Electricity & Electronics, 10th Edition Page 62 (62 of 528)

62 Fundamentals of Electricity and Electronics
Switch ratings
Switches are rated for ampacity and voltage. The
ampacity rating of a switch is an indication of how much
current it can safely handle. The voltage rating is the
maximum voltage for which a switch is designed.
Exceeding the maximum voltage rating will cause the
electrical-mechanical circuitry inside the switch to fail.
For example, if a toggle switch is rated as one amp and 24
volts, a current in excess of one amp will burn out the
switching circuitry inside the switch. If the 24-volt switch
A complete circuit
is provided by the
two SPDT switches.
Switch B is now
open and the
electron path is
now incomplete
to the lamp.
B
B
A
A
L
L
Figure 3-15. Two single-pole double-throw switches
(SPDT) can be used to control a lamp from two different
locations.
is connected to a 240-volt circuit, it may fail to open the
circuit sufficiently to stop the flow of electrons. This
action will result in a dangerous situation that can melt
the switch’s insulation and short circuit the switch.
Connectors
There are many types of connectors used with
electrical conductors. The type of connection used varies
according to the type and size of the conductor, the
purpose served by the connection, and the type of device
to be connected. Look at Figure 3-16. You will see many
common types of connectors. One general classification
is solderless connectors. A solderless connector does
not require the use of solder to make the connection.
These connectors generally require a crimping tool. The
crimping tool squeezes the connector to the conductor.
Figure 3-16 shows common wire crimps on terminals
and splices.
Some types of connectors use screws and bolts to
form the mechanical connection to conductors. These
connectors are used primarily for larger conductors. See
Figure 3-17.
Circuit Protection Devices
Common circuit protection devices are fuses and cir-
cuit breakers. Fuses, such as those shown in Figure 3-18,
are constructed from small, fine wire. This wire is engi-
neered to burn if certain amperages are exceeded. Fuses
are sized by their voltage and current capacity, primarily
current.
Toggle switch
Slide switch
Double-pole double-throw switch
Rotary switch
Roller switch
Figure 3-14. Typical switch types. Notice how many have
the same electrical symbol but different actuators.

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62 Fundamentals of Electricity and Electronics
Switch ratings
Switches are rated for ampacity and voltage. The
ampacity rating of a switch is an indication of how much
current it can safely handle. The voltage rating is the
maximum voltage for which a switch is designed.
Exceeding the maximum voltage rating will cause the
electrical-mechanical circuitry inside the switch to fail.
For example, if a toggle switch is rated as one amp and 24
volts, a current in excess of one amp will burn out the
switching circuitry inside the switch. If the 24-volt switch
A complete circuit
is provided by the
two SPDT switches.
Switch B is now
open and the
electron path is
now incomplete
to the lamp.
B
B
A
A
L
L
Figure 3-15. Two single-pole double-throw switches
(SPDT) can be used to control a lamp from two different
locations.
is connected to a 240-volt circuit, it may fail to open the
circuit sufficiently to stop the flow of electrons. This
action will result in a dangerous situation that can melt
the switch’s insulation and short circuit the switch.
Connectors
There are many types of connectors used with
electrical conductors. The type of connection used varies
according to the type and size of the conductor, the
purpose served by the connection, and the type of device
to be connected. Look at Figure 3-16. You will see many
common types of connectors. One general classification
is solderless connectors. A solderless connector does
not require the use of solder to make the connection.
These connectors generally require a crimping tool. The
crimping tool squeezes the connector to the conductor.
Figure 3-16 shows common wire crimps on terminals
and splices.
Some types of connectors use screws and bolts to
form the mechanical connection to conductors. These
connectors are used primarily for larger conductors. See
Figure 3-17.
Circuit Protection Devices
Common circuit protection devices are fuses and cir-
cuit breakers. Fuses, such as those shown in Figure 3-18,
are constructed from small, fine wire. This wire is engi-
neered to burn if certain amperages are exceeded. Fuses
are sized by their voltage and current capacity, primarily
current.
Toggle switch
Slide switch
Double-pole double-throw switch
Rotary switch
Roller switch
Figure 3-14. Typical switch types. Notice how many have
the same electrical symbol but different actuators.

