Electrical Symbols - Contacts and Field Devices The following table provides the IEC and BS Electrical Symbols for contacts. We have included the Normally Open and Normally Closed status for each contact.
Normally Open Conta ct (N/O)
Normally Close d Conta ct (N/C)
Change Over or 2 way Conta ct Made position
Fused Switch Open Cont act (N/O)
Limit Switch (N/O)
Limit Switch (N/C)
Flow Switch (N/O)
Time Delay (N/O) Delay on Closing
Flow Switch (N/C)
Time Delay Flow Switch (N/O) Delay on reopening Thermal
Thermal Switc h -Over load (N/O)
Switc h -Over load (N/C)
Temperature Switc h (N/O)
Temperature Switc h (N/O)
Pressure
Pressure Switc h
(N/O)
Switc h (N/C)
Electrical Symbols - Push-buttons and Lamps The following table provides the commonly used electrical wiring schematic symbols for push buttons and lamps which comply with with the IEC and BS Electrical Electrical Symbols. We have included the Normally Open and Normally Closed status for each contact.
Normally Open PB (N/O)
Normally Closed PB (N/C)
Emergency Stop PB (N/O) Indication Contact
Emergency Stop PB (N/C)
Pull Switch (N/O)
Pull Switch (N/C)
Turn/Rotary Switch (N/O)
Turn/Rotary Switch (N/C)
Lamp (Standard)
Lamp Standard
Lamp (Flashing)
Filament Lamp
Light Emitting Diode (LED)
Bell (Audible)
Siren (Audible)
Buzzer (Audible)
Electrical Symbols - Coils and Relays
The following table provides the commonly used electrical wiring schematic symbols for coils and relays which comply with the IEC and BS Electrical Symbols.
Contactor Coil
General Relay (DC Supply)
Relay with AC Supply
Slow Operating Relay - Delay On
Slow Release Relay Delay Off
Mechanically Latched Relay
Electrical Symbols - Connectors The following table provides the commonly used electrical wiring schematic symbols for connectors which comply with the IEC and BS Electrical Symbols. These connectors include plug and socket, coaxial, terminal and earth connectors.
Plug Male
Socket (plug female)
Coax Plug Male
Slow Operating Relay - Delay On
Wire Connections (Two Wires)
Wire Connections (crossed)
Wires Crossing (Not Connected)
Terminal Connector
Terminal Block
Earth Connection
Noiseless Earth
Protective Earth
Chassis Earth
Equipotentiality
Electrical Symbols - Semi Conductors The following table provides the commonly used electrical wiring schematic symbols for Semi Conductors including diodes, capacitors and transistors.
Diode
Diode Reverse Blocking
Diode Reverse Conducting
Zener Diode
Light Emitting Diode (LED)
Capacitor
Transistor (PNP)
Transistor (NPN)
Bi-directional Triode Thyristor (Triac)
Diac
FORMULAS, EQUATIONS & LAWS
Symbolic: E =VOLTS ~or~ (V = VOLTS) P =WATTS ~or~ (W = WATTS) R = OHMS ~or~ (R = RESISTANCE) I =AMPERES ~or~ (A = AMPERES) HP = HORSEPOWER PF = POWER FACTOR
kW = KILOWATTS kWh = KILOWATT HOUR VA = VOLT-AMPERES kVA = KILOVOLT-AMPERES C = CAPACITANCE EFF = EFFICIENCY (expressed as a decimal) DIRECT CURRENT AMPS=
WATTS÷VOLTS
I = P ÷E A= W ÷ V
WATTS=
VOLTS x AMPS
P=ExI W=VxA
VOLTS=
WATTS ÷ AMPS
E=P÷I V=W÷A
HORSEPOWER= (V x A x EFF)÷746 EFFICIENCY=
(746 x HP)÷(V x A) AC SINGLE PHASE ~ 1ø
AMPS=
WATTS÷(VOLTS x PF) I=P÷(E x PF) A=W÷(V x PF)
WATTS=
VOLTS x AMPS x PF
P=E x I x PF W=V x A x PF
VOLTS=
WATTS÷AMPS
E=P÷I
V=W÷A
VOLT-AMPS=
VOLTS x AMPS
VA=E x I
VA=V x A
HORSEPOWER=
(V x A x EFF x PF)÷746
POWERFACTOR= INPUT WATTS÷(V x A) EFFICIENCY=
(746 x HP)÷(V x A x PF) AC THREE PHASE ~ 3ø
AMPS=
WATTS÷(1.732 x VOLTS x PF) I = P÷(1.732 x E x PF)
WATTS=
1.732 x VOLTS x AMPS x PF
P = 1.732 x E x I x PF
VOLTS=
WATTS÷AMPS
E=P÷I
VOLT-AMPS=
1.732 x VOLTS x AMPS
VA=1.732 x E x I
HORSEPOWER=
(1.732 x V x A x EFF x PF)÷746
POWERFACTOR= INPUT WATTS÷(1.732 x V x A) EFFICIENCY=
