Amersham (with two sites working in parallel) and you get an idea of the time and numbers involved. At Amersham it's additionally complicated because many of the Rail Gap Indicators and shunt signal route indicators are switched over the points being worked on - these too need to be re-wired to migrate them away from the points.


A set of plate racks (seen here with all the links in the A-B position) looks something like this - though there will be a few more than twelve needed for Amersham and Rickmansworth!:

Yes, every interlocking and also every boundary.

The approach following commissioning varies - generally the A terminal wiring should be removed. The B-C terminal wiring (B being the common and C the new configuration) can either be removed and replaced with through wiring or left in situ; the approach varies between projects - though we still have examples of 1970s plate racks still in circuit at some sites.

202 points out of commission at Harrow-on-the-Hill, Uxbridge trains must therefore use pfm.3, pfm.4 being used for Aldgate-HoH service.

Yes, and I understand that the issue is related to the moveable angles.

Northbound approach to station, northbound local to northbound fast after JB26b signal.
No reason available

Trains to Uxbridge were booked to use platform 3, as the terminating trains from Aldgate were taking time to detrain in platform 4 and then go slowly into the siding.
As 202 points are out of commission Uxbridge trains couldn’t cross from local to fast before Harrow and were therefore sent fast from Wembley Park.

The reason 202 points were out of commission was because of an issue with the moveable angles on this crossover.

I assume this was the case this weekend just gone, only the other way round i.e. Watford/Chesham/Amersham trains needing to use platform 3 but the points before being out of commission with anything that would have been Uxbridge bound detraining at Harrow platform 4

I thought the Harrow Hot weather plan was only in reference for fast trains north of harrow resulting in southbound fast trains using the local line and northbound fast trains using platform 1 at harrow. I then believe this was changed to mean that both northbound and southbound fast trains use the local lines north of harrow/south of moor park

I did not realise this affected trains South of harrow running as all stations/semi fast which need to use platform 3.

If there is an issue with the points which means that all stations trains to Watford/Amersham or Chesham are unable to to switch from local to fast (coming from Northwick Park), they are still able to use the points just after platform 4 to switch to the correct line right? This therefore wouldn't be an issue off peak as the entire northbound service would be fine using only platform 4 at Harrow.

If the points are that much of an issue, why not implement a new timetable making all non-Uxbridge trains semi-fast? I doubt the majority of met line users would complain about this. Additionally, for any fast trains running north of harrow, a timetable designed to accommodate fast trains using local would be very useful as it is an absolute pain in the *** when fast trains get stuck behind a local service because the timetable is designed assuming that such trains are using the fast lines.

TFL need to wake up and smell the coffee. The points south of harrow should have been re-layed at the same time the equivalent points on the southbound were redone (which now allow line speed running to switch between local and fast or vice versa from platform 5 and 6). As this was not done, the only way to sort this out is to simply bring back off peak fast and semi fast services, or at least semi fast services, which are very popular. I am pretty sure that Preston Road and Northwick park would be fine with 8tph in the off peak.

Off course I am sure that the more informed members of the forum can cast their opinions on my thoughts above