{"id":1808,"date":"2026-07-27T10:32:46","date_gmt":"2026-07-27T02:32:46","guid":{"rendered":"https:\/\/jutrion.com\/?page_id=1808"},"modified":"2026-07-27T10:37:51","modified_gmt":"2026-07-27T02:37:51","slug":"%e3%83%a2%e3%83%bc%e3%82%bf%e3%83%bc%e9%81%8e%e8%b2%a0%e8%8d%b7%e3%83%aa%e3%83%ac%e3%83%bc%e8%a8%88%e7%ae%97%e6%a9%9f","status":"publish","type":"page","link":"https:\/\/jutrion.com\/ja\/tools\/motor-overload-relay-calculator\/","title":{"rendered":"\u30e2\u30fc\u30bf\u30fc\u904e\u8ca0\u8377\u7d99\u96fb\u5668\u8a2d\u5b9a\u8a08\u7b97\u30c4\u30fc\u30eb"},"content":{"rendered":"\n<!-- ===== JUTRION Motor Overload Relay Setting \u2014 paste into a WordPress \"Custom HTML\" block ===== -->\n<div class=\"jt-calc\">\n  <p class=\"eyebrow\">Motor &amp; switching<\/p>\n  <h1>Motor Overload Relay Setting Calculator<\/h1>\n  <p class=\"tool-lede\">Turn the motor nameplate current, service factor, and starting duty into a preliminary thermal-overload dial setting and trip class for a contactor-mounted overload relay. The nameplate current governs \u2014 these are starting points to be trimmed on commissioning.<\/p>\n\n  <div class=\"jt-card\"><div class=\"jt-grid\">\n    <div class=\"jt-inputs\">\n      <div class=\"jt-field\"><label for=\"jt-flc\">Motor nameplate current \u2014 FLC (A)<\/label><input type=\"number\" id=\"jt-flc\" value=\"18\" min=\"0.1\" step=\"0.1\" inputmode=\"decimal\"><\/div>\n      <div class=\"jt-field\"><label for=\"jt-sf\">Service factor<\/label>\n        <select id=\"jt-sf\"><option value=\"1.0\">1.0 \u2014 no service factor<\/option><option value=\"1.15\" selected>1.15 \u2014 with service factor<\/option><\/select>\n      <\/div>\n      <div class=\"jt-field\"><label for=\"jt-start\">Starting duty<\/label>\n        <select id=\"jt-start\"><option value=\"10\" selected>Normal \u2014 start &lt; 10 s (pumps, fans)<\/option><option value=\"20\">Heavy \u2014 10\u201320 s (loaded conveyors)<\/option><option value=\"30\">Very heavy \u2014 &gt; 20 s (crushers, centrifuges)<\/option><\/select>\n      <\/div>\n      <div class=\"jt-field\"><label class=\"jt-check\"><input type=\"checkbox\" id=\"jt-amb\"> Relay ambient differs from motor (needs temperature compensation)<\/label><\/div>\n    <\/div>\n    <div class=\"jt-readout\">\n      <div><div class=\"jt-rl\">Recommended dial setting<\/div><div class=\"jt-big\"><span id=\"jt-set\">\u2014<\/span> <span>A<\/span><\/div><\/div>\n      <div class=\"jt-rec row\"><div class=\"k\">Setting range<\/div><div class=\"v\" id=\"jt-range\">\u2014<\/div><\/div>\n      <div class=\"jt-rec row\"><div class=\"k\">Trip class<\/div><div class=\"v\" id=\"jt-class\">\u2014<\/div><\/div>\n      <div class=\"jt-rec\"><div class=\"k\">Guidance<\/div><div class=\"v\" id=\"jt-guide\" style=\"font-size:13px\">\u2014<\/div><\/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>Setting: dial to the motor, not the cable<\/h2>\n    <p>A thermal overload relay protects the <b>motor windings<\/b>, so it is set from the motor&#8217;s actual full-load current, taken from the nameplate. The service factor sets the allowable margin above it:<\/p>\n    <div class=\"jt-eq\">Service factor 1.0   : set \u2248 100\u2013115 % of FLC\nService factor 1.15+ : set \u2248 115\u2013125 % of FLC<\/div>\n    <p>Start at the FLC on the dial and trim upward within the range only if the motor nuisance-trips at a genuinely acceptable load. Setting above the range removes winding protection; setting far below it causes nuisance trips.<\/p>\n\n    <h2>Trip class: match the start time<\/h2>\n    <div class=\"jt-table-wrap\"><table>\n      <thead><tr><th>Class<\/th><th>Trip time at 7.2 \u00d7 setting<\/th><th>Use<\/th><\/tr><\/thead>\n      <tbody>\n        <tr><td class=\"mono\">Class 10<\/td><td class=\"mono\">\u2264 10 s<\/td><td>Normal starting \u2014 pumps, fans, standard loads<\/td><\/tr>\n        <tr><td class=\"mono\">Class 20<\/td><td class=\"mono\">\u2264 20 s<\/td><td>Heavy starting \u2014 loaded conveyors, mixers<\/td><\/tr>\n        <tr><td class=\"mono\">Class 30<\/td><td class=\"mono\">\u2264 30 s<\/td><td>Very heavy \/ high-inertia \u2014 crushers, centrifuges<\/td><\/tr>\n      <\/tbody>\n    <\/table><\/div>\n    <p>The class must let the motor accelerate without tripping, yet still protect the windings during a stalled or locked-rotor condition. A long-starting motor on a Class 10 relay trips on every start; too high a class on a quick-starting motor slows protection.<\/p>\n\n    <div class=\"jt-note\"><span>\u26a0<\/span><span><b>Temperature compensation matters.<\/b> A non-compensated bimetallic relay shifts its trip point with its own ambient. Where the relay sits in a hot enclosure or a different ambient from the motor, use a temperature-compensated relay or apply the manufacturer&#8217;s correction.