DIN EN 61439: The key standard for low-voltage switchgear assemblies

For the first interface—the grid connection—the type and configuration of the utility grid, the rated voltage and frequency, and the grounding and neutral conductor configuration must be specified; separate specifications apply to DC applications. Of central importance is the prospective short-circuit current at the installation site, from which parameters such as the uninfluenced short-circuit current Icp, the conditional rated short-circuit current Icc specified by the manufacturer of the switchgear assembly, the rated short-time withstand current Icw, and the rated breaking capacity Icu. Systems up to 10 kA, as well as current-limited devices up to 17 kA, are exempt from the testing requirement. The second aspect concerns installation and environmental conditions: indoor or outdoor installation, ambient temperature (including daily average), pollution degree, relative humidity, elevation above sea level, electromagnetic environment, as well as space requirements and accessibility. For example, protection class IP20 is often sufficient for dry indoor environments, while different conditions require higher protection classes. In the black-box concept, these specifications are considered normal operating conditions; any deviation must be expressly agreed upon, as it directly affects the thermal analysis, protection class, and device derating.

The third interface concerns the circuits and loads: This includes the number and type of outlets, the rated operating currents of the individual circuits, and the simultaneous use factor or rated load factor, which determines how many outlets can be operated simultaneously and with what load. Cable cross-sections and the direction in which the cables enter must also be specified, as these influence the internal layout of the functional units. In addition, there are selectivity requirements between upstream and downstream protective devices, as well as special requirements related to motor starts or harmonics, which can cause additional heating. The fourth interface governs operation and maintenance: The user group must be clarified—that is, whether qualified personnel or laypeople have access—as well as requirements for potential operation while the system is energized. Equally relevant is whether functional units can be expanded or replaced during operation, what internal compartmentalization is required for this, and how accessibility for maintenance work must be designed. This information regarding interfaces 3 and 4 significantly determines the design and thus the price of the system and should therefore be clarified early in the ordering process between the designer and the manufacturer.

Even after a switchgear assembly has been completed, the issue of responsibility remains relevant as soon as retroactive modifications are made to existing systems. The replacement of components, the retrofitting of additional outputs, or the increase of rated values are permitted only within the limits specified by the existing type approval for the original system. If these limits are exceeded, the role of the original manufacturer may transfer to the company performing the modifications—with the result that the latter must provide its own certifications for the modified scope. For operators, this results in a clear course of action: First, the system’s existing documentation must be reviewed; then, the design rules of the original system provider must be followed. Every modification made must be documented, and the component-by-component verification must be repeated for the modified scope of the system. This principle applies regardless of the system’s size or the extent of the modification and applies to both individual component replacements and more extensive expansions of existing switchgear assemblies.

In the practical collaboration between the client and the switchgear manufacturer, the designer is responsible for clearly defining all interface data for the black-box model and formulating this data in the request for proposals in a verifiable manner—this includes the applicable standard, the rated values, the degree of protection, the internal compartmentalization, selectivity requirements, and environmental conditions. Only a request that is this specific will later enable a reliable comparison of bids from multiple manufacturers. In turn, upon delivery, the user or purchaser verifies that the relevant supporting documents are complete: the individual test report, the information on the nameplate and markings—such as the manufacturer’s name, type designation, rated voltage, rated frequency, rated current, and rated short-circuit current—confirmation of the type approval, and a complete operating and maintenance manual. A sample checklist can serve as a guide for what information a complete inquiry should typically include, such as the scope of delivery, installation site, required expansion capacity, and deadlines for factory acceptance and delivery. It is important to note that a CE marking in accordance with the Low-Voltage Directive 2014/35/EU does not replace the declaration of conformity according to the DIN EN 61439 series of standards, as it refers to the requirements of the directive and not to the product-specific test procedures of the standard. Operators are therefore advised to request both forms of proof separately and to document this in writing during the ordering process.

The design verification encompasses a wide range of technical characteristics, which, depending on their nature, can be substantiated through type testing, calculation, or comparison with a reference design. These include the strength of materials and components, the enclosure’s protection class, air and creepage distances, and protection against electric shock, including the continuity of the protective conductor system. The installation of equipment, internal circuits and connections, the terminals for incoming conductors, insulation properties, heating, short-circuit withstand capability, electromagnetic compatibility, and mechanical function are also tested. For enclosures that have already been tested in accordance with DIN EN 62208, this compliance may be credited toward the type approval required by DIN EN 61439, provided that no significant changes have been made; however, an additional separate test of the mechanical properties remains required. The original manufacturer provides all supporting documentation and retains it for ten years. The binding design rules, within which the switchgear manufacturer —as the manufacturer of the switchgear assembly—is permitted to select and assemble components, are derived from this documentation. This combination of testing, calculation, and reference comparison ensures a uniform level of safety that specialist planners can use as a reliable benchmark when evaluating manufacturer documentation.

