EET 110 - Electronics Survey
Chapter 9 - Circuit Conductors &
Most common form is wire
Copper is the most popular metal
• Low resistance
• ease of handing - malleable
Available in solid or stranded form
• solid is less expensive to build
• stranded wire is more flexible
Cable can refer to LARGER stranded wire
Wires are available as single conductors or
bundled into multi-conductor cables.
i.e.. Power cord for electrical equipment
Printed circuit cards - copper cladding is
etched to provide conductor connections.
Conductors are generally covered with an
• magnet wires
Colored insulation is used to identify wires
The size of wire is determined by its
diameter - usually referred to by WIRE
AWG - American Wire Gauge see Fig. 9-9
Circular Mils (CM) is a measure of cross-
sectional area. Used to calculate resistance.
Wire size is measured only at the copper -
not including insulating layer.
A wire gauge is used to measure the
diameter (AWG) of wire.
The maximum amount of current a wire can
Based on material, size, insulating layer and the
• ie: underground versus in wall/conduit
NEC tabulates the ratings of conductors in
Resistance proportional to the material,
cross-sectional area and length of the wire.
R = l /A - where is the resistivity of the
material in question.
is frequently in ohm-CM/ft
A variety of other factors can affect the
resistance of a given conductor.
Voltage drop and power loss
normally wire is taken as having 0 ohms
For long distances or for large currents, this
can become an issue
V = I x R (ohms law)
The power dissipated in a line is given by
P = I2 x R
For Example - take a 12 Gauge wire
carrying 20 Amps
From the chart, wire has 1.588 per 1000’
V = IxR = 31.76 volts
If the source was a 110 volt line,
VL = 110 - 31.76 = 78.24 volts or 29% drop
P = I2R = 635 watts dissipated in the wire
The solution to running this much power
(20A) that far (1000 feet) would be to either
use a larger diameter wire
10 gauge - loss would be 400 W
5 gauge - 125 W
0 gauge - 39 W
Here we increase the Area - to decrease
Typically to deliver large amounts of
power, the Power Company, uses P=V x I
to reduce the loss in a give size of wire
110V x 20A = 2200W
Using transformers, the voltage can be
stepped up (and current down) to put on the
wire and vice versa at the other end.
Step voltage up to 1100 v reduces current to
2A in transport wire
Loss in 12 gauge is 6.35 W versus 635 watts
voltage drop in wire is only 3.176 volts - or