{"id":1832,"date":"2026-07-27T10:31:34","date_gmt":"2026-07-27T02:31:34","guid":{"rendered":"https:\/\/jutrion.com\/?page_id=1832"},"modified":"2026-07-27T10:38:43","modified_gmt":"2026-07-27T02:38:43","slug":"%d8%ad%d8%a7%d8%b3%d8%a8%d8%a9-%d8%aa%d9%8a%d8%a7%d8%b1-%d8%a7%d9%84%d9%82%d8%b5%d8%b1","status":"publish","type":"page","link":"https:\/\/jutrion.com\/ar\/tools\/short-circuit-current-calculator\/","title":{"rendered":"\u062d\u0627\u0633\u0628\u0629 \u062a\u064a\u0627\u0631 \u0627\u0644\u0642\u0635\u0631"},"content":{"rendered":"\n<!-- ===== JUTRION Short-Circuit Current Calculator \u2014 paste into a WordPress \"Custom HTML\" block ===== -->\n<div class=\"jt-calc\">\n  <p class=\"eyebrow\">Circuit protection<\/p>\n  <h1>Short-Circuit Current Calculator (Prospective I<sub>sc<\/sub>)<\/h1>\n  <p class=\"tool-lede\">Estimate the prospective short-circuit current at a transformer secondary from the transformer rating and impedance, and find the minimum breaker breaking capacity (I<sub>cu<\/sub>) you need. This is the maximum at the transformer terminals \u2014 real values downstream are lower once cable impedance is included.<\/p>\n\n  <div class=\"jt-card\"><div class=\"jt-grid\">\n    <div class=\"jt-inputs\">\n      <div class=\"jt-field\"><label>Supply<\/label>\n        <div class=\"jt-seg\" id=\"jt-phase\"><button type=\"button\" data-ph=\"3\" aria-pressed=\"true\">Three-phase<\/button><button type=\"button\" data-ph=\"1\" aria-pressed=\"false\">Single-phase<\/button><\/div>\n      <\/div>\n      <div class=\"jt-two\">\n        <div class=\"jt-field\"><label for=\"jt-s\">Transformer rating (kVA)<\/label><input type=\"number\" id=\"jt-s\" value=\"1000\" min=\"1\" step=\"1\" inputmode=\"numeric\"><\/div>\n        <div class=\"jt-field\"><label for=\"jt-v\">Secondary voltage (V)<\/label><input type=\"number\" id=\"jt-v\" value=\"400\" min=\"1\" step=\"1\" inputmode=\"numeric\"><\/div>\n      <\/div>\n      <div class=\"jt-field\"><label for=\"jt-uk\">Impedance voltage u<sub>k<\/sub> (%)<\/label><input type=\"number\" id=\"jt-uk\" value=\"6\" min=\"0.1\" step=\"0.1\" inputmode=\"decimal\"><\/div>\n      <div class=\"jt-note\"><span>\u24d8<\/span><span>u<sub>k<\/sub> is on the transformer nameplate (typically 4\u20136 % for distribution transformers). Lower u<sub>k<\/sub> means a higher fault current.<\/span><\/div>\n    <\/div>\n    <div class=\"jt-readout\">\n      <div><div class=\"jt-rl\">Prospective I<sub>sc<\/sub><\/div><div class=\"jt-big\"><span id=\"jt-isc\">\u2014<\/span> <span>kA<\/span><\/div><\/div>\n      <div class=\"jt-rec\"><div class=\"k\">Transformer full-load I<sub>n<\/sub><\/div><div class=\"v\" id=\"jt-in\">\u2014 A<\/div><\/div>\n      <div class=\"jt-rec\"><div class=\"k\">Minimum breaker I<sub>cu<\/sub><\/div><div class=\"v\" id=\"jt-icu\">\u2014<\/div>\n        <div class=\"jt-bar\"><i id=\"jt-fill\" style=\"width:0%\"><\/i><\/div>\n        <div class=\"jt-ticks\"><span>10<\/span><span>36<\/span><span>70<\/span><span>100 kA<\/span><\/div>\n      <\/div>\n      <button type=\"button\" class=\"jt-copy\" id=\"jt-copy\">Copy result<\/button>\n    <\/div>\n  <\/div><\/div>\n\n  <div class=\"jt-content\">\n    <h2>How it is calculated<\/h2>\n    <p>The transformer rated secondary current and the prospective fault current at its terminals are:<\/p>\n    <div class=\"jt-eq\">I<sub>n<\/sub> = S \/ (\u221a3 \u00d7 V)        I<sub>sc<\/sub> = I<sub>n<\/sub> \u00d7 100 \/ u<sub>k<\/sub><\/div>\n    <p>where <b>S<\/b> is the transformer rating (VA), <b>V<\/b> the secondary line voltage, and <b>u<sub>k<\/sub><\/b> the impedance voltage in percent. This simplified method assumes an infinite upstream source and ignores cable impedance, so it gives the maximum credible fault current at the transformer secondary. A rigorous value follows IEC 60909, adding source, cable, and motor contributions.<\/p>\n    <p>The selected breaker&#8217;s rated breaking capacity \u2014 I<sub>cu<\/sub> for an MCCB, I<sub>cn<\/sub> for an MCB \u2014 must be at least this I<sub>sc<\/sub> at the operational voltage. The tool rounds up to the next common capacity tier (10, 15, 25, 36, 50, 70, 85, 100 kA).<\/p>\n\n    <h2>Frequently asked questions<\/h2>\n    <div class=\"jt-faq\">\n      <details><summary>Is this the fault current everywhere in the installation?<\/summary><p>No \u2014 it is the maximum at the transformer secondary. Cable impedance reduces the fault current downstream, so devices further from the transformer can use a lower breaking capacity if a study confirms it.<\/p><\/details>\n      <details><summary>Why does a lower impedance give a higher fault current?