Electrical Training Symbol Functions

Front 1

stores DC voltage

Back 1

Battery

Front 2

Electrical grounding connection to earth. Also used as a chassis ground on EMD Locomotive

Back 2

Earth Ground

Front 3

Electrical grounding connection to the chassis or frame of a piece of equipment

Back 3

Chassis Ground

Front 4

Allows current flow in one direction only

Back 4

Diode

Front 5

A diode which allows current to follow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the inverse direction when the voltage is above a certain value known as the breakdown voltage

Back 5

Zener Diode

Front 6

Indicates applied voltage when illuminated

Back 6

Light Emitting Diode (LED)

Front 7

A gated diode. Only conducts electricity when a voltage is applied to the gate wire

Back 7

Silicon controlled Rectifier (SCR)

Front 8

High speed switching device

Back 8

NPN Transistor

PNP Transistor

Front 9

Temorarily stores an electrical charge. May be polarized

Back 9

Cpacitor

Front 10

Produces an output voltage that is typically hundreds of thousands of times larger than the voltage difference between its input terminals

Back 10

Operational Amplifier

Front 11

Representative of a more in depth circuit May include diodes transistors, capacitors, Zeners, resistors, etc.

Back 11

Transistorized Circuit

Front 12

A protective device which must be replaced when it fails

Back 12

Fuse

Front 13

Circuit protection device which be reset after it is tripped

Back 13

Instant Trip Circuit Breaker

Thermal Circuit Breaker

Front 14

Limits current flow, has a fixed value

Back 14

Resistor

Front 15

Resistance cannot be adjusted

Back 15

Tapped Resistor

Front 16

Resistance can Vary when manually adjusted

Back 16

Slider Resistor

Front 17

Low voltage Resistor

Back 17

Shut

Front 18

A resistor whose value changes due to applied voltage change

Back 18

Varistor

Front 19

A resistance will vary as arm rotates.

The two methods of drawing this symbol are shown here.

Back 19

Rheostat

Potentiometer

Front 20

Part of the excitation circuit for traction motors and alternators. When voltage is applied a magnetic field is created that then induces a voltage into the output windings of the motor or altarnator. Windings are also found in transformer.

Back 20

Field Winding

Front 21

Generates AC voltage when its field windings are excited. Used to supplu high voltage for the traction motors

Back 21

Three Phase Alternator

Front 22

Steps AC Voltage Up or Down

Back 22

Transformer

Multiple Transformer

Front 23

Convert AC voltage to DC voltage

Back 23

Full wave Bridge Rectifier

Front 24

Magnetic device that opens or closes sets of contacts in relay or contactor. May also be used with air or fluid valves

Back 24

Relay coil

Front 25

Opens or closes a circuit base on the condition of its associated relay coil

Back 25

Normally Open Contact or Interlock - Single Break (NO)

Normally Closed Contact or Interlock - Single Break (NC)

Normally Open Contact or Interlock - Double Break (NO)

Normally Closed Contact or Interlock - Double Break (NC)

Front 26

Manually operated switch to open or close a circuit

Back 26

Single Pole Single Throw Switch

Single Pole Double Throw Switch

Double Pole Single Throw Switch

Double Pole Double Throw Switch

Front 27

Manually operated, momentary contact switch to open or close a circuit

Back 27

Push Button Swithc

Front 28

Open or closes a circuit based on applied pressure. Can be operated by air, water, fuel,etc.

Back 28

Pressure Switch

Front 29

Opens or closes a circuit based on applied temperature. Can be used in air, water, fuel, etc.

Back 29

Thermal Switch

Front 30

Rotational switch that open or closes a circuit "air or electrically operated"

Back 30

Cam Operated Switch

Front 31

Drives axles to move locomotive. Shown in two parts, the armature and the field

Back 31

Traction Motor

Front 32

Senses current flow in cables or wires passing through their center. These do not emit a current. Their resistance value changes based on applied EMF.

Back 32

Transducer

Front 33

Measure current going to the traction motors

Back 33

Load Ammeter

Front 34

Mounted to traction axle. supplies current for operation of the speed indicator.

Back 34

Axle Alternator

Front 35

Mounted in the cab. Supplies warning to the crew of a trouble.

Back 35

Bell