{"id":375,"date":"2017-05-10T14:55:32","date_gmt":"2017-05-10T14:55:32","guid":{"rendered":"http:\/\/www.the-regs.co.uk\/blog\/?p=375"},"modified":"2017-05-10T14:55:32","modified_gmt":"2017-05-10T14:55:32","slug":"earth-fault-loop-impedance-zs","status":"publish","type":"post","link":"https:\/\/the-regs.co.uk\/blog\/?p=375","title":{"rendered":"Earth Fault Loop Impedance (Zs)"},"content":{"rendered":"<p>The earth fault loop impedance (Zs) directly effects the amount of current that flows under earth fault conditions. (Ipf = V \/ Zs).<\/p>\n<p>As I&#8217;ve mentioned in a previous post (<a href=\"http:\/\/www.the-regs.co.uk\/blog\/?p=342\">see here<\/a>) fuses and circuit breakers need a certain amount of current in order to meet their maximum disconnection times. ie a 20A type B\u00a0circuit breaker\u00a0would require 5 x its rating (100A) in order to meet its disconnection times.<\/p>\n<p>If the earth fault loop impedance is too high then disconnection of the protective device will take too long due to the earth fault current not being high enough for the protective device to meet its maximum disconnection time.<\/p>\n<p>This is why we have the maximum loop impedance (Zs) values in Chapter 41 BS 7671. Remember though. When testing, the\u00a0results measured are compared to 80% of these value in Chapter 41.<\/p>\n<p>Components of an Earth Loop Impedance Path (Zs)<\/p>\n<p>Zs = Ze + (R1 + R2)<\/p>\n<p><a href=\"https:\/\/i0.wp.com\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path.png\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-376 aligncenter\" src=\"https:\/\/i0.wp.com\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png?resize=300%2C174\" alt=\"\" width=\"300\" height=\"174\" srcset=\"https:\/\/i0.wp.com\/the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path.png?resize=300%2C174&amp;ssl=1 300w, https:\/\/i0.wp.com\/the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path.png?resize=768%2C444&amp;ssl=1 768w, https:\/\/i0.wp.com\/the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path.png?resize=624%2C361&amp;ssl=1 624w, https:\/\/i0.wp.com\/the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path.png?w=866&amp;ssl=1 866w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p>Zs: Overall loop impedance including the source and the installation<br \/>\nZe: Loop impedance external to the installation<br \/>\nR1: Impedance of the line conductor of the circuit<br \/>\nR2: Impedance of the CPC protecting the circuit<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The earth fault loop impedance (Zs) directly effects the amount of current that flows under earth fault conditions. (Ipf = V \/ Zs). As I&#8217;ve mentioned in a previous post (see here) fuses and circuit breakers need a certain amount of current in order to meet their maximum disconnection times. ie a 20A type B\u00a0circuit&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1,8],"tags":[],"class_list":["post-375","post","type-post","status-publish","format-standard","hentry","category-general","category-whats-it-about","th-blog blog-single has-post-thumbnail"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.0 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Earth Fault Loop Impedance (Zs) - the-Regs : BS7671 18th Edition Online Training<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/the-regs.co.uk\/blog\/?p=375\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Earth Fault Loop Impedance (Zs) - the-Regs : BS7671 18th Edition Online Training\" \/>\n<meta property=\"og:description\" content=\"The earth fault loop impedance (Zs) directly effects the amount of current that flows under earth fault conditions. (Ipf = V \/ Zs). As I&#8217;ve mentioned in a previous post (see here) fuses and circuit breakers need a certain amount of current in order to meet their maximum disconnection times. ie a 20A type B\u00a0circuit...\" \/>\n<meta property=\"og:url\" content=\"https:\/\/the-regs.co.uk\/blog\/?p=375\" \/>\n<meta property=\"og:site_name\" content=\"the-Regs : BS7671 18th Edition Online Training\" \/>\n<meta property=\"article:published_time\" content=\"2017-05-10T14:55:32+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png\" \/>\n<meta name=\"author\" content=\"the Regs Guy\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@theregsguy\" \/>\n<meta name=\"twitter:site\" content=\"@theregsguy\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"the Regs Guy\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"1 minute\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375\"},\"author\":{\"name\":\"the Regs Guy\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#\\\/schema\\\/person\\\/0d7feabc48e1ab05b0c346e599ea65cf\"},\"headline\":\"Earth Fault Loop Impedance (Zs)\",\"datePublished\":\"2017-05-10T14:55:32+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375\"},\"wordCount\":190,\"commentCount\":0,\"publisher\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#primaryimage\"},\"thumbnailUrl\":\"http:\\\/\\\/www.the-regs.co.uk\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/05\\\/Zs-path-300x174.png\",\"articleSection\":[\"General\",\"What's