{"id":100277,"date":"2026-02-15T20:31:33","date_gmt":"2026-02-15T20:31:33","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100277"},"modified":"2026-03-05T15:37:24","modified_gmt":"2026-03-05T15:37:24","slug":"vfd-selection-calculator","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/bn\/calculators\/vfd-selection-calculator\/","title":{"rendered":"VFD Selection Calculator \u2014 Size Your Drive Free | Vibromera"},"content":{"rendered":"\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"VFD Selection Calculator\",\"alternateName\":[\"Variable Frequency Drive Sizing\",\"Inverter Selection Calculator\"],\"description\":\"Size a variable frequency drive based on motor power, voltage, and overload requirements.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/vfd-selection-calculator\/\",\"applicationCategory\":\"Engineering Calculator\",\"operatingSystem\":\"Any (Web Browser)\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\",\"priceCurrency\":\"EUR\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"datePublished\":\"2024-01-01\",\"dateModified\":\"2025-06-01\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true,\"featureList\":[\"Motor current calculation\",\"VFD current rating with overload\",\"Standard VFD size recommendation\",\"Heavy\/Normal duty selection\",\"Auto-calculation\"],\"keywords\":\"VFD selection, variable frequency drive, inverter sizing, motor drive\"}\n<\/script>\n\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[\n{\"@type\":\"Question\",\"name\":\"How do I size a VFD for a motor?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Calculate the motor's full-load current (FLA), then select a VFD with a continuous current rating equal to or greater than the motor FLA. Add margin for overload capability \u2014 typically 110% for normal duty (variable torque) or 150% for heavy duty (constant torque).\"}},\n{\"@type\":\"Question\",\"name\":\"What is the difference between normal duty and heavy duty VFD rating?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Normal duty (ND) is for variable-torque loads like fans and pumps \u2014 typically 110% overload for 60 seconds. Heavy duty (HD) is for constant-torque loads like conveyors and mixers \u2014 typically 150% overload for 60 seconds. The same VFD is often rated for a higher kW in ND vs HD.\"}},\n{\"@type\":\"Question\",\"name\":\"Should I oversize the VFD?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"It is common practice to select one frame size above the motor rating for: high starting torque requirements, frequent starts\/stops, high ambient temperature, or altitude above 1000m. Oversizing by one frame also extends VFD lifetime.\"}},\n{\"@type\":\"Question\",\"name\":\"What voltage should I select for the VFD?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The VFD input voltage must match your supply. Common ratings: 230V single-phase (small motors), 400V three-phase (Europe\/Asia), 480V three-phase (North America), 690V (large industrial). The VFD output voltage matches the motor rating.\"}},\n{\"@type\":\"Question\",\"name\":\"Can I use a VFD with any motor?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"VFDs work best with inverter-duty motors (designed for PWM waveforms). Standard motors can be used but may need derating above base speed, and bearing insulation may be required for motors above 30 kW to prevent EDM bearing damage.