Electrical Panel Load Capacity Calculator

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

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Electrical Panel Load Capacity Calculator

Determine your electrical panel's total capacity, current load, available capacity, and whether your panel can handle additional loads — based on NEC (National Electrical Code) guidelines.

Panel Main Breaker Size (Amps)

Common sizes: 100A, 150A, 200A, 400A

Panel Voltage

120V (Single Phase) 240V (Split Phase — Residential Standard) 208V (Three Phase) 480V (Three Phase — Commercial)

Phase Type

Single Phase Three Phase

Current Connected Load (Amps)

Sum of all breaker amperage currently in use (or leave blank to enter watts)

— OR — Current Connected Load (Watts)

Total wattage of all connected loads (optional alternative to amps above)

Demand Factor (%)

NEC recommends 80% continuous load limit for panel capacity planning

Additional Load to Add (Amps) (optional)

Size of new circuit or appliance you want to add

Calculate Panel Capacity

function eleCalc() { const resultDiv = document.getElementById('ele-result'); resultDiv.style.display = 'none'; resultDiv.innerHTML = '';

const panelAmps = parseFloat(document.getElementById('ele-panel-amps').value); const voltage = parseFloat(document.getElementById('ele-voltage').value); const phase = parseInt(document.getElementById('ele-phase').value); const currentAmps = document.getElementById('ele-current-load').value.trim(); const currentWatts = document.getElementById('ele-current-watts').value.trim(); const demandFactor = parseFloat(document.getElementById('ele-demand-factor').value); const newLoad = document.getElementById('ele-new-load').value.trim();

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

if (isNaN(panelAmps) || panelAmps 100) errors.push("Demand factor must be between 1 and 100.");

let loadAmps = NaN; if (currentAmps !== '' && currentWatts !== '') { errors.push("Please enter current load in Amps OR Watts — not both."); } else if (currentAmps !== '') { loadAmps = parseFloat(currentAmps); if (isNaN(loadAmps) || loadAmps 0) { resultDiv.style.display = 'block'; resultDiv.innerHTML = 'Please fix the following:' + errors.map(e => '').join('') + ''; return; }

// --- Core Calculations ---

// Total panel capacity in watts // Single phase: P = V × I // Three phase: P = V × I × √3 let totalCapacityWatts; if (phase === 1) { totalCapacityWatts = voltage * panelAmps; } else { totalCapacityWatts = voltage * panelAmps * Math.sqrt(3); }

// NEC 80% continuous load rule: usable capacity const usableCapacityAmps = panelAmps * (demandFactor / 100); const usableCapacityWatts = totalCapacityWatts * (demandFactor / 100);

// Current load in watts let currentLoadWatts; if (phase === 1) { currentLoadWatts = voltage * loadAmps; } else { currentLoadWatts = voltage * loadAmps * Math.sqrt(3); }

// Load percentage of total capacity const loadPctOfTotal = (loadAmps / panelAmps) * 100; const loadPctOfUsable = (loadAmps / usableCapacityAmps) * 100;

// Available capacity const availableAmps = usableCapacityAmps - loadAmps; const availableWatts = usableCapacityWatts - currentLoadWatts;

// Can add the new load?
const totalAfterNewAmps = loadAmps + addAmps;
const totalAfterNewWatts = (phase === 1)
? voltage * totalAfterNewAmps
voltage * totalAfterNewAmps * Math.sqrt(3); const canAddLoad = totalAfterNewAmps n.toFixed(d); const fmtW = (w) => w >= 1000 ? (w/1000).toFixed(2) + ' kW' : w.toFixed(0) + ' W';

// --- Build result HTML --- let html = '### Panel Load Capacity Results ';

html += ''; html += 'ParameterValue'; html += 'Panel Main Breaker' + panelAmps + ' A @ ' + voltage + 'V (' + (phase===1?'Single':'Three') + '-Phase)'; html += 'Total Panel Capacity' + fmt(panelAmps,0) + ' A / ' + fmtW(totalCapacityWatts) + ''; html += 'Usable Capacity (' + demandFactor + '% Demand Factor)' + fmt(usableCapacityAmps,1) + ' A / ' + fmtW(usableCapacityWatts) + ''; html += 'Current Connected Load' + fmt(loadAmps,1) + ' A / ' + fmtW(currentLoadWatts) + ''; html += 'Load as % of Total Capacity' + fmt(loadPctOfTotal,1) + '%'; html += 'Load as % of Usable Capacity' + fmt(loadPctOfUsable,1) + '%'; html += 'Available Capacity' + fmt(availableAmps,1) + ' A / ' + fmtW(availableWatts) + ''; html += '';

html += 'Panel Status: ' + statusLabel + '';

if (addAmps > 0) { html += '#### New Load Analysis (' + fmt(addAmps,0) + ' A Additional) '; html += ''; html += 'ParameterValue'; html += 'Total Load After Addition' + fmt(totalAfterNewAmps,1) + ' A / ' + fmtW(totalAfterNewWatts) + ''; html += 'Remaining Available After Addition' + fmt(remainingAfterNew,1) + ' A'; html += 'Can Panel Support New Load?' + (canAddLoad ? '✅ Yes — Within Safe Limits' : '🚨 No — Exceeds Usable Capacity') + ''; html += ''; if (!canAddLoad) { html += '⚠️ Adding this load would exceed the ' + demandFactor + '% safe capacity limit. Consider upgrading your panel or redistributing loads.'; } }

// Recommendations html += '#### Recommendations '; if (loadPctOfUsable > 100) { html += ''; html += ''; } else if (loadPctOfUsable > 80) { html += ''; html += ''; } else { html += ''; } html += ''; html += ''; html += '';

resultDiv.style.display = 'block'; resultDiv.innerHTML = html; }

#### Formulas Used

Total Panel Capacity (Single Phase): Ptotal = V × Ipanel e.g., 240V × 200A = 48,000 W (48 kW)

Total Panel Capacity (Three Phase): Ptotal = V × Ipanel × √3 e.g., 208V × 200A × 1.732 = 72,070 W (72 kW)

Usable Capacity (NEC 80% Rule): Iusable = Ipanel × (Demand Factor / 100) e.g., 200A × 0.80 = 160A usable

Available Capacity: Iavailable = Iusable − Icurrent load

Load from Watts (Single Phase): I = P / V

Load from Watts (Three Phase): I = P / (V × √3)

Load Percentage: Load% = (Iload / Iusable) × 100

#### Assumptions & References

More Calculators

Read Next

Study Time Planner Authority Network America › Life Services Authority › National Calculator Authority .calc-container { max-width: 640px;...

References

Related Authorities

Life Services Authority › Professional Services Authority › Trade Services Authority › United States Authority ›