Picking the Right Patch Cables

Although not really part of a discussion on picking cable types for horizontal cable, the subject of patch cords should be addressed. Patch cables (or patch cords) are the cables that are used to connect 110-type connecting blocks, patch-panel ports, or telecommunication outlets (wall-plate outlets) to network equipment or telephones.

We've mentioned this before but it deserves repeating: you should purchase factory-made patch cables. Patch cables are a critical part of the link between a network device (such as a PC) and the network equipment (such as a hub). Determining appropriate transmission requirements and testing methodology for patch cords was one of the holdups in completing the ANSI/TIA/EIA-B.2-1 Category 6 specification. Low-quality, poorly made, and damaged patch cables very frequently contribute to network problems. Often the patch cable is considered the weakest link in the structured cabling system. Poorly made patch cables will contribute to attenuation loss and increased crosstalk.

Factory-made patch cables are constructed using exacting and controlled circumstances to assure reliable and consistent transmission-performance parameters. These patch cables are tested and guaranteed to perform correctly.

Patch cables are made of stranded-conductor cable to give them additional flexibility. However, stranded cable has up to 20 percent higher attenuation values than solid-conductor cable, so lengths should be kept to a minimum. The ANSI/TIA-568-C standard allows for a 5-meter (16′) maximum-length patch cable in the wiring closet and a 5-meter (16′) maximum-length patch cable at the workstation area.

Here are some suggestions to consider when purchasing patch cables:

• Don't make them yourself. Many problems result from bad patch cables.
• Choose the correct category for the performance level you want to achieve.
• Make sure the patch cables you purchase use stranded conductors for increased flexibility.
• Purchase a variety of lengths and make sure you have a few extra of each length.
• Consider purchasing patch cords from the same manufacturer that makes the cable and connecting hardware, or from manufacturers who have teamed up to provide compatible cable, patch cords, and connecting hardware. Many manufacturers are a part of such alliances.
• Consider color-coding your patch cords in the telecommunication closet. Here's an example:
  • Blue cords for workstations
  • Gray cords for voice
  • Red cords for servers
  • Green cords for hub-to-hub connections
  • Yellow for other types of connections

Patch Cords

Patch cords are used in patch panels to provide the connection between field-terminated horizontal cables and network connectivity devices (such as switches and hubs) and connections between the telecommunications outlets and network devices (such as computers, printers, and other Ethernet-based devices). They are the part of the network wiring you can actually see. As the saying goes, a chain is only as strong as its weakest link. Because of their exposed position in structured cable infrastructures, patch cords are almost always the weakest link.

Whereas horizontal UTP cables contain solid conductors, patch cords are made with stranded conductors because they are more flexible. The flexibility allows them to withstand the abuse of frequent flexing and reconnecting. Although you could build your own field-terminated patch cords, we strongly recommend against it.

The manufacture of patch cords is very exacting, and even under controlled factory conditions it is difficult to achieve and guarantee consistent transmission performance. The first challenge lies within the modular plugs themselves. The parallel alignment of the contact blades forms a capacitive plate, which becomes a source of signal coupling or crosstalk. Further, the untwisting and splitting of the pairs as a result of the termination process increases the cable's susceptibility to crosstalk interference. If that weren't enough, the mechanical crimping process that secures the plug to the cable could potentially disturb the cable's normal geometry by crushing the conductor pairs. This is yet another source of crosstalk interference and a source of attenuation.

Tip

Patch cords that have been factory terminated and tested are required to achieve consistent transmission performance.

At first glance, patch cords may seem like a no-brainer, but they may actually be the most crucial component to accurately specify. When specifying patch cords, you may also require that your patch cords be tested to ensure that they meet the proper transmission-performance standards for their category.