{"id":20255,"date":"2026-09-23T10:52:35","date_gmt":"2026-09-23T08:52:35","guid":{"rendered":"https:\/\/www.logic-pavia.it\/sil2-interlock-on-earthing-systems-what-the-standard-requires-and-what-changes-in-practice\/"},"modified":"2026-09-25T10:09:59","modified_gmt":"2026-09-25T08:09:59","slug":"sil2-interlock-on-earthing-systems-what-the-standard-requires-and-what-changes-in-practice","status":"publish","type":"post","link":"https:\/\/www.logic-pavia.it\/en\/sil2-interlock-on-earthing-systems-what-the-standard-requires-and-what-changes-in-practice\/","title":{"rendered":"SIL2 Interlock on Earthing Systems: What the Standard Requires and What Changes in Practice"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"20255\" class=\"elementor elementor-20255 elementor-20223\" data-elementor-post-type=\"post\">\n\t\t\t\t\t\t<section class=\"elementor-section elementor-top-section elementor-element elementor-element-0c59b8e elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"0c59b8e\" data-element_type=\"section\" data-e-type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-100 elementor-top-column elementor-element elementor-element-62b963a\" data-id=\"62b963a\" data-element_type=\"column\" data-e-type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-d137c2a elementor-widget elementor-widget-text-editor\" data-id=\"d137c2a\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p dir=\"ltr\">During the loading or unloading of a tanker truck, drum, or IBC in an ATEX zone, earthing is the only barrier standing between a routine operation and an accidental ignition. Yet not all earthing clamps offer the same level of protection \u2014 and the difference isn&#8217;t in the price, it&#8217;s in how they work.<\/p><p dir=\"ltr\">In this article, we look at what separates a &#8220;signal-only&#8221; earthing clamp from one with a SIL2 interlock, what the regulations require, and how to determine \u2014 when choosing equipment or during an audit \u2014 whether your plant is genuinely covered.<\/p><p dir=\"ltr\"><strong>In short<\/strong>: a SIL2 interlock on an earthing system is a safety device that physically prevents a transfer operation from starting in an ATEX zone (Zone 1\/21) if the electrical continuity of the earth connection has not been verified \u2014 unlike a signal-only system, which merely alerts the operator without stopping the operation.<\/p><h2 dir=\"ltr\">The problem: a warning light isn&#8217;t a barrier<\/h2><p dir=\"ltr\">Many earthing clamps simply signal the connection status through an indicator light or a signal contact. They work like this:<\/p><ul dir=\"ltr\"><li>the operator connects the clamp to the earthing point<\/li><li>an LED (or a panel signal) indicates whether contact has been made<\/li><li>starting the transfer remains a manual decision made by the operator<\/li><\/ul><p dir=\"ltr\">The limitation is obvious: <strong>safety depends on human attention<\/strong>. If the operator starts the transfer without checking the light, or if the connection loosens during the operation, the system flags the problem but doesn&#8217;t stop it. In a classified area, this means the only real barrier against electrostatic charge accumulation can be bypassed by a simple moment of distraction.<\/p><h2 dir=\"ltr\">Interlock vs. signal-only: what&#8217;s the difference?<\/h2><p dir=\"ltr\">A system with an interlock contact does more than signal a fault: it <strong>physically prevents the operation from starting<\/strong> if earthing hasn&#8217;t been electrically verified, whereas a signal-only system alerts the operator but leaves the final call to them. In practice, an interlocked system:<\/p><ul dir=\"ltr\"><li>measures the actual electrical continuity of the earth connection, not just the physical presence of the clamp<\/li><li>withholds permission to start the transfer (pump, loading valve) until the reading falls within the safety threshold<\/li><li>automatically interrupts an operation already in progress if the earth connection is lost, not only at start-up<\/li><\/ul><p dir=\"ltr\">The difference between the two approaches is conceptual before it&#8217;s technical: a signal-only system <strong>informs <\/strong>the operator, while an interlocked system <strong>decides on their behalf<\/strong> when safety isn&#8217;t guaranteed.<\/p><h2 dir=\"ltr\">Why SIL2, and not just any interlock<\/h2><p dir=\"ltr\">Not all interlocks offer the same level of reliability. SIL (Safety Integrity Level) is the classification, defined by the IEC 61508 standard, that measures how reliable a safety function is \u2014 in other words, how low the probability is that the system will fail exactly when it&#8217;s needed.<\/p><p dir=\"ltr\">An interlock contact certified to <strong>SIL2 <\/strong>provides a level of reliability appropriate for industrial safety functions where failure could have serious consequences \u2014 which is exactly the case for a transfer operation in a classified area. Choosing it isn&#8217;t excessive caution: it&#8217;s matching the actual risk of the operation to the required level of protection.<\/p><p dir=\"ltr\">It&#8217;s not by chance that our range no longer includes signal-only solutions: a system that can only inform, without being able to stop the operation, leaves a margin of risk we consider unacceptable in a classified area.