Level 2 specification
NR/L2/TEL/30160
Specification for Loose-Tube Optical Fibre Network Design
Issue 5, 05 September 2026 · Fibre design
What the standard is for: the principles behind adding to or changing NR's existing loose-tube fibre network so capacity is protected. Issue 5 note: High Count Fibre Cable (HCFC) is now the default for new trunk cable under NR/L1/TEL/30102 — new trunk fibre is designed to NR/L2/TEL/31200; 30160 is for upkeep of, and designs interfacing with, existing loose-tube assets
Clause map — what each clause deals with
| 1 | Purpose | What the standard is for: the principles behind adding to or changing NR's existing loose-tube fibre network so capacity is protected. Issue 5 note: High Count Fibre Cable (HCFC) is now the default for new trunk cable under NR/L1/TEL/30102 — new trunk fibre is designed to NR/L2/TEL/31200; 30160 is for upkeep of, and designs interfacing with, existing loose-tube assets |
| 2 | Scope | What it covers: cabling parameters, permissible loss and configuration of the loose-tube fibre network |
| 3 | Abbreviations | Abbreviations used in the standard (ADM, BTS, CWDM/DWDM, OTDR, ZHLS and so on) |
| 4 | Definitions | Definitions: access node, core node, spur, spliceless joint and the other terms the standard relies on |
| 5.1 | General principles | How NR's fibre is organised overall: FTN, FTNx and the separate signalling/electrical networks that interface with them |
| 5.2 | FTN core nodes | What an FTN core node is and its role in the transmission rings |
| 5.3 | FTN/FTNx access nodes | What FTN/FTNx access nodes do and how they are classed |
| 5.4 | FTNx core nodes | FTNx core nodes and the DWDM equipment they house |
| 5.5 | FTNx in-line amplifier sites | FTNx in-line amplifier sites and where they are usually accommodated |
| 5.6 | FTNx sub access sites | FTNx sub-access sites — the small lineside locations that hang off the access layer |
| 6.1 | General matters | Why a cable route survey comes first and what the survey has to establish |
| 6.1.1 | Centre to centre cable lengths | How centre-to-centre cable lengths are measured, the length allowances to add (joints, terminations, slack), and where spur cables may terminate |
| 6.2 | Joint locations | How joint locations are chosen — spacing, drum handling, access, theft and vandalism considerations |
| 6.3 | Sheath gaps | Why and where the metallic sheath is gapped; points to NR/L3/TEL/30162 for the detail |
| 6.4 | FTN core node sites | Siting of FTN core nodes and the diverse cabling they need |
| 6.5 | Access node sites | Where access nodes are housed and how a single spur cable connects them to the main cable — spur fibre count and routing |
| 6.6 | FTNx core node sites | Siting of FTNx core nodes relative to FTN core nodes |
| 6.7 | FTNx in-line amplifier sites | Siting of in-line amplifier sites and the span lengths they support |
| 6.8.1 | General | The family of cable types that may be used (armoured, duct, ZHLS, DI-SAC, blown fibre) |
| 6.8.2 | PE sheathed steel tape armoured cables | PE-sheathed steel-tape armoured cable — the default lineside cable; how far it may run into a building, REB or equipment room before you must change to ZHLS (low smoke), and how to make the transition |
| 6.8.3 | PE sheathed non-armoured (duct) cables | Non-armoured duct cable — what it is for and where it is allowed |
| 6.8.4 | ZHLS sheathed steel tape armoured cables | ZHLS (low smoke zero halogen) cable — where it is mandatory: subsurface stations, long tunnels, and internal runs inside a building or REB beyond the entry allowance to the ODF |
| 6.8.5 | DI-SAC | DI-SAC heavily armoured cable for lines with no cable route |
| 6.8.6 | Blown fibre | Blown fibre — what it is and when it suits |
| 6.9 | Choice of cable type | The table that maps environment to cable type |
| 7.1 | General | Why cabling arrangements differ between core and access nodes (resilience) |
| 7.2 | Optical joint closures | What an optical joint closure has to provide — sealing, re-entry, protection |
| 7.3 | Optical terminations | What an optical termination (ODF, pigtails, patching) has to provide |
| 7.4 | FTN/FTNx Core nodes | Cabling at FTN/FTNx core nodes — diverse entries, how rings are brought in |
| 7.5 | FTN/FTNx access nodes | Cabling at FTN/FTNx access nodes, what to do when fibres are short, and the point-to-point WDM option |
| 7.6 | Spliceless joints | Spliceless joints — when they are used instead of a full splice and how the cable loop passes through |
| 7.7.1 | General | Adding a new access node (REB, cabinet, ATEH) to an existing cable — why spur cables are kept short, and the maximum spur length from a joint for the first spur and for a second resilience spur |
| 7.7.2 | Access nodes | Figure 3 — the three drawn scenarios (A, B, C) for connecting a new access node by spur depending on how far it sits from the nearest joint, and when a new joint pair is cut in instead |
| 7.7.3 | Core nodes | Inserting a new core node into an existing cable |
| 8.1 | General | General splicing requirements and the limit on how many splices a fibre may carry |
| 8.2 | Through joints | Through (straight) joints — fibre-to-fibre splicing by colour and tube, including DI-SAC to standard cable; Issue 5 makes the tube-handling rule mandatory (only tubes with fibres in use are stripped, uncut tubes coiled and stored in the closure) |
| 8.3 | Spur joints | Spur joints — connecting additional sites into a main cable (not limited to FTN access nodes since Issue 4), and the rule that a spur joint is never a distribution point or a spur-to-spur connection |
| 8.4 | Terminations at core nodes | How fibres are terminated at core nodes (pigtails or DWDM connectors) |
| 8.5 | Terminations at access nodes | Which fibres are pigtailed at an access node; points to 30161 for pigtails |
| 8.6 | Termination at ILA sites | Terminations at in-line amplifier sites and hard-splicing across a core node for DWDM |
| 9 | Allocation of fibres | Which fibres are allocated to what in a 24-fibre cable — the schedule that says which fibres get spliced or terminated at access and core nodes |
| 10.1 | General | Resilience — identifying and removing common-mode failures: separate building entries for diverse cables, one cable buried 600 mm in duct where separation is tight, cables at least 5 m apart |
| 11.1 | General | What the loss budget is and why it matters |
| 11.2 | Optical cable attenuation | Cable attenuation figures used in loss calculations |
| 11.3 | Splice loss | Splice loss — how it is measured and budgeted; points to NR/L3/TEL/30162 |
| 11.4 | Connector loss | Connector loss — what it includes |
| 11.5 | Calculation of expected section loss | How to calculate expected loss over a core-to-core section |
| 11.6 | Calculation of expected sub-section loss | How to calculate expected loss over a core-to-access or access-to-access sub-section |
| Appendix A | Fibre splicing drawings | Fibre splicing drawings — spurs into access nodes, with and without resilience, cable-type transitions |
| Appendix B | Node cabling drawings | Node cabling drawings — cable entries into housings, REBs and buildings |