Electrical Relay Diagram
and
P&ID Symbols
From
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Control and PLCs
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Electrical Relay
Diagram Symbols
ELECTRICAL RELAY DIAGRAM SYMBOLS
SWITCHES
Limit
Circuit Circuit
Disconnect
Normally Normally
Interrupter Breaker
Neutral Position
Open Closed
LS LS
Actuated
LS
DISC C1
LS
CB
Held Held
NP
Closed Open
NP
LS LS
Limit (cont.) Liquid Level Vacuum & Pressure Temperature
Proximity Switch
Maintained Normally Normally Normally Normally Normally Normally
Position Open Closed Open Closed Open Closed
Closed Open
LS
PRS PRS FS FS PS PS TS TS
Flow (Air, Water) Foot Toggle Cable Plugging Nonplug
Operated
F FF
Normally Normally Normally Normally
(Emerg.)
PLS PLS PLS
Open Closed Open Closed
Switch
TGS
FLS FLS FTS FTS
COS
PB
PB
R R
Selector Rotary Selector
Plugging
w/Lockout
Nonbridging Bridging
2-Position 3-Position
Coil
Contacts Contacts
SS SS
RSS RSS
1 2 3
F
12
PLS
OR OR
RSS RSS
1
LO
Total Contacts To Suit Needs
Push Buttons Connections, Etc.
Thermocouple
Single Double Circuit Maintained
Conductors
Switch
Circuit Contact
Mushroom Not
Connected
PB
TCS Normally Head Connected
Open
 + PB
PB
PB
OFF
Normally
1  +
Closed
2  + PB
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Electrical Relay
Diagram Symbols
Connections, Etc. (cont.) Contacts
Chassis Time Delay After Coil Relay, Etc.
Plug
Thermal
Or Frame
Ground
and
Over-
Normally Normally Normally Normally Normally Normally
Not Necessarily
Recp.
Load
Open Closed Open Closed Open Closed
Grounded
GRD CH PL TR TR TR TR CR M CR M OL
CON CON IDL
RECP
Coils
Relays, Solenoids, Brakes, Etc. Thermal Control
Timers, Overload Circuit
2-Position 3-Position 2-Position
General
Etc. Hydraulic Pneumatic Lubrication Element Transformer
CR TR SOL SOL SOL SOL OL H1 H3 H2 H4
IOL
M CON
2-H 3-P 2-L
T
X1 X2
Coils (cont.) Motors
Reactors (cont.)
3-Phase DC Motor
Adjustable Magnetic Amplifier
Air Core Motor Armature
Iron Core Winding
MAX MTR MTR
X
A
X
Pilot Lights Horns, Siren, Etc. Buzzer Bell
Push to Test
AH ABU ABE
PL PL
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P&ID
Symbols
P&ID SYMBOLS
I NSTRUMENT LI NE S YMBOLS
Capillary tube
Electric signal
EM, sonic, radioactive
Hydraulic
Pneumatic
Process
SYMBOLS FOR TRANSDUCERS AND ELEMENTS
FE
FE
10
104
Orifice plate Venturi or nozzle
FI
EE
4 5
Magnetic Rotameter
FV
101
Control valve
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P&ID
Symbols
I NSTRUMENT I DENTI FI CATI ON L ETTERI NG
First Letter Second Letter
A Analysis Alarm
B Burner, combustion User s choice*
C User s choice Control
D User s choice
E Voltage Sensory (primary element)
F Flow rate
G User's choice Glass (sight tube)
H Hand (manually initiated)
I Current (electric) Indicate
J Power
K Time or time schedule Control station
L Level Light (pilot)
M User s choice
N User s choice User s choice
O User s choice Orifice, restriction
P Pressure, vacuum Point (test connection)
Q Quantity
R Radiation Record or print
S Speed or frequency Switch
T Temperature Transmit
U Multivariable Multifunction
V Vibration, mechanical analysis Valve, damper, louver
W Weight, force Well
X Unclassified** Unclassified
Y Event, state, or presence Relay, compute
Z Position, dimension Driver, actuator, unclassified
* User s choice may be used to denote a particular meaning, having one
meaning as a first letter and another meaning as a second letter. The user
must describe the particular meaning(s) in the legend. This letter can be used
repetitively in a particular project.
** Unclassified letters may be used only once or to a limited extent. If used, the
letter may have one meaning as a first letter and another meaning as a second
letter. The user must specify the meaning(s) in the legend.
Reference: ANSI/ISA-S5.1-1984, Instrumentation Symbols and Identification, ISBN 0-87664-844-8
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