58 Fundamentals of Electricity and Electronics
the source voltage of 120 leaves only 87.1 volts for the
load. This amount of voltage is undesirable, and will no
doubt cause equipment failure, especially for an electrical
motor load, such as a drill.
LESSON IN SAFETY:
When using long extension cords to operate lights and
tools, be sure that they have sufficient conductor size.
The larger the wire size used, the smaller the voltage
drop created. Small-diameter extension cord conduc-
tors may heat up and burn. Motor-driven tools at the
end of a long extension cord can heat up and operate
inefficiently.
Temperature of material
A fourth consideration in conductivity is tempera-
ture. Most metals used in conductors, such as copper
and aluminum, increase in resistance as the ambient
temperature rises. Ambient temperature is the tempera-
ture of the material surrounding the conductor, such as
air, water, or soil. In many electronic products, careful
design is necessary to ensure proper ventilation and
radiation of heat from the current carrying conductors.
Many electrical products such as computers have a fan
installed inside the appliance to circulate heat away
from electronic components. These components can be
damaged by heat easily.
When many conductive materials are exposed to
extremely low temperatures, their resistance value app-
roaches zero. These materials become superconductors.
Figure 3-9 is a picture of a superconducting cable. Mag-
nets can be produced from these superconductors. Early
experiments with supermagnets, using superconductors,
produced magnetic fields so powerful that the mag-
net’s housing was crushed by the tremendous force.
Since electrical motors operate on the principles of
magnetism, the more powerful the magnet, the more
powerful the electric motor will be. Superconductive
material is also used in some magnetic imaging med-
ical equipment. The superconductive materials have
made it possible to peer deep into the human body.
Magnetism and electromagnetism will be explained in
detail in Chapter 9.
To make a superconductor, the temperature of the
conductive material must be lowered to nearly absolute
zero, –273°C or –460°F. Liquid nitrogen is used to cool
conductive materials to such a low temperature. Today,
some materials display superconductive properties at
much higher temperatures. In 1987, a team of scientists
produced a superconductor at approximately –270°F.
New applications for superconductors are appearing
everywhere.
Safety Organizations and Standards
There are many different organizations that work
together to protect the worker and the general public from
dangerous conditions and hazards, such as those caused
by improper wiring. These organizations create and use
safety standards, which may then be adopted by govern-
ment agencies.
National Fire Protection Agency
The National Fire Protection Agency (NFPA) is an
organization dedicated to fire protection. The NFPA pro-
vides information about how fires are started and specific
fire prevention methods. NFPA provides many publica-
tions dealing with topics of how to handle volatile chem-
icals and flammable materials. The NFPA produces the
National Electrical Code (NEC), which is a special pub-
lication that relates directly to your course of study of
electricity and electronics.
National Electrical Code
The National Electrical Code (NEC) is a set of elec-
trical standards that should be followed to ensure the
safety of people and property. The set of standards was
developed by NFPA and contains over 700 pages describ-
ing how electrical equipment and systems should be
installed. This is the main guide used for all electrical
construction in the United States. Government agencies
at the city, county, state, and federal levels often adopt the
code in its entirety and may rewrite some of the code to
meet higher standards. The set of standards defines how
electrical work should be accomplished and lists the min-
imal specifications for materials being used.
Figure 3-9. Superconducting cable with insulating wrap-
ping exposed. (Fermi National Accelerator Laboratory)