Circuit Load and Overload Risk Calculator

ANA›Life Services Authority›National Calculator Authority›Circuit Load and Overload Risk Calculator

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Circuit Load and Overload Risk Calculator

Calculate total circuit load, capacity utilization percentage, and assess overload risk for residential or commercial electrical circuits.

Circuit Voltage (V)

120 V (Standard US) 240 V (High-voltage US) 208 V (3-phase derived) 230 V (European)

Circuit Breaker Rating (A)

15 A 20 A 30 A 40 A 50 A 60 A 100 A

Wire Gauge (AWG)

14 AWG (15 A max) 12 AWG (20 A max) 10 AWG (30 A max) 8 AWG (40 A max) 6 AWG (55 A max) 4 AWG (70 A max) 2 AWG (95 A max) 1/0 AWG (125 A max)

Power Factor

1.00 (Purely resistive) 0.95 (Mostly resistive) 0.90 (Mixed loads) 0.85 (Typical household) 0.80 (Motor-heavy) 0.75 (Industrial)

### Connected Devices / Loads

Device Name

Power (W)

Quantity

✕

Device Name

Power (W)

Quantity

✕

Device Name

Power (W)

Quantity

✕

Calculate Load & Risk

Total Load

Watts

Total Current

Amperes

Apparent Power

VA

Capacity Used

% of breaker

Load Utilization

0%80% (NEC safe limit)100% (breaker trips)

#### Detailed Breakdown

Device Qty W each Total W Amps

#### Recommendations

var cirDeviceCount = 3; var cirDeviceIds = [0, 1, 2];

// Wire gauge ampacity limits (NEC 310.15, 60°C/140°F rating, copper) var cirWireAmpacity = { 14: 15, 12: 20, 10: 30, 8: 40, 6: 55, 4: 70, 2: 95, 1: 125 };

function cirAddDevice() { var id = cirDeviceCount++; cirDeviceIds.push(id); var container = document.getElementById('cir-devices-container'); var row = document.createElement('div'); row.className = 'calc-row cir-device-row'; row.id = 'cir-device-' + id; row.innerHTML = 'Device Name' + '' + 'Power (W)' + '' + 'Quantity' + '' + '' + '✕'; container.appendChild(row); }

function cirRemoveDevice(id) { var row = document.getElementById('cir-device-' + id); if (row) row.remove(); cirDeviceIds = cirDeviceIds.filter(function(x){ return x !== id; }); }

function cirCalc() { var voltage = parseFloat(document.getElementById('cir-voltage').value); var breakerA = parseFloat(document.getElementById('cir-breaker').value); var wireGauge = parseInt(document.getElementById('cir-wire-gauge').value); var pf = parseFloat(document.getElementById('cir-pf').value);

// Collect devices var devices = []; var totalW = 0; var errors = [];

for (var i = 0; i 50000) { errors.push('"' + name + '" exceeds 50,000 W — check input'); continue; }

var rowW = watts * qty; totalW += rowW; devices.push({ name: name, watts: watts, qty: qty, totalW: rowW }); }

if (errors.length > 0) { alert('Input errors: ' + errors.join(' ')); return; } if (devices.length === 0) { alert('Please add at least one device.'); return; }

// Core calculations // Real power (W) = sum of device watts // Apparent power (VA) = Real power / Power Factor // Current (A) = Apparent power (VA) / Voltage var apparentVA = totalW / pf; var totalAmps = apparentVA / voltage; var breakerCapacityW = breakerA * voltage * pf; var utilizationPct = (totalAmps / breakerA) * 100;

// NEC 210.19(A)(1): continuous loads must not exceed 80% of breaker rating var necSafeAmps = breakerA * 0.80; var necSafeW = necSafeAmps * voltage * pf;

// Wire ampacity var wireMaxAmps = cirWireAmpacity[wireGauge] || 15;

// Risk level var riskLevel, riskColor, riskBg, riskMsg; if (totalAmps > breakerA) { riskLevel = 'OVERLOAD — Circuit Will Trip'; riskColor = '#fff'; riskBg = '#c53030'; riskMsg = '🔴'; } else if (totalAmps > necSafeAmps) { riskLevel = 'HIGH RISK — Exceeds NEC 80% Safe Limit'; riskColor = '#7b341e'; riskBg = '#fbd38d'; riskMsg = '🟠'; } else if (totalAmps > necSafeAmps * 0.875) { riskLevel = 'MODERATE RISK — Approaching Safe Limit'; riskColor = '#744210'; riskBg = '#fefcbf'; riskMsg = '🟡'; } else { riskLevel = 'SAFE — Within Normal Operating Range'; riskColor = '#1a4731'; riskBg = '#c6f6d5'; riskMsg = '🟢'; }

// Progress bar color var barColor; if (utilizationPct > 100) barColor = '#c53030'; else if (utilizationPct > 80) barColor = '#dd6b20'; else if (utilizationPct > 70) barColor = '#d69e2e'; else barColor = '#38a169';

var barWidth = Math.min(utilizationPct, 100);

