Circuit diagrams, schematic diagrams, or circuit diagrams are an important component of electronic devices and, therefore, also of our UL 508A-certified control cabinets. Here, we explain exactly what a circuit diagram is and what its function is.
What is a circuit diagram?
The term ” wiring diagram” refers to a simple graphical overview of an electrical circuit. Other terms for a wiring diagram include circuit diagram or circuit sketch. The diagram focuses solely on the function of the individual components and their electrical connections. For this reason, wiring diagrams are presented in an abstract and simplified manner. Lines and components are the main elements of these diagrams. With clearly defined and standardized symbols for the components and their connection types, the diagram is easy for experts to understand. The circuit symbols used in Europe comply with the international standard IEC 60617. In North America, the representation formats of the ANSI Y32 standard are used. These diagrams are extremely important in electronics and are created, for example, for the circuits andgrounding of control cabinets.
Example:
Below, we’ll look at the various components of a circuit diagram, using a control cabinet as an example.
How does a circuit diagram work?
When a layperson looks at a circuit diagram, it’s hard to understand the symbols right away. The lines represent the conductive connections. They run between the components. To keep the diagram easy to follow, it’s advisable to avoid having too many intersecting lines. However, if this does happen, you must distinguish whether the connections actually make contact or whether they do not touch in the circuit and merely cross on the sketch. If there is contact—that is, a connection—this is indicated by a black dot. Each component has its own symbol, and a labeling system is often added to ensure unambiguous understanding. It is also important to follow the applicable standard. For example, depending on the standard, the symbol for electrical resistance is either a rectangle or a zigzag line. In Europe, the rectangle is commonly used. In addition to the graphical representation, information is provided through parameters and specific attributes that, for example, more precisely define the electrical parameters of the connections between components. Furthermore, individual elements may include information such as the part number and the manufacturer.
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How do I identify the components in a circuit diagram?
At first glance, the electrical components in a circuit diagram can be identified by their symbols. Below, we show the most important circuit symbols that can be found on every circuit diagram.
Resistance
A resistor is inserted into a circuit to limit the voltage. The purpose of this is to reduce the current. Because the resistor acts as a kind of brake, friction generates heat.
Fuse As the name suggests, fuses are responsible for safety. These electrical components protect the circuit from excessive currents and prevent overloads. For this reason, they are installed in the electrical system so that all the current flows through them.
Capacitor, general
Capacitors consist of two conductive metal plates separated by an insulating material. They are necessary for storing electrical energy and can counteract rapid changes in voltage.
Coil Coils are also referred to as inductors or chokes. They serve as conductors and are usually made of enameled copper wire or high-frequency stranded wire. When an electrical voltage is applied to a coil, the current does not change abruptly, and a rapid rise in current is prevented.
Diode Diodes are, so to speak, like little traffic cops in an electrical circuit. They allow current to flow in one direction and block it in the other. These are referred to as the forward direction and the reverse direction.
The Circuit Diagram as an Important Document
A schematic diagram is an indispensable guide for troubleshooting and resolving malfunctions. Since the schematic diagram provides information about the wiring of the individual circuits and the installed parts and components, it usually allows for quick identification of the cause of the malfunction. With this information, faults can be located, narrowed down, and resolved. In addition, the information about the individual components recorded on the schematic facilitates the procurement of replacement parts. In short: A structured and detailed diagram is the most important foundation for proper and reliable maintenance and servicing of control cabinets.
The Schematic as Documentation for UL Certification
However, circuit diagrams play an important role not only in troubleshooting and fault correction. The circuit diagram is also indispensable for UL certification. A circuit diagram must be submitted for every control cabinet that is permitted to bear a UL label. The schematic diagram is of particular importance in the context of assessing short-circuit withstand capability, known as the SCCR rating. Furthermore, UL certification applies only to the design configuration of the control cabinet at the time of certification. This configuration is documented on the schematic diagram. In other words: If changes are made to the design at a later date, this can be verified using the schematic diagram; the UL certification will then become invalid.
What software is used to create circuit diagrams?
Nowadays, circuit diagrams are, of course, created using computer programs. As with almost all applications, the selection of software for creating circuit diagrams is vast, ranging from freeware for ambitious hobbyists to complex programs with a wide range of features for professional use. In control panel construction, two applications in particular have become the industry standard: SCAD and EPLAN.
Creating Circuit Diagrams with OpenSCAD
OpenSCAD is free CAD software that creates 3D models using its own text-based programming language. The advantage of this program is that, because it uses simple text files, it provides a completely free—that is, unlicensed—file format.
EPLAN
With EPLAN, you can not only draw a two-dimensional schematic but also create a three-dimensional model of the entire control cabinet, resulting in a digital twin of the original. This allows the positioning of all components to be checked and, if necessary, adjusted as early as the planning phase. The digital replica also facilitates the planning and execution of maintenance work on the actual control cabinet. Through its interfaces, EPLAN also ensures a direct connection between planning software and production; EPLAN is therefore fully Industry 4.0-compatible.
What are the advantages of a circuit diagram?
Circuit diagrams make it easier and faster to understand complex electronic systems, such as control panels. The key components of the circuit and their interconnections are represented using standardized symbols and circuit notation. This not only makes the diagrams easier to read—and thus improves understanding of the systems—but also ensures a consistent presentation. The standardized approach and clear layout also facilitate communication among experts and enable more effective troubleshooting and ensure proper power supply.
In addition to providing general information, a circuit diagram also serves the following purposes:
- The sketch of the final circuit diagram serves as the template for the PCB layout design.
- The circuit diagram as input for circuit simulations. Using this graphical representation, the circuit can be simulated and tested on a computer.
Rules for Creating a Circuit Diagram
There are certain rules to follow when creating a schematic diagram. Here, we’ll show you some of the basics for creating a professional schematic:
- Cables are drawn at right angles when there is a change in direction
- Components are never drawn in corners
- Do not route wires through other components
- If possible, place the outputs on the right and the inputs on the left
- Always Keep Things Clear and Organized
- Marking with a dot at branch points
- Tensions higher than those above
- Avoiding Too Many Cable Crossings
- Place component names and values where they are clearly legible
- Rotate, flip, and move elements to avoid cable crossings
- Components spaced sufficiently apart and aligned with one another
- Avoid bends in the line
Zusammenfassung
A schematic diagram—that is, a graphical representation of an electrical circuit—is indispensable both for troubleshooting and for the UL certification of a control cabinet. This is because design changes can be documented using the schematic diagram. It is also of particular importance for the SCCR rating.
Each component in the schematic diagram has its own symbol. The symbols conform to the representations specified in ANSI Standard 32; however, a labeling system is often added to ensure unambiguous understanding. Software programs such as OpenSCAD or EPLAN can be used to create digital representations of control cabinets. However, certain rules apply to their creation; for example, components should never be drawn in corners, and wires should not be routed through other components. A correctly created schematic allows for quick comprehension and simplified communication regarding complex electronic systems.
