Electrical Panel Load Balancing Calculator

ANA›Life Services Authority›National Calculator Authority›Electrical Panel Load Balancing Calculator

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Electrical Panel Load Balancing Calculator

Calculate load distribution across electrical panel phases, identify imbalances, and optimize circuit assignments for single-phase and three-phase panels.

Panel Type

Single-Phase (120/240V) Three-Phase (120/208V or 277/480V)

System Voltage (V)

120/240V (Residential) 120/208V (Commercial 3-Phase) 277/480V (Industrial 3-Phase)

Main Breaker Rating (A)

### Circuit Loads

Enter each circuit's amperage and assign it to a phase. Add up to 20 circuits.

Circuit 1

Load (A)

Phase

Phase A Phase B Phase C

Label

Circuit 2

Load (A)

Phase

Phase A Phase B Phase C

Label

Circuit 3

Load (A)

Phase

Phase A Phase B Phase C

Label

Circuit 4

Load (A)

Phase

Phase A Phase B Phase C

Label

Calculate Load Balance

var eleCircuitCount = 4; var eleMaxCircuits = 20;

function eleUpdatePhaseInputs() { var panelType = document.getElementById('ele-panel-type').value; var cOpts = document.querySelectorAll('.ele-phase-c-opt'); cOpts.forEach(function(opt) { opt.style.display = (panelType === 'three') ? '' : 'none'; }); // Reset any Phase C selections to Phase A if switching to single-phase if (panelType === 'single') { for (var i = 1; i = eleMaxCircuits) { alert('Maximum of ' + eleMaxCircuits + ' circuits allowed.'); return; } eleCircuitCount++; var n = eleCircuitCount; var panelType = document.getElementById('ele-panel-type').value; var cDisplay = (panelType === 'three') ? '' : 'none'; var div = document.createElement('div'); div.className = 'ele-circuit-row'; div.id = 'ele-circuit-' + n; div.innerHTML = '' + 'Circuit ' + n + '' + 'Load (A)' + '' + 'Phase' + '' + 'Phase APhase B' + 'Phase C' + 'Label' + '' + ''; document.getElementById('ele-circuits-container').appendChild(div); }

function eleRemoveCircuit() { if (eleCircuitCount Error: Invalid system voltage.'; return; } if (isNaN(mainBreaker) || mainBreaker 4000) { document.getElementById('ele-result').style.display = 'block'; document.getElementById('ele-result').innerHTML = 'Error: Main breaker rating must be between 1 and 4000 A.'; return; }

// Collect circuits var circuits = []; for (var i = 1; i Error: Circuit ' + i + ' has an invalid load value. Must be 0 or greater.'; return; } if (load > mainBreaker) { document.getElementById('ele-result').style.display = 'block'; document.getElementById('ele-result').innerHTML = 'Error: Circuit ' + i + ' load (' + load + ' A) exceeds main breaker rating (' + mainBreaker + ' A).'; return; } circuits.push({ id: i, load: load, phase: phaseEl.value, label: labelEl ? (labelEl.value || 'Circuit ' + i) : 'Circuit ' + i }); }

if (circuits.length === 0) { document.getElementById('ele-result').style.display = 'block'; document.getElementById('ele-result').innerHTML = 'Error: No circuits found.'; return; }

// Phase loads var phaseA = 0, phaseB = 0, phaseC = 0; circuits.forEach(function(c) { if (c.phase === 'A') phaseA += c.load; else if (c.phase === 'B') phaseB += c.load; else if (c.phase === 'C') phaseC += c.load; });

var totalLoad = phaseA + phaseB + phaseC; var numPhases = (panelType === 'three') ? 3 : 2;

// Average load per phase var avgLoad = totalLoad / numPhases;

// Load imbalance calculation // For single-phase: imbalance = |A - B| / avg * 100 // For three-phase: imbalance = max deviation from avg / avg * 100 (NEMA/IEEE method) var imbalancePct; var maxPhaseLoad, minPhaseLoad; if (panelType === 'single') { maxPhaseLoad = Math.max(phaseA, phaseB); minPhaseLoad = Math.min(phaseA, phaseB); imbalancePct = (avgLoad > 0) ? (Math.abs(phaseA - phaseB) / avgLoad * 100) : 0; } else { maxPhaseLoad = Math.max(phaseA, phaseB, phaseC); minPhaseLoad = Math.min(phaseA, phaseB, phaseC); // NEMA MG-1 voltage imbalance method adapted for current: // % Imbalance = (max deviation from average / average) * 100 var deviations = [Math.abs(phaseA - avgLoad), Math.abs(phaseB - avgLoad), Math.abs(phaseC - avgLoad)]; var maxDev = Math.max.apply(null, deviations); imbalancePct = (avgLoad > 0) ? (maxDev / avgLoad * 100) : 0; }

// Power calculations: P = V * I (single-phase per leg) or P = V * I (line-to-neutral per phase) // For single-phase 240V panel: each leg is 120V to neutral // For three-phase: each phase is line-to-neutral voltage var lineToNeutral = voltage; // voltage field stores line-to-neutral var powerA = lineToNeutral * phaseA; // Watts var powerB = lineToNeutral * phaseB; var powerC = lineToNeutral * phaseC; var totalPower = powerA + powerB + powerC;

// Panel capacity // Single-phase: capacity = mainBreaker * 240 (both legs) // Three-phase: capacity = mainBreaker * voltage * sqrt(3) for line-to-line, but per-phase = mainBreaker * V_LN var panelCapacityW; if (panelType === 'single') { panelCapacityW = mainBreaker * 240; // 240V single-phase } else { panelCapacityW = mainBreaker * lineToNeutral * 3; // sum of all three phases } var loadPct = (panelCapacityW > 0) ? (totalPower / panelCapacityW * 100) : 0;