<\/summary><p>The impedance voltage limits how much current flows into a short circuit. A 4 % transformer lets more fault current through than a 6 % one of the same rating, so it demands a higher breaker breaking capacity.<\/p><\/details>\n      <details><summary>What about motor contribution?<\/summary><p>Large running motors briefly feed additional current into a fault. For a rigorous result, add motor contribution per IEC 60909; this simplified tool does not include it.<\/p><\/details>\n    <\/div>\n\n    <div class=\"jt-cta\">\n      <h2>Match the breaking capacity<\/h2>\n      <p>Select an MCCB whose I<sub>cu<\/sub> \/ I<sub>cs<\/sub> at your operational voltage covers this fault level.<\/p>\n      <div class=\"jt-cta-btns\">\n        <a class=\"jt-btn\" href=\"https:\/\/jutrion.com\/mccb\/\">Explore JUTRION MCCBs<\/a>\n        <a class=\"jt-btn ghost\" href=\"https:\/\/jutrion.com\/contact\/\">Get a free quote<\/a>\n      <\/div>\n      <p class=\"jt-related\">Related products: <a href=\"https:\/\/jutrion.com\/mccb\/\">MCCB<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/acb\/\">ACB<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/products\/\">All products<\/a><\/p>\n    <\/div>\n\n    <div class=\"jt-std\"><strong>Standards referenced<\/strong>IEC 60909 (short-circuit current calculation) \u00b7 IEC 60947-2 (MCCB Icu\/Ics) \u00b7 IEC 60898-1 (MCB Icn).<\/div>\n    <p class=\"jt-fine\">Estimate for guidance only. A rigorous short-circuit study to IEC 60909, including source, cable, and motor contributions, and verification by a qualified person, governs the final device selection.<\/p>\n  <\/div>\n<\/div>\n\n<script>\n(function(){\n  var $=function(id){return document.getElementById(id);};\n  var s=$('jt-s'),v=$('jt-v'),uk=$('jt-uk'),iscEl=$('jt-isc'),inEl=$('jt-in'),icuEl=$('jt-icu'),fill=$('jt-fill');\n  var phase=3, TIERS=[10,15,25,36,50,70,85,100];\n  document.querySelectorAll('#jt-phase button').forEach(function(b){b.addEventListener('click',function(){phase=parseInt(b.dataset.ph,10);document.querySelectorAll('#jt-phase button').forEach(function(x){x.setAttribute('aria-pressed',x===b?'true':'false');});if(phase===1&&v.value==='400')v.value='230';if(phase===3&&v.value==='230')v.value='400';calc();});});\n  function nextTier(x){for(var i=0;i<TIERS.length;i++){if(TIERS[i]>=x)return TIERS[i];}return null;}\n  function calc(){\n    var S=parseFloat(s.value),V=parseFloat(v.value),U=parseFloat(uk.value);\n    if(!(S>0&&V>0&&U>0)){iscEl.textContent='\u2014';inEl.textContent='\u2014 A';icuEl.textContent='\u2014';fill.style.width='0%';return;}\n    var Inn=(phase===3?(S*1000)\/(Math.sqrt(3)*V):(S*1000)\/V);\n    var isc=Inn*100\/U\/1000;\n    inEl.textContent=Math.round(Inn)+' A';iscEl.textContent=isc.toFixed(1);\n    var t=nextTier(isc);icuEl.textContent=t?('\u2265 '+t+' kA'):('> 100 kA \u2014 special');\n    fill.style.width=Math.min(100,(isc\/100)*100).toFixed(0)+'%';\n  }\n  [s,v,uk].forEach(function(el){el.addEventListener('input',calc);el.addEventListener('change',calc);});\n  $('jt-copy').addEventListener('click',function(){var b=$('jt-copy');var txt='Transformer: '+s.value+' kVA, '+v.value+' V, uk '+uk.value+'%\\nFull-load In: '+inEl.textContent+'\\nProspective Isc: '+iscEl.textContent+' kA\\nMinimum breaker Icu: '+icuEl.textContent;navigator.clipboard.writeText(txt).then(function(){var o=b.textContent;b.textContent='Copied \u2713';setTimeout(function(){b.textContent=o;},1500);}).catch(function(){b.textContent='Press Ctrl+C';});});\n  calc();\n})();\n<\/script>\n<!-- ===== end block ===== -->\n\n","protected":false},"excerpt":{"rendered":"<p>Circuit protection Short-Circuit Current Calculator (Prospective Isc) Estimate the prospective short-circuit current at a transformer secondary from the transformer rating and impedance, and find the minimum breaker breaking capacity (Icu) you need. This is the maximum at the transformer terminals \u2014 real values downstream are lower once cable impedance is included. Supply Three-phaseSingle-phase Transformer rating [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1778,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1832","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/pages\/1832","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/comments?post=1832"}],"version-history":[{"count":1,"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/pages\/1832\/revisions"}],"predecessor-version":[{"id":1833,"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/pages\/1832\/revisions\/1833"}],"up":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/pages\/1778"}],"wp:attachment":[{"href":"https:\/\/jutrion.com\/ar\/wp-json\/wp\/v2\/media?parent=1832"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}