{"id":100242,"date":"2026-02-15T20:29:18","date_gmt":"2026-02-15T20:29:18","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100242"},"modified":"2026-07-15T15:29:09","modified_gmt":"2026-07-15T15:29:09","slug":"star-delta-starter-calculator","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/tr\/calculators\/star-delta-starter-calculator\/","title":{"rendered":"Idealized Star-vs-Delta Starting Ratio Worksheet"},"content":{"rendered":"<div class=\"vbm242\">\n<style>\n.vbm242{--ink:#172235;--muted:#556276;--line:#d8e0e9;--soft:#f4f7fa;--blue:#135ca8;--blue2:#0d447e;--amber:#8a5700;--amber-bg:#fff7df;--red:#a52828;--red-bg:#fff0f0;--green:#17613a;--green-bg:#edf9f1;max-width:1040px;margin:0 auto;padding:18px 14px 44px;color:var(--ink);font:15px\/1.55 system-ui,-apple-system,\"Segoe UI\",sans-serif}.vbm242 *{box-sizing:border-box}.vbm242 h1,.vbm242 h2,.vbm242 h3{line-height:1.2}.vbm242 h1{font-size:clamp(27px,4vw,42px);margin:8px 0 12px}.vbm242 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.vbm242-result-value{font-size:22px;color:var(--blue2)}.vbm242-status{margin-top:14px;border-left:4px solid var(--green);background:var(--green-bg);padding:12px 14px}.vbm242-formula{overflow-x:auto;border:1px solid var(--line);border-radius:9px;background:var(--soft);padding:12px 14px;margin:10px 0;font:600 14px\/1.7 ui-monospace,SFMono-Regular,Consolas,monospace}.vbm242 table{width:100%;border-collapse:collapse;margin:12px 0}.vbm242 th,.vbm242 td{border:1px solid var(--line);padding:9px 10px;text-align:left;vertical-align:top}.vbm242 th{background:#eaf0f6}.vbm242 ul{padding-left:22px}.vbm242 details{border-top:1px solid var(--line);padding:11px 0}.vbm242 summary{cursor:pointer;font-weight:760}.vbm242-small{font-size:13px;color:var(--muted)}.vbm242 .vbm242-result-grid{grid-template-columns:1fr 1fr!important}\n@media(max-width:700px){.vbm242{padding-left:10px;padding-right:10px}.vbm242-card{padding:16px}.vbm242-grid,.vbm242 .vbm242-result-grid{grid-template-columns:1fr!important}.vbm242-field.full{grid-column:auto}.vbm242 table{display:block;overflow-x:auto}}\n<\/style>\n<header class=\"vbm242-header\">\n<div class=\"vbm242-kicker\">same motor \u00b7 locked rotor \u00b7 \u0394 reference to Y estimate<\/div>\n<h1>Idealized Star-vs-Delta Starting Ratio Worksheet<\/h1>\n<p class=\"vbm242-lead\">Compare winding voltage, locked-rotor line current and locked-rotor torque for one documented motor that runs in delta at the supply line voltage.<\/p>\n<div class=\"vbm242-badges\"><span class=\"vbm242-badge\">VY = VL\/\u221a3<\/span><span class=\"vbm242-badge\">IY \u2248 I\u0394\/3<\/span><span class=\"vbm242-badge\">TY \u2248 T\u0394\/3<\/span><\/div>\n<\/header>\n<div class=\"vbm242-notice\"><strong>Not a starter, contactor, protection or timer selector.<\/strong> The one-third current and torque relations are idealized locked-rotor comparisons for the same winding and supply. They do not predict acceleration, transition current, heating, voltage dip, load capability or equipment ratings.<\/div>\n<form id=\"vbm242-form\" class=\"vbm242-card\" novalidate>\n<h2>Documented inputs and traceability<\/h2>\n<div class=\"vbm242-grid\">\n<div class=\"vbm242-field\"><label for=\"vbm242-voltage\">Supply line-to-line voltage V<sub>L<\/sub> (V)<span class=\"vbm242-hint\">positive RMS value for the documented start condition<\/span><\/label><input id=\"vbm242-voltage\" type=\"text\" inputmode=\"decimal\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-delta-current\">Documented \u0394 DOL locked-rotor line current I<sub>\u0394,LR<\/sub> (A)<span class=\"vbm242-hint\">positive manufacturer\/test value at the stated voltage and frequency<\/span><\/label><input