OFC cable is optical fibre cable, the term used across India for cable that carries signals as light through glass fibres. It is specified by core count, meaning the number of fibres (2 to 48 and higher), by fibre type, usually single-mode G.652.D, and by construction: unitube or multitube loose tube, armoured or unarmoured, aerial ADSS or figure-8, duct or direct burial.
What OFC cable means
OFC is short for optical fibre cable. The full form is used in telecom tenders, railway and highway projects, CCTV installations and building specifications across India, where an OFC cable or OFC line means the fibre route between two sites. An OFC cable holds one or more glass fibres, each 125 µm across the cladding, inside protective tubes, strength members and an outer sheath.
The same letters mean something different in the United States. In NEC Article 770, OFC is a cable listing for optical fibre conductive cable, meaning the cable contains metal such as armour or a metallic strength member. Indian buyers rarely meet this usage, but it can appear on cable printed for the US market.
What core means, and common core counts
In Indian trade usage, core means fibre. A 4 core OFC has four fibres and a 24 core OFC has twenty-four. Most links use two fibres, one to transmit and one to receive, so a 6 core cable carries three duplex links or fewer links with spares. This is different from the core of an individual fibre, the light-carrying centre, which is 9 µm in single-mode and 50 or 62.5 µm in multimode. A search for a 12 core fiber optic cable is a search by fibre count.
Common counts are 2, 4, 6, 8, 12, 24 and 48, then 96, 144 and higher on backbone routes. Laying cable costs far more than the fibre inside it, so designers usually buy more cores than today's links need.
| Core count | Usual construction | Typical uses |
|---|---|---|
| 2 core | Flat drop cable or unitube | FTTH drop to one home, a single camera or one duplex link |
| 4 core | Unitube | CCTV and building-to-building links, one duplex link with a spare pair |
| 6 core | Unitube | CCTV rings, small campus links, up to three duplex links |
| 8 core | Unitube | Campus and building links with room for growth |
| 12 core | Unitube or multitube | Campus backbone, ring networks, FTTH distribution |
| 24 core | Multitube | FTTH distribution, campus and building backbone |
| 48 core and higher | Multitube | Backbone, metro and feeder routes between exchanges, towers and data centres |
Fibres are colour coded inside each tube, and tubes are coloured in turn, so each core can be identified at both ends. Many cables follow the TIA-598 sequence, starting blue, orange, green, brown; the fibre colour codes guide lists it in full.
Single-mode and multimode OFC
Most OFC laid in India is single-mode, usually ITU-T G.652.D fibre, because telecom, FTTH and CCTV routes run over distances multimode cannot cover. Bend-insensitive G.657.A1 or G.657.A2 fibre is used in drop and indoor cable that turns tight corners. Multimode OFC, mainly OM3 and OM4, is used inside campuses and data centres where links are short and the equipment uses multimode optics.
Single-mode and multimode fibres cannot be joined in one link, so match the cable to the transceivers at both ends. The guide to single-mode vs multimode fibre compares reach and optics.
OFC constructions used in India
- Unitube loose tube: one central tube, gel-filled or dry, holding commonly up to 12 or 24 fibres, with strength from steel wires or FRP rods in the sheath or from aramid yarn. It is small and low in cost, and is widely used for CCTV, building and access links.
- Multitube loose tube: several colour-coded tubes, commonly 6 or 12 fibres each, stranded around a central strength member, usually FRP. It is used from about 24 cores upward and wherever groups of fibres have to be dropped at different joints.
- Armoured: a corrugated steel tape under the outer sheath resists rodents and crushing. It is the usual choice for direct burial and for ducts on routes with rodents.
- Unarmoured: lighter and smaller, for HDPE duct, cable trays and protected indoor routes.
- Aerial ADSS: all-dielectric self-supporting cable carries its own weight between poles. It has no metal, so it is used on power line poles, and it is chosen for the span length and loading on the route.
- Aerial figure-8: a steel messenger wire is moulded into a separate part of the sheath, giving the cross-section its figure-8 shape. The messenger is clamped at each pole.
