London underground cabling

[ban-all-sheds]

Anybody familiar with/worked on stuff on the Underground?

Just curious - I keep seeing trackside cables on trays which have been fashioned into a square loop - I guess about 1m wide. i.e. the cables run along, then go round 360° and carry on in the same direction, same height etc.

Wondered why.

 

[plugwash]

I wonder if it's to allow some slack for alterations/repairs.

 

[ban-all-sheds]

I wondered that too

 

[Chri5]

I did 2 years on the LUL Central line.

Orange and purple are comms and fibre feeds. Nearly all cabling will have make off loops along the run.

The idea being that it gives half a chance of a quick splice / remake would a section get stolen, or busted by a train crash or fire.

Most cabling is well documented with routes and hanger (to use) detail as part of the works order.

 

[JohnW2]

I wonder if it's to allow some slack for alterations/repairs.

That sounds credible. When, more moons ago that I care to remember, I was in the Royal Signals Section of my school's cadet corps, when we were running 'telephone' wires through fields and forests etc., whenever the wire crossed a path (buried), stream (submerged) or whatever, we were required to coil up enough on one side to be able to re-do the crossing if it became necessary.

Kind Regards, John

 

[davelx]

I wonder if it's to allow some slack for alterations/repairs.

That sounds credible. When, more moons ago that I care to remember, I was in the Royal Signals Section of my school's cadet corps, when we were running 'telephone' wires through fields and forests etc., whenever the wire crossed a path (buried), stream (submerged) or whatever, we were required to coil up enough on one side to be able to re-do the crossing if it became necessary.

Kind Regards, John

Ah, D10 cable - that brings back memories. Vicious stuff, always stabbing myself with the steel cores. Remember the canvas packs with centre feed?

D3 wasn't much better!

 

[ericmark]

I remember on one job we had to make pig tail loops as the cable connected to each item we were told so cable would not be stressed by vibration.

However we were also required to make everything look neat so the loop was tie wrapped so it was solid and clearly would absorb no vibration.

I think there are many things done because it has always been done that way with very little thought as to why it's done and the original reason has gone.

 

[Simon35]

I remember on one job we had to make pig tail loops as the cable connected to each item we were told so cable would not be stressed by vibration.

However we were also required to make everything look neat so the loop was tie wrapped so it was solid and clearly would absorb no vibration.

I think there are many things done because it has always been done that way with very little thought as to why it's done and the original reason has gone.

On industrial installs I would usually expect the electrician to pigtail the cable, so if needs be the motor/sensor/whatever can be removed without disconnection. Unless the cable size doesnt permit of course.

 

[JohnW2]

Ah, D10 cable - that brings back memories. Vicious stuff, always stabbing myself with the steel cores. Remember the canvas packs with centre feed?

Indeed - and what about the 'self-soldering joints' - a sort-of cross between a hollow (non-safety) match and a sparkler, filled with solder and flux?!!

Kind Regards, John

 

[IJWS15]

I did 2 years on the LUL Central line.

Orange and purple are comms and fibre feeds. Nearly all cabling will have make off loops along the run.

The idea being that it gives half a chance of a quick splice / remake would a section get stolen, or busted by a train crash or fire.

Most cabling is well documented with routes and hanger (to use) detail as part of the works order.

Purple is the LSH stuff that came in in the 90s following KinsX. First contract we had that used it was signed before the stuff was released to the marker. Fibre cable can be any colour, normally black like the Model T Ford.

 

[bernardgreen]

Those are fibre optic cables on 'remake' frames. It is not just about providing slack in case a repair is needed. In order to achieve good joints in an optical cable the fibre needs to ideally be the same diameter on both sides of the splice. However, the thickness of a fibre does vary in the length and of course with a multicore the thicknesses of individual cores will not be guaranteed to be the same at any given point. Within the joint housing, allowance is made for slack to be coiled either side of each individual splice, each splice and coiled slack held in its own enclosure called a tray. Thus there is some flexibility in where each splice is made within a cable and the 'remake' frame is a means of neatly tidying up the slack.

In the event of a copper cable being damaged by train derailment, blown out traction section switch, exploded 11kV or 22kV main or some equally destructive disaster, standard practice would be to run in a new length of cable and 'closure' joints to bypass the area of damage. I expect the same would apply to the fibre optic cables in most cases but it is 10 years since I retired and I have no idea how the technology and working practices have moved on in that time.

There are also coiled pipes for the compressed air that operates points and train stops. ( I assume they are still pneumatic )

 

[Chri5]

IJWS15

On the central all fibre was orange