EVSE Circuit Breaker Sizing Calculator

ANA›Life Services Authority›National Calculator Authority›EVSE Circuit Breaker Sizing Calculator

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EVSE Circuit Breaker Sizing Calculator

Calculate the minimum circuit breaker size required for Electric Vehicle Supply Equipment (EVSE) installations per NEC Article 625.42 and NEC 210.20(A). EVSE loads are treated as continuous loads (3+ hours), requiring the circuit breaker to be sized at 125% of the EVSE rated current.

Charger Level

Custom / Enter Manually Level 1 – 12A (1.44 kW @ 120V) Level 1 – 16A (1.92 kW @ 120V) Level 2 – 16A (3.84 kW @ 240V) Level 2 – 24A (5.76 kW @ 240V) Level 2 – 32A (7.68 kW @ 240V) Level 2 – 40A (9.6 kW @ 240V) Level 2 – 48A (11.52 kW @ 240V) Level 2 – 80A (19.2 kW @ 240V)

EVSE Rated Current (A)

A

Supply Voltage (V)

120V (Level 1 / Single-phase) 208V (Three-phase / Commercial) 240V (Level 2 / Single-phase) 277V (Single-phase commercial) 480V (Three-phase commercial)

Number of EVSE Units on Circuit

units

Demand Factor (%)

% Use 100% for NEC 625.42 compliance. Reduced demand factors may apply per NEC 625.42(B) for managed charging systems.

Phase Configuration

Single-phase (1Ø) Three-phase (3Ø)

Calculate

(function() {

// Standard OCPD sizes per NEC 240.6(A) in amperes const STANDARD_BREAKER_SIZES = [ 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400 ];

// Preset charger configurations [current_A, voltage_V] const CHARGER_PRESETS = { "level1-12": [12, 120], "level1-16": [16, 120], "level2-16": [16, 240], "level2-24": [24, 240], "level2-32": [32, 240], "level2-40": [40, 240], "level2-48": [48, 240], "level2-80": [80, 240], };

window.evsUpdateChargerType = function() { const type = document.getElementById("evs-charger-type").value; if (type === "custom") return; const [current, voltage] = CHARGER_PRESETS[type]; document.getElementById("evs-evse-current").value = current; const voltSel = document.getElementById("evs-voltage"); voltSel.value = String(voltage); // Default to single-phase for level 1/2 document.getElementById("evs-phases").value = "1"; };

function getNextStandardBreakerSize(minSize) { for (let i = 0; i = minSize) { return STANDARD_BREAKER_SIZES[i]; } } return null; // Exceeds standard sizes }

window.evsCalculate = function() { const resultDiv = document.getElementById("evs-result");

// --- Input retrieval --- const evseCurrentRaw = document.getElementById("evs-evse-current").value.trim(); const voltage = parseFloat(document.getElementById("evs-voltage").value); const numEvse = parseInt(document.getElementById("evs-num-evse").value, 10); const demandPct = parseFloat(document.getElementById("evs-demand-factor").value); const phases = parseInt(document.getElementById("evs-phases").value, 10);

// --- Validation --- const errors = [];

if (evseCurrentRaw === "" || isNaN(parseFloat(evseCurrentRaw))) { errors.push("EVSE Rated Current is required and must be a number."); } const evseCurrent = parseFloat(evseCurrentRaw); if (!isNaN(evseCurrent) && (evseCurrent 400)) { errors.push("EVSE Rated Current must be between 1 A and 400 A."); } if (isNaN(numEvse) || numEvse 50) { errors.push("Number of EVSE units must be between 1 and 50."); } if (isNaN(demandPct) || demandPct 100) { errors.push("Demand Factor must be between 1% and 100%."); }

if (errors.length > 0) { resultDiv.style.display = "block"; resultDiv.className = "calc-result calc-result--error"; resultDiv.innerHTML = "Please fix the following errors:" + errors.map(e => "").join("") + ""; return; }

// --- Core Calculations ---

// Step 1: Total EVSE load current (before demand factor) // NEC 625.42: Each EVSE outlet is a continuous load const totalRatedCurrent = evseCurrent * numEvse;

// Step 2: Apply demand factor (NEC 625.42(B) managed charging) const demandFactor = demandPct / 100.0; const adjustedCurrent = totalRatedCurrent * demandFactor;

// Step 3: Apply 125% continuous load factor per NEC 210.20(A) and NEC 625.42 // Minimum circuit ampacity = EVSE rated current × 125% const continuousFactor = 1.25; const minCircuitAmpacity = adjustedCurrent * continuousFactor;