id=\"vbm242-delta-current\" type=\"text\" inputmode=\"decimal\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-delta-torque\">Documented \u0394 DOL locked-rotor torque T<sub>\u0394,LR<\/sub> (N\u00b7m)<span class=\"vbm242-hint\">positive manufacturer\/test value for the same condition<\/span><\/label><input id=\"vbm242-delta-torque\" type=\"text\" inputmode=\"decimal\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-record\">Calculation \/ comparison record ID<\/label><input id=\"vbm242-record\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-motor\">Motor, nameplate and datasheet identifiers<\/label><input id=\"vbm242-motor\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-terminals\">Six-terminal winding diagram and connection revision<\/label><input id=\"vbm242-terminals\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-voltage-source\">Line-voltage source, RMS method and uncertainty<\/label><input id=\"vbm242-voltage-source\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-delta-rating\">Evidence of \u0394 continuous-run rating at line voltage<\/label><input id=\"vbm242-delta-rating\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-current-source\">Locked-rotor current source, voltage, frequency and revision<\/label><input id=\"vbm242-current-source\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-torque-source\">Locked-rotor torque source, voltage, frequency and revision<\/label><input id=\"vbm242-torque-source\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-design\">Motor frequency, IEC design and starting-performance record<\/label><input id=\"vbm242-design\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-load\">Load torque-speed curve, inertia and acceleration study<\/label><input id=\"vbm242-load\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-supply\">Supply capacity, voltage-drop and network-limit study<\/label><input id=\"vbm242-supply\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-circuit\">Open\/closed-transition circuit and interlocking drawing<\/label><input id=\"vbm242-circuit\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-coordination\">Contactor, overload and SCPD coordination record<\/label><input id=\"vbm242-coordination\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-transition\">Transition criterion and measured current\/speed record<\/label><input id=\"vbm242-transition\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-person\">Responsible electrical engineer \/ reviewer<\/label><input id=\"vbm242-person\" type=\"text\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field\"><label for=\"vbm242-date\">Review date<\/label><input id=\"vbm242-date\" type=\"text\" inputmode=\"numeric\" placeholder=\"YYYY-MM-DD\" autocomplete=\"off\"><\/div>\n<div class=\"vbm242-field full\"><label for=\"vbm242-notes\">Notes and exclusions<span class=\"vbm242-hint\">Optional: saturation, supply impedance, open-transition transients, thermal limits and hazardous-area requirements.<\/span><\/label><textarea id=\"vbm242-notes\"><\/textarea><\/div>\n<\/div>\n<div class=\"vbm242-checks\">\n <label class=\"vbm242-check\"><input id=\"vbm242-c1\" type=\"checkbox\"><span>The motor has six accessible winding terminals, is intended to run in \u0394 at the stated line voltage and is approved for star-delta starting by its manufacturer\/project documentation.<\/span><\/label><br \/>\n <label class=\"vbm242-check\"><input id=\"vbm242-c2\" type=\"checkbox\"><span>I<sub>\u0394,LR<\/sub> and T<sub>\u0394,LR<\/sub> are documented for the same motor, \u0394 connection, line voltage, frequency and locked-rotor condition; neither value is inferred from rated current or power.