<\/p><h2 dir=\"ltr\">What the regulations require<\/h2><p dir=\"ltr\">The ATEX Directive 2014\/34\/EU sets the safety requirements for equipment intended for use in areas with an explosion hazard \u2014 including earthing systems installed in those areas. But there&#8217;s a second, often less closely watched, regulatory layer: Directive 1999\/92\/EC, which requires employers to classify hazardous zones and document the prevention measures adopted in the Explosion Protection Document (EPD). We have examined the differences between the two directives, and the respective responsibilities, in<a href=\"https:\/\/www.logic-pavia.it\/en\/differences-between-directive-2014-34-eu-and-directive-1999-92-ec\/\"> this article<\/a>.<\/p><p dir=\"ltr\">During an audit or inspection, it isn&#8217;t enough to show that you have &#8220;an earthing clamp&#8221;: you need to demonstrate that the system chosen matches the risk level of the classified zone, and that the safety function is verifiable, not just declared on paper.<\/p><h2 dir=\"ltr\">Checklist: what to check before choosing (or during an audit)<\/h2><ul dir=\"ltr\"><li>Does the system only signal, or does it physically block the start of the operation when earthing isn&#8217;t verified?<\/li><li>Does the interlock contact carry a declared SIL certification (and at what level)?<\/li><li>Does the system detect a loss of connection during the operation, not only at start-up?<\/li><li>Is the device&#8217;s ATEX marking consistent with the installation zone (gas\/vapor or dust, category and group)?<\/li><\/ul><h2 dir=\"ltr\">The Logic solution<\/h2><p dir=\"ltr\">Logic has been designing earthing systems and ATEX equipment for over 40 years, with installations across the chemical, cosmetics, and pharmaceutical industries. Our <a href=\"https:\/\/www.logic-pavia.it\/en\/electronic-instrumentation\/atex-earthing-systems\/\">ECS-RF<\/a> earthing clamps come standard with a SIL2 interlock contact, certified under ATEX Directive 2014\/34\/EU for use in Zone 1\/21 (up to Zone 0\/20 depending on configuration). The system electrically verifies the continuity of the earth connection and withholds permission to start the transfer until earthing is confirmed \u2014 covering tanker truck loading bays as well as systems for drums, IBCs, and big bags.<\/p><p dir=\"ltr\">If you need to verify the compliance of an existing plant, or you&#8217;re evaluating a new earthing system for a transfer line, get in touch with us for a risk assessment specific to your process.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<section class=\"elementor-section elementor-top-section elementor-element elementor-element-2987524 elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"2987524\" data-element_type=\"section\" data-e-type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-100 elementor-top-column elementor-element elementor-element-14eab77\" data-id=\"14eab77\" data-element_type=\"column\" data-e-type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-15a2641 elementor-widget elementor-widget-industrium_heading\" data-id=\"15a2641\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"industrium_heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"industrium-heading-widget\"><h2 class=\"industrium-heading\"><span class=\"industrium-heading-content\">Frequently Asked Questions (FAQ)\n<\/span><\/h2><\/div>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6ef06fd elementor-widget elementor-widget-accordion\" data-id=\"6ef06fd\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"accordion.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<div class=\"elementor-accordion\">\n\t\t\t\t\t\t\t<div class=\"elementor-accordion-item\">\n\t\t\t\t\t<div id=\"elementor-tab-title-1161\" class=\"elementor-tab-title\" data-tab=\"1\" role=\"button\" aria-controls=\"elementor-tab-content-1161\" aria-expanded=\"false\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon elementor-accordion-icon-left\" aria-hidden=\"true\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-closed\"><i class=\"fas fa-plus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-opened\"><i class=\"fas fa-minus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-accordion-title\" tabindex=\"0\">What is a SIL2 interlock on an earthing system?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div id=\"elementor-tab-content-1161\" class=\"elementor-tab-content elementor-clearfix\" data-tab=\"1\" role=\"region\" aria-labelledby=\"elementor-tab-title-1161\"><p>It&#8217;s a safety device that physically prevents a transfer operation from starting in an ATEX zone (Zone 1\/21) if the electrical continuity of the earth connection hasn&#8217;t been verified. Unlike a signal-only system, it doesn&#8217;t just alert the operator \u2014 it stops the operation until safety is confirmed. <\/p>\n<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<div class=\"elementor-accordion-item\">\n\t\t\t\t\t<div id=\"elementor-tab-title-1162\" class=\"elementor-tab-title\" data-tab=\"2\" role=\"button\" aria-controls=\"elementor-tab-content-1162\" aria-expanded=\"false\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon elementor-accordion-icon-left\" aria-hidden=\"true\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-closed\"><i class=\"fas fa-plus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-opened\"><i class=\"fas fa-minus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-accordion-title\" tabindex=\"0\">What's the difference between a signal-only earthing clamp and one with an interlock?