EVSE Circuit Breaker and Ampacity Sizing Calculator

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

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EVSE Circuit Breaker and Ampacity Sizing Calculator

Calculate the minimum circuit breaker size and conductor ampacity required for EVSE (Electric Vehicle Charging Station) installations in accordance with NEC Article 625 and NEC 210.20.

EVSE Continuous Output Current Rating (A)

The rated continuous output current of the EVSE unit (from nameplate or spec sheet)

Number of EVSE Units on Circuit

Number of EVSE units sharing the same branch circuit

Supply Voltage

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

Phase Configuration

Single Phase Three Phase

Conductor Temperature Rating

60°C (140°F) — NM-B, UF-B 75°C (167°F) — THWN, XHHW 90°C (194°F) — THWN-2, XHHW-2

Ambient Temperature (°C)

Installation ambient temperature (NEC Table 310.15(B)(1) correction applies above 30°C)

Number of Current-Carrying Conductors in Conduit

Used to apply NEC Table 310.15(C)(1) bundling derating factor

Calculate

function evsCalc() { // --- Gather Inputs --- const evseRating = parseFloat(document.getElementById('evs-evse-rating').value); const numEvse = parseInt(document.getElementById('evs-num-evse').value); const voltage = parseFloat(document.getElementById('evs-voltage').value); const phase = parseInt(document.getElementById('evs-phase').value); const tempRating = parseInt(document.getElementById('evs-temp-rating').value); const ambientTemp = parseFloat(document.getElementById('evs-ambient-temp').value); const conductors = parseInt(document.getElementById('evs-conduit-fill').value);

// --- Validation --- const errors = []; if (isNaN(evseRating) || evseRating 90) errors.push("Ambient temperature must be between -20°C and 90°C."); if (isNaN(conductors) || conductors 0) { document.getElementById('evs-result').innerHTML = 'Input Error:' + errors.map(e => '').join('') + ''; return; }

// ============================================================ // STEP 1: Total EVSE Continuous Load Current // NEC 625.42: EVSE is treated as a continuous load (100% of rated current) // NEC 210.20(A): Branch circuit must be sized at 125% of continuous load // ============================================================ const totalEvseCurrent = evseRating * numEvse; // A, total continuous load

// ============================================================ // STEP 2: Minimum Circuit Breaker / OCPD Size // NEC 625.42 & 210.20(A): OCPD >= 125% × continuous load // ============================================================ const minOcpdContinuous = totalEvseCurrent * 1.25;

// Standard breaker sizes per NEC 240.6(A) const standardBreakers = [15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200]; let selectedBreaker = null; for (let i = 0; i = minOcpdContinuous) { selectedBreaker = standardBreakers[i]; break; } } if (!selectedBreaker) selectedBreaker = Math.ceil(minOcpdContinuous / 100) * 100;

// ============================================================ // STEP 3: Temperature Correction Factor // NEC Table 310.15(B)(1) — Ambient temperature correction // CF = sqrt((TempRating - AmbientTemp) / (TempRating - 30)) // ============================================================ let tempCorrectionFactor = 1.0; if (ambientTemp !== 30) { const numerator = tempRating - ambientTemp; const denominator = tempRating - 30; if (denominator Ambient temperature exceeds or equals conductor temperature rating. Installation not feasible.'; return; } tempCorrectionFactor = Math.sqrt(numerator / denominator); }

// ============================================================ // STEP 4: Bundling / Conduit Fill Derating Factor // NEC Table 310.15(C)(1) // ============================================================ let bundlingFactor = 1.0; if (conductors = requiredBaseAmpacity) { selectedWire = wireTable[i]; break; } }

// ============================================================ // STEP 8: Power Calculations // ============================================================ const sqrtPhase = (phase === 3) ? Math.sqrt(3) : 1.0; const chargingPower = totalEvseCurrent * voltage * sqrtPhase / 1000; // kW const chargingPower125 = chargingPower * 1.25; // kW at 125% for circuit sizing

// ============================================================ // STEP 9: Ground Wire Size (NEC Table 250.122) // ============================================================ const groundTable = [ { ocpd: 15, gnd: "14 AWG" }, { ocpd: 20, gnd: "12 AWG" }, { ocpd: 60, gnd: "10 AWG" }, { ocpd: 100, gnd: "8 AWG" }, { ocpd: 200, gnd: "6 AWG" }, { ocpd: 300, gnd: "4 AWG" }, { ocpd: 400, gnd: "3 AWG" }, { ocpd: 500, gnd: "2 AWG" }, { ocpd: 600, gnd: "1 AWG" }, { ocpd: 800, gnd: "1/0 AWG"}, { ocpd: 1000, gnd: "2/0 AWG"}, { ocpd: 1200, gnd: "3/0 AWG"}, ]; let groundWire = "4/0 AWG or larger"; for (let i = 0; i 750 kcmil)";

const derateNote = combinedDerate ⚠️ Combined derating factor is very low (' + (combinedDerate * 100).toFixed(1) + '%). Consider reducing conductors per conduit or using a higher-rated conductor.'
'';

document.getElementById('evs-result').innerHTML = ` ${warningHtml} ### EVSE Circuit Sizing Results

ParameterValueReference Total EVSE Continuous Load${totalEvseCurrent.toFixed(1)} ANEC 625.42 Charging Power (actual)${chargingPower.toFixed(2)} kWP = I × V${phase===3?' × √3':''} 125% Continuous Load (circuit basis)${minOcpdContinuous.toFixed(1)} ANEC 210.20(A) Ambient Temp Correction Factor${tempCorrectionFactor.toFixed(4)}NEC Table 310.15(B)(1) Bundling Derating Factor${bundlingFactor.toFixed(2)} (${conductors} conductors)NEC Table 310.15(C)(1) Combined Derating Factor${(combinedDerate * 100).toFixed(1)}%NEC 310.15 Required Conductor Base Ampacity${requiredBaseAmpacity.toFixed(1)} A${derateNote}NEC 310.15 ✅ Minimum OCPD (Circuit Breaker)${selectedBreaker} ANEC 240.6(A), 625.42 ✅ Minimum Conductor Size (Copper)${wireDisplay}NEC Table 310.16 ✅ Equipment Grounding Conductor${groundWire} CuNEC Table 250.122

Note: Results are for copper conductors in conduit. For aluminum conductors, increase one wire size. Always verify with local AHJ (Authority Having Jurisdiction) and applicable local codes.

`; }

#### Formulas Used

1. Total Continuous Load: Itotal = IEVSE × Nunits

2. Minimum OCPD Size (NEC 210.20(A) & 625.42): IOCPD ≥ 1.25 × Itotal → rounded up to next standard breaker per NEC 240.6(A)

3. Temperature Correction Factor (NEC Table 310.15(B)(1)): CFtemp = √[(Trating − Tambient) / (Trating − 30)]

4. Bundling Derating Factor (NEC Table 310.15(C)(1)): CFbundle = 1.00 (≤3), 0.80 (4–6), 0.70 (7–9), 0.50 (10–20), 0.45 (21–30), 0.40 (31–40), 0.35 (>40)

5. Required Base Conductor Ampacity: Irequired = (1.25 × Itotal) / (CFtemp × CFbundle)

6. Charging Power: P = I × V (single-phase)  |  P = I × V × √3 (three-phase)

#### Assumptions & References

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