it about\"],\"inLanguage\":\"en-GB\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375\",\"url\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375\",\"name\":\"Earth Fault Loop Impedance (Zs) - the-Regs : BS7671 18th Edition Online Training\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#primaryimage\"},\"thumbnailUrl\":\"http:\\\/\\\/www.the-regs.co.uk\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/05\\\/Zs-path-300x174.png\",\"datePublished\":\"2017-05-10T14:55:32+00:00\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#breadcrumb\"},\"inLanguage\":\"en-GB\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-GB\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#primaryimage\",\"url\":\"http:\\\/\\\/www.the-regs.co.uk\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/05\\\/Zs-path-300x174.png\",\"contentUrl\":\"http:\\\/\\\/www.the-regs.co.uk\\\/blog\\\/wp-content\\\/uploads\\\/2017\\\/05\\\/Zs-path-300x174.png\"},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?p=375#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Earth Fault Loop Impedance (Zs)\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#website\",\"url\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/\",\"name\":\"the-Regs.co.uk 18th Edition Online Training Specialist\",\"description\":\"BS 7671: 18th Edition Wiring Regulations - Study when you want and pass your exam  when you&#039;re ready...\",\"publisher\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-GB\"},{\"@type\":\"Organization\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#organization\",\"name\":\"the-Regs : BS7671 18th Edition Online Training\",\"url\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-GB\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#\\\/schema\\\/logo\\\/image\\\/\",\"url\":\"https:\\\/\\\/i0.wp.com\\\/the-regs.co.uk\\\/blog\\\/wp-content\\\/uploads\\\/2025\\\/10\\\/favicon-192x192-1.png?fit=192%2C192&ssl=1\",\"contentUrl\":\"https:\\\/\\\/i0.wp.com\\\/the-regs.co.uk\\\/blog\\\/wp-content\\\/uploads\\\/2025\\\/10\\\/favicon-192x192-1.png?fit=192%2C192&ssl=1\",\"width\":192,\"height\":192,\"caption\":\"the-Regs : BS7671 18th Edition Online Training\"},\"image\":{\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#\\\/schema\\\/logo\\\/image\\\/\"},\"sameAs\":[\"https:\\\/\\\/x.com\\\/theregsguy\"]},{\"@type\":\"Person\",\"@id\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/#\\\/schema\\\/person\\\/0d7feabc48e1ab05b0c346e599ea65cf\",\"name\":\"the Regs Guy\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-GB\",\"@id\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/f10b538b4ce6fdea13c84ac1ce266ae912ec071c6775b6ce8df5fdad3ac24bb0?s=96&d=mm&r=g\",\"url\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/f10b538b4ce6fdea13c84ac1ce266ae912ec071c6775b6ce8df5fdad3ac24bb0?s=96&d=mm&r=g\",\"contentUrl\":\"https:\\\/\\\/secure.gravatar.com\\\/avatar\\\/f10b538b4ce6fdea13c84ac1ce266ae912ec071c6775b6ce8df5fdad3ac24bb0?s=96&d=mm&r=g\",\"caption\":\"the Regs Guy\"},\"description\":\"A professional qualified electrician with nearly forty years of under paid, hard work within the electrical installation industry. I've also been a successful electrical installation tutor since 2008. Delivering both City &amp; Guilds \\\/ EAL level 3 courses including \\\"18th Edition Wiring Regulations, Inspection &amp; Testing (initial verification and periodic inspection, testing and reporting), Building Regulations, PAT and Part P etc.\\\" both in the private sector and local FE colleges. I've also been running my own training center since 2015. See www.waybrite.co.uk\",\"sameAs\":[\"http:\\\/\\\/www.the-regs.co.uk\"],\"url\":\"https:\\\/\\\/the-regs.co.uk\\\/blog\\\/?author=1\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Earth Fault Loop Impedance (Zs) - the-Regs : BS7671 18th Edition Online Training","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/the-regs.co.uk\/blog\/?p=375","og_locale":"en_GB","og_type":"article","og_title":"Earth Fault Loop Impedance (Zs) - the-Regs : BS7671 18th Edition Online Training","og_description":"The earth fault loop impedance (Zs) directly effects the amount of current that flows under earth fault conditions. (Ipf = V \/ Zs). As I&#8217;ve mentioned in a previous post (see here) fuses and circuit breakers need a certain amount of current in order to meet their maximum disconnection times. ie a 20A type B\u00a0circuit...","og_url":"https:\/\/the-regs.co.uk\/blog\/?p=375","og_site_name":"the-Regs : BS7671 18th Edition Online Training","article_published_time":"2017-05-10T14:55:32+00:00","og_image":[{"url":"http:\/\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png","type":"","width":"","height":""}],"author":"the Regs Guy","twitter_card":"summary_large_image","twitter_creator":"@theregsguy","twitter_site":"@theregsguy","twitter_misc":{"Written