The arrangement of wires that connects your telephone with the central
office and with the telephones of other subscribers is something like a
tree. Just as twigs lead to branches, branches to limbs, and limbs to
the trunk, so individual telephone wires come together in small
_distribution cables_. In turn, these cables come together in _feeder
cables_ that increase in size as they approach the central office. Often
as many as 2,121 pairs of fine copper wires enter the telephone office
in main feeder cables about as big around as a baseball bat.
[Illustration: _Splicers “cutting in” wires in a new cable, below
the street in manhole._]
[Illustration: _Bell telephone installer connects drop wire to new
subscriber’s home._]
Most wire in city telephone cables lies underground in tile conduits and
comes into the telephone office through a _cable vault_ in the basement.
If the city has more than one central office, _trunk cables_
interconnect the offices.
At each telephone office the cables run to the _terminal room_, where
their hundreds or thousands of pairs of wires fan out to _terminal
blocks_ on one side of a large _distributing frame_. Other wires run
from the opposite side of the distributing frame to the switchboard or
dial equipment. Cross-connections on the distributing frame bring each
telephone user’s line to its proper terminal in the switching equipment.
A telephone office is dependent on electric power, both direct and
alternating. The direct current comes from storage batteries. These are
kept charged by generators driven by the regular current supplied by the
power company, which also provides the electricity needed for other
purposes. Standby generators, usually driven by gasoline or diesel
engines, are provided for emergencies in most large offices and in many
smaller ones.
Ringing machines generate alternating current to operate your telephone
bell and provide the various signals you hear in your telephone
receiver. These machines are installed in pairs so that there will be no
interruption of telephone service should one machine fail to operate
properly.
[Illustration: _Technicians check for trouble at a desk in a central
office. Preventive maintenance, outside as well as inside telephone
offices, helps provide good service._]
Preventive maintenance, both inside and outside telephone offices, is
vital in furnishing dependable, satisfactory telephone service.
Telephone men periodically check the condition of telephone plant. Using
steadily improving techniques, they often discover faults or weaknesses
and have them corrected before the customer is aware of them.
Test desks, where testmen also track down troubles in the telephone
plant, are essential to giving good service. These are special
switchboards with equipment that enables the testman to diagnose the
cause and location of trouble on a customer’s line.