Rev. 11/10/00
1
Mastering The Fundamentals
BASIC ELECTRONICS
This section provides an overview of basic electronics and the theory
associated with outside plant telephone circuitry. Those not familiar with
electronics should review this material for a basic understanding of how the
various electrical characteristics in a circuit interact. It is important to know that
each twisted pair of copper wires in a telephone cable forms a circuit. Topics
covered include copper wire, resistance, current, voltage, Ohm’s law, capacitance,
capacitive reactance, inductance, inductive reactance, power formulas, and the
factors that affect these characteristics.
Copper Wire
Copper wire is the most commonly used material as a conductor in electrical
and telephone circuits due to its excellent electrical properties. Copper wire is
available in many gauges (diameters). The lower the gauge number, the larger the
diameter of the wire. For example, a 10 gauge wire is larger in diameter than a 19
gauge wire. As the gauge increases, the diameter decreases; and the resistive and
capacitive characteristics of the wire to electrical flow increase. Temperature,
humidity and other factors affect the properties of copper wire.
Even though smaller wire diameters offer more resistance, it is the physical
concerns of size and weight of larger wires and cables that lead to the use of small
wires. In a typical environment of 68º Fahrenheit and normal humidity, the length
of different gauge wires when reading 1 ohm resistance on a meter would be: 19
gauge = 125 ft, 22 gauge = 62 ft, 24 gauge = 40 ft, 26 gauge = 25 ft.
Voltage
Voltage is the measurement of electromotive force or difference in potential
between two points. Formulas use the letter V or E. Voltage measurements are
expressed in terms of alternating current (AC) or direct current (DC). Typical
U.S. household voltage is 120 volts AC. Typical automobile batteries are 12 volts
DC. AC voltage can be converted to DC voltage through diode bridges called
rectifiers. Voltages can be increased or decreased through the use of transformers
that either step up or step down the voltage level through a ratio of turns between
the input (primary) and the output (secondary) coils.
