{"id":71299,"date":"2025-06-11T09:59:28","date_gmt":"2025-06-11T12:59:28","guid":{"rendered":"https:\/\/a3aengenharia.com\/en-us\/?post_type=articles&#038;p=71299"},"modified":"2026-04-23T08:34:21","modified_gmt":"2026-04-23T11:34:21","slug":"coordination-selection-surge-protective-devices-electrical-installations","status":"publish","type":"articles","link":"https:\/\/a3aengenharia.com\/en-us\/content\/technical-articles\/coordination-selection-surge-protective-devices-electrical-installations\/","title":{"rendered":"Coordination and Selection of Surge Protective Devices (SPDs) in Electrical Installations"},"content":{"rendered":"<p>The growing complexity and density of modern electrical installations require careful strategies for protection against transient surges. The emergence of sensitive electronic devices and the risks associated with lightning discharges and network switching operations make the selection and coordination of Surge Protective Devices (SPDs) a central topic for operational continuity and system integrity.<\/p>\n<p>This article provides an in-depth discussion of the technical and regulatory criteria for SPD selection and coordination, highlighting methodologies, critical evaluation points, regulatory parameters and procedures for coordinated protection systems. The objective is to support technical decision-making for the specification, installation and maintenance of SPDs in different electrical risk scenarios.<\/p>\n<p>Check it out!<\/p>\n<p>[elementor-template id=&#8221;24446&#8243;]<\/p>\n<h2>Regulatory Criteria<\/h2>\n<p>Every SPD must meet requirements defined in applicable standards, such as IEC 61643-1 and IEC 61643-11, and must be specified according to the following essential parameters:<\/p>\n<ul>\n<li><strong>Protection level (Up):<\/strong> The SPD Up value must be compatible with the withstand level of the equipment according to its installation category. It is recommended that Up be lower than the impulse withstand level of the devices in the installation.<\/li>\n<li><strong>Maximum continuous operating voltage (Uc):<\/strong> Uc must be higher than the maximum nominal voltage of the circuit where the SPD will be installed.<\/li>\n<li><strong>Temporary overvoltage withstand (TOV):<\/strong> The SPD must withstand temporary overvoltages typical of the installation.<\/li>\n<li><strong>Nominal discharge current (In) and impulse current (Iimp\/Imax):<\/strong> Defines the SPD conduction capacity under high-energy surges and must be compatible with the installation\u2019s surge risk, such as direct or indirect lightning discharges.<\/li>\n<li><strong>Short-circuit current withstand:<\/strong> The SPD must have adequate resistance to the available fault current at the installation point.<\/li>\n<\/ul>\n<h3>Adaptation to Location and Installation Parameters<\/h3>\n<p>SPD selection must also consider its position in the installation, such as the structure entrance, distribution boards and proximity to critical loads, as well as the maximum current expected at each point. In locations exposed to direct lightning discharges, SPDs with greater impulse current conduction capacity are mandatory, while lower-capacity SPDs can be used in internal boards to complement the coordination strategy.<\/p>\n<p>Installing SPDs in series (cascaded) or at multiple points in the installation requires careful coordination to ensure effective sharing of surge energy, avoiding overload of individual devices and ensuring protection across all zones of the structure (Lightning Protection Zones \u2013 LPZ).<\/p>\n<h2>Coordination Practices<\/h2>\n<ol>\n<li><strong>Energy coordination:<\/strong> Cascaded SPDs must have their energy capacities sized and coordinated according to IEC 61643-12 or IEC 61643-22, ensuring that, in the event of a major surge, the upstream SPD absorbs most of the energy, protecting downstream SPDs.<\/li>\n<li><strong>Proximity to equipment:<\/strong> The closer the SPD is to the equipment to be protected, the more effective the reduction of residual voltage at the point of interest will be.<\/li>\n<li><strong>Conductor cross-section and length:<\/strong> SPD interconnections must be made according to the minimum cross-section values established in standards and with the shortest possible length, minimizing additional impedance and the increase in Up.<\/li>\n<li><strong>Zone coordination:<\/strong> It is recommended to install coordinated SPD systems at conductor entry points (LPZ 1 boundary), at intermediate points and near internal equipment.<\/li>\n<\/ol>\n<h3>Procedure for Installing a Coordinated SPD System<\/h3>\n<ul>\n<li>Install the primary SPD at the structure entrance, respecting the lightning discharge current conduction capacity parameters and Up compatible with the system.<\/li>\n<li>Determine the impulse withstand level of the internal system to ensure that the Up of subsequent SPDs is lower than this value.<\/li>\n<li>Size secondary SPDs to absorb residual components, locating them as close as possible to sensitive loads.<\/li>\n<\/ul>\n<p>The SPD manufacturer should provide sufficient information to enable correct coordination between devices with different characteristics.<\/p>\n<p>Multiple factors determine the stress to which an SPD will be subjected throughout its service life. These include the regional lightning flash density, the location in the installation, the type of grounding system, the circuit topology and the operating regime of the protected system.