Electrical Symbols with Connection Points
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Input Terminals
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Output Terminals
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I/O Terminals
Circuit Breakers
Circuit Breaker (single pole)
IN
OUT
Input: Top terminal | Output: Bottom terminal
Circuit Breaker (double pole)
L1
L2
T1
T2
Input: L1, L2 | Output: T1, T2
Circuit Breaker (triple pole)
L1
L2
L3
T1
T2
T3
Input: L1, L2, L3 | Output: T1, T2, T3
Control Elements
Push button (start)
I
IN
OUT
Normally Open Contact | Closes when pressed
Push button (stop)
O
IN
OUT
Normally Closed Contact | Opens when pressed
Switch (single pole)
IN
OUT
Manual switch | Controls circuit continuity
Coils and Contactors
Coil (contactor)
A1
A2
C
Coil terminals: A1, A2 (24V AC/DC typical)
Contactor (triple)
1
2
3
4
5
6
A1
A2
Power: 1,3,5 → 2,4,6 | Control: A1, A2
Contacts
Contact of contactor (n/o - normally open)
C
IN
OUT
Opens when contactor is energized
Contact of contactor (n/c - normally close)
C
IN
OUT
Closes when contactor is energized
Contact of time relay (n/o - normally open)
T
IN
OUT
Time delayed opening contact
Contact of time relay (n/c - normally close)
T
IN
OUT
Time delayed closing contact
Relays
Overload relay (triple pole)
O/L
L1
L2
L3
T1
T2
T3
Power: L1,L2,L3 → T1,T2,T3
Motors
Motor (A.C.)
M
~
L
N
Single phase AC motor | L-N connection
Motor Three-phase induction (direct on line)
M
3~
U
V
W
Three-phase motor | U, V, W terminals
Motor Three-phase induction (star-delta)
M
3~
U1
V1
W1
U2
V2
W2
Star-Delta starter motor | U1,V1,W1 and U2,V2,W2
Measurements
Energy meter (kilo Watt hour meter)
kWh
L
N
L
N
Measures energy consumption | In series with load
Ammeter
A
IN
OUT
Measures current | Connect in series with load
Voltmeter
V
+
-
Measures voltage | Connect in parallel
Earth connection
Protective earth connection
Lamps
Lamp (incandescent)
L
N
Incandescent lamp | L-N connection
Lamp (indication)
P
+
-
Pilot light | Status indication
Passive Components
Resistor
1
2
Fixed resistor | Non-polarized
Variable Resistor
1
2
Variable resistor | Terminals: 1, 2
Capacitor
+
-
Capacitor | Polarity marked if electrolytic
Safety Components
Fuse
IN
OUT
F1
Protection device | Breaks on overcurrent
Power Distribution
Connections to supply
L1
L2
L3
N
L1
L2
L3
N
Three-phase power distribution | L1, L2, L3, N