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div id=\"elementor-tab-content-1162\" class=\"elementor-tab-content elementor-clearfix\" data-tab=\"2\" role=\"region\" aria-labelledby=\"elementor-tab-title-1162\"><p>A signal-only earthing clamp alerts the operator with an indicator light once the connection is made, but starting the transfer remains a manual decision. An interlocked clamp measures the actual electrical continuity and withholds permission to start the pump or loading valve until the reading falls within the safety threshold. <\/p>\n<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<div class=\"elementor-accordion-item\">\n\t\t\t\t\t<div id=\"elementor-tab-title-1163\" class=\"elementor-tab-title\" data-tab=\"3\" role=\"button\" aria-controls=\"elementor-tab-content-1163\" aria-expanded=\"false\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon elementor-accordion-icon-left\" aria-hidden=\"true\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-closed\"><i class=\"fas fa-plus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-opened\"><i class=\"fas fa-minus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-accordion-title\" tabindex=\"0\">What does SIL2 certification mean for an interlock contact?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div id=\"elementor-tab-content-1163\" class=\"elementor-tab-content elementor-clearfix\" data-tab=\"3\" role=\"region\" aria-labelledby=\"elementor-tab-title-1163\"><p>SIL (Safety Integrity Level) is the classification, defined by the IEC 61508 standard, that measures how reliable a safety function is \u2014 in other words, how low the probability is that the system will fail exactly when it&#8217;s needed. An interlock contact certified to SIL2 provides a level of reliability appropriate for transfer operations in a classified area. <\/p>\n<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<div class=\"elementor-accordion-item\">\n\t\t\t\t\t<div id=\"elementor-tab-title-1164\" class=\"elementor-tab-title\" data-tab=\"4\" role=\"button\" aria-controls=\"elementor-tab-content-1164\" aria-expanded=\"false\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon elementor-accordion-icon-left\" aria-hidden=\"true\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-closed\"><i class=\"fas fa-plus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-opened\"><i class=\"fas fa-minus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-accordion-title\" tabindex=\"0\">What do the regulations require regarding earthing?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div id=\"elementor-tab-content-1164\" class=\"elementor-tab-content elementor-clearfix\" data-tab=\"4\" role=\"region\" aria-labelledby=\"elementor-tab-title-1164\"><p>The ATEX Directive 2014\/34\/EU sets the safety requirements for equipment used in areas with an explosion hazard, including earthing systems. Directive 1999\/92\/EC requires employers to classify hazardous zones and document the prevention measures adopted in the Explosion Protection Document (EPD). <\/p>\n<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<div class=\"elementor-accordion-item\">\n\t\t\t\t\t<div id=\"elementor-tab-title-1165\" class=\"elementor-tab-title\" data-tab=\"5\" role=\"button\" aria-controls=\"elementor-tab-content-1165\" aria-expanded=\"false\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon elementor-accordion-icon-left\" aria-hidden=\"true\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-closed\"><i class=\"fas fa-plus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t<span class=\"elementor-accordion-icon-opened\"><i class=\"fas fa-minus\"><\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-accordion-title\" tabindex=\"0\">How can you check whether your earthing system is compliant during an audit?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<div id=\"elementor-tab-content-1165\" class=\"elementor-tab-content elementor-clearfix\" data-tab=\"5\" role=\"region\" aria-labelledby=\"elementor-tab-title-1165\"><p>You need to verify that the system physically blocks the operation (not just signals it), that the interlock contact carries a declared SIL certification, that it detects a loss of connection during the operation and not only at start-up, that the ATEX marking matches the installation zone, and that technical documentation is aligned with the plant&#8217;s Explosion Protection Document.<\/p>\n<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t\t\t<script type=\"application\/ld+json\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"What is a SIL2 interlock on an earthing system?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"<p>It&#8217;s a safety device that physically prevents a transfer operation from starting in an ATEX zone (Zone 1\\\/21) if the electrical continuity of the earth connection hasn&#8217;t been verified. 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Yet not all earthing clamps offer the same level of protection&#8230;<\/p>\n","protected":false},"author":3,"featured_media":20265,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-20255","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-non-categorizzato"],"_links":{"self":[{"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/posts\/20255","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/comments?post=20255"}],"version-history":[{"count":8,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/posts\/20255\/revisions"}],"predecessor-version":[{"id":20268,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/posts\/20255\/revisions\/20268"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/media\/20265"}],"wp:attachment":[{"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/media?parent=20255"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/categories?post=20255"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.logic-pavia.it\/en\/wp-json\/wp\/v2\/tags?post=20255"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}