\"}}\n]}\n<\/script>\n\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"BreadcrumbList\",\"itemListElement\":[\n{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/vibromera.eu\/\"},\n{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Calculators\",\"item\":\"https:\/\/vibromera.eu\/calculators\/\"},\n{\"@type\":\"ListItem\",\"position\":3,\"name\":\"VFD Selection\",\"item\":\"https:\/\/vibromera.eu\/calculators\/vfd-selection-calculator\/\"}\n]}\n<\/script>\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin>\n\n<link 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print{.vc-section-body{max-height:none!important}.vc-faq-a{max-height:none!important}.vc-results{max-height:none!important;padding:24px!important}.vc-copy-btn,.vc-section-chevron,.vc-faq-chevron,.vc-presets,.vc-promo{display:none!important}}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-vfd-selection-calculator\">\n\n<header class=\"vc-header\">\n    <p class=\"vc-header-eyebrow\">Free Engineering Tool<\/p>\n    <h1 class=\"vc-header-title\">VFD Selection Calculator<\/h1>\n    <p class=\"vc-header-subtitle\">Size a Variable Frequency Drive for your motor. Calculate rated current, required VFD current rating with overload margin, and recommended drive size.<\/p>\n    <div class=\"vc-badges\">\n        <span class=\"vc-badge\">Normal \/ Heavy Duty<\/span>\n        <span class=\"vc-badge\">Overload Margin<\/span>\n        <span class=\"vc-badge\">Standard Sizes<\/span>\n    <\/div>\n<\/header>\n\n<div class=\"vc-card\">\n    <form class=\"vc-form\" id=\"vc-form\" autocomplete=\"off\">\n        <div class=\"vc-form-grid\">\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-power\">Motor Rated Power <span class=\"vc-label-hint\">(kW)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-power\" inputmode=\"decimal\" step=\"any\" min=\"0\" placeholder=\"e.g. 15\" value=\"15\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-voltage\">Supply Voltage <span class=\"vc-label-hint\">(V)<\/span><\/label>\n                <select class=\"vc-select\" id=\"vc-voltage\">\n                    <option value=\"230\">230 V (1-ph \/ 3-ph)<\/option>\n                    <option value=\"400\" selected>400 V (3-phase)<\/option>\n                    <option value=\"480\">480 V (3-phase)<\/option>\n                    <option value=\"690\">690 V (3-phase)<\/option>\n                <\/select>\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-pf\">Motor Power Factor <span class=\"vc-label-hint\">(cos \u03c6)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-pf\" inputmode=\"decimal\" step=\"0.01\" min=\"0\" max=\"1\" placeholder=\"0.85\" value=\"0.85\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-eff\">Motor Efficiency \u03b7 <span class=\"vc-label-hint\">(0\u20131)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-eff\" inputmode=\"decimal\" step=\"0.01\" min=\"0\" max=\"1\" placeholder=\"0.91\" value=\"0.91\">\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-duty\">Duty Type<\/label>\n                <select class=\"vc-select\" id=\"vc-duty\">\n                    <option value=\"normal\">Normal Duty (fans, pumps \u2014 110% OL)<\/option>\n                    <option value=\"heavy\">Heavy Duty (conveyors, mixers \u2014 150% OL)<\/option>\n                <\/select>\n            <\/div>\n            <div class=\"vc-field\">\n                <label class=\"vc-label\" for=\"vc-overload\">Overload Margin <span class=\"vc-label-hint\">(%)<\/span><\/label>\n                <input class=\"vc-input\" type=\"number\" id=\"vc-overload\" inputmode=\"decimal\" step=\"1\" min=\"0\" max=\"200\" placeholder=\"e.g. 10\" value=\"10\">\n            <\/div>\n        <\/div>\n\n        <div class=\"vc-presets\">\n            <div class=\"vc-presets-label\">Quick presets<\/div>\n            <button type=\"button\" class=\"vc-preset-btn\" data-p=\"7.5\" data-v=\"400\" data-d=\"normal\">7.5 kW Fan<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-p=\"15\" data-v=\"400\" data-d=\"normal\">15 kW Pump<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-p=\"37\" data-v=\"400\" data-d=\"heavy\">37 