Copyright Goodheart-Willcox Co., Inc.
230 Engineering Fundamentals
Series-Parallel Combination
Circuits
Series-parallel combination circuits are not
simply series or parallel. They are a combina-
tion of both types of circuits. Therefore, the
rules and formulas for solving a series or paral-
lel circuit cannot be used. In order to study a
series-parallel circuit, the parallel parts must be
broken down and studied as if they were series
elements. Figure  11-13 shows a series-parallel
circuit with three lights where the fi rst light is
in series and the other two lights are in paral-
lel. The light in series would be much brighter
because it receives roughly twice the current of
each of the other two.
See Workbook Activity 11-6 to use Ohm’s
Law and Watt’s Law to calculate values in
series and parallel circuits and Workbook
Activity 11-7 to reinforce circuit identification.
Circuit Components
Electrical engineers must fully understand
each component that can be used in a circuit.
Electrical engineers often design, build, and
troubleshoot electrical circuits. They must know
how each component of the circuit works so
they can select the best parts to solve a given
design problem or troubleshoot a circuit that is
not working properly.
Conductors
Conductors provide a path for current to
fl ow to the parts that will control and use it.
Materials with very low resistance are conduc-
tors. They easily share electrons from one atom to
the next when a charge is applied. Copper is the
most common conductor. Aluminum is not quite
as good as copper, but is lighter and less expen-
sive. Aluminum is often used in thick service
entrance cables that bring electricity into houses.
Silver and gold are better conductors than copper
and aluminum, but are only used in very specifi c
applications due to their cost.
Conductors come in a wide variety of confi g-
urations. They can be solid wire, stranded wire,
ribbon, and bar shapes based on their intended
use. For example, solid copper wire is commonly
used in residential wiring because it does not
need to move once it is installed. If a solid conduc-
tor is bent back and forth too many times, it will
break like a paper clip that is bent repeatedly.
Stranded copper wire is used in extension cords
because it bends easily and will not break when
bent repeatedly.
Conductors are sized based on their cross-
sectional area. The size of round conductors
is determined using the American Wire Gage
(AWG) system. In the AWG system, smaller
numbers represent larger wire. For instance,
12-gage wire is larger than 30-gage wire. 14-gage
wire is commonly used in houses for general
lighting and receptacle circuits. Figure  11-14
shows common wire types.
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Figure 11-13. 
This schematic shows a series-parallel lighting circuit.
Goodheart-Willcox Publisher
Figure 11-14. 
Common solid, stranded, one-conductor, two-conductor,
and three-conductor wire types are shown.