<\/p>\n<h2>Statistical Quantification and Technical Assessment<\/h2>\n<ol>\n<li>Estimate, using statistical methods and historical records, the probable level of surge stresses, including annual number of events, average energy and peaks.<\/li>\n<li>Analyze current-sharing factors between different coordinated SPDs. It must be considered that the path with the lowest impedance will conduct the largest fraction of the surge energy.<\/li>\n<li>Select appropriate nominal characteristics for Iimp, Imax, In and Uc, taking into account the maximum expected stress and the specific conditions of the site.<\/li>\n<li>Consider environmental factors, ambient temperature and accelerated aging due to severe operating regimes.<\/li>\n<\/ol>\n<p>Inefficient coordination can lead to improper energy transfer to lower-capacity SPDs, impairing selectivity and reducing equipment service life.<\/p>\n<h2>Main Technical Conditions<\/h2>\n<p>When selecting an SPD at each point of the system, it is recommended to verify the following conditions:<\/p>\n<ul>\n<li><strong>Protection level (Up):<\/strong> Compatibility with the category of the protected equipment.<\/li>\n<li><strong>Maximum continuous operating voltage (Uc):<\/strong> Higher than the maximum steady-state voltage.<\/li>\n<li><strong>Discharge and impulse current (In, Iimp, Imax):<\/strong> Capacity compatible with the energy of incident surges.<\/li>\n<li><strong>Short-circuit withstand capacity:<\/strong> Adequate for the interrupting capacity of the electrical power system at the installation point.<\/li>\n<\/ul>\n<h3>Example Flow for Selection and Coordination<\/h3>\n<ol>\n<li>Risk assessment and determination of the need for primary and secondary SPDs.<\/li>\n<li>Definition of Up and Uc values for each location.<\/li>\n<li>Specification of current capacities according to electrical risk analysis.<\/li>\n<li>Verification of coordination requirements when cascaded SPDs are present.<\/li>\n<li>Adjustment of conductor cross-sections and the physical arrangement of SPDs according to the detailed design.<\/li>\n<\/ol>\n<h2>Good Installation Practices<\/h2>\n<ul>\n<li>Ensure that the SPD is physically as close as possible to the protection point, minimizing connection paths.<\/li>\n<li>Use minimum conductor cross-sections appropriate for SPD connection, according to the regulatory table.<\/li>\n<li>If necessary, protect the SPD against overcurrents with dedicated devices, ensuring harmonious integration with the protection system.<\/li>\n<li>Observe the type of grounding system and adjust the protection topology according to technical and safety requirements.<\/li>\n<\/ul>\n<h3>Maintenance and Verification<\/h3>\n<ul>\n<li>Regularly inspect the condition of SPDs, replacing units that have suffered significant degradation.<\/li>\n<li>Monitor integrated status indicators and record preventive and corrective maintenance interventions.<\/li>\n<li>Perform tests, when required, to verify the response capacity of the devices after severe surges.<\/li>\n<\/ul>\n<p>Careful management of SPD coordination and selection is a key factor in the resilience of electrical systems against high-energy transient events. Correct specification, based on technical assessment, regulatory parameters and proper energy coordination, ensures robust protection for equipment and processes, reducing costs related to corrective maintenance and unplanned downtime. Valuing the practices described in this article contributes to safer, more durable installations adapted to demanding operating regimes. It is recommended that each project be assessed individually, considering technical and risk particularities, and that specification, installation and maintenance of the coordinated SPD system be integrated as part of the electrical asset management cycle.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The growing complexity and density of modern electrical installations require careful strategies for protection against transient surges. The emergence of sensitive electronic devices and the risks associated with lightning discharges and network switching operations make the selection and coordination of Surge Protective Devices (SPDs) a central topic for operational continuity and system integrity. This article [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":31160,"parent":0,"template":"","meta":{"_a3a_post_lang":"en-us","_a3a_translation_group_id":"articles-31161","_a3a_i18n_canonical_slug":"coordination-selection-surge-protective-devices-electrical-installations"},"categories":[308],"class_list":["post-71299","articles","type-articles","status-publish","has-post-thumbnail","hentry"],"_links":{"self":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles\/71299","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles"}],"about":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/types\/articles"}],"author":[{"embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":1,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles\/71299\/revisions"}],"predecessor-version":[{"id":71300,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles\/71299\/revisions\/71300"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/media\/31160"}],"wp:attachment":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/media?parent=71299"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/categories?post=71299"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}