London Underground - why so many cables?

[Bletchleyite]

Using Chiltern from Aylesbury it has occurred to me that when you pass Amersham onto the London Underground section there are supports carrying a huge number of exposed cables compared to the mainline. Why are there so many cables on London Underground? Is it an antiquated signalling system, or are unused ones simply never removed?

 

[pdeaves]

Using Chiltern from Aylesbury it has occurred to me that when you pass Amersham onto the London Underground section there are supports carrying a huge number of exposed cables compared to the mainline. Why are there so many cables on London Underground? Is it an antiquated signalling system, or are unused ones simply never removed?

Is it simply different infrastructure owner's policy? NR is (mainly) buried, LU is above ground.

 

[popeter45]

power cables?, both DC for the rails and AC for conversion to DC

 

[Beebman]

AIUI there's also pipes carrying pressurised air to the trainstops.

 

[swt_passenger]

Previously asked about a few years back, in the LU sub-forum here:

Trackside cables

Alongside tube tracks there are many cables in racks, usually neat but also ugly. You don’t see this in BR tracks. Do tube trains need more cabling or is it just hidden?

www.railforums.co.uk

 

[Tim M]

This answer only applies to signalling cables and trackside systems and is in three parts:

1. Mainline signalling with relay interlockings use trackside apparatus cases (normally called Location Cases, the grey cabinets by signals, points etc.), these contain power supplies, track circuit equipment and relays. The relays are connected to the nearest relay interlocking using multicore cables, standard sizes being 12, 19, 27, 37 and 48 cores. These cables are laid in concrete troughs or special troughs on bridges etc., short ‘tail’ cables run from the location cases to point machines, signal heads, track circuits etc. Power supply cables to serve location cases with 650V are laid in the same troughs.

2. Mainline signalling with Solid State Interlockings also use location cases with many relays being replaced by Tracksde Functional Modules and multicore cables replaced by smaller Data Link Cables, smaller cable troughs might be used. Otherwise power supplies and cables to signals, points etc. are the same as above.

3. On London Underground (and most mass transit railways around the world), the use of location cases is impractical. Older LU installations use smaller boxes on posts at the trackside in open areas housing track circuit equipment, air operated points using electrically operated trackside valves. Signals and other devices are direct fed from Station Equipment Rooms housing interlocking machines, relay interlockings or Computer Based Interlockings dependant on the age of the installation. This means that larger numbers of trackside cables are required. LU policy over the years required separate cables for each function, with very little use of multicore cables. That plus the fact that older cables were heavier duty, some being lead covered using co-axial configuration results in a greater number of cables, LU also preferring above ground cable routes and signal cable bridges means the trackside can look more cluttered than on Network Rail.

The above only touches the very basics of this subject, but hopefully will be of interest. Please don’t ask about overseas mainline signalling or we will be here all night!

 

[Annetts key]

For signalling, also the general policy on the U.K. mainland in most areas, is to keep the length of the tail cables feeding the trackside equipment (signals, AWS, point machines, track circuits, etc.) as short as practical. If there is insufficient space for a full size location cupboard, instead a “dis. box” may be provided where the tail cable(s) terminate and the functions are then carried in a larger capacity lineside cable to the “controlling” location cupboard. This arrangement is also used in busy station areas.

Telephone cables generally follow a similar arrangement, but the tail cables are often much, much longer, as modern practice is to have completely separate and independent telecom location cupboards.

 

[Hellzapoppin]

Also worth noting is that sunlight destroys modern cables, something which the LU doesn't really have a problem with, so cable hangers are a great way to contain them and are used in mainline tunnels.

 

[Annetts key]

Also worth noting is that sunlight destroys modern cables, something which the LU doesn't really have a problem with, so cable hangers are a great way to contain them and are used in mainline tunnels.

I believe that’s the reason that cables are normally black in colour. To help counter the UV light from the Sun.
PCP rubber cable (which signal cables are normally made from) is actually better off when not left in wet or damp conditions. So either a good SCT route, or cable hangers works well.