The 8P8C (8 position 8 contact, also backronymed as 8 position 8 conductor) is a modular connector commonly used to terminate twisted pair and multiconductor flat cable. These connectors are commonly used for Ethernet over twisted pair, registered jacks and other telephone applications, RS-232 serial using the EIA/TIA 561 and Yost standards, and other applications involving unshielded twisted pair, shielded twisted pair, and multiconductor flat cable.
An 8P8C modular connector has two paired components: the male plug and the female jack, each with eight equally-spaced conducting channels. On the plug, these conductors are flat contacts positioned parallel with the connector body. Inside the jack, the contacts are suspended diagonally toward the insertion interface. When an 8P8C plug is mated with an 8P8C jack, the contacts meet and create an electrical connection. Spring tension in the jack's contacts ensures a good interface with the plug and allows for slight travel during insertion and removal.
Although commonly referred to as an "RJ45" in the context of Ethernet and category 5 cables, it is incorrect to refer to a generic 8P8C connector as an RJ45. A telephone-system-standard RJ45 plug has a key which excludes insertion in an un-keyed 8P8C socket. The registered jack (RJ) standard specifies a different mechanical interface and wiring scheme for an RJ45S from TIA/EIA-568-B which is often used for modular connectors used in Ethernet and telephone applications. 8P8C modular plugs and jacks look very similar to the plugs and jacks used for FCC's registered jack RJ45 variants, although the RJ45S is not compatible with 8P8C modular connectors.
See also: Registered jack naming confusionThe original RJ45S used a keyed 8P2C modular connector, with Pins 5 and 4 (the middle 2 positions) wired for tip and ring of a single telephone line and Pins 7 and 8 shorting a programming resistor. It was meant to be used with a high speed modem, and is obsolete today.
Telephone installers who wired RJ45S modem jacks or RJ61X telephone jacks were familiar with the pin assignments that were part of the standard. However, the standard un-keyed modular connectors became ubiquitous for computer networking, and informally inherited the name "RJ45". While RJ45S uses a "keyed" variety of the 8P body, meaning it may have an extra tab that a common modular connector is unable to mate with, the visual difference is subtle and likely caused the confusion.
Understandably, because telephone RJ61 and data RJ45/RJ48 connectors never saw wide usage and computer 8P8C connectors are quite well known today, "RJ45" is used to refer to 8P8C, un-keyed modular connectors with Ethernet-type wiring pin-outs. Electronics catalogs commonly advertise 8P8C modular connectors as "RJ45", many electronic equipment manuals using an 8P8C connector will document it as an "RJ45" connector. In common usage, RJ45 may also refer to the pin assignments for the attached cable, which are actually defined as T568A and T568B in wiring standards such as TIA/EIA-568-B.
Read more about this topic: Modular Connector