Telephone Line

In 1876 the earliest lines were single electrically conducting metal wires directly connecting one telephone to another with the Earth forming the return circuit. Later in 1878 the Bell Telephone Company ran lines (called the Local Loop ) from each user's telephone to End Office s which performed any necessary electrical switching to allow voice signals to be transmitted to more distant telephones.

These wires were typically Copper , although Aluminium has also been used, and were carried in pairs separated by about 25cm (10") on poles above the ground, and later as Twisted Pair cables. Modern lines may run underground to A Device That Converts the Analogue signal to digital for Transmission on Optical Fiber .

Most houses in the U.S. are wired with four- Conductor RJ-14 copper wire that is capable of handling two telephone lines. Those conductors run to the local Telephone Exchange . When a local call is made, a Telephone Switch connects that Local Loop to the local loop of the number that was dialed. A few homes have four-conductor wires, but are technically one-line RJ-11 , as the second pair was used to provide power for dialpad illumination in some older telephones.

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Telephone Line