Cable routes and installation: ducts, burial, aerial, indoor

A fibre link's loss budget is decided on paper; whether the installed plant meets it is decided by how the cable got from A to B — the tension it was pulled with, the radius it was bent to, the slack left in closures, the fire rating chosen for the riser, the depth of the trench. This page covers outdoor and indoor installation methods, the mechanical limits that protect the glass, planning and permits, labelling and documentation, and the installation mistakes that show up years later as unexplained loss.

Outdoor installation methods

Method	How	Cable type	Typical use	Watch
Duct / conduit	HDPE ducts (32–110 mm) with subducts; cable pulled with winch and lubricant or blown (jetted) with compressed air	loose-tube, dielectric or armoured	urban, campus, along roads	pulling tension limit (typ. 1 000–2 700 N), fill ratio ≤ 40 %, duct integrity (mandrel test), water
Microduct / air-blown fibre	5–16 mm microducts in a bundle; micro-cables (200 µm fibres) blown 1–2 km per shot	micro-cable, 12–432 f	FTTH, metro, incremental fibre adds	blowing speed/pressure, duct cleanliness, low-friction cable
Direct burial	trench or plough at 0.6–1.2 m; warning tape and marker posts	armoured (steel or FRP), rodent-protected	rural, long routes	depth by soil and frost line, backfill without stones, locate services first
Microtrenching	2–4 cm slot 20–40 cm deep in road surface	micro-cable in microduct	dense urban FTTH	pavement damage, shallow depth risk
Aerial, lashed	cable lashed to a steel messenger strand between poles	standard loose-tube	rural, where poles exist	sag and tension, ice and wind loading, clearance
Aerial, self-supporting (ADSS)	all-dielectric cable with aramid strength member	ADSS	power-line rights of way, spans 100–1 000 m	electric field tracking near HV, hardware, vibration dampers
Figure-8 / drop	integrated messenger; FTTH drops	figure-8, flat drop	last span to buildings	span ≤ 80 m, service loops
OPGW / wrap	fibre inside the ground wire or wrapped on it	OPGW, OPPC	HV transmission lines	utility procedures
Submarine	armoured, repeatered; ship-laid	submarine	sea crossings	separate discipline

Indoor pathways

Pathway	Cable rating	Notes
Plenum (air-handling spaces)	OFNP / OFCP (NEC), or LSZH per IEC 60332-3 + low smoke in the EU	plenum cable is mandatory where air circulates
Riser (vertical shafts)	OFNR / OFCR	riser-rated or better; firestop every floor penetration
General purpose / horizontal	OFN / OFC	trays, conduits, J-hooks every 1.5 m
Under-floor / overhead in DC	LSZH; MPO trunks with pulling eyes	separate fibre trays from heavy copper; bend-radius guides at drops
Outdoor → indoor transition	outdoor cable ≤ 15 m indoors, or indoor/outdoor rated, or transition splice in the entrance facility	gel-filled outdoor cables are not flame-rated
Between buildings	duct with indoor/outdoor cable, or outdoor cable to entrance facility	ground armour, lightning consideration

Mechanical limits that protect the glass

Parameter	Limit	Why
Pulling tension	cable datasheet (600 N for small indoor, 1 000–2 700 N loose tube, higher for armoured); never pull on fibres, only on strength member via grip/swivel	exceeded tension = fibre strain, microcracks, future breaks
Bend radius during installation	≥ 20 × cable diameter (under tension)	kinks and stress at sheaves
Bend radius installed, no tension	≥ 10 × cable diameter; cords ≥ 30 mm (SMF), G.657 cords 15/7.5 mm	macrobend loss (Light in fibre)
Crush	datasheet (typ. 1 000–2 000 N/10 cm)	vehicles over surface-laid cable, heavy cable on top in trays
Vertical rise	max unsupported vertical run per datasheet (typ. 500 m+ for loose tube with proper clamping)	cable weight loads fibres
Temperature	installation −10…+50 °C typical; operation −40…+70	cold cable is stiff and brittle; gel stiffens
Slack	10–20 m at each closure (both directions), 3–5 m at building entries, 1–2 m in panels	re-splicing and re-routing without new cable
Cable ties	hook-and-loop, never tight nylon ties on fibre	ties are the #1 cause of macrobends in racks

Route planning

Survey: existing ducts and their occupancy, poles and their loading, soil, crossings (roads, rivers, rail), other utilities.
Permits and rights of way: road authority, landowners, pole attachment agreements, railway/pipeline crossings.
Diversity: separate physical routes for protection paths (Topologies).
Fibre count and cable type per segment; splice-point and closure locations (manholes, poles, cabinets) at 2–4 km spacing on trunks.
Loss budget per link from the route: length, splices, connectors (Link budget engineering).
Documentation plan: GIS layer, cable/fibre numbering, labelling scheme (TIA-606), test plan.
Safety plan: traffic management, confined spaces, working at height, laser safety (Safety & handling).

Splice points and closures

Item	Practice
Closure placement	manhole, pole, cabinet; accessible, above flood level where possible
Type	dome (butt) for trunks, inline for mid-span, wall boxes indoors (Passive plant)
Sealing	heat-shrink or mechanical (gel) seals; IP68; re-enterable
Grounding	armour and messenger bonded and grounded at closures and building entries
Fibre organisation	trays by tube colour, splice protectors, bend guides; every fibre labelled
Records	splice diagram per closure with fibre-to-fibre mapping, photos before closing

Splicing technique: Splicing and termination.

Labelling and documentation

Item	Standard practice
Cable ID	unique per cable, printed on jacket at entries and closures
Fibre numbering	tube colour + fibre colour → sequential number (1–144…) per TIA-598
Panel ports	rack/panel/port with far-end reference
Cords	both ends labelled with far-end position (Port naming & LEDs)
As-built	GIS route with chainage, closure locations, cable types and lengths, splice diagrams
Test records	OTDR traces and loss per fibre at commissioning (Testing & measurement)
Change log	every re-splice, re-route, added splitter

Acceptance after installation

Visual: closures sealed, slack stored, labels present, bend radii respected.
Continuity and polarity of every fibre (VFL or OTDR).
Bidirectional OTDR of every fibre at 1310/1550 (and 1625 for bends); splice loss ≤ 0.1 dB, no reflective events above design.
Insertion loss of every link at working wavelengths vs budget.
Documentation handed over and matched to the field.

Installation mistakes that surface later

Mistake	Later symptom
Pulled by fibres / over tension	random breaks months later; high loss increasing with time
Tight nylon ties, sharp trays	wavelength-dependent loss, worse at 1550/1625 (Plant faults)
No slack	cannot re-splice after a dig-up without a new cable section
Outdoor gel cable through the building	fire-code violation; gel migration into panels
Unsealed closure	water, loss rising at 1383/1550, freeze damage
Mixed 50/62.5 µm or SMF/MMF patching	2–4 dB or no link (Physical mismatches)
No labels, no as-built	hours per incident; wrong fibre cut
Shared trench for "diverse" paths	both paths cut together

In CodingBox

Installation quality shows up in DDM: a link whose Rx power sits 2 dB below the design value on day one has an installation problem, not a module problem. Recording each module's Tx and Rx at commissioning in CodingBox gives the baseline that separates the two (DDM in the app, Rx power & budget).

Choosing the cable for the route — designs, armour, fire ratings, tensile and crush values: Cable construction; recording what was installed — identifiers, labels, splice schedules, as-built and test archives: Documentation & labelling.