{"id":100162,"date":"2026-02-15T20:21:47","date_gmt":"2026-02-15T20:21:47","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100162"},"modified":"2026-07-12T21:55:16","modified_gmt":"2026-07-12T21:55:16","slug":"motor-starting-current","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/sr\/calculators\/motor-starting-current\/","title":{"rendered":"Documented Motor Starting-Current Arithmetic Worksheet"},"content":{"rendered":"\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Documented Motor Starting-Current Arithmetic Worksheet\",\"description\":\"Calculate balanced three-phase starting line current from a documented current ratio or documented starting apparent power without universal DOL,star-delta,soft-starter or VFD multipliers.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/motor-starting-current\/\",\"applicationCategory\":\"Engineering Reference\",\"operatingSystem\":\"Any\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\",\"priceCurrency\":\"EUR\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"dateModified\":\"2026-07-12\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true}<\/script>\n<style>\n.sc-wrap{--ink:#17212b;--muted:#596775;--line:#d8e0e7;--soft:#f4f7f9;--blue:#1769aa;--blue2:#0f4f84;--warn:#fff7e5;max-width:980px;margin:0 auto;padding:20px 16px 46px;color:var(--ink);font:15px\/1.58 system-ui,-apple-system,\"Segoe UI\",sans-serif}.sc-wrap *{box-sizing:border-box}.sc-wrap [hidden]{display:none!important}.sc-hero{padding:38px 30px;border:1px solid var(--line);border-radius:18px;background:linear-gradient(135deg,#eef7ff,#fff 68%);box-shadow:0 10px 30px rgba(20,54,80,.07)}.sc-kicker{color:var(--blue);font-size:12px;font-weight:800;letter-spacing:.1em;text-transform:uppercase}.sc-hero h1{margin:8px 0 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12px}.sc-textarea{min-height:100px;resize:vertical}.sc-input:focus,.sc-select:focus,.sc-textarea:focus{outline:3px solid rgba(23,105,170,.16);border-color:var(--blue)}.sc-error{min-height:24px;margin:14px 0 0;color:#a22727;font-weight:700}.sc-results{margin-top:20px;border:1px solid #b9d4e8;border-radius:12px;background:#f7fbff;padding:20px}.sc-rhead{display:flex;justify-content:space-between;gap:14px;align-items:flex-start}.sc-rtitle{font-size:19px;font-weight:800}.sc-rsub{max-width:590px;text-align:right;color:var(--muted);font-size:12px}.sc-rgrid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:11px;margin-top:14px}.sc-card{padding:14px;border:1px solid #d7e5f0;border-radius:10px;background:#fff}.sc-card h3{margin:0 0 7px;color:var(--muted);font-size:12px;text-transform:uppercase;letter-spacing:.04em}.sc-val{font-size:20px;font-weight:800;overflow-wrap:anywhere}.sc-unit{margin-top:3px;color:var(--muted);font-size:11px}.sc-alert{margin-top:18px;padding:15px 17px;border:1px solid #e8cf91;border-radius:10px;background:var(--warn);color:#624b13}.sc-section{margin-top:18px;padding:22px 24px}.sc-section p{margin:8px 0;color:var(--muted)}.sc-section ul{margin:10px 0 0;padding-left:22px;color:var(--muted)}.sc-code{font-family:ui-monospace,SFMono-Regular,Consolas,monospace;color:#113d62}.sc-table{width:100%;border-collapse:collapse;margin-top:12px}.sc-table th,.sc-table td{padding:10px;border:1px solid var(--line);text-align:left;vertical-align:top}.sc-table th{background:var(--soft)}.sc-section a{color:var(--blue2)}@media(max-width:680px){.sc-grid,.sc-rgrid{grid-template-columns:1fr}.sc-wide{grid-column:auto}.sc-hero{padding:26px 20px}.sc-panel,.sc-section{padding:19px}.sc-rhead{display:block}.sc-rsub{text-align:left;margin-top:5px}}@media print{.sc-wrap{max-width:none}.sc-hero,.sc-panel,.sc-section{box-shadow:none}}\n<\/style>\n<div class=\"sc-wrap\">\n<header class=\"sc-hero\"><div class=\"sc-kicker\">Documented RMS quantity \u00b7 stated start configuration \u00b7 no universal method multiplier<\/div><h1>Documented Motor Starting-Current Arithmetic Worksheet<\/h1><p class=\"sc-lead\">Calculate balanced three-phase starting line current from either a documented current ratio or documented starting apparent power. The worksheet does not assign DOL,star-delta,soft-starter or VFD multipliers and does not estimate rated current from guessed power factor or efficiency.