Copyright Goodheart-Willcox Co., Inc. 200
Introduction
Project plans provide a road map, or set of instructions, that contractors
follow to execute the job as envisioned by an architect or project owner.
This includes being able to understand and use electrical wiring diagrams
to complete a project. Electrical diagrams are different from mechanical
drawings, which show the location of mechanical equipment in an
HVACR or plumbing system. Instead, electrical diagrams indicate the
path of the fl ow of electrical current through wiring and other system
components, such as sensors and control devices.
Properly installing and connecting electrical components ensures
that the system functions as intended. An HVACR contractor must
understand system wiring and know how to read various electrical
wiring diagrams. This chapter introduces different types of wiring
diagrams and how to understand them. You will then learn how to
apply this knowledge to effectively and effi ciently troubleshoot various
pieces of HVACR equipment.
9.1 Electrical Devices
Many types of electrical devices used in an HVACR system are noted in
electrical wiring diagrams. Electrical circuits are employed to control the
system devices that regulate or maintain the operation of an HVACR sys-
tem. Some circuits respond to sensed external conditions, such as room
temperature, to ensure the system operates as intended. Other circuits
control electrical fl ow in response to internal system conditions, such as
the unit’s operating temperatures and pressures.
Some electrical devices are operational devices that open and close their
contacts during the normal operation of the system. Other devices are clas-
sifi ed as safety devices that remain closed and allow current to fl ow through
them as long as the system is operating within its design parameters. If unsafe
conditions are present, safety devices respond by de-energizing the entire sys-
tem, or parts thereof. You must understand the function of electrical compo-
nents to determine how they operate within an HVACR system.
A switch is a device that opens or closes one or more connections in an
electrical circuit. Simple switches have only two positions: closed, where an
electrical connection is completed and open, where an electrical connection
is interrupted. Switches are used for many HVACR applications and can
respond to a number of different conditions, including pressure, tempera-
ture, humidity, water level, time, light, motion, and fl uid fl ow.
Switches can be confi gured in many different ways, but are commonly
identifi ed by the number of poles and throws with which they have been
fabricated. The term pole indicates how many power lines can be open,
closed, or redirected at the same time. For example, a single-pole switch
can open or close one single power line, while a two-pole switch can open
or close two lines simultaneously. The term throw indicates how many
possible circuits or current paths the switch controls. A single-throw switch
controls the current fl ow through a single path. A double-throw switch
directs current fl ow through either one of two possible current paths.
A switch opens or closes a circuit by connecting or disconnecting
contacts. A contact is the part that is touched or manipulated to complete
Technical Terms
contact
electrical wiring diagram
ladder diagram
normally closed (NC)
normally open (NO)
pictorial wiring diagram
pole
relay
schematic diagram
sequence of operations
solenoid
switch
thermostat
throw
Introduction
Project plans provide a road map, or set of instructions, that contractors
follow to execute the job as envisioned by an architect or project owner.
This includes being able to understand and use electrical wiring diagrams
to complete a project. Electrical diagrams are different from mechanical
drawings, which show the location of mechanical equipment in an
HVACR or plumbing system. Instead, electrical diagrams indicate the
path of the fl ow of electrical current through wiring and other system
components, such as sensors and control devices.
Properly installing and connecting electrical components ensures
that the system functions as intended. An HVACR contractor must
understand system wiring and know how to read various electrical
wiring diagrams. This chapter introduces different types of wiring
diagrams and how to understand them. You will then learn how to
apply this knowledge to effectively and effi ciently troubleshoot various
pieces of HVACR equipment.
9.1 Electrical Devices
Many types of electrical devices used in an HVACR system are noted in
electrical wiring diagrams. Electrical circuits are employed to control the
system devices that regulate or maintain the operation of an HVACR sys-
tem. Some circuits respond to sensed external conditions, such as room
temperature, to ensure the system operates as intended. Other circuits
control electrical fl ow in response to internal system conditions, such as
the unit’s operating temperatures and pressures.
Some electrical devices are operational devices that open and close their
contacts during the normal operation of the system. Other devices are clas-
sifi ed as safety devices that remain closed and allow current to fl ow through
them as long as the system is operating within its design parameters. If unsafe
conditions are present, safety devices respond by de-energizing the entire sys-
tem, or parts thereof. You must understand the function of electrical compo-
nents to determine how they operate within an HVACR system.
A switch is a device that opens or closes one or more connections in an
electrical circuit. Simple switches have only two positions: closed, where an
electrical connection is completed and open, where an electrical connection
is interrupted. Switches are used for many HVACR applications and can
respond to a number of different conditions, including pressure, tempera-
ture, humidity, water level, time, light, motion, and fl uid fl ow.
Switches can be confi gured in many different ways, but are commonly
identifi ed by the number of poles and throws with which they have been
fabricated. The term pole indicates how many power lines can be open,
closed, or redirected at the same time. For example, a single-pole switch
can open or close one single power line, while a two-pole switch can open
or close two lines simultaneously. The term throw indicates how many
possible circuits or current paths the switch controls. A single-throw switch
controls the current fl ow through a single path. A double-throw switch
directs current fl ow through either one of two possible current paths.
A switch opens or closes a circuit by connecting or disconnecting
contacts. A contact is the part that is touched or manipulated to complete
Technical Terms
contact
electrical wiring diagram
ladder diagram
normally closed (NC)
normally open (NO)
pictorial wiring diagram
pole
relay
schematic diagram
sequence of operations
solenoid
switch
thermostat
throw