{"id":1828,"date":"2026-07-27T10:31:45","date_gmt":"2026-07-27T02:31:45","guid":{"rendered":"https:\/\/jutrion.com\/?page_id=1828"},"modified":"2026-07-27T10:35:27","modified_gmt":"2026-07-27T02:35:27","slug":"%e0%b9%80%e0%b8%84%e0%b8%a3%e0%b8%b7%e0%b9%88%e0%b8%ad%e0%b8%87%e0%b8%84%e0%b8%b3%e0%b8%99%e0%b8%a7%e0%b8%93%e0%b8%82%e0%b8%99%e0%b8%b2%e0%b8%94-ats","status":"publish","type":"page","link":"https:\/\/jutrion.com\/th\/tools\/ats-sizing-calculator\/","title":{"rendered":"\u0e40\u0e04\u0e23\u0e37\u0e48\u0e2d\u0e07\u0e04\u0e33\u0e19\u0e27\u0e13\u0e02\u0e19\u0e32\u0e14 ats"},"content":{"rendered":"\n<!-- ===== JUTRION ATS Sizing Calculator \u2014 paste into a WordPress \"Custom HTML\" block ===== -->\n<div class=\"jt-calc\">\n  <p class=\"eyebrow\">Motor &amp; switching<\/p>\n  <h1>Automatic Transfer Switch (ATS) Sizing Calculator<\/h1>\n  <p class=\"tool-lede\">Get the load current, the utilization category, the next standard ATS rating, and the pole configuration from the load and the system. Motor-heavy feeders need the AC-33 category and extra margin \u2014 confirm the final rating against the ATS AC-33 table.<\/p>\n\n  <div class=\"jt-card\"><div class=\"jt-grid\">\n    <div class=\"jt-inputs\">\n      <div class=\"jt-field\"><label>Load<\/label>\n        <div class=\"jt-inline\"><input type=\"number\" id=\"jt-load\" value=\"150\" min=\"0\" step=\"0.1\" inputmode=\"decimal\" aria-label=\"Load value\">\n          <select id=\"jt-unit\" aria-label=\"Load unit\"><option value=\"kw\" selected>kW<\/option><option value=\"kva\">kVA<\/option><option value=\"a\">A<\/option><\/select>\n        <\/div>\n      <\/div>\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-volt\">Voltage (V)<\/label><input type=\"number\" id=\"jt-volt\" value=\"400\" min=\"1\" step=\"1\" inputmode=\"numeric\"><\/div>\n        <div class=\"jt-field\"><label for=\"jt-pf\">Power factor (kW)<\/label><input type=\"number\" id=\"jt-pf\" value=\"0.85\" min=\"0.1\" max=\"1\" step=\"0.01\" inputmode=\"decimal\"><\/div>\n      <\/div>\n      <div class=\"jt-field\"><label for=\"jt-char\">Load character<\/label>\n        <select id=\"jt-char\"><option value=\"ac31\">Resistive \/ lighting (AC-31)<\/option><option value=\"ac33\" selected>Mixed with motors (AC-33)<\/option><\/select>\n      <\/div>\n      <div class=\"jt-field\"><label for=\"jt-earth\">System earthing<\/label>\n        <select id=\"jt-earth\"><option value=\"TN\" selected>TN \u2014 neutral not switched<\/option><option value=\"TT\">TT \u2014 switched neutral<\/option><\/select>\n      <\/div>\n    <\/div>\n    <div class=\"jt-readout\">\n      <div><div class=\"jt-rl\">Load current<\/div><div class=\"jt-big\"><span id=\"jt-ib\">\u2014<\/span> <span>A<\/span><\/div><\/div>\n      <div class=\"jt-rec\"><div class=\"k\">Utilization category<\/div><div class=\"v\" id=\"jt-cat\" style=\"font-size:17px\">\u2014<\/div><\/div>\n      <div class=\"jt-rec\"><div class=\"k\">Recommended ATS rating<\/div><div class=\"v\"><span id=\"jt-ats\">\u2014<\/span> <small id=\"jt-poles\"><\/small><\/div>\n        <div class=\"jt-bar\"><i id=\"jt-fill\" style=\"width:0%\"><\/i><b id=\"jt-mark\" style=\"left:0%\"><\/b><\/div>\n        <div class=\"jt-ticks\"><span>load<\/span><span id=\"jt-frame\">frame<\/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 the ATS is sized<\/h2>\n    <p>The transfer switch must carry the full load continuously and switch it between sources, so it is sized from the load current at the operational voltage:<\/p>\n    <div class=\"jt-eq\">Three-phase: I = P \/ (\u221a3 \u00d7 V \u00d7 cos \u03c6)   \u00b7   from kVA: I = S \/ (\u221a3 \u00d7 V)<\/div>\n    <p>Pick an ATS whose rated current is at least the load current. The <b>utilization category<\/b> matters: AC-31 is for resistive loads, AC-33 for feeders with motors \u2014 where a switch is tested against high inrush. If motors are more than about 30 % of the feeder current, use AC-33 and confirm the rating from the AC-33 table, which can be lower than the AC-31 rating for the same frame. Neutral switching sets the poles: 3-pole where the neutral is not switched, 4-pole for TT systems and where a switched neutral is required between independent sources.<\/p>\n\n    <h2>Frequently asked questions<\/h2>\n    <div class=\"jt-faq\">\n      <details><summary>What size ATS do I need?<\/summary><p>At least the feeder load current at the operating voltage, in the correct utilization category. For motor-heavy feeders use AC-33 and select from the AC-33 rating, which accounts for inrush.