Cable terminations: T568A vs B, punchdowns, and keystones

When setting up a network, understanding the different cable termination methods is crucial for ensuring reliable connections. This guide covers the differences between T568A and T568B wiring standards, as well as how to use keystone jacks and patch panels.

Wiring Standards: T568A vs B

There are two main wiring standards used in Ethernet cables: T568A and T568B. Both define the color code for each pin in an RJ45 connector, but they differ slightly:

• T568B (De facto default in the US):

  • White-orange
  • Orange
  • White-green
  • Blue
  • White-blue
  • Green
  • White-brown
  • Brown

• T568A (Common for government work):

  • White-green
  • Green
  • White-orange
  • Blue
  • White-blue
  • Orange
  • White-brown
  • Brown

The only rule that matters is to use the same standard on both ends of a cable. Mixing T568A and T568B accidentally creates a crossover cable, which modern auto-MDIX equipment can handle but may cause issues with older devices.

Termination Types

Crimped Plug (Male RJ45)

• Use for: Patch cables with stranded wire.
• Craft:
  • Untwist the wires as little as possible (the twist provides noise immunity).
  • Trim the jacket evenly and place it inside the strain relief.
  • Verify color order through the clear plastic before crimping.
  • Pass-through connectors make alignment easier for occasional users.

Keystone Jack (Female, Punched Down)

• Use for: Solid in-wall runs.
• Termination:
  • Press wires into IDC slots with a punchdown tool (110 blade).
  • The trick is to cut the wire on the wrong side of the blade to avoid damaging it.

Patch Panel

• Use for: Connecting all in-wall runs to short patch cables leading to switches.
• Function:
  • Keystones/IDC strips allow easy connections and reconnections without flexing the permanent wall cable.

Golden Rule of Structured Cabling

The key rule is to use solid core wire for in-wall runs terminated with keystone jacks or panels, and crimped plugs on stranded patch cables for the last meter. Crimping a plug onto solid in-wall cable can lead to intermittent failures, making it a risky DIY shortcut.

Field Termination Extras

• Shielded (STP) terminations: Bond the shield at the jack.
• Coupler inline joins: Use as a last resort; each one is a signal event.
• Label both ends of every run: Ensure future maintenance is easier by clearly identifying cables.