RJ45 Connectors and Wiring Standards

The clear plastic plug on the end of an Ethernet cable is an RJ45 connector (more precisely an 8P8C, meaning 8 positions, 8 contacts). It holds the eight wires of a twisted-pair cable in a fixed order so they line up with the matching jack. Knowing how to terminate, or attach, an RJ45 to a cable is a hands-on skill every technician needs, and the wiring standards behind it appear on the exam.

A twisted-pair Ethernet cable has eight wires arranged in four pairs. Each pair has a solid-colored wire and a matching white-striped wire: orange, green, blue, and brown. Keeping pairs twisted right up to the connector preserves their noise resistance. Untwisting too much before the plug increases crosstalk and can cause errors, so careful termination matters for performance.