What is an FC connector?
The FC connector, short for Ferrule Connector, is a round fiber optic connector that locks with a threaded coupling nut: you line up its key with the slot in the adapter, push it in and screw the nut down. It holds the fiber in a 2.5 mm ceramic ferrule, the same size used by ST and SC connectors. The threaded nut keeps it firmly seated, which made it popular where vibration is a concern.
FC connectors were widely used on older single-mode telecom links and are still often found on test and measurement equipment, such as optical power meters, light sources and OTDRs. In most new network installs, SC and especially LC connectors have taken their place.
What is a ferrule?
Every common fiber connector has a ferrule: a precision cylinder, usually ceramic (zirconia), with a hole down the center that holds the bare fiber. When two connectors mate in an adapter, their ferrules line the fiber cores up end to end. The tip of the ferrule is polished (PC, UPC or APC), which is why you see names like FC/PC and FC/APC. "Ferrule connector" is the FC's full name, but the ferrule itself isn't unique to it.
FC vs. ST, SC and LC
| Connector | Coupling | Ferrule | In the A+ objectives? |
|---|---|---|---|
| FC (Ferrule Connector) | Threaded screw-on nut, keyed | 2.5 mm | No |
| ST (Straight Tip) | Bayonet: push in and twist | 2.5 mm | Yes |
| SC (Subscriber Connector) | Push-pull, square body | 2.5 mm | Yes |
| LC (Lucent Connector) | Push-pull with a latch, small form factor | 1.25 mm | Yes |
FC and ST look alike at a glance because both are round with a metal coupling. Screw threads mean FC; a bayonet that locks with a quarter turn means ST.
FC connector vs. Fibre Channel
FC is also the abbreviation for Fibre Channel, a high-speed protocol used to connect servers to storage in a storage area network (SAN). Fibre Channel is a networking technology, not a connector, and its links usually use LC connectors on SFP transceivers. Don't read "FC" on a SAN switch as the screw-on FC connector.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.2 lists ST, SC and LC as the fiber connectors to recognize; FC isn't on the list. Expect it as a distractor at most. If you see a round fiber connector with screw threads, it's FC; round with a twist-lock bayonet is ST.