How to Choose a Fibre Optic Cable: ADSS, Loose Tube, and Ribbon Explained

A 72 fibre loose tube cable and a 72 fibre ADSS cable can carry exactly the same glass, and still be completely different products. One is built to be pulled through a duct, the other to hang between poles and hold its own weight in a storm. So the choice is almost never about the fibre. It is about the construction, the jacket and the environment the cable has to survive.

This guide gives you the answer first, then the reasoning. Skip to whichever section you came for.

Which Fibre Cable Should You Choose?

Work through it in this order:

1. Fibre grade. Singlemode G.652.D for anything that leaves a building or runs for kilometres. A bend tolerant G.657 grade for tight drops and building risers. Laser optimised multimode, OM3 or OM4, only for short links inside a data centre or campus.
2. Fibre count. The tightest standard count that covers your working fibres plus real spares, stepping through 12, 24, 48, 72, 96, 144 and 288.
3. Installation method and environment. This is what actually picks the construction. The table below is the whole decision on one screen.

If you would rather not work through a catalogue by hand, the Fibre Optic Cable Selector filters real manufacturer cables against exactly these constraints, fibre count, installation method, armour, sheath, temperature and duct clearance, and for aerial routes it checks your pole span against the datasheet sag and tension table. The rest of this guide explains the reasoning behind each column.

Types of Fibre Optic Cable

There are six constructions you will meet in outside plant, and the difference between them is mechanical, not optical. The same fibre can go into most of them.

Loose Tube Cable

The workhorse of outside plant. Fibres sit loosely inside gel filled or dry buffer tubes, with room to move so the cable can expand, contract and bend without straining the glass. The tubes are stranded around a central strength member and jacketed, often with armour. Loose tube handles wide temperature swings, takes high fibre counts, and suits duct, direct buried and lashed aerial routes. When someone says a generic outside plant cable, they usually mean this.

ADSS Cable

All Dielectric Self Supporting cable is built to hang in the air between poles and carry its own weight with no messenger wire. It contains no metal, which is the point, because it is routinely strung on the same structures as high voltage power lines. The load is carried by aramid or glass yarn between an inner and outer sheath. ADSS is specified by span rather than pulling tension, and it is covered in full below.

Ribbon Cable

Ribbon bonds fibres side by side into flat ribbons, then stacks them into the core. It packs the highest fibre count into the smallest cable, which is why it dominates data centre feeds and dense backbone routes. It also splices fastest, because a mass fusion splicer joins a whole ribbon of twelve fibres at once. The trade off is that it needs mass fusion tooling, so it earns its place on high count routes rather than small builds.

Micro Core and Blown Fibre

A slimmed down loose tube design made to be air blown into pre installed micro duct rather than winched in. It lets an operator lay cheap empty micro duct now and blow fibre in later, adding or upgrading cables without re trenching. It suits congested duct banks and phased builds where duct space and future flexibility matter most.

Tight Buffered Cable

Each fibre carries its own thick buffer bonded to the glass, so it can be connectorised without a breakout kit. That makes tight buffered the natural choice for indoor, riser and patch work where cables are terminated by hand in tight spaces. It is less suited to long external routes, because the buffer couples temperature and stress more directly into the fibre than a loose tube does.

Armoured Cable

Armour is a layer added to a loose tube or micro core cable, not a construction of its own. Corrugated steel tape resists rodents and adds crush strength for direct burial, at the cost of making the cable metallic and heavier. Where a metal free cable is required, a dielectric equivalent uses a hard nylon or fibreglass layer and a rodent or termite resistant jacket instead of steel.

ADSS vs Loose Tube Fibre Cable

This is the comparison people search for most, because the two look interchangeable on a fibre count and are not. They can carry the same G.652.D glass, but they are selected against different limits.

The rule is short. Choose ADSS when the cable has to hang between poles and support itself. Choose loose tube for everything that is pulled through duct, buried in the ground, or lashed to a separate messenger wire. Pick the wrong one for an aerial span and a loose tube cable, which cannot carry its own weight, will simply fail.