kW Conveyor<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-p=\"75\" data-v=\"400\" data-d=\"heavy\">75 kW Crusher<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-p=\"110\" data-v=\"690\" data-d=\"normal\">110 kW \/ 690 V<\/button>\n        <\/div>\n    <\/form>\n\n    <div class=\"vc-results\" id=\"vc-results\">\n        <div class=\"vc-results-head\">\n            <h2 class=\"vc-results-title\">Results<\/h2>\n            <button type=\"button\" class=\"vc-copy-btn\" id=\"vc-copy-btn\">\n                <svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><rect x=\"9\" y=\"9\" width=\"13\" height=\"13\" rx=\"2\"\/><path d=\"M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1\"\/><\/svg> Copy\n            <\/button>\n        <\/div>\n        <div class=\"vc-result-grid\">\n            <div class=\"vc-rcard vc-rcard-primary\">\n                <div class=\"vc-rcard-label\">Min VFD Current Rating Needed<\/div>\n                <div class=\"vc-rcard-value\" id=\"vc-r-vfdcurrent\">\u2014<\/div>\n            <\/div>\n            <div class=\"vc-rcard\">\n                <div class=\"vc-rcard-label\">Motor Full-Load Current<\/div>\n                <div class=\"vc-rcard-value\" id=\"vc-r-fla\">\u2014<\/div>\n            <\/div>\n            <div class=\"vc-rcard\">\n                <div class=\"vc-rcard-label\">Motor Apparent Power<\/div>\n                <div class=\"vc-rcard-value\" id=\"vc-r-kva\">\u2014<\/div>\n            <\/div>\n            <div class=\"vc-rcard\">\n                <div class=\"vc-rcard-label\">Duty \/ Overload<\/div>\n                <div class=\"vc-rcard-value\" id=\"vc-r-duty\">\u2014<\/div>\n            <\/div>\n            <div class=\"vc-rcard\">\n                <div class=\"vc-rcard-label\">Recommended VFD Size<\/div>\n                <div class=\"vc-rcard-value\" id=\"vc-r-vfdsize\">\u2014<\/div>\n            <\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-section vc-open\" id=\"vc-sec-theory\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"true\">\n        <span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udcd8<\/span><span class=\"vc-section-title\">Theory &amp; Formulas<\/span><\/span>\n        <svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg>\n    <\/button>\n    <div class=\"vc-section-body\">\n        <div class=\"vc-section-inner vc-theory\">\n            <h3>Motor Full-Load Current<\/h3>\n            <div class=\"vc-formula-box\" id=\"vc-katex-1\"><\/div>\n            <h3>VFD Current Rating<\/h3>\n            <div class=\"vc-formula-box\" id=\"vc-katex-2\"><\/div>\n            <p>Where the overload margin accounts for transient conditions and safety factor.<\/p>\n            <h3>Standard VFD Sizes<\/h3>\n            <table class=\"vc-table\">\n                <thead><tr><th>kW (400 V)<\/th><th>Typical FLA (A)<\/th><th>VFD Frame<\/th><\/tr><\/thead>\n                <tbody>\n                    <tr><td>0.75<\/td><td>2.1<\/td><td>Size A<\/td><\/tr>\n                    <tr><td>1.5<\/td><td>3.8<\/td><td>Size A<\/td><\/tr>\n                    <tr><td>4.0<\/td><td>9.5<\/td><td>Size B<\/td><\/tr>\n                    <tr><td>7.5<\/td><td>17<\/td><td>Size B<\/td><\/tr>\n                    <tr><td>15<\/td><td>32<\/td><td>Size C<\/td><\/tr>\n                    <tr><td>22<\/td><td>46<\/td><td>Size C<\/td><\/tr>\n                    <tr><td>37<\/td><td>73<\/td><td>Size D<\/td><\/tr>\n                    <tr><td>55<\/td><td>106<\/td><td>Size D<\/td><\/tr>\n                    <tr><td>75<\/td><td>145<\/td><td>Size E<\/td><\/tr>\n                    <tr><td>110<\/td><td>210<\/td><td>Size E<\/td><\/tr>\n                <\/tbody>\n            <\/table>\n            <div class=\"vc-warning-box\"><p style=\"margin:0;font-size:14px;color:var(--vc-ink-secondary)\"><strong>\u26a0\ufe0f Note:<\/strong> Always verify VFD selection against manufacturer datasheets. Derate for ambient temperature &gt;40\u00b0C, altitude &gt;1000m, or switching frequency &gt;4 kHz.