<\/span><\/label><br \/>\n <label class=\"vbm242-check\"><input id=\"vbm242-c3\" type=\"checkbox\"><span>The one-third values are idealized standstill estimates. Saturation, supply voltage drop and winding-impedance variation can make measured results differ.<\/span><\/label><br \/>\n <label class=\"vbm242-check\"><input id=\"vbm242-c4\" type=\"checkbox\"><span>No transition time\/current, acceleration, contactor, overload, short-circuit protection, thermal adequacy or acceptance verdict will be inferred.<\/span><\/label>\n<\/div>\n<div class=\"vbm242-actions\"><button class=\"vbm242-primary\" type=\"submit\">Calculate documented ratios<\/button><button class=\"vbm242-secondary\" id=\"vbm242-clear\" type=\"button\">Clear<\/button><\/div>\n<div id=\"vbm242-error\" class=\"vbm242-error\" role=\"alert\"><\/div>\n<\/form>\n<section id=\"vbm242-results\" class=\"vbm242-card vbm242-results\" aria-live=\"polite\">\n<h2>Idealized locked-rotor comparison<\/h2>\n<div class=\"vbm242-result-grid\">\n<div class=\"vbm242-result\">\n<div class=\"vbm242-result-label\">\u0394 winding voltage<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-delta-voltage\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result primary\">\n<div class=\"vbm242-result-label\">Y winding voltage<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-star-voltage\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result\">\n<div class=\"vbm242-result-label\">Documented \u0394 DOL locked-rotor line current<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-delta-current\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result primary\">\n<div class=\"vbm242-result-label\">Idealized Y locked-rotor line current<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-star-current\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result\">\n<div class=\"vbm242-result-label\">Documented \u0394 DOL locked-rotor torque<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-delta-torque\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result primary\">\n<div class=\"vbm242-result-label\">Idealized Y locked-rotor torque<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-star-torque\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result\">\n<div class=\"vbm242-result-label\">Y\/\u0394 winding-voltage ratio<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-voltage-ratio\">\u2014<\/div>\n<\/div>\n<div class=\"vbm242-result\">\n<div class=\"vbm242-result-label\">Idealized Y\/\u0394 current and torque ratios<\/div>\n<div class=\"vbm242-result-value\" id=\"vbm242-r-third-ratio\">\u2014<\/div>\n<\/div>\n<\/div>\n<div class=\"vbm242-status\" id=\"vbm242-r-status\"><\/div>\n<\/section>\n<section class=\"vbm242-card\">\n<h2>Formula, units and classification<\/h2>\n<div class=\"vbm242-formula\">V<sub>\u0394,winding<\/sub> = V<sub>L<\/sub> &nbsp; [V RMS]<br \/>V<sub>Y,winding<\/sub> = V<sub>L<\/sub>\/\u221a3 &nbsp; [V RMS]<br \/>I<sub>Y,line,LR<\/sub> \u2248 I<sub>\u0394,line,LR<\/sub>\/3 &nbsp; [A RMS]<br \/>T<sub>Y,LR<\/sub> \u2248 T<sub>\u0394,LR<\/sub>\/3 &nbsp; [N\u00b7m]<\/div>\n<table>\n<thead>\n<tr>\n<th>Quantity<\/th>\n<th>Meaning<\/th>\n<th>Boundary<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>V<sub>L<\/sub><\/td>\n<td>supply line-to-line RMS voltage<\/td>\n<td>not automatically the voltage present at motor terminals during starting<\/td>\n<\/tr>\n<tr>\n<td>I<sub>\u0394,LR<\/sub><\/td>\n<td>documented DOL \u0394 locked-rotor line current<\/td>\n<td>not rated current multiplied by a generic factor<\/td>\n<\/tr>\n<tr>\n<td>T<sub>\u0394,LR<\/sub><\/td>\n<td>documented DOL \u0394 locked-rotor torque<\/td>\n<td>not a universal multiple of rated torque<\/td>\n<\/tr>\n<tr>\n<td>I<sub>Y,LR<\/sub>,T<sub>Y,LR<\/sub><\/td>\n<td>idealized star-start standstill estimates<\/td>\n<td>not acceleration curves, transition peaks, thermal duty or equipment ratings<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"vbm242-small\">The one-third relations are manufacturer-supported engineering approximations for the same motor winding at locked rotor. They are not themselves acceptance formulae from an IEC standard.