Fibre optic cable types are grouped by the fibre (single-mode OS2 or multimode OM1 to OM5), by construction (tight-buffered, loose tube, ribbon, distribution or breakout), by protection (armoured, tactical, aerial, direct burial), by jacket and fire rating (LSZH, riser, plenum, outdoor PE) and by fibre count. Patch cords, trunks and MPO breakouts are assemblies built from these cables.
Types of fibre optic cable by fibre
The fibre fixes the reach and the transceivers that will work. Every construction below can be built with either family, so choose the fibre first. US catalogues list the same types of fiber optic cable by core and cladding size, written 9/125 or 50/125.
| Fibre | Core/cladding | Main wavelengths | Typical use | Premises jacket colour (TIA-598) |
|---|---|---|---|---|
| OS2 single-mode | 9/125 µm | 1310, 1550 nm | Backbones, campus, FTTx, longer data centre links | Yellow |
| OM1 multimode | 62.5/125 µm | 850, 1300 nm | Legacy building plant, replacement cords | Orange |
| OM2 multimode | 50/125 µm | 850, 1300 nm | Legacy short links | Orange |
| OM3 multimode | 50/125 µm | 850 nm | 10G to 100G short links | Aqua |
| OM4 multimode | 50/125 µm | 850 nm | Data centre links and MPO trunks | Aqua, or violet in some markets |
| OM5 multimode | 50/125 µm | 850 to 953 nm | Shortwave WDM links | Lime green |
For single-mode, also name the fibre standard, such as ITU-T G.652.D or bend-insensitive G.657.A1. For new multimode work OM4 is the usual default. The guide to single-mode vs multimode fibre compares reach and optics cost, and the single-mode fibre optic cable guide covers OS2 in detail.
Buffer and construction
Construction describes how the coated fibre, normally 250 µm across, is packaged inside the cable.
| Construction | Fibre packaging | Usual environment | Termination |
|---|---|---|---|
| Tight-buffered | 900 µm plastic buffer on each fibre | Indoor cable and patch cords | Connectorised directly |
| Loose tube | 250 µm fibres in gel-filled or dry water-blocked tubes | Outdoor duct, aerial and burial routes | Spliced to pigtails, or fitted with a fan-out kit |
| Ribbon | Fibres bonded side by side, commonly 12 per ribbon | High-count backbones and data centre trunks | Mass fusion splicing, 12 fibres at a time |
| Distribution | Several tight-buffered fibres under one jacket | Risers and equipment rooms | Inside a panel or enclosure |
| Breakout | Each fibre in its own jacketed sub-unit with aramid yarn | Equipment rooms, field leads, direct runs to devices | Each leg connectorised and routed on its own |
Loose tube isolates the glass from cable tension and from the jacket expanding and shrinking with temperature, which is why it is the standard for outside plant. Simplex and duplex patch cord cable, commonly 2.0 mm or 3.0 mm in diameter, is tight-buffered fibre inside aramid strength yarn and a jacket.
Breakout cable is larger and costs more than distribution cable, but each leg survives handling outside an enclosure.
Protection: armoured, tactical, aerial and buried
Protection layers sit over the construction and are chosen for the route rather than the signal.
- Armoured: corrugated steel tape for burial and rodent areas, interlocking aluminium armour indoors in North America, stainless steel spiral tube in armoured patch cords, and steel wire armour in much UK and Gulf utility work. Dielectric armour of glass yarns or rods resists rodents with no metal to earth. Metallic armour normally has to be bonded to earth where the cable enters a building. See armoured fibre optic cables.
- Tactical: tight-buffered fibres with aramid strength and a polyurethane jacket for repeated deployment from reels at broadcast events, defence sites and temporary links, often with expanded beam connectors. The tactical fibre optic cable guide covers constructions and connectors.
- Aerial: all-dielectric self-supporting (ADSS) cable spans between poles on its own strength. Figure-8 cable has a steel messenger wire moulded into the jacket, and standard loose tube can be lashed to a separate messenger. Specify span lengths and the wind and ice loading on the route.
- Direct burial: water-blocked loose tube with a polyethylene jacket, usually armoured, laid straight in the trench.
- Indoor/outdoor: water-blocked and UV-resistant like outside plant cable, with a flame-retardant jacket, so one cable can run from the street into a building without a splice at the entrance.