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Chapter 3 Introduction to Basic Electrical Circuit Materials 63
For example, a three-amp fuse is designed to burn
and open the circuit when the current exceeds three amps.
A load that draws three amps or greater will generate suf-
ficient heat in the fuse to melt the fuse link inside the
glass tube. The time required to melt the fuse link is
inversely proportional to the amount of overload. This
means that the higher the overload current, the faster the
melting action occurs. When a fuse melts, it must be
replaced.
A circuit breaker, sometimes called a reset, is
another device used to protect a circuit from overload and
short circuit conditions. See Figure 3-19. The main
advantage of a circuit breaker over the fuse link is that the
circuit breaker need not be replaced after tripping. It can
be reset by moving the handle to the off position and then
returning it to the on position. Some circuit breakers have
Ring terminal
Insulated ring terminal
Flange terminal
Inline splice
Crimping area
Termination block
Fork terminal
Stranded conductor
Wire
cutter
crimping
holes
Insulation
stripping
holes
Insulated
handles
Figure 3-16. Some wire connectors are made to be crimped on the end of stranded conductors. After the connector is
crimped on the wire, the wire can be easily secured under a termination block screw.
Wire nut
connector
Conductors are twisted
together and then
inserted inside the wire
nut solderless connector.
The wire nut is then
twisted onto the
conductors, finishing
the connection.
Two or more conductors are
inserted into the slot. The nut
is turned with a wrench and tightens
the conductors together.
Nut
Split-bolt connector
Figure 3-17. Two types of solderless connectors are the
wire nut connector and the split-bolt connector. The wire
nut is used extensively in residential and commercial
wiring. The split-bolt connector is used mainly on large
diameter conductors.
Figure 3-18. A typical fuse and the schematic symbol that
represents the fuse.

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Chapter 3 Introduction to Basic Electrical Circuit Materials 61
economics. If a low number of boards are to be produced,
hand assembly is less costly. If thousands of boards are to
be produced and assembled, automated systems are used.
Chassis
In the early years of electronics, components were
mounted on metallic surfaces called chassis. The chassis
itself served as part of the circuitry. Use of a chassis as a
conductor is not as common today, but it is still in great
use. One of the most visible uses of the chassis as a con-
ductor is in the automobile. The metal frame and body
parts serve as a chassis providing a conductor path for the
negative side (ground) of the circuit. See Figure 3-13.
The positive line leaves the positive battery terminal
and connects to a device such as the car’s headlamps. A
fuse or circuit breaker is in series with the lamps for pro-
tection. A switch is also in series for turning the lamps on
and off. The return to the negative side of the battery is
through the frame or car chassis itself. The negative
conductor for the lamp simply terminates at the lamp
location, connecting to the metallic shell of the car. The
electrons return to the battery through the metallic frame
of the car.
4. Connection of devices to a PCB is usually made by
__________.
5. What other types of transportation could use the
frame for part of the electrical circuit?
3.3 COMMON CIRCUIT DEVICES
There are several common circuit devices that are
present in most electrical and electronic circuits. They
provide a means of controlling electron flow through the
conductor paths and provide for safe operation of circuits.
The three important items discussed here are switches,
connectors, and circuit protection devices.
Switches
Switches are installed in circuits to control the flow
of electrons through the circuit. They can be categorized
by their actuator and electrical switching path. The
actuator is the mechanical device that causes the circuit
to open and close. Various types of switches are illus-
trated in Figure 3-14. The schematic symbol associated
with each type of switch is also included.
Some of the most common actuators are the slide,
toggle, rotary, and push button. As you can see, the name
of the switch indicates the type of actuator used to turn
the circuit on and off. The electrical circuit inside the
switch is described in terms of poles and throws. The
simplest type of switch is the single-pole single-throw
switch, which is abbreviated SPST. The term single-pole
means that the switch provides one path for the electron
flow and that it can be turned on or off. The term
single-throw means that the switch controls only one
circuit.
A single-pole double-throw switch (SPDT) has one
common connection point and can complete a circuit path
to two different circuits. However, only one circuit can be
completed at a time. There are many possibilities and
combinations for a switch of this type.
A useful application of the single-pole double-throw
switch is its ability to control a load, such as a lamp, from
two different locations. In residential wiring systems, the
single-pole double-throw switch is referred to as a
three-way switch. In Figure 3-15, two single-pole
double-throw switches are connected to a lamp. Either
switch is capable of turning the lamp on or off.
A double-pole double-throw switch (DPDT) has two
common connection points and can provide two circuit
paths simultaneously. The DPDT switch is like having
two SPST switches connected in parallel.
Negative side of the
car battery is connected
to the chassis.
The taillight
circuit is completed
by connecting the
return wire to the
chassis.
The break pedal acts as a switch
to complete the circuit between
the battery and taillight.
Figure 3-13. The frame of the car is used as the return
path for the taillight circuit. This type of wiring is referred to
as chassis wiring.
Review Questions for Section 3.2
1. A temporary circuit is usually wired using a
__________.
2. The most economical way to mass-produce an elec-
tronic circuit is using __________.
3. The automobile is an example of __________
wiring.

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Page 16Section 1 Fundamentals of Electricity and Electronics click to expand contents

Page 102Section 2 Basic Circuits click to expand contents

Page 124Section 3 Motors, Generators, and Power Distribution click to expand contents

Page 208Section 4 Advanced Electronic Circuits click to expand contents

Page 354Section 5 Electronic Communication and Data Systems click to expand contents

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