<\/p><div class=\"sc-badges\"><span class=\"sc-badge\">Starts blank<\/span><span class=\"sc-badge\">Rated current entered directly<\/span><span class=\"sc-badge\">RMS\u2014not first-cycle peak<\/span><span class=\"sc-badge\">No protection sizing<\/span><\/div><\/header>\n<main class=\"sc-main\"><section class=\"sc-panel\"><h2>Document the starting quantity<\/h2><p class=\"sc-note\">Use voltage,current ratio and apparent power for the same motor,connection,supply and starting configuration. Define whether the source quantity is locked-rotor,maximum RMS,ramp-limited or measured over another interval.<\/p><form id=\"sc-form\" novalidate><div class=\"sc-grid\">\n<div class=\"sc-field sc-wide\"><label class=\"sc-label\" for=\"sc-basis\">Calculation basis<\/label><select class=\"sc-select\" id=\"sc-basis\"><option value=\"\">Select\u2026<\/option><option value=\"documented-current-ratio\">Documented RMS starting\/rated line-current ratio<\/option><option value=\"documented-starting-kva\">Documented balanced three-phase starting apparent power<\/option><\/select><\/div>\n<div class=\"sc-field\"><label class=\"sc-label\" for=\"sc-voltage\">Line-to-line RMS voltage U<sub>LL<\/sub> (V)<\/label><input class=\"sc-input\" id=\"sc-voltage\" inputmode=\"decimal\" autocomplete=\"off\"><span class=\"sc-help\">Voltage applicable to the stated starting configuration.<\/span><\/div>\n<div class=\"sc-field\"><label class=\"sc-label\" for=\"sc-rated\">Rated line current I<sub>rated<\/sub> (A)<\/label><input class=\"sc-input\" id=\"sc-rated\" inputmode=\"decimal\" autocomplete=\"off\"><span class=\"sc-help\" id=\"sc-rated-help\">Required for ratio basis;optional for kVA basis.<\/span><\/div>\n<div class=\"sc-field sc-wide\" id=\"sc-ratio-field\" hidden><label class=\"sc-label\" for=\"sc-ratio\">Documented current ratio k=I<sub>start<\/sub>\/I<sub>rated<\/sub><\/label><input class=\"sc-input\" id=\"sc-ratio\" inputmode=\"decimal\" autocomplete=\"off\"><span class=\"sc-help\">Positive manufacturer,test or licensed-source value for this exact configuration.<\/span><\/div>\n<div class=\"sc-field sc-wide\" id=\"sc-kva-field\" hidden><label class=\"sc-label\" for=\"sc-kva\">Documented starting apparent power S<sub>start<\/sub> (kVA)<\/label><input class=\"sc-input\" id=\"sc-kva\" inputmode=\"decimal\" autocomplete=\"off\"><span class=\"sc-help\">Balanced three-phase apparent power for the stated RMS interval.<\/span><\/div>\n<div class=\"sc-field sc-wide\"><label class=\"sc-label\" for=\"sc-config\">Starting configuration and quantity definition<\/label><input class=\"sc-input\" id=\"sc-config\" maxlength=\"320\" autocomplete=\"off\" placeholder=\"Exact connection,starter\/PDS settings,supply and definition of the RMS\/locked-rotor quantity\"><\/div>\n<div class=\"sc-field sc-wide\"><label class=\"sc-label\" for=\"sc-source\">Motor and source record<\/label><textarea class=\"sc-textarea\" id=\"sc-source\" maxlength=\"2400\" placeholder=\"Manufacturer,type\/serial and winding rating;voltage\/frequency;source document\/test and edition;current-transformer\/analyser method;time interval and uncertainty;supply impedance;starter\/PDS settings;load\/inertia and acceleration data\"><\/textarea><\/div>\n<\/div><p class=\"sc-error\" id=\"sc-error\" role=\"alert\"><\/p><\/form>\n<section class=\"sc-results\" id=\"sc-results\" hidden data-json=\"\"><div class=\"sc-rhead\"><div class=\"sc-rtitle\">Starting-current