by":"the Regs Guy","Estimated reading time":"1 minute"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#article","isPartOf":{"@id":"https:\/\/the-regs.co.uk\/blog\/?p=375"},"author":{"name":"the Regs Guy","@id":"https:\/\/the-regs.co.uk\/blog\/#\/schema\/person\/0d7feabc48e1ab05b0c346e599ea65cf"},"headline":"Earth Fault Loop Impedance (Zs)","datePublished":"2017-05-10T14:55:32+00:00","mainEntityOfPage":{"@id":"https:\/\/the-regs.co.uk\/blog\/?p=375"},"wordCount":190,"commentCount":0,"publisher":{"@id":"https:\/\/the-regs.co.uk\/blog\/#organization"},"image":{"@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#primaryimage"},"thumbnailUrl":"http:\/\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png","articleSection":["General","What's it about"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/the-regs.co.uk\/blog\/?p=375#respond"]}]},{"@type":"WebPage","@id":"https:\/\/the-regs.co.uk\/blog\/?p=375","url":"https:\/\/the-regs.co.uk\/blog\/?p=375","name":"Earth Fault Loop Impedance (Zs) - the-Regs : BS7671 18th Edition Online Training","isPartOf":{"@id":"https:\/\/the-regs.co.uk\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#primaryimage"},"image":{"@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#primaryimage"},"thumbnailUrl":"http:\/\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png","datePublished":"2017-05-10T14:55:32+00:00","breadcrumb":{"@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/the-regs.co.uk\/blog\/?p=375"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#primaryimage","url":"http:\/\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png","contentUrl":"http:\/\/www.the-regs.co.uk\/blog\/wp-content\/uploads\/2017\/05\/Zs-path-300x174.png"},{"@type":"BreadcrumbList","@id":"https:\/\/the-regs.co.uk\/blog\/?p=375#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/the-regs.co.uk\/blog"},{"@type":"ListItem","position":2,"name":"Earth Fault Loop Impedance (Zs)"}]},{"@type":"WebSite","@id":"https:\/\/the-regs.co.uk\/blog\/#website","url":"https:\/\/the-regs.co.uk\/blog\/","name":"the-Regs.co.uk 18th Edition Online Training Specialist","description":"BS 7671: 18th Edition Wiring Regulations - Study when you want and pass your exam  when you&#039;re ready...","publisher":{"@id":"https:\/\/the-regs.co.uk\/blog\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/the-regs.co.uk\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-GB"},{"@type":"Organization","@id":"https:\/\/the-regs.co.uk\/blog\/#organization","name":"the-Regs : BS7671 18th Edition Online Training","url":"https:\/\/the-regs.co.uk\/blog\/","logo":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/the-regs.co.uk\/blog\/#\/schema\/logo\/image\/","url":"https:\/\/i0.wp.com\/the-regs.co.uk\/blog\/wp-content\/uploads\/2025\/10\/favicon-192x192-1.png?fit=192%2C192&ssl=1","contentUrl":"https:\/\/i0.wp.com\/the-regs.co.uk\/blog\/wp-content\/uploads\/2025\/10\/favicon-192x192-1.png?fit=192%2C192&ssl=1","width":192,"height":192,"caption":"the-Regs : BS7671 18th Edition Online Training"},"image":{"@id":"https:\/\/the-regs.co.uk\/blog\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/x.com\/theregsguy"]},{"@type":"Person","@id":"https:\/\/the-regs.co.uk\/blog\/#\/schema\/person\/0d7feabc48e1ab05b0c346e599ea65cf","name":"the Regs Guy","image":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/secure.gravatar.com\/avatar\/f10b538b4ce6fdea13c84ac1ce266ae912ec071c6775b6ce8df5fdad3ac24bb0?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/f10b538b4ce6fdea13c84ac1ce266ae912ec071c6775b6ce8df5fdad3ac24bb0?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/f10b538b4ce6fdea13c84ac1ce266ae912ec071c6775b6ce8df5fdad3ac24bb0?s=96&d=mm&r=g","caption":"the Regs Guy"},"description":"A professional qualified electrician with nearly forty years of under paid, hard work within the electrical installation industry. I've also been a successful electrical installation tutor since 2008. Delivering both City &amp; Guilds \/ EAL level 3 courses including \"18th Edition Wiring Regulations, Inspection &amp; Testing (initial verification and periodic inspection, testing and reporting), Building Regulations, PAT and Part P etc.\" both in the private sector and local FE colleges. I've also been running my own training center since 2015. See www.waybrite.co.uk","sameAs":["http:\/\/www.the-regs.co.uk"],"url":"https:\/\/the-regs.co.uk\/blog\/?author=1"}]}},"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p32IMi-63","jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/375","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=375"}],"version-history":[{"count":0,"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/375\/revisions"}],"wp:attachment":[{"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=375"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=375"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/the-regs.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=375"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}