Jacket material and fire ratings
Indoor cable must meet the fire rules of the country where it is installed. The rating is printed on the jacket.
| Jacket or rating | Where it applies | What it means |
|---|---|---|
| LSZH (also LS0H) | Indoor work in India, the UK, the EU, the Gulf and much of Asia; tunnels, ships, transport | Low smoke and no halogens. Tested for flame spread (IEC 60332), smoke density (IEC 61034) and acid gas (IEC 60754) |
| EU CPR Euroclass | Cable fixed in buildings in the EU | Reaction to fire class under EN 50575, from Aca to Fca, with suffixes for smoke, droplets and acidity. National rules set the minimum class per building type |
| OFNP (plenum) | US air-handling spaces | Highest NEC Article 770 listing, tested to NFPA 262 for flame spread and smoke |
| OFNR (riser) | US vertical shafts between floors | NEC listing that passes a vertical flame test |
| OFN (general purpose) | US runs within one floor | Lowest NEC indoor listing |
| Outdoor PE | Outside plant | Black UV-stabilised polyethylene, moisture resistant, not fire rated for indoor use |
LSZH and plenum are different tests. An LSZH cable is not automatically listed for US plenums, and many plenum compounds contain fluorine, so they are not halogen free. In NEC codes the N means non-conductive; OFC variants contain metal. Unlisted outside plant cable may run only 15 m (50 ft) into a US building before it terminates in an enclosure.
Fibre count
Counts run from 1 (simplex) and 2 (duplex) for patch cords, through 12, 24, 48, 96 and 144 in typical backbones, to several thousand in ribbon cable. Fibres are identified by the 12-colour sequence in TIA-598: blue, orange, green, brown, slate, white, red, black, yellow, violet, rose and aqua, repeated with tube colours or stripes at higher counts.
Size the count for today's links plus spares. For MPO systems, match the count to the connector: multiples of 8, 12 or 24 fill MPO trunks without dark positions.
Pre-terminated assemblies
Many buyers order cable with connectors fitted and tested in the factory.
- Patch cords: simplex or duplex cable with connectors at both ends, such as LC to LC or LC to SC, for panels and equipment.
- Pigtails: one connectorised end and one bare end, fusion spliced onto loose tube cable.
- Trunk cables: multi-fibre cable terminated at both ends with MPO connectors or LC fan-outs and pulled in as one tested unit. See MTP/MPO trunk cables.
- Breakout harnesses: an MPO at one end splitting to LC or SC legs at the other, linking parallel optics or cassettes to duplex ports.
- MPO patch cords: short MPO to MPO cords for parallel optics such as 100G SR4 and 400G DR4.
Factory termination gives a measured loss for every connector and removes field splicing. Measure the route first and allow slack for service loops.
What to specify for each cable type
- Fibre: grade (OS2, OM3, OM4 or OM5) and, for single-mode, the ITU-T fibre standard.
- Construction: tight-buffered, loose tube, ribbon, distribution or breakout, with outer diameter.
- Protection: armour type and whether it must be dielectric, or aerial span and loading details.
- Jacket: material, colour and the fire rating for the country of installation.
- Fibre count, including spares.
- Assemblies: connector and polish at each end, polarity, length and tolerance, breakout leg lengths, pulling grip, labels and the test report required.
Radix Fibrotech builds single-mode and multimode assemblies to drawing in Pune. Send the list above with a request for a quote and ask for the loss values that apply to your build.
Questions buyers ask
What is the difference between tight-buffered and loose tube cable?
Tight-buffered cable puts a 900 µm buffer directly on each fibre, so it is flexible and can be connectorised directly. Loose tube cable lets 250 µm fibres lie free in water-blocked tubes, which protects them from tension and temperature outdoors. Loose tube is normally spliced to pigtails for termination.
Is LSZH cable the same as plenum cable?
No. LSZH is tested to IEC methods for smoke density, flame spread and halogen acid gas. Plenum (OFNP) is a US NEC listing tested to NFPA 262. A cable can meet one without meeting the other, so specify the rating required where the cable will be installed.
Can outdoor fibre cable be run inside a building?
Standard outdoor cable with a PE jacket is not fire rated, so it should be spliced to rated indoor cable near the entrance. The US NEC allows unlisted outside plant cable to run up to 15 m (50 ft) inside. Indoor/outdoor cable avoids the transition.
Which fibre cable type is used in data centres?
Most new data centres use OM4 multimode or OS2 single-mode in pre-terminated MPO trunks, with LC duplex patch cords and MPO breakout harnesses at the racks. Jackets are usually LSZH, or OFNR or OFNP in US buildings.
Does armoured fibre cable need earthing?
Cable with metallic armour, such as steel tape or steel wire, normally has to be bonded to earth at building entrances. Dielectric armour made of glass yarns or rods contains no metal and needs no earthing.