Chapter 9 Electrical Wiring Diagram Basics 201
Copyright Goodheart-Willcox Co., Inc.
an electrical circuit. Sets of contacts are identifi ed as normally open (NO)
or normally closed (NC). Normally open (NO) indicates contacts that are
open in their de-energized state. Normally closed (NC) indicates contacts
that are closed in their de-energized state.
A relay is an electrical switch that is controlled by an external electri-
cal signal. Its electrical contacts are operated by electromagnets. When
an external electrical signal is applied, the relay’s coil becomes energized
and a magnetic fi eld is generated. This magnetic fi eld moves an armature
to change the contact’s positions. Relay contacts are either NO or NC.
A solenoid is an electromagnetic device that converts electric current to
mechanical movement by producing a magnetic fi eld. This device is com-
monly installed into a valve body and used to control the direction of fl ow
of refrigerant, gas, or water by opening, closing, or repositioning the valve.
9.2 Electrical Symbols and Wiring Diagrams
Many symbols used in wiring diagrams represent specifi c electrical com-
ponents and devices in a circuit. These symbols may vary based on who
creates the prints, but they typically follow a standard convention. A
separate reference document is sometimes used in completed diagrams
that identifi es the symbols employed in the diagram. Common electrical
symbols are shown in Figure 9-1. A list of abbreviations is often provided
with many electrical wiring diagrams and is shown in Figure 9-2.
An electrical wiring diagram is a representation of an electrical cir-
cuit and shows how electrical loads, switches, and other devices are con-
nected in an appliance or system. These diagrams provide information
that can be used by both installers and service personnel to install and
troubleshoot electrical systems. There are three common types of electri-
cal wiring diagrams: pictorial diagrams, schematic diagrams, and ladder
diagrams. Each is used for a specifi c purpose. Depending on the type of
wiring diagram being used, the information it contains may vary.
Goodheart-Willcox Publisher
Figure 9-1. Commonly used electrical symbols in wiring.
(continued on next page)
Electrical Symbols
Device Type Symbol
Contacts Normally open
Normally closed
Timed-controlled
Relays Relay coil
Motor starter
MS
Sensors Light-dependent resistor
Thermistor
Electric sensor
Copyright Goodheart-Willcox Co., Inc.
an electrical circuit. Sets of contacts are identifi ed as normally open (NO)
or normally closed (NC). Normally open (NO) indicates contacts that are
open in their de-energized state. Normally closed (NC) indicates contacts
that are closed in their de-energized state.
A relay is an electrical switch that is controlled by an external electri-
cal signal. Its electrical contacts are operated by electromagnets. When
an external electrical signal is applied, the relay’s coil becomes energized
and a magnetic fi eld is generated. This magnetic fi eld moves an armature
to change the contact’s positions. Relay contacts are either NO or NC.
A solenoid is an electromagnetic device that converts electric current to
mechanical movement by producing a magnetic fi eld. This device is com-
monly installed into a valve body and used to control the direction of fl ow
of refrigerant, gas, or water by opening, closing, or repositioning the valve.
9.2 Electrical Symbols and Wiring Diagrams
Many symbols used in wiring diagrams represent specifi c electrical com-
ponents and devices in a circuit. These symbols may vary based on who
creates the prints, but they typically follow a standard convention. A
separate reference document is sometimes used in completed diagrams
that identifi es the symbols employed in the diagram. Common electrical
symbols are shown in Figure 9-1. A list of abbreviations is often provided
with many electrical wiring diagrams and is shown in Figure 9-2.
An electrical wiring diagram is a representation of an electrical cir-
cuit and shows how electrical loads, switches, and other devices are con-
nected in an appliance or system. These diagrams provide information
that can be used by both installers and service personnel to install and
troubleshoot electrical systems. There are three common types of electri-
cal wiring diagrams: pictorial diagrams, schematic diagrams, and ladder
diagrams. Each is used for a specifi c purpose. Depending on the type of
wiring diagram being used, the information it contains may vary.
Goodheart-Willcox Publisher
Figure 9-1. Commonly used electrical symbols in wiring.
(continued on next page)
Electrical Symbols
Device Type Symbol
Contacts Normally open
Normally closed
Timed-controlled
Relays Relay coil
Motor starter
MS
Sensors Light-dependent resistor
Thermistor
Electric sensor