<\/p>\n<\/section>\n<section class=\"vbm242-card\">\n<h2>Removed unsafe selection claims<\/h2>\n<ul>\n<li><strong>No invented starting torque.<\/strong> The former page hard-coded DOL torque as 1.5\u00d7 rated torque. Starting torque must come from the motor manufacturer or a controlled test at the stated voltage\/frequency.<\/li>\n<li><strong>No timer by motor kW.<\/strong> Fixed 3\u20135, 5\u201310, 8\u201315 and 10\u201320 second bands ignored load torque, inertia, acceleration, supply behaviour and transition method.<\/li>\n<li><strong>No contactor sizing from amperes alone.<\/strong> Device selection requires circuit position, utilization category, duty, coordination, overload\/SCPD arrangement, switching frequency, ambient conditions and manufacturer data under current IEC 60947-4-1.<\/li>\n<li><strong>No universal changeover speed or transient.<\/strong> ABB notes high transition currents and requires the chosen transition point to be verified; this worksheet does not generate an 80%\/75\u201385% rule or a 10\u201315\u00d7 current claim.<\/li>\n<li><strong>No generic application verdict.<\/strong> Starting succeeds only if accelerating torque remains positive through the speed range and thermal\/network limits are satisfied.<\/li>\n<li><strong>No hidden state.<\/strong> Power\/rated-current defaults, multipliers, auto-calculation, dynamic tables, clipboard output and generated FAQ HTML were removed.<\/li>\n<\/ul>\n<\/section>\n<section class=\"vbm242-card\">\n<h2>Source traceability<\/h2>\n<table>\n<thead>\n<tr>\n<th>Claim<\/th>\n<th>Classification<\/th>\n<th>Evidence<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>IEC 60034-1:2026 Edition 15 is the current rating-and-performance base publication; IEC 60034-1:2022 was withdrawn on 13 March 2026.<\/td>\n<td>Official IEC status and scope<\/td>\n<td><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/89961\" target=\"_blank\" rel=\"noopener\">IEC 60034-1:2026<\/a><\/td>\n<\/tr>\n<tr>\n<td>IEC 60034-12:2024 Edition 4 covers starting-performance parameters for specified single-speed three-phase cage motors intended for DOL or star-delta starting, including qualifying dual-voltage motors.<\/td>\n<td>Official IEC status and scope<\/td>\n<td><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/78133\" target=\"_blank\" rel=\"noopener\">IEC 60034-12:2024<\/a><\/td>\n<\/tr>\n<tr>\n<td>IEC 60947-4-1:2023 Edition 5 covers electromechanical contactors and motor-starters and has Corrigendum 1:2026 incorporated in the corrected 2026-03 version.<\/td>\n<td>Official IEC status and scope<\/td>\n<td><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/74487\" target=\"_blank\" rel=\"noopener\">IEC 60947-4-1:2023<\/a>; <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/111823\" target=\"_blank\" rel=\"noopener\">COR1:2026<\/a><\/td>\n<\/tr>\n<tr>\n<td>For a qualifying motor, ABB states that star-delta start reduces current inrush and motor torque to one third of direct-start values, warns of high transition currents, and requires delta motor voltage equal to mains plus six terminal windings.<\/td>\n<td>Manufacturer engineering guide; page visually inspected<\/td>\n<td><a href=\"https:\/\/library.e.abb.com\/public\/15e87a4a627c26d2c1256f0800219d52\/1SBC009500R1002.pdf\" target=\"_blank\" rel=\"noopener\">ABB Starting Combinations, p. 1\/5 (PDF p. 7)<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"vbm242-small\">Accessed: 15 July 2026. Exact IEC starting-performance tables, device ratings, utilization categories and coordination requirements remain <strong>NEEDS_LICENSED_SOURCE<\/strong>.