Singlemode vs Multimode Fibre

The fibre core fixes both the distance a link can reach and the optics you buy for it.

Singlemode has a core around 9 microns. Light travels in effectively one path, so there is no modal dispersion and attenuation is low, near 0.35 dB per kilometre at 1310 nm and near 0.20 dB per kilometre at 1550 nm. It is the default for outside plant and anything measured in kilometres. The two grades you meet most are G.652.D, the standard grade for duct, buried and aerial cables, and G.657.A1 or A2, a bend tolerant grade that is compatible with G.652.D but survives the tight bends of drops and risers.

Multimode has a much larger core, 50 microns for modern grades and 62.5 for legacy OM1. Many paths travel at once, which makes cheap optics easy but limits reach. OM3 and OM4 carry 10, 40 and 100 Gigabit Ethernet over tens to a few hundred metres, so multimode belongs inside a building, a data centre or a single campus.

The practical test: if the run leaves the building or is measured in kilometres, it is singlemode. If it stays indoors and is measured in tens of metres at multi gigabit speeds, multimode can be the cheaper system once you count the optics.

Aerial Fibre Cable: Span, Sag and Tension

Aerial ADSS is the choice where the mechanics bite hardest, so it is worth working through.

Take a rural route with poles 450 metres apart that needs a 96 fibre aerial cable. The fibre grade is not in question, it is standard G.652.D. The real question is whether a given ADSS cable can span 450 metres without sagging into the traffic below or straining the fibres over its life.

The physics. The sag at mid span is roughly w × S² / (8 × T), where w is the cable weight per metre including any wind or ice load, S is the span, and T is the horizontal tension. A 96 fibre ADSS cable at about 0.18 kilograms per metre, strung at an everyday tension of 6000 newtons, sags around 7.5 metres over a 450 metre span. Because the sag grows with the square of the span, a longer span droops far faster than you might expect.

Why you read the table, not the formula. That equation is the idea, but it is not how you size a real cable, because the true behaviour depends on the cable’s stiffness, its temperature, and the wind and ice at the site. Every ADSS datasheet publishes a sag and tension table covering an everyday case and several severe wind and ice cases, each with a rated span, sag, tension and cable strain. The strain is the number that protects the fibre, because the glass has a maximum long term strain it can tolerate, typically well under half a percent, before its life is compromised. A span that looks comfortable on a calm day can push the fibre past that limit in a storm.

Select against the datasheet. Filter to aerial cables and enter the span. Short and mid span ADSS products fail on rating. A long span product passes, and its table tells you the tension the poles must anchor and the strain the fibres see at the worst case. The Fibre Optic Cable Selector normalises those tables from real datasheets and matches your span against the worst rated condition, warning you when the span is within ten percent of the longest the sheet covers.

Duct, Direct Buried and In Building Cable

Aerial is one of four ways a cable goes in, and each drives different requirements.

Duct and sub duct. The duct protects the cable, so the questions become the pulling tension during installation and the clearance inside the duct. Exceeding the maximum pulling tension during the haul is a common way to damage fibres before the link carries traffic. Clearance matters just as much, because a cable that fits a bare duct may not fit once one or two cables already occupy it. When space is tight, a micro core cable blown into micro duct often beats a larger armoured cable that will not fit.

Direct buried. Ploughing or trenching a cable straight into the ground removes the duct’s protection, so the cable resists crush from backfill and traffic, moisture, and animals on its own. Steel tape armour handles rodents and crush, and a hard nylon jacket is the usual answer to termites in the north. Choosing an unarmoured cable for a buried route is one of the more expensive mistakes in outside plant, because the repair means digging the trench up again.

In building. Inside a building fire safety usually outranks mechanical strength. A low smoke zero halogen jacket, marked LSZH, is required for risers and occupied spaces because it does not release dense toxic smoke or corrosive gases when it burns. Tight buffered and bend tolerant G.657 constructions suit the tight bends and hand termination of risers. An outdoor gel filled cable, or a non LSZH jacket, will usually fail a fire inspection and must transition at the building entry.

