What is a wall jack?
In network cabling, a wall jack is the port in a wall where a computer, phone or other device plugs into the building's cabling. It's usually a keystone jack snapped into a wall plate (faceplate): an RJ45 jack for Ethernet data or an RJ11 jack for an analog phone line. In this sense the term doesn't mean an electrical power outlet.
A single plate can hold one jack or several, for example a data jack and a phone jack, or two data jacks.
Where the wall jack fits
A typical structured cabling path in an office looks like this:
- A patch cable runs from the computer to the wall jack.
- Behind the plate, the jack is punched down to the horizontal cable (solid-core Cat5e or Cat6, for example) that runs through the wall and ceiling.
- That cable ends on a patch panel in the wiring closet (telecommunications room).
- A short patch cable connects the patch panel port to a switch port.
Structured cabling standards allow 90 meters for the permanent run from jack to patch panel, leaving 10 meters for patch cords, to stay within Ethernet's 100-meter channel.
Terminating a wall jack
- Most keystone jacks use 110-style insulation displacement contacts on the back. A punchdown tool seats each conductor and trims the excess; some jacks are tool-less and use a cap that presses the wires in.
- Follow the color code printed on the jack for T568A or T568B, and use the same standard at the patch panel end.
- Keep each pair twisted as close to the contacts as possible to limit crosstalk.
- Label the plate with the same ID as its patch panel port so the run can be found later.
Testing and tracing
- A cable tester connected at the wall jack and the patch panel port checks for opens, shorts and miswired pairs.
- A toner probe finds which patch panel port a jack goes to when the runs aren't labeled.
- A loopback plug checks whether a port or NIC can send and receive.
If a device gets no link at one jack, try a known-good patch cable, then another device at the same jack. If the device works at a different jack, the problem is in that run: its terminations, the patch panel connection or the switch port, including its VLAN setting.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.2 covers the RJ45 and RJ11 connectors and punchdown blocks, objective 2.5 covers patch panels, and objective 2.8 covers the punchdown tool, cable tester and toner probe. "Wall jack" isn't an objective term, but scenarios often start at one: a user's PC has no network connection at their desk jack, and you trace the path back to the closet.