<\/p>\n<\/section>\n<section class=\"vbm242-card\">\n<h2>Reference check<\/h2>\n<p>For V<sub>L<\/sub>=400 V, documented I<sub>\u0394,LR<\/sub>=294 A and T<sub>\u0394,LR<\/sub>=150 N\u00b7m: V<sub>Y,winding<\/sub>=230.940107676 V, I<sub>Y,LR<\/sub>\u224898 A and T<sub>Y,LR<\/sub>\u224850 N\u00b7m. The winding-voltage ratio is 57.735026919% and the idealized current\/torque ratios are 33.3333333333%.<\/p>\n<\/section>\n<section class=\"vbm242-card\">\n<h2>Questions<\/h2>\n<details>\n<summary>Can this choose a contactor or overload relay?<\/summary>\n<p>No. Use the manufacturer\u2019s coordinated starter tables and the applicable current IEC 60947 documents for the actual circuit, duty and fault level.<\/p>\n<\/details>\n<details>\n<summary>Can I enter rated current instead of locked-rotor current?<\/summary>\n<p>No. This worksheet requires a documented delta-connected locked-rotor line-current value. It does not invent a DOL multiplier.<\/p>\n<\/details>\n<details>\n<summary>Does one-third torque prove the load will accelerate?<\/summary>\n<p>No. Compare the full motor and load torque-speed curves, inertia, supply voltage drop and thermal duty across the entire start.<\/p>\n<\/details>\n<\/section>\n<p><script>\n(function(){'use strict';var form=document.getElementById('vbm242-form'),error=document.getElementById('vbm242-error'),results=document.getElementById('vbm242-results'),SQRT3=Math.sqrt(3);\nfunction text(id){return document.getElementById(id).value.trim()}function requiredText(id,label){var v=text(id);if(!v)throw new Error(label+' is required.');return v}function decimal(id,label){var raw=text(id);if(!\/^(?:\\d+(?:[.,]\\d*)?|[.,]\\d+)$\/.test(raw))throw new Error(label+' must be one positive plain decimal using a point or comma.');var v=Number(raw.replace(',','.'));if(!Number.isFinite(v)||v<=0)throw new Error(label+' must be finite and greater than zero.');return v}function fmt(v){if(!Number.isFinite(v))throw new Error('The calculated result is outside the finite numeric range.');return Number(v.toPrecision(12)).toString()}function setText(id,value){document.getElementById(id).textContent=value}\nfunction compute(voltage,deltaCurrent,deltaTorque){var starVoltage=voltage\/SQRT3,starCurrent=deltaCurrent\/3,starTorque=deltaTorque\/3,voltageRatio=100\/SQRT3,thirdRatio=100\/3;[voltage,deltaCurrent,deltaTorque,starVoltage,starCurrent,starTorque,voltageRatio,thirdRatio].forEach(function(v){if(!Number.isFinite(v))throw new Error('The calculated result is outside the finite numeric range.')});return{voltage:voltage,deltaCurrent:deltaCurrent,deltaTorque:deltaTorque,starVoltage:starVoltage,starCurrent:starCurrent,starTorque:starTorque,voltageRatio:voltageRatio,thirdRatio:thirdRatio}}\nfunction render(r){setText('vbm242-r-delta-voltage',fmt(r.voltage)+' V RMS');setText('vbm242-r-star-voltage',fmt(r.starVoltage)+' V RMS');setText('vbm242-r-delta-current',fmt(r.deltaCurrent)+' A RMS');setText('vbm242-r-star-current',fmt(r.starCurrent)+' A RMS');setText('vbm242-r-delta-torque',fmt(r.deltaTorque)+' N\u00b7m');setText('vbm242-r-star-torque',fmt(r.starTorque)+' N\u00b7m');setText('vbm242-r-voltage-ratio',fmt(r.voltageRatio)+'%');setText('vbm242-r-third-ratio',fmt(r.thirdRatio)+'% \/ '+fmt(r.thirdRatio)+'%');setText('vbm242-r-status','Idealized locked-rotor ratios only. No acceleration, transition current\/time, contactor, overload, SCPD, thermal or acceptance result has been generated. 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