e1 – electrical fundamentals # 4 - symbols and wiring diagrams

E1 – Electrical Fundamentals

# 4 - Symbols and Wiring Diagrams

© 2005 Refrigeration Training Services - E1#4 Symbols and Wiring Diagrams v1.2 2

Electrical Loads

• Loads– Consume electricity– Do work

• Examples:– Motors– Solenoids– Heaters – Lights


Motors

Common symbols:

(Letters tell what motor is represented)

COMP EFM IFM

CFM OFMCOMP

COMP

COMP

COMPressor

EFM

Evaporator Fan Motor

CFM

Condenser Fan Motor

IFM

Indoor Fan Motor

OFM

Outdoor Fan Motor


Solenoid

• This will cause an action in a relay or valve

• When current flows through a coil of wire it creates a magnetic field

• Electrical symbol for a solenoid coil:


Solenoid Valve

Magnetic coil energized Plunger

pulled up

Fluid flowsFluid stops

Power off

Plunger drops

Plunger

Seat


Heaters

• Convert electrical energy to heat

• Symbol for resistance heaters:

• Examples of heaters:– Auxiliary strip heaters– Crankcase heaters


Signal Lights

Used to show when something is operating,

or when there is a problem.

Symbol for signal lights:

Letter in the center denotes bulb color:

R RedB Blue

G Green, etc.

RBG


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”


LOAD

CONTROL CIRCUIT

LINE

1 Power In

4 Power Out

Contactor Cutaway

3 Contacts2 Coil


Symbols for Contactors

Symbols are shown “de-energized” (no power) with contacts “normally open”

Coil

Single pole

Contact

Double pole

Triple pole

115v 208-230v, 1 208-230v, 3


Visualizing symbols with power on

• The following slide illustrates what happens when the power is turned on


Contactor coil “energized”

Contacts close

Single pole

Double pole

Triple pole

115v 208-230v, 1 208-230v, 3

Coil Contact


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


Symbols for RELAYSCoil “de-energized” (no power)

Single pole

Normally Closed“NC”

#1 NO#2 NC

#1 NC#2 NO#3 NC

Normally Open“NO”

Double pole

Triple pole

1 2 1 2 3


Visualizing symbols with power on

• The following slide illustrates what happens when the power is turned on


Symbols for RELAYSCoil “energized” (powered up)

Single pole

Normally Closed“NC”

#1 NO#2 NC

#1 NC#2 NO#3 NC

Normally Open“NO”

Double pole

Triple pole

1 2 1 2 3


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


Single Throw Switch Symbols

Single Pole – Single Throw(SPST)

Double Pole – Single Throw(DPST)

Switch openSwitch closed

L2

Switch openSwitch closed

L1


Double Throw Switches

• Each switch position closes a circuit


Single Pole - Double Throw (SPDT)

Contacts 1-3 open Contacts 1-3 closed

1

2

3

Contacts 1-2 closedContacts 1-2 open


Double Pole – Double Throw (DPDT)

1

2

3

4

5

6

Contacts 1-2 closed

Contacts 4-5 closed

Contacts 1-3 closed

Contacts 4-6 closed


Thermostats

CO

OL

OFF

HEAT ONFAN

AU

TO

BO

W

Y

G

R

70 8060

50

6050

7080

• Symbol depicts a bimetal spring which closes and opens the contacts

• Tstats are usually shown in their “normal” position, which is open


Symbols for Thermostats

Cooling thermostat

In actual operationAs the temperature goes up

the rise in temperature causes the bimetal to expandthe expanded bimetal raises the arm

the raised arm closes the contacts


Symbols for Thermostats

Heating thermostat

In actual operationAs the room temperature falls

the fall in temperature causes the bimetal to contractthe contracted bimetal pulls down on the arm

the arm closes the contacts


Pressure Controls

• Symbol depicts a bellows which operates the contacts

• Pressure safety controls are usually shown in their “normal” position, which is closed


Low Pressure Control


Symbols for Pressure Controls

Low pressure control

In actual operationAs the system pressure falls

the fall in pressure causes the bellows to deflatethe deflated bellows pulls down on the arm

the arm opens the contacts


Symbols for Pressure Controls

In actual operationAs the system pressure rises

the rise in pressure causes the bellows to inflatethe inflated bellows raises the arm

the raised arm opens the contacts

High pressure control


Fuses and Overloads

• Symbols for safety devices, such as fuses and overloads, are usually shown closed


Safety Device Symbols

Bimetal overload:

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.

High heat and high amperage open this overload switch.


Introduction to Wiring Diagrams

• The following slide is a diagram of an attic exhaust fan– The fan is controlled by a standard switch


N

Switch controls fan

FM

Attic Exhaust Fan

L1


Adding controls to the diagram

• A thermostat replaces the standard switch • This allows the fan to operate automatically,

based on attic temperatures


L1 N

Add a Thermostat

FM

Simple Circuit for Attic Exhaust Fan

e1 – electrical fundamentals # 4 - symbols and wiring diagrams

Documents

diagrams v1

coil slide

contactors symbols

nc slide

visualizing symbols

following slide

coilcontact slide

motors common symbols