// NEC 80% rule: continuous load should not exceed 80% of breaker rating var necLimit = mainBreaker * 0.8; var maxPhaseCurrentLoad = (panelType === 'single') ? Math.max(phaseA, phaseB) : Math.max(phaseA, phaseB, phaseC); var necCompliant = maxPhaseCurrentLoad 20%) — Immediate Action Required'; imbalanceColor = '#e74c3c'; }

// Load status var loadStatus, loadColor; if (loadPct ' + '' + c.label + '' + '' + c.phase + '' + '' + c.load.toFixed(1) + ' A' + '' + (phasePower / 1000).toFixed(3) + ' kW' + ''; });

// Rebalancing suggestion: find most overloaded phase and suggest moving a circuit var suggestion = ''; if (imbalancePct > 5) { var heaviestPhase, lightestPhase, heaviestLoad, lightestLoad; if (panelType === 'single') { if (phaseA >= phaseB) { heaviestPhase = 'A'; heaviestLoad = phaseA; lightestPhase = 'B'; lightestLoad = phaseB; } else { heaviestPhase = 'B'; heaviestLoad = phaseB; lightestPhase = 'A'; lightestLoad = phaseA; } } else { var phases = [{p:'A',l:phaseA},{p:'B',l:phaseB},{p:'C',l:phaseC}]; phases.sort(function(a,b){return b.l - a.l;}); heaviestPhase = phases[0].p; heaviestLoad = phases[0].l; lightestPhase = phases[phases.length-1].p; lightestLoad = phases[phases.length-1].l; } var targetMove = (heaviestLoad - lightestLoad) / 2; // Find circuit on heaviest phase closest to targetMove var candidates = circuits.filter(function(c){ return c.phase === heaviestPhase && c.load > 0; }); if (candidates.length > 0) { candidates.sort(function(a,b){ return Math.abs(a.load - targetMove) - Math.abs(b.load - targetMove); }); var best = candidates[0]; suggestion = '' + '💡 Rebalancing Suggestion: Consider moving "' + best.label + '" (' + best.load.toFixed(1) + ' A) ' + 'from Phase ' + heaviestPhase + ' to Phase ' + lightestPhase + '. ' + 'This would reduce the imbalance from ' + imbalancePct.toFixed(1) + '% toward a more balanced distribution.'; } }

var phaseRowC = (panelType === 'three') ? 'Phase C' + phaseC.toFixed(1) + ' A' + (powerC/1000).toFixed(3) + ' kW' + '' + (avgLoad > 0 ? ((phaseC/avgLoad)*100).toFixed(1) : '0.0') + '%' : '';

var html = '### ⚡ Load Balance Results ' +

'' +

'' + 'Total Panel Load' + '' + (totalPower/1000).toFixed(2) + ' kW' + '' + totalLoad.toFixed(1) + ' A total' +

'' + 'Panel Utilization' + '' + loadPct.toFixed(1) + '%' + '' + loadStatus + '' +

'' + 'Load Imbalance' + '' + imbalancePct.toFixed(1) + '%' + '' + imbalanceStatus + '' +

'' + 'NEC 80% Rule' + '' + (necCompliant ? '✓ Pass' : '✗ Fail') + '' + 'Limit: ' + necLimit.toFixed(0) + ' A per phase' +

'' +

'#### Phase Load Summary ' + '' + '' + 'Phase' + 'Current (A)' + 'Power (kW)' + '% of Avg' + 'Phase A' + phaseA.toFixed(1) + ' A' + '' + (powerA/1000).toFixed(3) + ' kW' + '' + (avgLoad > 0 ? ((phaseA/avgLoad)100).toFixed(1) : '0.0') + '%' + 'Phase B' + phaseB.toFixed(1) + ' A' + '' + (powerB/1000).toFixed(3) + ' kW' + '' + (avgLoad > 0 ? ((phaseB/avgLoad)100).toFixed(1) : '0.0') + '%' + phaseRowC + 'Average' + avgLoad.toFixed(1) + ' A' + '' + (totalPower/numPhases/1000).toFixed(3) + ' kW100.0%' + '' +

'#### Circuit Detail ' + '' + '' + 'Circuit' + 'Phase' + 'Current' + 'Power' + circuitRows + '' +

suggestion +

'' + 'Panel Capacity: ' + (panelCapacityW/1000).toFixed(1) + ' kW total | ' + 'NEC 80% Continuous Limit: ' + (panelCapacityW0.8/1000).toFixed(1) + ' kW | ' + 'Remaining Capacity: ' + Math.max(0, (panelCapacityW0.8 - totalPower)/1000).toFixed(2) + ' kW';

var resultEl = document.getElementById('ele-result'); resultEl.style.display = 'block'; resultEl.innerHTML = html; }

#### Formulas Used

Phase Power (W): Pphase = VL-N × Iphase

Total Load: Ptotal = PA + PB + PC

Average Phase Load: Iavg = (IA + IB [+ IC]) / Nphases

Load Imbalance % (Three-Phase, NEMA MG-1): % Imbalance = (max|Iphase − Iavg| / Iavg) × 100

Load Imbalance % (Single-Phase): % Imbalance = (|IA − IB| / Iavg) × 100

Panel Utilization %: (Ptotal / Pcapacity) × 100

NEC 80% Continuous Load Rule: Icontinuous ≤ 0.8 × Ibreaker

#### Assumptions & References

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References

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