Rail telecoms terms, at a glance

What each thing is, where the rules are, and what to order. In plain words.

• Access node

  A node on the FTN/FTNx network that connects local users and equipment into the fibre network, fed from the main cable by a spur.

• BOP / distribution cabinet

  A lineside box or cabinet where copper cables are terminated and pairs are broken out to local users (phones, signalling, equipment).

• Cable marker (Critchley)

  A durable ID label clipped onto a cable so it can be identified on site: cable ID, type and route.

• Cable troughing

  The concrete or composite channel units (with lids) laid along the lineside that the cables sit in. Sizes are named C/1/x, e.g. C/1/8, C/1/29, C/1/43.

• Core node

  A main node on the FTN/FTNx network where transmission rings meet. FTNx core nodes house the DWDM equipment.

• DI-SAC cable

  A heavily armoured, double-insulated fibre cable tough enough to lay on the ground without troughing.

• Induced voltage / immunisation

  Voltage that appears on lineside cables because they run parallel to traction power. Immunisation is the set of measures that keep it within safe limits.

• Joint bay

  A widened spot or pit off the main cable route where a cable joint closure sits, with room for the spare cable loop needed to make and re-make the joint.

• Manhole / cable chamber

  An underground box on a buried or ducted route where cables can be pulled through, turned, or jointed, with a cover at the surface.

• ODF (optical distribution frame)

  The frame or panel where fibre cables are terminated onto pigtails and connectors, so equipment can be patched in.

• Optical loss budget

  The expected total light loss over a fibre section: cable attenuation plus every splice and connector, compared against what the equipment can tolerate.

• Pigtail

  A short fibre tail with a factory-fitted connector on one end, spliced onto a cable fibre so it can plug into an ODF port.

• REB (relocatable equipment building)

  A small prefabricated building beside the line that houses telecoms and signalling equipment. In FTN terms it's often an access node site.

• Screening conductor

  An aluminium conductor run alongside telecoms cables and earthed at intervals, to reduce the voltage induced in them by AC traction.

• Sheath gap

  A deliberate break in a cable's metal layers (armour, metallic sheath, moisture barrier), made with a gapping kit, so the metal is not one long continuous conductor.

• Spliceless joint

  A joint position where the cable loops through the closure uncut, so fibres can be spliced into later without opening a new joint.

• SPT (signal post telephone)

  A telephone at a signal (or other lineside point) that lets a driver or track worker speak directly to the signaller.

• Spur cable

  A short cable branching off the main (trunk) fibre cable at a spur joint, to bring fibres into an access node such as an REB, cabinet or ATEH.

• Straight (through) joint

  A joint where two lengths of the same main cable are spliced together, fibre to fibre, by colour and tube.

• UTX (under-track crossing)

  A duct (or set of ducts) running under the tracks so cables can get from one side of the railway to the other without crossing over the rails.

• ZHLS cable

  Cable with a sheath that gives off little smoke and no halogen gases if it burns. ZHLS = zero halogen, low smoke.