{"id":4095,"date":"2023-01-05T14:02:59","date_gmt":"2023-01-05T13:02:59","guid":{"rendered":"https:\/\/www.gt-engineering.it\/normative-tecniche\/%tipologia_normativa%\/ul-508a\/"},"modified":"2026-04-25T12:02:57","modified_gmt":"2026-04-25T11:02:57","slug":"ul-508a","status":"publish","type":"normativa_tecnica","link":"https:\/\/www.gt-engineering.it\/en\/technical-standards\/ul-and-nfpa-standards\/ul-508a\/","title":{"rendered":"UL 508A: Industrial Control Panels"},"content":{"rendered":"\n\n \n \n \n
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UL 508A<\/strong> is the primary technical standard governing the design and construction of industrial control panels in the United States. Its Canadian equivalent is CSA C22.2 No. 286.<\/h3>\n

Origins of UL 508A: the “Drawer Standard”<\/u><\/strong><\/h3>\n

UL 508A originated as what is informally known as a \u201cdrawer standard.\u201d<\/em> This term refers to internal documents developed by engineers at UL Solutions<\/span><\/span><\/strong> and used exclusively within UL for product certification.<\/p>\n

In the 1970s, the Authority Having Jurisdiction (AHJ) in Chicago, approached UL requesting a formal set of rules to ensure the safe design and construction of industrial control panels. In response, UL engineers drafted an internal document\u2014kept within UL laboratories and not publicly available\u2014literally stored in engineers\u2019 desks, hence the name \u201cdrawer standard.\u201d<\/p>\n

\n

Transition to a Public Standard<\/u><\/strong><\/h3>\n

As occurred with several UL documents developed during the 1970s and 1980s, UL later decided to formalize and publish these internal standards. Through UL Standards & Engagement<\/strong>, such documents were initially released as \u201cOutline of Investigation\u201d (OOI)<\/em>, enabling other certification bodies to apply the same technical criteria.<\/p>\n

This transition occurred for UL 508A in 1995<\/strong>.<\/p>\n

\n

Formal Publication and Editions<\/u><\/strong><\/h3>\n
    \n
  • April 25, 2001<\/strong> \u2192 First official edition of UL 508A published as a full consensus standard, developed by a technical committee comprising engineers from multiple companies.<\/li>\n
  • July 31, 2017<\/strong> \u2192 Second edition released<\/li>\n
  • April 24, 2018<\/strong> \u2192 Third edition published (currently in force, with subsequent revisions)<\/li>\n<\/ul>\n

    On June 26, 2025<\/strong>, UL 508A (Edition 3) was designated as an American National Standard (ANSI)<\/strong>. This designation confirms that the standard was developed through a balanced, open consensus process ensuring fairness and stakeholder representation.<\/p>\n

    \n

    Technical Scope and Relationship with Other Standards<\/u><\/strong><\/h3>\n

    UL 508A builds upon the fundamental electrical safety principles defined in the National Electrical Code (NEC)<\/span><\/span><\/strong> and aligns with requirements from NFPA 79<\/span><\/span><\/strong>.<\/p>\n

      \n
    • NFPA 79<\/strong> applies to the electrical equipment of machinery<\/strong> (both inside and outside the control panel)<\/li>\n
    • UL 508A<\/strong> specifically focuses on the design and construction of safe industrial control panels<\/strong><\/li>\n<\/ul>\n

      A major development occurred around 2005<\/strong>, when Supplement SB<\/strong> was introduced, providing a standardized method to determine the Short-Circuit Current Rating (SCCR)<\/strong> of industrial control panels\u2014now a central aspect of the standard.<\/p>\n

      \n

      Comparison with the European Framework<\/u><\/strong><\/h3>\n

      There is no direct one-to-one equivalent to UL 508A in Europe.\u00a0However, related standards include:<\/p>\n

        \n
      • IEC 61439-2<\/span><\/span><\/strong> \u2192 comparable to UL 891<\/span><\/span><\/strong> (power distribution switchboards)<\/li>\n
      • IEC 60204-1<\/span><\/span><\/strong> \u2192 comparable to NFPA 79<\/span><\/span><\/strong><\/li>\n<\/ul>\n<\/div> <\/div>\n \n \n
        <\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
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        \n JUNE 2025 UPDATE <\/h2>\n <\/div>\n <\/div>\n \n \n
        \n \n
        \n

        A new update of the standard was officially published on 26 June 2025.<\/u><\/strong>\u00a0Being members of the UL 508A Committee, hereafter we give you some insights of the main changes.<\/p>\n<\/div> <\/div>\n \n \n

        <\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
        \n\n \n
        \n \n
        \n \n \n

        \n Limits to Control Circuit Voltages; \u00a7 66.12.1 and \u00a7 66.12.2 <\/h2>\n <\/div>\n <\/div>\n \n \n
        \n \n
        \n

        The reason for the change is to align the requirements in UL 508A to the ones in NFPA 79. The maximum voltage limit for control circuits is now set at 120 Vac or 250 Vdc<\/p>\n