- Duct: cable pulled or blown into HDPE duct laid in a trench, so cable can be added or replaced later without digging again.
- Direct burial: cable laid straight in the trench, usually armoured with a PE sheath. Burial depth and warning tape follow the project specification.
Jacket, armour and strength members
Outdoor OFC uses a black UV-stabilised polyethylene sheath, often HDPE. Water blocking is either gel inside the tubes or dry swellable yarns and tapes; dry cable is quicker and cleaner to prepare at joints. Polyethylene is not fire rated for indoor use, so outdoor OFC entering a building should be spliced to LSZH indoor cable near the entry, or replaced by an indoor/outdoor design.
The pulling load is carried by the strength members (FRP rods, steel wires or aramid yarn), not usually by the armour. Armour adds crush and rodent resistance at the cost of diameter, weight and bend radius, and metallic armour has to be bonded to earth at buildings. The sheath is normally printed with the fibre count, fibre type and a length mark every metre, which helps when measuring a route or a remaining drum.
How OFC is terminated at each end
Loose tube OFC is not connectorised directly. At each end the fibres are spliced to pigtails, which provide factory-polished connectors on a panel. The termination box goes by several names in India: ODF (optical distribution frame), LIU (light interface unit) or FMS (fibre management system), depending on size and vendor. Along the route, cable lengths are joined in a sealed joint closure, dome or inline, mounted on a pole or in a manhole or handhole. The fibre pigtail guide covers pigtail types, colour order and splicing.
For short routes of known length, a factory-terminated assembly can replace splicing. The cable arrives with connectors fitted and tested and plugs straight into a panel or equipment. This suits CCTV links on a campus, temporary links and equipment rooms, but the route has to be measured before ordering.
What to specify when buying OFC
- Core count, including spares.
- Fibre type: G.652.D single-mode, G.657 for tight bends, or the multimode grade.
- Construction: unitube or multitube, and fibres per tube.
- Protection: armoured or unarmoured; for aerial routes, ADSS with span length or figure-8 with messenger size.
- Sheath and water blocking: PE outdoors, LSZH indoors, gel-filled or dry.
- Drum length and sheath marking.
- Test report: an OTDR trace for each fibre on each drum, with attenuation at 1310 and 1550 nm for single-mode.
- Termination: number of ODFs or joint closures, and the pigtail connector and polish (SC or LC, UPC or APC).
Radix does not sell bulk OFC on drums; it builds terminated assemblies and armoured and tactical cables to order, for example the 6-fibre armoured tactical cable. For a link that should arrive terminated rather than spliced, see the range of armoured fibre optic cables and send the core count, fibre type, connectors and length in a request for a quote.
Questions buyers ask
What is the full form of OFC?
OFC stands for optical fibre cable, cable that carries data as light through glass fibres. The term is used across India in telecom, railway, CCTV and building projects. In the US electrical code, OFC is also a listing for optical fibre cable that contains metal.
What does 6 core OFC mean?
A 6 core OFC contains six optical fibres. Most links use two fibres each, so it can carry up to three duplex links, or fewer links with spare fibres kept for repairs and growth. It is a common size for CCTV and small campus routes.
Which OFC is used for CCTV?
CCTV routes commonly use 4, 6 or 12 core single-mode unitube OFC. Armoured cable suits direct burial or rodent-prone ducts, and unarmoured cable suits HDPE duct and trays. Each camera or switch link usually takes two fibres.
What is the difference between unitube and multitube OFC?
Unitube OFC has one central loose tube holding all the fibres and is used for lower counts, commonly up to 12 or 24. Multitube OFC has several colour-coded tubes stranded around a central strength member and is used for 24 cores and above.
Can OFC be connected directly to a switch?
Not usually. Loose tube OFC fibres are spliced to pigtails in an ODF or LIU, and a patch cord then connects the panel port to the switch transceiver. A factory-terminated assembly can plug in directly when the route length is known in advance.