RJ45 keystone jacks: role, termination and best practices

What a keystone jack does

The keystone jack turns the end of a solid cable into an RJ45 port that a cord can plug into. You find one at each end of a link: in the wall jack on the user side, and on the patch panel on the rack side.

How termination works

The cable is terminated at the back of the jack on insulation displacement contacts: each conductor is pressed into a slot that cuts through its insulation and makes contact. Depending on the model, this is done with a punch-down tool or with a tool-less closing mechanism.

Key points

• strip only what is needed: the jacket is removed over the required length without nicking the conductors;
• keep the pair twists as close as possible to the contacts: cabling standards limit the untwisted length to a few millimeters;
• follow the color code of the chosen wiring scheme;
• maintain shield continuity for shielded cables, all the way to a panel bonded to the rack ground.

T568A or T568B?

There are two wiring schemes, T568A and T568B, which differ in the order of two pairs. Both work. The key rule is to pick one and apply it throughout the installation, at both ends of every link.

Keystone jacks vs crimping

Crimping applies to male RJ45 plugs fitted at the end of cords. A keystone jack is punched down instead. In a professional installation, the permanent cabling ends on keystone jacks, and patch cords are preferably factory-made.

Check every termination

A visual check reveals a badly seated pair or a jacket stripped too far. A continuity test then confirms that each conductor reaches the right contact at the other end. The mapping between wall jack and panel port is then recorded in the documentation.