<\/span><\/div>\n\n    <h2>Frequently asked questions<\/h2>\n    <div class=\"jt-faq\">\n      <details><summary>Do I use the nameplate current or the cable rating?<\/summary><p>Always the motor nameplate FLC. The overload protects the motor; the cable and short-circuit protection are handled separately by the breaker or fuse.<\/p><\/details>\n      <details><summary>My motor trips during start \u2014 raise the setting?<\/summary><p>Usually no. First check the trip class matches the start time \u2014 a heavy or high-inertia load often needs Class 20 or 30. Only trim the current setting within its range, and never above the service-factor limit.<\/p><\/details>\n      <details><summary>Electronic overload or bimetallic?<\/summary><p>Electronic overloads offer wider setting ranges, selectable classes, phase-loss and phase-imbalance protection, and better temperature stability. Bimetallic relays are simple and economical for standard duties.<\/p><\/details>\n    <\/div>\n\n    <div class=\"jt-cta\">\n      <h2>Build the starter<\/h2>\n      <p>Pair the overload relay with a correctly rated AC contactor and short-circuit protection for a complete motor starter.<\/p>\n      <div class=\"jt-cta-btns\">\n        <a class=\"jt-btn\" href=\"https:\/\/jutrion.com\/ac-contactor\/\">Explore JUTRION contactors<\/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\/ac-contactor\/\">AC Contactor<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/mccb\/\">MCCB<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/relay\/\">Relay<\/a><\/p>\n    <\/div>\n\n    <div class=\"jt-std\"><strong>Standards referenced<\/strong>IEC 60947-4-1 (contactors &amp; motor-starters, overload relays &amp; trip classes) \u00b7 motor nameplate data.<\/div>\n    <p class=\"jt-fine\">Preliminary setting for guidance only. The final overload setting and trip class must be confirmed by a qualified person against the motor nameplate, the driven load, and the relay manufacturer&#8217;s data, then verified on commissioning.<\/p>\n  <\/div>\n<\/div>\n\n<script>\n(function(){\n  var $=function(id){return document.getElementById(id);};\n  var flc=$('jt-flc'),sf=$('jt-sf'),start=$('jt-start'),amb=$('jt-amb'),\n      setEl=$('jt-set'),rangeEl=$('jt-range'),classEl=$('jt-class'),guideEl=$('jt-guide');\n  function r1(x){return Math.round(x*10)\/10;}\n  function calc(){\n    var I=parseFloat(flc.value),s=parseFloat(sf.value);\n    if(!(I>0)){setEl.textContent='\u2014';rangeEl.textContent=classEl.textContent=guideEl.textContent='\u2014';return;}\n    var hiFac=(s>=1.15)?1.25:1.15;\n    var rec=(s>=1.15)?I*1.15:I; \/\/ start at FLC (or 115% with SF), trim up to limit\n    setEl.textContent=r1(rec);\n    rangeEl.textContent=r1(I)+' \u2013 '+r1(I*hiFac)+' A';\n    classEl.textContent='Class '+start.value;\n    guideEl.textContent=amb.checked?'Use a temperature-compensated relay':'Dial to nameplate, trim on test';\n  }\n  [flc,sf,start].forEach(function(el){el.addEventListener('input',calc);el.addEventListener('change',calc);});\n  amb.addEventListener('change',calc);\n  $('jt-copy').addEventListener('click',function(){var b=$('jt-copy');var txt='Motor FLC: '+flc.value+' A, SF '+sf.value+'\\nRecommended setting: '+setEl.textContent+' A\\nSetting range: '+rangeEl.textContent+'\\nTrip class: '+classEl.textContent+'\\nGuidance: '+guideEl.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>Motor &amp; switching Motor Overload Relay Setting Calculator Turn the motor nameplate current, service factor, and starting duty into a preliminary thermal-overload dial setting and trip class for a contactor-mounted overload relay. The nameplate current governs \u2014 these are starting points to be trimmed on commissioning. Motor nameplate current \u2014 FLC (A) Service factor 1.0 \u2014 no service factor1.15 \u2014 with service factor Starting duty Normal \u2014 start &lt; 10 s (pumps, fans)Heavy \u2014 10\u201320 s (loaded conveyors)Very heavy \u2014 &gt; 20 s (crushers, centrifuges) Relay ambient differs from motor (needs temperature compensation) Recommended dial setting \u2014 A Setting range \u2014 Trip class \u2014 Guidance \u2014 Copy result Setting: dial [&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-1808","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1808","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/comments?post=1808"}],"version-history":[{"count":1,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1808\/revisions"}],"predecessor-version":[{"id":1809,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1808\/revisions\/1809"}],"up":[{"embeddable":true,"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/pages\/1778"}],"wp:attachment":[{"href":"https:\/\/jutrion.com\/ja\/wp-json\/wp\/v2\/media?parent=1808"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}