<\/p><\/details>\n      <details><summary>3-pole or 4-pole?<\/summary><p>3-pole where the neutral is solidly earthed and common and not switched (typical TN). 4-pole for TT systems, and where the neutral must be switched between a utility and a separately derived generator.<\/p><\/details>\n      <details><summary>AC-31 or AC-33?<\/summary><p>AC-31 for resistive and non-inductive loads; AC-33 for feeders with significant motor load. When in doubt on a mixed feeder, choose AC-33.<\/p><\/details>\n    <\/div>\n\n    <div class=\"jt-cta\">\n      <h2>Specify the ATS<\/h2>\n      <p>With the rating, category, and poles set, choose a PC- or CB-class transfer switch and its controller.<\/p>\n      <div class=\"jt-cta-btns\">\n        <a class=\"jt-btn\" href=\"https:\/\/jutrion.com\/ats\/\">Explore JUTRION ATS<\/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\/ats\/\">ATS<\/a> \u00b7 <a href=\"https:\/\/jutrion.com\/ac-contactor\/\">AC Contactor<\/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 60947-6-1 (transfer switching equipment, AC-31 \/ AC-33 utilization categories).<\/div>\n    <p class=\"jt-fine\">Estimate for guidance only. Final ATS rating, utilization category, poles, controller, and source coordination must be verified by a qualified person against the load, the earthing arrangement, and the manufacturer&#8217;s datasheet.<\/p>\n  <\/div>\n<\/div>\n\n<script>\n(function(){\n  var $=function(id){return document.getElementById(id);};\n  var load=$('jt-load'),unit=$('jt-unit'),volt=$('jt-volt'),pf=$('jt-pf'),chr=$('jt-char'),earth=$('jt-earth'),\n      ibEl=$('jt-ib'),catEl=$('jt-cat'),atsEl=$('jt-ats'),polesEl=$('jt-poles'),fill=$('jt-fill'),mark=$('jt-mark'),frameEl=$('jt-frame');\n  var phase=3, LADDER=[63,100,125,160,200,250,315,400,630,800,1000,1250,1600];\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&&volt.value==='400')volt.value='230';if(phase===3&&volt.value==='230')volt.value='400';calc();});});\n  function nextFrame(i){for(var k=0;k<LADDER.length;k++){if(LADDER[k]>=i)return LADDER[k];}return null;}\n  function calc(){\n    var val=parseFloat(load.value),v=parseFloat(volt.value),f=parseFloat(pf.value),ib;\n    if(unit.value==='a'){ib=val;}else{if(!(v>0)){reset();return;}var base=(phase===3?Math.sqrt(3)*v:v);ib=(unit.value==='kva')?(val*1000)\/base:((f>0)?(val*1000)\/(base*f):NaN);}\n    if(!(ib>0)){reset();return;}\n    ibEl.textContent=Math.round(ib*10)\/10;catEl.textContent=(chr.value==='ac33')?'AC-33':'AC-31';\n    var nf=nextFrame(ib);atsEl.textContent=nf?(nf+' A'):'> 1600 A';polesEl.textContent=(earth.value==='TT')?'4-pole':'3-pole';frameEl.textContent=nf?(nf+' A frame'):'\u2014';\n    if(nf){var p=Math.min(100,(ib\/nf)*100).toFixed(0);fill.style.width=p+'%';mark.style.left=p+'%';}else{fill.style.width='100%';}\n  }\n  function reset(){ibEl.textContent='\u2014';catEl.textContent='\u2014';atsEl.textContent='\u2014';polesEl.textContent='';frameEl.textContent='frame';fill.style.width='0%';mark.style.left='0%';}\n  [load,unit,volt,pf,chr,earth].forEach(function(el){el.addEventListener('input',calc);el.addEventListener('change',calc);});\n  $('jt-copy').addEventListener('click',function(){var b=$('jt-copy');var txt='Load: '+load.value+' '+unit.value.toUpperCase()+', '+(phase===3?'3-phase':'1-phase')+', '+volt.value+' V\\nLoad current: '+ibEl.textContent+' A\\nCategory: '+catEl.textContent+'\\nRecommended ATS: '+atsEl.textContent+' ('+polesEl.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 Automatic Transfer Switch (ATS) Sizing Calculator Get the load current, the utilization category, the next standard ATS rating, and the pole configuration from the load and the system. Motor-heavy feeders need the AC-33 category and extra margin \u2014 confirm the final rating against the ATS AC-33 table. Load kWkVAA Supply Three-phaseSingle-phase Voltage [&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-1828","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/pages\/1828","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/comments?post=1828"}],"version-history":[{"count":1,"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/pages\/1828\/revisions"}],"predecessor-version":[{"id":1829,"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/pages\/1828\/revisions\/1829"}],"up":[{"embeddable":true,"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/pages\/1778"}],"wp:attachment":[{"href":"https:\/\/jutrion.com\/th\/wp-json\/wp\/v2\/media?parent=1828"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}