In English, the term ” wiring diagram ” refers to electrical circuit diagrams or schematics. They play a particularly important role in the design, certification, and installation of UL control panels.
Relation to UL
The schematic diagram is a fundamental component of a UL-certified control cabinet. On the one hand, it serves as proof of compliance, and on the other hand, it is also required during maintenance or repairs!
What is a wiring diagram?
A wiring diagram is a circuit diagram. It graphically depicts all wires, circuits, components, etc., as well as the electrical circuits formed by them, in schematic form. Standardized symbols are used for this purpose. The circuit diagram is usually part of a whole series of different technical drawings, which are collectively referred to in English as “electrical drawings.” These also include, for example, the types of plans that we refer to in German as “installation plans.”
What is the significance of the wiring diagram for UL?
UL imposes certain requirements on the wiring diagrams that accompany a control cabinet; however, the specifications regarding the provision of the wiring diagram to the end customer —even for a UL-listed control cabinet—are generally more in the nature of general guidelines or recommendations.
The relevant standards contain detailed information on the mandatory documentation required for UL certification. For control cabinets, these are UL 508A and UL 1203, respectively, if the cabinet is located in potentially explosive atmospheres (Ex zones).
The wiring of the circuits must be clearly visible
The complete wiring of the control cabinet (known as “field wiring”) should be clearly shown in the schematic diagram. This may sound trivial, but proper documentation is of great importance (not only) for UL certification.
The wiring diagram shows each component
In addition to the wiring, the schematic should also include every component that was installed in the control cabinet. This means that every coil, terminal block, resistor, etc., is shown in the schematic.
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Of course, the schematic must also be provided to the customer. According to UL, this should ideally be done along with the control cabinet.
How do you find the right wiring diagram for a UL-certified control panel?
To prevent any confusion, the nameplates or type labels on the control cabinet should explicitly refer to the circuit diagram that accompanies the product.
The Environment Surrounding Switches and Electrical Circuits
In addition, a circuit diagram may also include information about components that are not part of the control cabinet but connect it to the local installations at the site.
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The Role of the Wiring Diagram in the SCCR Rating
For the legally required assessment of short-circuit withstand capability (the so-called SCCR rating), the circuit diagram of the corresponding control panel is used, among other things. In this process, the short-circuit withstand capability of each individual component must be tested. The short-circuit withstand capability of the entire control panel is limited to that of its weakest component.
Zusammenfassung
A ” wiring diagram” refers to a circuit diagram. It shows the wiring of the individual circuits in electrical and electronic devices and the components used in their construction. For UL control panels, it is (along with other documents) an important part of the documentation.