        Similar prescriptions are also in IEC 60204-1, even if the limits are higher.<\/p>\n<\/div> <\/div>\n \n \n

        <\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
        \n\n \n
        \n \n
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        \n Need for Emergency Stop Function; \u00a7 66.11.2 <\/h2>\n <\/div>\n <\/div>\n \n \n
        \n \n
        \n

        In the past, the UL 508A standard required an emergency stop button to be installed on each industrial control panel for machinery equipped with operator controls, such as pushbuttons. NFPA 79 specifies that an emergency stop is required when indicated by a risk assessment, an approach also adopted by B11.19. ISO 13850, as referenced in NFPA 79, follows a similar philosophy.<\/p>\n

        The proposal aligns UL 508A with this approach.<\/p>\n

        [UL 508A: 2025]\u00a066.11 Operator controls<\/strong><\/em><\/p>\n

        66.11.2 An industrial control panel provided with operator controls, such as pushbuttons and selector switches,\u00a0can be provided with an emergency stop button.<\/u><\/em><\/p>\n<\/div> <\/div>\n \n \n

        <\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
        \n\n \n
        \n \n
        \n \n \n

        \n Disconnecting Means \u2013 Industrial Machinery; 66.6.1, 66.6.1A, Table 52.1 <\/h2>\n <\/div>\n <\/div>\n \n \n
        \n \n
        \n

        In the past, all industrial control panels (ICPs) for industrial machinery were required\u00a0to have an external handle connected to a disconnecting means<\/strong>\u00a0for each incoming supply source. In some cases, however, multiple panels might supply a single machine through a single external feeder line.<\/p>\n

        The 2021 edition of\u00a0NFPA 79 \u2013 The Standard for Industrial Machinery<\/strong>\u00a0now requires a disconnecting means with an external operating handle\u00a0for each\u00a0machine supply circuit<\/em><\/strong>. In addition to the main machine supply circuit disconnecting means, additional devices may be provided to disconnect electrical equipment so that work can be performed on individual portions of the machine. But that is not mandatory!<\/p>\n

        Under these requirements, panels that form part of a group controlling a single machine may be supplied from a panel containing the machine supply circuit disconnecting means. In such cases, these auxiliary panels are permitted\u2014but not required\u2014to have their own disconnecting means. If such a disconnecting means is provided, it does not need an external operating handle.<\/p>\n

        With this revision,\u00a0UL 508A<\/strong>\u00a0aligns with the same approach as\u00a0NFPA 79<\/strong>.<\/p>\n<\/div> <\/div>\n \n \n

        <\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
        \n\n \n
        \n \n
        \n \n \n

        \n Location of Ventilation Opening; 21.2.2 and Figure 21.1 <\/h2>\n <\/div>\n <\/div>\n \n \n
        \n \n
        \n

        Panels, that include drives, often need to include fans to provide positive airflow for cooling heatsinks. These panels are installed with other panels located on either side which limits the areas where the outflow air can be directed. In these cases, the front of the panel needs to be used for the ventilation openings. The requirement in 21.2.2 applies whenever any type of control button, switch HMI or handle is mounted on the front of the panel, regardless of the amount of operator interaction needed. There is no specific hazard that is addressed by this requirement, only to prohibit exhaust air from being directed to an assumed area an operator may occupy. For panels operating in normal conditions, the outflow air from semiconductor heatsinks does not pose a hazard to an operator.<\/p>\n

        The change addresses and relaxes this prescription, adding the following exception:<\/p>\n

        [UL 508A: 2025]\u00a021.2 Location of ventilation opening<\/em><\/strong><\/p>\n

        Exception No. 3:\u00a0<\/em><\/strong>An enclosure containing external switch actuators or\u00a0displays that only require a short time presence of an operator<\/strong>, such as handles for disconnecting means, emergency stop buttons, external overload reset buttons, simple control devices (such as start \/ stop pushbuttons, selector switches), indicator lights, non-interactive digital displays, electrical meter faces and similar devices,\u00a0is not required to comply with 21.2.2.<\/strong><\/em><\/p>\n<\/div> <\/div>\n \n \n

        <\/div>\n \n\n <\/div>\n <\/section>\n\n \n","protected":false},"excerpt":{"rendered":"

        UL 508A is the technical standard for Industrial Control Panels in the USA. Starting from the basics of electrical safety, stated by the NEC and looking at…<\/p>\n","protected":false},"author":1,"featured_media":50069,"parent":0,"menu_order":2,"template":"","meta":{"_acf_changed":false,"footnotes":""},"normative-tecniche":[59],"class_list":["post-4095","normativa_tecnica","type-normativa_tecnica","status-publish","has-post-thumbnail","hentry","tipologia_normativa-ul-and-nfpa-standards"],"acf":{"sottotitolo":"Standard for Safety, Industrial Control Panels","allegati":null},"yoast_head":"\nUL 508 A | Standard for Industrial Control Panels<\/title>\n<meta name=\"description\" content=\"UL 508A is the technical standard for\u00a0Industrial Control Panels in the USA. 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