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# Electrical engineering ā The circuit diagram
With electrification in the 19th century a new language emerged: the **Circuit diagram**.
* It describes **components, connections, current paths and functions**.
* Internationally standardized symbols (IEC, DIN) ensure comprehensibility.
* Special role: Until 1968 the circuit diagram also contained the **Logic** ā documented directly via relays, contacts and contactors.
š The circuit diagram made electrical function **visible, traceable and safe**.
Historical development
* **1830s**: First depictions of simple circuits (Faraday, Ohm)
* **1850sā1900**: Expansion of telegraphy and power grids ā need for standardized circuit diagrams
* **20th century**: DIN/IEC symbols, circuit diagrams as a universal language
* **Until 1968**: Circuit diagram = electrical + logic (relays, contactors, contacts)
* **After 1968**: Logic migrated into PLC programs, circuit diagram remained for electrical engineering
## The circuit diagram ā universal language of electrical engineering
Since the mid-19th century circuit diagrams have been the language of electrical engineering. They depict the functioning of electrical systems precisely and comprehensibly worldwide.
One **Circuit diagram** is the central form of representation of electrical and electronic systems. It follows clear standards and regulations (e.g. IEC, DIN, EN) and is, like the technical drawing in mechanical engineering, a **language**, which is understood worldwide. The circuit diagram is not only documentation, but the **exact translation of function and purpose** of an electrical installation.
#### Circuit diagram as language
In the circuit diagram wires, components and their interconnections are represented by **standardized symbols** Each symbol has a unique meaning that is valid internationally. This allows engineers, electricians and manufacturers to work together regardless of language and origin.
A circuit diagram describes:
* **What** is electrically connected (components, wires, terminals)
* **How** it works (switching sequences, current paths, signal routes)
* **What for** it is used for (protection, control, drive, communication)
Thus the circuit diagram is the **central means of communication** between planning, manufacturing, commissioning and maintenance.
#### Historical development
The history of circuit diagrams is closely linked to the development of electrical engineering:
* **Early 19th century**: With the work of Georg Simon Ohm (1827) and Michael Faraday the foundations of electrical engineering were laid. Early depictions of circuits arose as simple sketches.
* **Mid 19th century**: With the expansion of telegraphy and later power plants circuit drawings became necessary. Engineers developed the first symbols for switches, wires and sources.
* **Late 19th century**: With the spread of electric power supply and electric motors standardized circuit diagrams became indispensable.
* **20th century**: International standards (e.g. DIN 40700, later IEC 60617) established uniform symbols for components. This turned the circuit diagram into the **universal technical language** of electrical engineering.
* **Today**: Modern CAE programs (Computer Aided Engineering) enable the digital creation, management and simulation of circuit diagrams. Nevertheless the circuit diagram remains the **legally binding document** for construction, function and testing of electrical systems.
#### Importance in electrical engineering and mechanical engineering
The circuit diagram is in mechanical and electrical engineering **indispensable**:
1. **Clarity** ā it shows the function clearly and according to standards.
2. **safety** ā only through circuit diagrams can electrical systems be tested and operated reliably.
3. **Communication** ā all parties involved (design, assembly, commissioning, service) speak the same language.
4. **Legal certainty** ā the circuit diagram is an official document that is decisive for approvals, tests and liability issues.
š In summary:\
Since the mid-19th century **circuit diagrams have been the language of electrical engineering**. They depict the functioning of electrical systems precisely and comprehensibly worldwide. Like the technical drawing in mechanical engineering, they are a **cornerstone of modern technology** ā without them neither safe operation nor international collaboration would be possible.
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