How Many Fibres Do You Need?

The commonest ordering error is the fibre count, not the construction. Under provision, and splicing in a second cable later costs far more than the spare fibres would have. Over provision, ordering a 144 fibre cable for a 24 fibre job because bigger felt safer, and you pay for a heavier cable that is harder to pull, larger in the duct and dearer per metre, with most fibres never lit. The right count is the tightest standard size that covers your working fibres plus a genuine spare allowance.

Standards for Fibre Optic Cable Selection

A handful of standards govern the choice, and it helps to know which answers which question:

• IEC 60793 specifies the optical fibre and its grades.
• IEC 60794 specifies the cable, its constructions and its mechanical and environmental tests.
• ITU-T G.652 and G.657 define the singlemode grades, standard and bend tolerant.
• AS/CA S008 and AS 1049 cover customer and network cabling in the Australian context.
• AS/NZS 11801 and TIA-598 cover generic cabling and the fibre colour code, which runs blue, orange, green, brown, slate, white, red, black, yellow, violet, rose and aqua for the first twelve fibres.

Selecting the Cable vs Calculating the Loss Budget

Keep these two steps separate, because they use different data. An outside plant datasheet publishes mechanical and environmental figures, weight, diameter, tension, bend radius and temperature, and usually not the attenuation, which belongs to the fibre grade. So you select the cable on its mechanical and environmental fit, then calculate the loss budget separately from the attenuation of the grade you chose. Our guide on what a fibre optic loss budget is and how to calculate optical power and margin covers that step, and the PON Optical Budget and Connector and Splice Loss calculators do the maths.

Common Cable Selection Mistakes

• A non ADSS cable on a self supporting aerial span. Loose tube and micro core cannot carry their own weight between poles and need a messenger wire to lash to.
• Ignoring the worst case wind and ice on an aerial route. The severe condition, not the calm day, sets the choice.
• A gel filled or non LSZH cable run into a building. It usually fails a fire inspection, so it has to transition at the entry.
• An unarmoured cable direct buried. Rodents, termites and crush loads make this a dig it up again decision.
• Sizing the fibre count by feel. Under ordering means a second cable later, and over ordering means a heavier, dearer cable you never fully use.

Frequently Asked Questions

What is the difference between loose tube and ADSS cable? Loose tube is a general construction for duct, buried and lashed aerial routes, selected by pulling tension. ADSS is a self supporting aerial construction with no metal, selected by pole span. They can carry the same fibre.

Singlemode or multimode for an outside plant link? Almost always singlemode, normally G.652.D. Multimode only makes sense on short indoor, data centre or campus links where the cheaper optics dominate the cost.

What fibre grade suits a building riser or drop cable? A bend tolerant G.657.A1 or A2 singlemode grade. It is compatible with the G.652.D outside and survives the tight bends of a riser or drop.

How do I know if an ADSS cable will handle my pole span? Check the manufacturer’s sag and tension table. If it covers your span at its worst wind and ice condition without exceeding the fibre strain limit, the cable suits. Within ten percent of the longest rated span, confirm with a full stringing calculation.

Does a fibre cable datasheet give me the optical loss? Usually not. It gives mechanical and environmental data. The attenuation comes from the fibre grade, in a separate loss budget calculation.

How much spare fibre count should I allow? Size for the working fibres, add a real allowance for growth and breakages, and round up to the next standard count. Avoid the reflex of ordering the largest count on the shelf.

The Short Version

Fix the fibre grade so the link works, let the installation method and environment choose the construction, then confirm the mechanical numbers, the span for aerial, the tension and clearance for duct, the armour and fire rating everywhere else, against the datasheet rather than a rule of thumb. When you are ready to choose against real cables, the Fibre Optic Cable Selector ranks a manufacturer catalogue on all of those constraints at once and shows you why each cable passed or failed.