Registered Jack 45 (RJ45) most commonly seen with Ethernet cables and networks is a standard type of physical connector for network cables.

Modern Ethernet cables feature small plastic plugs on each end that are inserted into RJ45 jacks of Ethernet devices. “Plug” technically refers to the cable or “male” end of the connection while “Jack” refers to the port or “female” end.

RJ-45 ConnectorRJ45 plugs feature eight (8) pins to which the wire strands of a cable interface electrically. Each plug has eight locations (positions), spaced about 1mm apart, into which individual wires are inserted using special cable crimping tools .This type of connector is called 8P8C (Eight Position, Eight Contact).

Ethernet cables and 8P8C connectors must be crimped into the RJ-45 wiring pattern to function properly. Technically, 8P8C can be used with other types of connections besides Ethernet; it is also used with RS-232 serial cables.

Traditional dial-up modems used a variation of RJ45 called RJ45s which features only 2 contacts (8P2C configuration) instead of eight. The close physical similarity of RJ45 and RJ45s made it difficult for an untrained eye to tell the two apart.

RJ-45 Connector 02Two standard RJ45 pinouts define the arrangement of the individual eight wires needed when attaching connectors to a cable – the T568A and T568B standards. Both follow a convention of coating individual wires in one of five colors – brown, green, orange, blue and white – with certain stripe and solid combinations.

Following these conventions is essential when building cables to ensure electrical compatibility with other equipment. For historical reasons, T568B has become the more popular standard.  

Several other kinds of connectors closely resemble RJ45 and can be easily confused for each other. The RJ11 connectors used with telephone cables, for example, use six position instead of eight position connectors, making them slightly narrower than RJ-45 connectors.

To help form a tight connection between the plug and the network port, few RJ45 plugs utilize a small, bendable piece of plastic called a “tab.”  The tab helps make a tighter seal between a cable and a port on insertion, requiring a person to apply some downward pressure on the tab to allow unplug. This helps prevent a cable from accidentally coming loose (“unseated”). Unfortunately, these tabs easily break when bent backward, which too easily happens when the connector snags on another cable. Care must be taken while removing the connector in order to keep the tab from breaking.

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