<\/p><\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-related\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\">\n        <span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udd17<\/span><span class=\"vc-section-title\">Related Calculators<\/span><\/span>\n        <svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg>\n    <\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-related\">\n        <a class=\"vc-related-link\" href=\"\/calculators\/three-phase-motor-power\/\">Three-Phase Motor Power<\/a>\n        <a class=\"vc-related-link\" href=\"\/calculators\/motor-starting-current\/\">Motor Starting Current<\/a>\n        <a class=\"vc-related-link\" href=\"\/calculators\/braking-resistor-calculator\/\">Braking Resistor<\/a>\n        <a class=\"vc-related-link\" href=\"\/calculators\/motor-nameplate-current\/\">Motor Nameplate Current<\/a>\n    <\/div><\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-faq\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\">\n        <span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\u2753<\/span><span class=\"vc-section-title\">Frequently Asked Questions<\/span><\/span>\n        <svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg>\n    <\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-faq-list\" id=\"vc-faq-list\"><\/div><\/div><\/div>\n<\/div>\n\n<div class=\"vc-promo\"><div class=\"vc-promo-text\"><strong>Vibromera \u2014 Portable Balancing &amp; Vibration Analysis<\/strong><br>Professional field balancing instruments and software. Used in 50+ countries.<\/div><a class=\"vc-promo-link\" href=\"https:\/\/vibromera.eu\/\" target=\"_blank\" rel=\"noopener\">Learn More<\/a><\/div>\n<footer class=\"vc-footer\"><p>\u00a9 2024\u20132025 <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a> \u2014 Engineering Calculators<\/p><p style=\"font-size:12px;margin-top:4px;\">Last updated: June 2025<\/p><div class=\"vc-footer-links\"><a href=\"\/calculators\/engineering-calculators\/\">All Calculators<\/a><a href=\"https:\/\/vibromera.eu\/contacts\/\">Contact<\/a><\/div><\/footer>\n<\/div>\n\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/katex@0.16.11\/dist\/katex.min.js\"><\/script>\n<script>\n(function(){\n    'use strict';\n    var SLUG='vfd-selection-calculator';\n    function $(id){return document.getElementById(id)}\n    function fmt(n,d){if(isNaN(n)||!isFinite(n))return'\u2014';var f=n.toFixed(d===undefined?2:d);return f.replace(\/(\\.\\d*?)0+$\/,'$1').replace(\/\\.$\/,'')}\n\n    var stdSizes=[0.75,1.5,2.2,3,4,5.5,7.5,11,15,18.5,22,30,37,45,55,75,90,110,132,160,200,250,315,400,500,630];\n\n    function nextStdSize(kw){for(var i=0;i<stdSizes.length;i++){if(stdSizes[i]>=kw)return stdSizes[i]}return kw}\n\n    function calculate(){\n        var P=parseFloat($('vc-power').value);\n        var V=parseFloat($('vc-voltage').value);\n        var pf=parseFloat($('vc-pf').value);\n        var eff=parseFloat($('vc-eff').value);\n        var duty=$('vc-duty').value;\n        var olMargin=parseFloat($('vc-overload').value)||0;\n        if(!P||!V||!pf||!eff||P<=0||V<=0){$('vc-results').classList.remove('vc-visible');return}\n        var sqrt3=Math.sqrt(3);\n        var Ielec=(P*1000)\/(sqrt3*V*pf*eff);\n        var dutyFactor=duty==='heavy'?1.5:1.1;\n        var Ivfd=Ielec*(1+olMargin\/100);\n        var S=sqrt3*V*Ielec\/1000;\n        var recKW=nextStdSize(P*(1+olMargin\/100));\n\n        $('vc-r-vfdcurrent').innerHTML=fmt(Ivfd,1)+' <span class=\"vc-rcard-unit\">A<\/span>';\n        $('vc-r-fla').innerHTML=fmt(Ielec,1)+' <span