SFTP stands for Screened Fully shielded Twisted Pair. This is a special type of cable that uses multiple versions of metal shielding to block outside interference from disrupting signals transmitted across the wires. It incorporates the methods employed by several other cables to achieve maximum protection.
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Twisted cables were invented by Alexander Graham Bell. These cables have the forward and return wires of one single circuit twisted together within the cable. This is one of the most basic methods of helping prevent electromagnetic interference from an outside source.
Shielded cables use electromagnetic shielding to add another layer of protection against electromagnetic interference. This shielding is traditionally wrapped around the cable, covering the twisted wires, which are then covered by their own plastic insulation on the outside. The shielding is designed to attract any outside interference and then run that interference into a ground cable.
A screened twisted pair cable has an outer layer of metal shielding that surrounds the entire set of twisted wires within the cable and is then covered by the cable's insulation. Some twisted pair cables have only the outer screening without the shielding on the individual wires. However, an SFTP cable uses all three methods--the twisting, the shielding of each wire and the outer screening--for the maximum protection against outside electromagnetic interference.
Screened and shielded cables are primarily used in many forms of telecommunication, with SFTP cable being the most expensive and usually regarded as the highest quality available. They can be used as telephone cables when they share the same poles as electrical wires. They can also be used in data transmission.
SFTP cables can allow for the fastest transmission because of their maximum protection. However, a shielded cable must be grounded at both ends, or the shielding's protection is greatly compromised. SFTP cables can also be fragile. This type of cable usually requires installation by a professional who can properly ground the cables.
Some people suspect that shielded cable like SFTP cable might act like an antenna because it is designed to attract interference. While shielding and screening does act like an antenna to a small degree, the effect is very minimal because the wires are well defined to impede the interference.