Patch Cables and their Application

The term Patch Cable is used to describe many situations where two optical or electronic devices are patched together using either an optical patch cable or electrical patch cable. A patch cable is the primary means of connecting the two devices for the purpose of transmitting signalling information and serialised or packetized content. Another term used to describe a patch cable is a patch cord and the two terms are interchangeable.

Patch Cables or cords used for Computer Networking are quite often constructed of copper cabling, commonly twisted pair, copper coaxial cable or fibre optic cable made from silica glass. Some coaxial patch cables can be used to with audio equipment to carry amplified audio signals from amplifiers to speakers. Types of patch cords include:

Headphone extension cables

Microphone Cables

Audio and Video Cables with TRS or RCA connectors

Modular Ethernet Patch Cables (Twisted Pair

Audio Multicore cables (Carrying a number of shielded twisted pair audio cables)

Copper twisted pair patch cables are normally used to connect an Ethernet switch to a Router, or a Computer or Server to a switch or hub. These patch cords come in a variety of colours to enable a colour coded plan to be observed in the network in which they are deployed. These different  coloured patch cables can distinguish one type of connection from another. Ethernet patch cables consist of 4 pairs of stranded copper wire and were designed so that the Ethernet data signals were carried on 2 pairs, leaving 2 pairs for Telephone Signals. In most cases today Ethernet patch cables leave 2 redundant pairs except when the other pairs can be used for providing power to a terminal device, as in the case of an IP Phone or Wireless Access Point receiving 48 Volts DC over the normally unused pairs.

Ethernet patch cords have minimal cable lengths depending on the Ethernet standard in use, with 100 Metres normally being the maximum length for a single patch cable connecting two devices using the 10, 100 and 1000Mbps Ethernet standards. The reason for the maximum length is because of the collision detection function employed by Ethernet on 10, 100 an 1000Mbps connections in half-duplex mode.

Ethernet patch cables sometimes have to be deployed as Crossover Cables when used in certain applications with certain vendor equipment. In this situation the wires 2 pairs in use are crossed over from end to end with the wire on pin 1 connecting to pin 3 and pin 2 connecting to pin 6 end to end. Applications were this might be used include:

Computer to Computer

Hub to Hub

Switch to Switch

Router to Router

Hub to Router

Fibre Optic patch cords or patch cables perform more or less the same function as twisted pair Ethernet patch cables, but can provide higher speed connections. The jacket on Fibre patch cables is normally colour coded to indicate which type of fibre is in use. The two main categories are as follows

Orange                   Multimode Fibre

Yellow                    Single Mode Fibre

In addition to colour coding of the jacket or sleeve, each fibre optic patch cable will normally have a strain relief boot that protects the fibre from being damaged near the connector. These fibre optic strain relief boots are often colour coded to indicate what type of connector is in use as follows:

Blue                        Single Mode Fibre Connector

Grey                       Multi Mode Fibre Connector

Red                         This indicates high optical power is in use

Additionally, individual fibres within a multi-fibre cable may have individually colour coded jackets to distinguish one from another.

Fibre Optic Pigtails are a form of patch cord used with a optical connector on one end to connect to a specific piece of equipment, the other end being left as exposed fibre. The purpose of the exposed fibre end is to allow it to be spliced to a single strand of fibre from a multi-fibre cable. These pigtails can either have female or male connectors on one end to connect to a specific equipment type or patch panel.