The Science of Patch Cords

A patch cord, patch cable or patch lead is an electrical or optical cable of predefined length used to connect ("patch in") one electronic or optical device to another. Even though patch cords are quite common, they perform an important part in transmitting data signals within the LAN (Local Area Network). An Ethernet cable and a patch cable can be the same, but the latter is usually shorter.

One common use of patch cords is to connect a laptop or desktop computer to a wall jack. In a Data Center, patch cords are used to connect equipment in one rack or enclosure to equipment on another shelf of the same rack, or to equipment on a different rack or enclosure.

Copper Patch Cords
Copper patch cords can be STP (Shielded Twisted Pair) or UTP (Unshielded Twisted Pair) and have an RJ45, TERA or GG45 connector on both ends, although hybrid versions exist that have different types of connectors. They are either made with solid or stranded copper and typically shorter than other connector cables due to potential signal loss. A copper patch cord with a smaller outside diameter takes up less space and has a smaller bend radius. This allows it to be installed in smaller areas.

Fiber Patch Cords
Fiber patch cords, also called fiber jumpers, are made of fiber optics with connectors at both ends. The caps allow the cord to be rapidly connected to an optical switch or other telecommunications or computer device. It is also used to connect an optical transmitter, receiver or terminal box.

Potential Problems with Patch Cords

Bit error rate in copper patch cords can affect transmissions, slow down computer operations, prevent signal communication and even alter data signals.

Signals can also “leak” and weaken the transmission. In addition, RFI (Radio Frequency Interference) and EMI (Electromagnetic Interference) can interfere with the signal, causing an increase in bit error rates.

Fiber patch cords have other problems including broken fibers due to too much tension or bending, insufficient transmitting power, excessive signal loss due to a cable that is too long, a faulty connector and faulty splices.

Homemade Patch Cords
It is difficult to build homemade patch cords. The twisted pairs must maintain their twists as close as possible to the RJ-45 connectors, and the connectors must be high quality for the best signal carrying capabilities. Homemade patch cords that don't meet specifications can cause problems.

Length
Patch cords can be as short as 3 inches (8 cm) to connect stacked components or as long as twenty feet (6 m), depending on the type and use. Fiber patch cords are available in lengths of 2 m, 3 m, or 5 m. It´s always wise to keep your patch cords as short as possible without creating undo strain on the connectors.

Testing Patch Cords

A “Channel Test” involves patch cords while a “Permanent Link Test” does not.

If you are troubleshooting an existing network or need to find out if it will support an application, channel testing is advised. If you are testing a new network or new connections, you will want to know if the cable performs to standards. In that case, the Permanent Link test is the recommended testing method.

The bottom line is that selecting, installing and maintaining the right patch cord can improve the performance of your network and help ensure as much uptime as possible.

Patch cords link switches, hubs, modems, and other devices together in a network environment.