arithmetic<\/div><div class=\"sc-rsub\" id=\"sc-summary\">\u2014<\/div><\/div><div class=\"sc-rgrid\">\n<article class=\"sc-card\"><h3>Starting line current<\/h3><div class=\"sc-val\" id=\"sc-r-current\">\u2014<\/div><div class=\"sc-unit\">RMS quantity under the documented definition<\/div><\/article>\n<article class=\"sc-card\"><h3>Starting apparent power<\/h3><div class=\"sc-val\" id=\"sc-r-kva\">\u2014<\/div><div class=\"sc-unit\">S=\u221a3 U<sub>LL<\/sub>I<sub>start<\/sub><\/div><\/article>\n<article class=\"sc-card\"><h3>Rated line current<\/h3><div class=\"sc-val\" id=\"sc-r-rated\">\u2014<\/div><div class=\"sc-unit\">manufacturer\/source value;not reconstructed<\/div><\/article>\n<article class=\"sc-card\"><h3>Start\/rated ratio<\/h3><div class=\"sc-val\" id=\"sc-r-ratio\">\u2014<\/div><div class=\"sc-unit\">documented or derived when rated current is supplied<\/div><\/article>\n<article class=\"sc-card\"><h3>Line-to-line voltage<\/h3><div class=\"sc-val\" id=\"sc-r-voltage\">\u2014<\/div><div class=\"sc-unit\">RMS starting configuration<\/div><\/article>\n<article class=\"sc-card\"><h3>Calculation basis<\/h3><div class=\"sc-val\" id=\"sc-r-basis\">\u2014<\/div><div class=\"sc-unit\">controlled input route<\/div><\/article>\n<article class=\"sc-card\"><h3>Configuration record<\/h3><div class=\"sc-val\" id=\"sc-r-config\">\u2014<\/div><div class=\"sc-unit\">verbatim evidence;not automatically decoded<\/div><\/article>\n<article class=\"sc-card\"><h3>First-cycle peak<\/h3><div class=\"sc-val\" id=\"sc-r-peak\">Not evaluated<\/div><div class=\"sc-unit\">requires waveform\/DC-offset\/system evidence<\/div><\/article>\n<article class=\"sc-card\"><h3>Starting duration<\/h3><div class=\"sc-val\" id=\"sc-r-duration\">Not evaluated<\/div><div class=\"sc-unit\">requires acceleration\/load\/PDS model<\/div><\/article>\n<\/div><\/section>\n<div class=\"sc-alert\"><strong>Decision boundary:<\/strong> this arithmetic does not size conductors,breakers,fuses,contactors,transformers,generators,voltage-drop limits,star-delta transitions,soft-starter settings or a VFD. Those decisions require the time-current waveform,supply impedance,protection rules and manufacturer system data.<\/div><\/section><\/main>\n<section class=\"sc-section\"><h2>Equations and scope<\/h2><table class=\"sc-table\"><thead><tr><th>Documented basis<\/th><th>Equation<\/th><th>Required evidence<\/th><\/tr><\/thead><tbody><tr><td>Current ratio<\/td><td><span class=\"sc-code\">Istart=k\u00b7Irated<\/span><br><span class=\"sc-code\">Sstart=\u221a3 ULL Istart\/1000<\/span><\/td><td>Rated line current and applicable RMS start\/rated ratio for the same configuration.<\/td><\/tr><tr><td>Starting apparent power<\/td><td><span class=\"sc-code\">Istart=Sstart\u00b71000\/(\u221a3 ULL)<\/span><\/td><td>Balanced three-phase starting kVA and line-to-line RMS voltage. Rated current is optional and used only to derive a ratio.<\/td><\/tr><\/tbody><\/table><p>These are general arithmetic relations,not a standard-assigned DOL,Y-\u0394,soft-starter or VFD multiplier. Apparent power does not by itself state power factor,active power,torque,duration or first-cycle peak.<\/p><\/section>\n<section class=\"sc-section\"><h2>Standards and source boundary<\/h2><p><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/78133\" target=\"_blank\" rel=\"noopener\">IEC60034-12:2024,Edition4<\/a> specifies starting-performance parameters for eight designs of single-speed three-phase50\/60Hz cage induction motors up to1000V,intended for DOL or star-delta starting and based on S1 duty. Its exact design values,test methods and tolerances are <span class=\"sc-code\">NEEDS_LICENSED_SOURCE<\/span>;the public scope does not justify universal6\u20138\u00d7 or2\u20133\u00d7 values.