class=\"vc-rcard-unit\">A<\/span>';\n        $('vc-r-kva').innerHTML=fmt(S,1)+' <span class=\"vc-rcard-unit\">kVA<\/span>';\n        $('vc-r-duty').innerHTML=(duty==='heavy'?'Heavy':'Normal')+' \/ '+fmt(dutyFactor*100,0)+'% OL';\n        $('vc-r-vfdsize').innerHTML=fmt(recKW,1)+' <span class=\"vc-rcard-unit\">kW<\/span> <span class=\"vc-rcard-unit\">(\u2265'+fmt(Ivfd,0)+' A)<\/span>';\n        $('vc-results').classList.add('vc-visible');\n\n        var u=new URL(window.location);u.searchParams.set('P',P);u.searchParams.set('V',V);u.searchParams.set('pf',pf);u.searchParams.set('eff',eff);u.searchParams.set('duty',duty);u.searchParams.set('ol',olMargin);history.replaceState(null,'',u.toString());\n        saveHistory({P:P,V:V,Ivfd:fmt(Ivfd,1),rec:fmt(recKW,1),_summary:P+' kW \u2192 VFD '+fmt(recKW,0)+' kW, '+fmt(Ivfd,0)+' A'});\n    }\n\n    document.querySelectorAll('.vc-preset-btn').forEach(function(btn){btn.addEventListener('click',function(e){\n        e.preventDefault();$('vc-power').value=this.getAttribute('data-p');$('vc-voltage').value=this.getAttribute('data-v');$('vc-duty').value=this.getAttribute('data-d');calculate();\n    })});\n\n    $('vc-form').addEventListener('input',calculate);\n    $('vc-form').addEventListener('change',calculate);\n\n    $('vc-copy-btn').addEventListener('click',function(){\n        var text='VFD Selection\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nMotor: '+$('vc-power').value+' kW\\nFLA: '+$('vc-r-fla').textContent+'\\nVFD Min Current: '+$('vc-r-vfdcurrent').textContent+'\\nRecommended Size: '+$('vc-r-vfdsize').textContent+'\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nvibromera.eu';\n        if(navigator.clipboard){navigator.clipboard.writeText(text).then(function(){var b=$('vc-copy-btn');b.classList.add('vc-copied');b.innerHTML='<svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><polyline points=\"20 6 9 17 4 12\"\/><\/svg> Copied!';setTimeout(function(){b.classList.remove('vc-copied');b.innerHTML='<svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><rect x=\"9\" y=\"9\" width=\"13\" height=\"13\" rx=\"2\"\/><path d=\"M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1\"\/><\/svg> Copy'},2000)})}\n    });\n\n    document.querySelectorAll('.vc-section-toggle').forEach(function(btn){btn.addEventListener('click',function(){var s=this.closest('.vc-section');s.classList.toggle('vc-open');this.setAttribute('aria-expanded',s.classList.contains('vc-open'))})});\n\n    var faqData=[\n        {q:'How do I size a VFD for a motor?',a:'<p>Calculate the motor FLA, then select a VFD with continuous current rating \u2265 FLA plus overload margin. Typical margin is 10% for variable torque (fans\/pumps) and up to 50% for constant torque applications.<\/p>'},\n        {q:'What is the difference between normal and heavy duty rating?',a:'<p>Normal duty (ND): 110% overload for 60s, for variable torque loads. Heavy duty (HD): 150% overload for 60s, for constant torque loads. Same VFD is often rated higher kW in ND than HD mode.<\/p>'},\n        {q:'Should I oversize the VFD?',a:'<p>Yes, consider one frame size up for: high starting torque, frequent starts\/stops, ambient >40\u00b0C, altitude >1000m, or high switching frequency. Oversizing also extends VFD lifetime.<\/p>'},\n        {q:'What voltage should I select?',a:'<p>Match VFD input to your supply: 230V (small), 400V (Europe), 480V (N. America), 690V (large industrial). VFD output voltage matches the motor rating.<\/p>'},\n        {q:'Can I use a VFD with any motor?',a:'<p>VFDs work best with inverter-duty motors. 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Size a variable frequency drive based on motor power, voltage, and overload requirements. 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