// Step 4: Find next standard breaker size per NEC 240.6(A) const recommendedBreaker = getNextStandardBreakerSize(minCircuitAmpacity);

// Step 5: Calculate power // Single-phase: P = V × I // Three-phase: P = √3 × V × I const sqrtThree = Math.sqrt(3); const powerFactor = (phases === 3) ? sqrtThree : 1.0; const evseKW = (voltage * evseCurrent * powerFactor) / 1000; const totalKW = evseKW * numEvse * demandFactor; const minWireSize = minCircuitAmpacity; // Wire must be rated ≥ min circuit ampacity

// Step 6: Determine wire gauge recommendation (simplified NEC 310 copper THWN-2 at 75°C) // Common ampacities: 14AWG=15A, 12AWG=20A, 10AWG=30A, 8AWG=50A, 6AWG=65A, // 4AWG=85A, 3AWG=100A, 2AWG=115A, 1AWG=130A, 1/0=150A, // 2/0=175A, 3/0=200A, 4/0=230A, 250kcmil=255A, 300kcmil=285A, // 350kcmil=310A, 400kcmil=335A const wireTable = [ [15, "14 AWG"], [20, "12 AWG"], [30, "10 AWG"], [50, "8 AWG"], [65, "6 AWG"], [85, "4 AWG"], [100, "3 AWG"], [115, "2 AWG"], [130, "1 AWG"], [150, "1/0 AWG"],[175, "2/0 AWG"],[200, "3/0 AWG"], [230, "4/0 AWG"],[255, "250 kcmil"],[285,"300 kcmil"],[310,"350 kcmil"], [335, "400 kcmil"] ]; let recommendedWire = "Consult engineer (>400A)"; for (let i = 0; i = minCircuitAmpacity) { recommendedWire = wireTable[i][1] + " Cu (THWN-2, 75°C)"; break; } }

// Step 7: Conduit fill note const conductorCount = (phases === 3) ? 4 : 3; // 3Ø: 3 hots + 1 ground; 1Ø: 2 hots + 1 ground

// --- Build result HTML ---
const breakerDisplay = recommendedBreaker
? recommendedBreaker + " A"
"Exceeds 400 A — consult licensed engineer";

const phaseLabel = phases === 3 ? "Three-phase (3Ø)" : "Single-phase (1Ø)";

resultDiv.style.display = "block"; resultDiv.className = "calc-result calc-result--success"; resultDiv.innerHTML = ` ### ✓ Circuit Breaker Sizing Results

Parameter Value Reference

EVSE Rated Current ${evseCurrent.toFixed(1)} A per unit Nameplate / NEC 625.42

Number of EVSE Units ${numEvse} —

Total Rated Current ${totalRatedCurrent.toFixed(1)} A ${evseCurrent.toFixed(1)} × ${numEvse}

Demand Factor ${demandPct.toFixed(0)}% NEC 625.42(B)

Adjusted Current ${adjustedCurrent.toFixed(2)} A ${totalRatedCurrent.toFixed(1)} × ${demandFactor.toFixed(2)}

Continuous Load Factor 125% NEC 210.20(A), NEC 625.42

Minimum Circuit Ampacity ${minCircuitAmpacity.toFixed(2)} A ${adjustedCurrent.toFixed(2)} × 1.25

⚡ Recommended Breaker Size ${breakerDisplay} NEC 240.6(A) standard size

Recommended Wire Size ${recommendedWire} NEC 310.16 (75°C column)

Supply Voltage ${voltage} V (${phaseLabel}) —

EVSE Power per Unit ${evseKW.toFixed(2)} kW ${phases === 3 ? "√3 × " : ""}${voltage}V × ${evseCurrent.toFixed(1)}A${phases === 3 ? " × √3" : ""}

Total Demand Load ${totalKW.toFixed(2)} kW ${evseKW.toFixed(2)} kW × ${numEvse} × ${demandFactor.toFixed(2)}

Minimum Conductors ${conductorCount} conductors ${phases === 3 ? "3 hots + 1 EGC" : "2 hots + 1 EGC"}

${recommendedBreaker === null ? '⚠ Warning: Calculated ampacity exceeds standard breaker sizes. A licensed electrical engineer must design this installation.

' : ''}

${demandPct

#### Formulas Used

NEC 625.42 — EVSE as Continuous Load (125% Rule):

Minimum Circuit Ampacity = (IEVSE × N × Df) × 1.25

Where:

Power Calculations:

Standard Breaker Selection: Per NEC 240.6(A), select the next standard size at or above the minimum circuit ampacity: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400 A.

#### Assumptions & References

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References

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