<\/p><p><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/89961\" target=\"_blank\" rel=\"noopener\">IEC60034-1:2026,Edition15<\/a> is the current motor rating\/performance standard. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/62105\" target=\"_blank\" rel=\"noopener\">IEC61800-2:2021,Edition3<\/a> treats an adjustable-speed AC power drive as a motor\/converter\/control\/protection system with selected performance and functional attributes. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/62103\" target=\"_blank\" rel=\"noopener\">IEC61800-5-1:2022,Edition3<\/a> covers PDS electrical,thermal,fire,mechanical and energy hazards;this page is not a safety design.<\/p><p>NEMA locked-rotor code-letter ranges were removed because no current licensed NEMA MG1 edition and exact table were verified. Do not infer a letter midpoint or current range from an unsourced online table.<\/p><\/section>\n<section class=\"sc-section\"><h2>Interpretation safeguards<\/h2><ul><li>DOL current depends on motor locked-rotor characteristics,voltage\/frequency,connection and supply impedance;it is not universally6\u20138\u00d7 rated current.<\/li><li>Star-delta behavior requires a motor intended to run in delta at the line voltage and a compatible load\/transition. Current and torque relations do not prove successful acceleration.<\/li><li>Soft-starter current depends on voltage\/current-limit,ramp,kick-start,bypass and load settings. VFD current depends on the complete PDS control,limits,speed\/torque curve and overload rating.<\/li><li>Starting current varies with time. RMS locked-rotor,current-limit,maximum-cycle and first asymmetric peak values are not interchangeable.<\/li><li>Rated current should come from the applicable manufacturer rating. Reconstructing it from output power with guessed efficiency and power factor compounds uncertainty.<\/li><\/ul><\/section>\n<section class=\"sc-section\"><h2>What was corrected<\/h2><p>The former page assigned default current multipliers7,2.5,3 and1.2 to DOL,star-delta,soft starter and VFD,then presented generic use\/power ranges and torque claims as if they selected the method. Those values were not tied to a motor design,connection,supply,starter settings or licensed table.<\/p><p>Defaults,presets,guessed rated current from output\/PF\/efficiency,method auto-fill,NEMA code-letter example,URL\/history persistence,automatic FAQ advice and unsafe protection links were removed. The replacement accepts only documented start quantities,uses strict parsing and reports no peak,duration,torque or protection result.<\/p><\/section>\n<\/div>\n<script>(function(){'use strict';function $(id){return document.getElementById(id)}function num(s){s=String(s).trim();if(!s||s.includes('.')&&s.includes(',')||!\/^[+-]?(?:\\d+(?:[.,]\\d*)?|[.,]\\d+)(?:[eE][+-]?\\d+)?$\/.test(s))return NaN;var n=Number(s.replace(',','.'));return Number.isFinite(n)&&Math.abs(n)<=1e100?n:NaN}function fmt(n){if(n===0)return'0';var a=Math.abs(n);return a>=1e12||a<1e-8?n.toExponential(9):Number(n.toPrecision(12)).toLocaleString('en-US',{maximumFractionDigits:20})}function clear(){['sc-r-current','sc-r-kva','sc-r-rated','sc-r-ratio','sc-r-voltage','sc-r-basis','sc-r-config','sc-summary'].forEach(function(id){$(id).textContent='\u2014'});$('sc-r-peak').textContent='Not evaluated';$('sc-r-duration').textContent='Not evaluated';$('sc-results').hidden=true;$('sc-results').dataset.json=''}function 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\u0418\u0437\u0440\u0430\u0447\u0443\u043d\u0430\u0458\u0442\u0435 \u0443\u0434\u0430\u0440\u043d\u0443 \u0441\u0442\u0440\u0443\u0458\u0443 \u0437\u0430 DOL, \u0437\u0432\u0435\u0437\u0434\u0430-\u0442\u0440\u043e\u0443\u0433\u0430\u043e, \u043c\u0435\u043a\u0438 \u0441\u0442\u0430\u0440\u0442\u0435\u0440 \u0438 VFD \u043c\u0435\u0442\u043e\u0434\u0435. 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