// Wire warning var wireWarning = ''; if (totalAmps > wireMaxAmps) { wireWarning = '⚠️ WARNING: The calculated current (' + totalAmps.toFixed(2) + ' A) exceeds the safe ampacity of ' + wireGauge + ' AWG wire (' + wireMaxAmps + ' A). This is a fire hazard. Upgrade wire gauge immediately.'; } else if (breakerA > wireMaxAmps) { wireWarning = '⚠️ CAUTION: The breaker rating (' + breakerA + ' A) exceeds the wire ampacity (' + wireMaxAmps + ' A for ' + wireGauge + ' AWG). The wire may overheat before the breaker trips. Consider upgrading wire or reducing breaker size.'; }

// Build breakdown table var tbodyHtml = ''; for (var j = 0; j ' + '' + d.name + '' + '' + d.qty + '' + '' + d.watts.toFixed(0) + '' + '' + d.totalW.toFixed(0) + '' + '' + devAmps.toFixed(2) + ' A(' + pctOfBreaker + '%)' + ''; } // Totals row tbodyHtml += '' + 'TOTAL' + '—' + '—' + '' + totalW.toFixed(0) + '' + '' + totalAmps.toFixed(2) + ' A' + '';

// Recommendations var recs = []; var remainingAmps = breakerA - totalAmps; var remainingW = remainingAmps * voltage * pf;

if (totalAmps > breakerA) { recs.push('Immediately reduce load by at least ' + (totalAmps - breakerA).toFixed(2) + ' A (' + ((totalAmps - breakerA) * voltage * pf).toFixed(0) + ' W) to prevent breaker tripping.'); recs.push('Consider splitting loads across multiple circuits.'); } else if (totalAmps > necSafeAmps) { recs.push('Reduce load by ' + (totalAmps - necSafeAmps).toFixed(2) + ' A (' + ((totalAmps - necSafeAmps) * voltage * pf).toFixed(0) + ' W) to comply with NEC 80% continuous load rule.'); } else { recs.push('Current load is within safe limits. You have ' + remainingAmps.toFixed(2) + ' A (' + remainingW.toFixed(0) + ' W) of remaining capacity.'); var necRemaining = necSafeAmps - totalAmps; recs.push('NEC 80% safe headroom remaining: ' + necRemaining.toFixed(2) + ' A (' + (necRemaining * voltage * pf).toFixed(0) + ' W).'); }

if (wireWarning) { recs.push('Address wire gauge mismatch as noted in the warning above before adding any loads.'); }

recs.push('For continuous loads (operating 3+ hours), NEC 210.19(A)(1) requires load ≤ 80% of breaker rating (' + necSafeAmps.toFixed(1) + ' A / ' + necSafeW.toFixed(0) + ' W on this circuit).'); recs.push('Total circuit capacity at 100%: ' + breakerA + ' A × ' + voltage + ' V × ' + pf + ' PF = ' + breakerCapacityW.toFixed(0) + ' W.');

var recsHtml = recs.map(function(r){ return ''; }).join('');

// Populate DOM document.getElementById('cir-risk-banner').textContent = riskMsg + ' ' + riskLevel; document.getElementById('cir-risk-banner').style.background = riskBg; document.getElementById('cir-risk-banner').style.color = riskColor;

document.getElementById('cir-total-watts').textContent = totalW.toFixed(0) + ' W'; document.getElementById('cir-total-amps').textContent = totalAmps.toFixed(2) + ' A'; document.getElementById('cir-total-va').textContent = apparentVA.toFixed(0) + ' VA'; document.getElementById('cir-utilization').textContent = utilizationPct.toFixed(1) + '%';

document.getElementById('cir-bar-label').textContent = utilizationPct.toFixed(1) + '% of ' + breakerA + ' A breaker'; document.getElementById('cir-progress-bar').style.width = barWidth + '%'; document.getElementById('cir-progress-bar').style.background = barColor;

var warnEl = document.getElementById('cir-wire-warning'); if (wireWarning) { warnEl.textContent = wireWarning; warnEl.style.display = 'block'; } else { warnEl.style.display = 'none'; }

document.getElementById('cir-breakdown-body').innerHTML = tbodyHtml; document.getElementById('cir-recommendations').innerHTML = recsHtml;

document.getElementById('cir-result').style.display = 'block'; }

#### Formulas Used

Total Real Power (W): Ptotal = Σ (Pdevice × Quantity)

Apparent Power (VA): S = Ptotal / PF  |  where PF = Power Factor (0–1)

Total Current (A): I = S / V  |  where V = Circuit Voltage

Capacity Utilization (%): U = (I / Ibreaker) × 100

NEC 80% Safe Limit (A): Isafe = Ibreaker × 0.80

Available Headroom (W): Premaining = (Ibreaker − I) × V × PF

#### Assumptions & References

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