Transcript E1 Subject 2

E1 – Electrical Fundamentals
# 4 - Symbols and Wiring Diagrams
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Electrical Loads
• Loads
– Consume electricity
– Do work
• Examples:
– Motors
– Solenoids
– Heaters
– Lights
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Motors
Common symbols:
(Letters tell what motor is represented)
COMP
EFM
IFM
COMPressor
Evaporator Fan Motor
Indoor Fan Motor
COMP
CFM
OFM
Condenser Fan Motor
Outdoor Fan Motor
COMP
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Solenoid
• When current flows through a coil of wire it
creates a magnetic field
• This will cause an action in a relay or valve
• Electrical symbol for a solenoid coil:
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Solenoid Valve
Magnetic coil
energized
Plunger
pulled up
Power off
Plunger drops
Plunger
Fluid flows
Fluid stops
Seat
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Heaters
• Convert electrical energy to heat
• Symbol for resistance heaters:
• Examples of heaters:
– Auxiliary strip heaters
– Crankcase heaters
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Signal Lights
Used to show when something is operating,
or when there is a problem.
Symbol for signal lights:
B
R
G
Letter in the center denotes bulb color:
R Red
B Blue
G Green, etc.
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Contactor
• It is a mechanical switch, operated by a
magnetic coil
• Energizing the coil closes the contacts
• Power flows through the contacts to the load
• For more on contactors:
– See Topic E2 Subject 3 “Contactors and Motor
Starters”
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Contactor Cutaway
LINE
1 Power In
CONTROL
CIRCUIT
2 Coil
3 Contacts
4 Power Out
LOAD
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Symbols for Contactors
Coil
Contact
Single
pole
115v
Double
pole
208-230v, 1
Triple
pole
208-230v, 3
Symbols are shown “de-energized” (no power)
with contacts “normally open”
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Visualizing symbols with power on
• The following slide illustrates what
happens when the power is turned on
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Contactor coil “energized”
Contacts close
Coil
Contact
Single
pole
115v
Double
pole
208-230v, 1
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Triple
pole
208-230v, 3
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Relays
• Similar to contactors
• Usually under 20 amp capacity
• Contacts may be:
– Normally open (NO)
– Normally closed (NC)
– Or a combination of NO and NC
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Symbols for RELAYS
Coil “de-energized” (no power)
Normally Open
“NO”
1
Single
pole
Double
pole
Triple
pole
#1 NO
#2 NC
#1 NC
#2 NO
#3 NC
2
Normally Closed
“NC”
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Visualizing symbols with power on
• The following slide illustrates what
happens when the power is turned on
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Symbols for RELAYS
Coil “energized” (powered up)
Normally Open
“NO”
1
Single
pole
Double
pole
Triple
pole
#1 NO
#2 NC
#1 NC
#2 NO
#3 NC
2
Normally Closed
“NC”
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Introduction to switches
• Switches open and close contacts to
control a load
– Contact:
• the conducting part of a switch
– Poles:
• the number of contacts in a switch
– Throw:
• the number of closed contact positions per pole
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Single Throw Switch Symbols
Switchclosed
open
Switch
Single Pole – Single Throw
(SPST)
L1
L2
Switchclosed
open
Switch
Double Pole – Single Throw
(DPST)
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Double Throw Switches
• Each switch position closes a circuit
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Single Pole - Double Throw (SPDT)
open
Contacts 1-2 closed
2
1
3
Contacts 1-3 closed
open
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Double Pole – Double Throw (DPDT)
Contacts 1-3
1-2 closed
2
1
3
5
4
6
Contacts 4-6
4-5 closed
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Thermostats
• Symbol depicts a bimetal
spring which closes and
opens the contacts
• Tstats are usually shown in
their “normal” position, which
is open
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B G
O
Y
R
W
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Symbols for Thermostats
Cooling thermostat
In actual operation
As the temperature goes up
the rise in temperature causes the bimetal to expand
the expanded bimetal raises the arm
the raised arm closes the contacts
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Symbols for Thermostats
Heating thermostat
In actual operation
As the room temperature falls
the fall in temperature causes the bimetal to contract
the contracted bimetal pulls down on the arm
the arm closes the contacts
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Pressure Controls
• Symbol depicts a bellows which
operates the contacts
• Pressure safety controls are usually
shown in their “normal” position, which
is closed
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Low Pressure Control
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Symbols for Pressure Controls
Low pressure control
In actual operation
As the system pressure falls
the fall in pressure causes the bellows to deflate
the deflated bellows pulls down on the arm
the arm opens the contacts
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Symbols for Pressure Controls
High pressure control
In actual operation
As the system pressure rises
the rise in pressure causes the bellows to inflate
the inflated bellows raises the arm
the raised arm opens the contacts
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Fuses and Overloads
• Symbols for safety devices, such as
fuses and overloads, are usually shown
closed
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Safety Device Symbols
Bimetal overload:
High heat and high amperage open this
overload switch.
Thermal overload relay:
Excessive amperage heats the thermal
element, which opens the switch.
Magnetic overload relay:
Excessive amperage creates a magnetic
field, which opens the switch.
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Introduction to Wiring Diagrams
• The following slide is a diagram of an
attic exhaust fan
– The fan is controlled by a standard switch
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Attic Exhaust Fan
L1
N
Switch controls fan
FM
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Adding controls to the diagram
• A thermostat replaces the standard switch
• This allows the fan to operate automatically,
based on attic temperatures
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Simple Circuit for Attic Exhaust Fan
L1
N
Add a Thermostat
FM
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