The main reason for twisting in a twisted pair cable (particularly where two conductors exist together) it to cancel out any electromagnetic interference (EMI) that may be given out by external sources. These external sources could include crosstalk from other nearby pairs of cables or electromagnetic radiation given out by pairs of twisted cables that are not shielded (UTP - unshielded twisted pair). This method was created by Alexander Graham Bell.
UTP cables are most commonly seen in telephone systems and Ethernet networks. The way that they are arranged in outside telephone cables (which may involve hundreds of pairs) and even though they may be twisted in different ways, a great degree of crosstalk may still be experienced, meaning that signals may be disrupted. The wires that are paired together must be carefully selected in order to keep the amount of crosstalk to a minimum.
Unlike in UTP cables, some twisted pairs may be shielded in an extra attempt to minimize electromagnetic interference from external sources. There are three different main types of shielding: Shielded twisted pair (STP or STP-A), Screened twisted pair (ScTP or F/TP) and Screened shielded twisted pair (S/STP or S/FTP). These types of shielding can either be applied to a single pair of cables or a collection of them but when a group of cables are shielded, it is called screening.
There are several advantages that come with twisting cables together, and possibly shielding them with a plastic cover:
• Twisting cables forms a thin and more flexible cable that is easy to string up between walls.
• Twisting means that more lines can be fed through the same ducts.
• An unshielded twisted pair costs a lot less per meter or foot than other types of cable.
• This method prevents electrical noise from going into the cable or being emitted from it.
• Crosstalk from other cables is minimized.
UTP cables are most commonly seen in telephone systems and Ethernet networks. The way that they are arranged in outside telephone cables (which may involve hundreds of pairs) and even though they may be twisted in different ways, a great degree of crosstalk may still be experienced, meaning that signals may be disrupted. The wires that are paired together must be carefully selected in order to keep the amount of crosstalk to a minimum.
Unlike in UTP cables, some twisted pairs may be shielded in an extra attempt to minimize electromagnetic interference from external sources. There are three different main types of shielding: Shielded twisted pair (STP or STP-A), Screened twisted pair (ScTP or F/TP) and Screened shielded twisted pair (S/STP or S/FTP). These types of shielding can either be applied to a single pair of cables or a collection of them but when a group of cables are shielded, it is called screening.
There are several advantages that come with twisting cables together, and possibly shielding them with a plastic cover:
• Twisting cables forms a thin and more flexible cable that is easy to string up between walls.
• Twisting means that more lines can be fed through the same ducts.
• An unshielded twisted pair costs a lot less per meter or foot than other types of cable.
• This method prevents electrical noise from going into the cable or being emitted from it.
• Crosstalk from other cables is minimized.