The unit inspection is performed as either an in-process or final inspection on each individual switchgear assembly and marks the completion of manufacturing at the plant before the system is released for shipment. First, a visual inspection of the design, wiring, and labeling is conducted, during which compliance with the approved schematic is also verified. Next, the effective protective measures and the continuity of the protective conductor circuit are tested, followed by an insulation test or voltage test. The functional test of the installed equipment and interlocks ensures that protective devices will respond as intended during subsequent operation; finally, the associated documentation is checked for completeness. Unlike the type test specified in the design verification, which is performed once in a laboratory, this testing procedure is repeated for every manufactured combination. The result is a test report that is handed over to the client along with the nameplate and system documentation. It makes sense for purchasers to explicitly request the individual unit test report as an acceptance document and to verify its submission before payment or commissioning. It is important to note that a properly conducted unit inspection does not replace the type approval, as the two forms of certification cover different levels of testing—the design on the one hand, and the actual implementation on the other.

In practice, the distinction between TSK and PTSK often proved to be a source of uncertainty, since the line between fully type-tested and only partially tested assemblies was not always clear, and designers and operators could hardly determine the actual scope of verification for a system designated as PTSK. Particularly in the case of custom-assembled switchgear combinations, it remained unclear which components were covered by type testing and which were supplemented only by calculations or manufacturer specifications. Today’s verification concept resolves this ambiguity by placing testing, comparison with a reference design, and calculation on an equal footing as clearly defined verification methods, among which a choice can be made depending on the characteristic, without this implying a reduced level of verification. For design engineers and procurement professionals, this provides a practical guideline: If the terms TSK or PTSK still appear in current bids, data sheets, or contract documents, this indicates an outdated version of the standard and should be explicitly questioned during the ordering process.

In day-to-day project work, certain misjudgments regarding the status of standards tend to recur; these can be clarified by asking manufacturers specific questions. It is often assumed that a CE marking renders product-specific documentation unnecessary, even though the two documents serve different purposes. Equally common is the assumption that a reference to the base standard alone is sufficient as a basis for conformity, without specifying the relevant product section. The notion that individually certified components automatically result in a tested combination also contradicts the fundamental principle of the standard, according to which the entire system must always be evaluated. Furthermore, an individual unit test is occasionally mistakenly equated with the more comprehensive type approval. Another critical issue is the retroactive installation of arbitrary components without a new evaluation by the manufacturer of the switchgear assembly. Last but not least, the term “TSK” appears in older documents and is mistakenly equated with today’s type approval. By specifically questioning such claims with planners and purchasers, one can determine early on whether the manufacturer’s specifications are actually reliable.

A structured checklist helps in preparing a request for proposals that covers all the relevant requirements for the switchgear manufacturer—it is explicitly intended as a template that should be adapted to each specific project. These include the applicable standard section along with the standard version, power supply type, and prospective short-circuit current at the installation site, as well as the rated values of the system and the individual circuits and the agreed-upon load factor. In addition, environmental conditions, installation type, required protection rating and protection class, as well as the internal layout, must be specified. A complete request for proposal should also include requirements for operation during normal service, planned reserve space for future expansions, and specifications regarding labeling, documentation, and required supporting documentation. Such a verifiable specification prevents subsequent back-and-forth clarifications and makes incoming quotes comparable with one another, since the manufacturer can calculate exclusively within the constraints defined by the planner. If any of this information is missing, the supplier must make its own assumptions—with the risk that subsequent amendments or discrepancies may arise during delivery and acceptance.

When taking delivery of a switchgear assembly, the operator first checks whether the documentation provided by the switchgear manufacturer is complete, including the wiring diagrams, individual test reports, and operating instructions. The information on the nameplate must be compared with the original specifications to identify any discrepancies in the rated values at an early stage. The individual test report serves as proof that the specific system was successfully tested prior to delivery; it must be archived along with the other supporting documents, as subsequent changes can hardly be evaluated without these documents. Furthermore, an initial inspection in accordance with DGUV Regulation 3 in conjunction with DIN VDE 0100-600 must be performed prior to the first commissioning; the system operator is subsequently responsible for ensuring that this inspection is repeated at regular intervals. During ongoing operation, the operator remains obligated to comply with the operating and environmental conditions as well as the load limits specified by the manufacturer, to adhere to maintenance intervals, and to ensure accessibility to the functional units. Periodic inspections must be performed by a qualified electrician in accordance with TRBS 1203 and are legally required under the Industrial Safety Regulation. Any retrofits or expansions must always be documented. Conformity with the DIN EN 61439 series of standards is maintained only as long as operation and modifications remain within the verified limits.