Electrical Symbols

Wires joined

A 'blob' should be drawn where wires are connected (joined), but it is sometimes omitted. Wires connected at 'crossroads' should be staggered slightly to form 2 T-junctions.

Inductor (coil, solenoid)

A coil of wire which creates a magnetic field when current passes through it. It may have an iron core inside the coil. It can be used as a transducer converting electrical energy to mechanical energy by pulling on something.

Earth (ground)

A connection to earth. For many electronic circuits this is the 0 V (zero volts) of the power supply, but for main electricity and some radio circuits it really means the earth. It is also known as ground.

Push Switch (push-to-make)

A push switch allows current to flow only when the button is pressed. This is the switch used to operate a doorbell.

Fuse

A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.

Heater

A transducer which converts electrical energy to heat.

Motor

A transducer which converts electrical energy to kinetic energy (motion).

Lamp (lighting)

A transducer which converts electrical energy to light. This symbol is used for a lamp providing illumination, for example a car headlamp/torch bulb. (bottom image)

Lamp (indicator)

A transducer which converts electrical energy to light. This symbol is used for a lamp which is an indicator, for example a warning light on a car dashboard.

Bell

A transducer which converts electrical energy to sound.

Buzzer

A transducer which converts electrical energy to sound.

Wires not joined

In complex diagrams it is often necessary to draw wires crossing even though they aren't connected. -use 'bridge' symbol shown on the right b/c the simple crossing on the left may be misread as a join where you have forgotten to add a 'blob'

On-Off Switch (SPST)

SPST = Single Pole, Single Throw. An on-off switch allows current to flow only when it is in the closed (on) position.

AC supply

Supplies electrical energy. AC = Alternating Current, continually changing direction.

DC supply

Supplies electrical energy. DC = Direct Current, always flowing in one direction.

Battery

Supplies electrical energy. A battery is more than one cell. The larger terminal (on the left) is positive (+).

Cell

Supplies electrical energy. The larger terminal is positive (+). A single cell is often called a battery, but strictly a battery is 2 or more cells joined together.

Push-to-Break Switch

This type of push switch is normally closed (on). It is open (off) only when the button is pressed.

Transformer

Two coils of wire linked by an iron core. Transformers are used to step up (increase) and step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is no electrical connection between the coils.

Wire

to pass current very easily from one part of a circuit to another