Twisted pair

In some countries, the tram companies were held responsible for disruption to existing telegraph lines and had to pay for remedial work.

Telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.

Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines.

[4] By 1900, the entire American telephone network was either twisted pair or open wire with transposition to guard against interference.

Today, most of the twisted pairs in the world are outdoor landlines, owned and maintained by telephone companies, used for voice service.

Unshielded twisted pair (UTP) cables are found in many Ethernet networks and telephone systems.

For indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T.

The cables are typically made with copper wires measured at 22 or 24 American Wire Gauge (AWG) (0.644 or 0.511 mm²),[5] with the colored insulation typically made from an insulator such as polyethylene or FEP and the total package covered in a polyethylene jacket.

[6] As UTP is a balanced transmission line, a balun is needed to connect to unbalanced equipment, for example any using BNC connectors and designed for coaxial cable.

The shield also provides a conduction path by which induced currents can be circulated and returned to the source via a ground reference connection.

Common shield construction types include: An early example of shielded twisted-pair was IBM STP-A, which is a two-pair 150 ohm S/FTP cable defined in 1985 by the IBM Cabling System specifications, and used with Token Ring or FDDI networks.

CW1293 used mostly solid colors on the cores making it difficult to identify the pair it was twisted with without stripping back a large amount of sheath.

These cables are no longer made but are still occasionally encountered in old buildings and in various external areas, commonly rural villages.

A loaded twisted pair has intentionally added inductance and was formerly common practice on telecommunication lines.

One key benefit is that the noise immunity performance of the cable can be protected despite potentially rough handling.

[23] The enhanced performance may be unnecessary and bonding reduces the flexibility of the cable and makes it prone to failure where it is flexed.

It is less flexible than stranded cable and is more prone to failure if repeatedly flexed due to work hardening.

These work via the insulation-displacement method, whereby the device pierces the sides of the insulation and "bites" into the copper conductor to form a connection.

Punchdown blocks are used as patch panels or as break-out boxes, for twisted pair cable.