Fiber optic cable types
The glass inside is the same; the cable around it is built for where it goes. Here is how to tell the common constructions apart and what each one is for.
Outside plant cables
| Type | Construction | Where it goes |
|---|---|---|
| Loose tube | Fibers ride loose in color-coded buffer tubes (commonly 6, 12 or 24 per tube) around a central strength member, either gel-filled or dry with water-swellable tape and yarn. | Underground duct, aerial lashed to a messenger, and direct buried when armored. The workhorse of OSP and FTTH feeder. |
| Ribbon | Fibers bonded side by side in 12-fiber ribbons, stacked in a central tube or in slotted cores. Rollable or flexible ribbons fold up to pack very high counts into small duct. | High-count feeder and data center links, spliced 12 at a time with a mass fusion splicer. |
| ADSS | All-dielectric self-supporting: strength in aramid yarn, no metal, built to hang on its own over a rated span. | Aerial on utility poles, often in the power space, where a metal messenger is unwanted. |
| Figure-8 | A fiber cable and a steel messenger joined in one jacket, so it looks like an 8 in cross-section. | Aerial without a separate lashing operation. |
| Armored | A corrugated steel tape (or a dielectric armor) under the outer jacket. | Direct burial and anywhere rodents chew. Metallic armor must be bonded and grounded. |
| Micro cable | Small, light loose tube cable with a slick jacket. | Blown or pushed into microduct. |
Drop cables
Drops run the last stretch from a terminal to the home or business. Common types are flat drops (fiber between two strength rods), round drops, and toneable drops with a copper tracer wire so the buried path can be located. Many are sold pre-terminated with hardened connectors that plug into terminals without opening a closure. Drop fiber is usually bend-insensitive G.657, because drops get routed around siding, corners and through walls.
Inside plant cables
- Tight buffered: each fiber has a 900 µm buffer, so it can be connectorized directly. Used for distribution cable inside buildings.
- Breakout: each tight-buffered fiber has its own jacket and strength yarn, so fibers can be split out and terminated individually.
- Indoor/outdoor: rated for both, so a cable can come in from outside without a transition splice at the building entrance (within the code's limits).
Building ratings (NEC)
| Marking | Meaning |
|---|---|
| OFNP | Nonconductive, plenum rated: air-handling spaces |
| OFNR | Nonconductive, riser rated: vertical runs between floors |
| OFN / OFNG | Nonconductive, general purpose |
| OFCP, OFCR, OFC | The same ratings for conductive cable (armor or metal strength members) |
A higher rating can replace a lower one (plenum can go where riser is required, not the other way). Outside plant cable generally has to transition to a rated cable within a short distance of entering a building; check the code edition your jurisdiction uses.
Reading the jacket
The jacket print usually gives the maker, fiber count and type, the rating, and sequential length marks. Those length marks are what you use to turn an OTDR distance into a place on the route. Inside, the tubes and fibers follow the TIA-598 color code.