Also known as an electrical diagram, a circuit diagram is a schematic drawing which works as a graphical representation of an electrical circuit. Its purpose is to simplify an electrical circuit and act as a visual tool depicting the laws of electricity, which enables a circuit to be designed, constructed and maintained, and for the fundamental design and purpose of the circuit to be understood.
A circuit diagram uses images and symbols to represent different components of the circuit, such as resistors, capacitors and switches, to show how the circuit’s elements are built and inter-connected. The circuit diagram uses solid lines to show conductors or wires, which determine the path of a circuit. On this path are symbols representing the various elements of a circuit, ie. the power source and resistors.
Circuit diagrams can be very simple, because a circuit effectively only needs three things; a power source, a conductive path and a resistor, but circuit diagrams can also be extremely complex to represent much bigger circuits.
What are circuit diagrams used for?
When a circuit diagram is created it enables engineers and technicians to understand the relative positions of components in a circuit and their relationship to each other. So, this enables the user to establish whether a circuit will work before it is actually built, or by consulting the circuit diagram of a circuit already built, to understand how it works or why a problem might be occurring. So when troubleshooting an electrical problem, the first step should always be to consult a circuit diagram to understand how the circuit has fundamentally been designed and how it ‘should’ be working.
As well as being an essential tool in designing, constructing and maintaining electrical circuits, circuit diagrams can also be used to calculate the current at different points and in different parts of the circuit.
How the components and paths in a circuit diagram are depicted
There are several different ways that the components and paths of a circuit are graphically represented on a circuit diagram. Here we have included the most popular elements of a circuit diagram:
- Electrical cells – These are represented by long and short parallel lines, with the long lines being positive terminals and the short lines being negative terminals
- Battery – These are multiple electrical cells connected together, so are represented by two or more electrical cell symbols connected in series
- Switches – A switch is represented as a line with a gap in it, the gap is bridged to indicate whether the switch is open or closed, ie. whether there is current flow or not
- Wire joint – This is depicted by a wire with a dot or a solid circle, where two or more wires intersect or connect
- Wires crossing without a joint – This is depicted by wires without a dot or solid circle, ie. the wires are not connected
- Electrical bulb – This is a circle with a cross in it
- Resistor – A resistor is depicted by a zigzag line
- Variable resistor – A variable resistor is depicted by a zigzag line with a pointed arrow running through it
- Inductor – This is a coil shaped wire to indicate the loops of a wire
- Fixed capacitor – This is two vertical parallel lines to signify the plates of the capacitor with a space between them
- Polarised capacitor – The two parallel lines as above, but one line is curved or an arrow, which indicates the positive terminal (the negative terminal remains straight)
- Ammeter – A circle with an A inside it
- Voltmeter – A circle with a V inside it
Please note that this section is for information purposes only. Anyone using equipment referred to in this section must be suitably qualified and/or experienced within the respective field. If in doubt before use, please consult a qualified electrician or engineer & thoroughly read all instruction booklets.