Voltage Drop Calculator for NC Wiring Projects

ANA›Life Services Authority›National Calculator Authority›Voltage Drop Calculator for NC Wiring Projects

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Voltage Drop Calculator for NC Wiring Projects

Calculate voltage drop, percentage drop, and receiving-end voltage for copper or aluminum conductors per NEC guidelines used in North Carolina wiring projects.

System Voltage (V)

Load Current (A)

One-Way Wire Length (ft)

Wire Size (AWG / kcmil)

-- Select Wire Size -- 14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 3 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG 250 kcmil 300 kcmil 350 kcmil 400 kcmil 500 kcmil

Conductor Material

Copper Aluminum

System Phase

Single-Phase Three-Phase

Calculate

function volCalc() { var resultDiv = document.getElementById('vol-result'); resultDiv.style.display = 'block'; resultDiv.className = 'calc-result';

var voltage = parseFloat(document.getElementById('vol-system-voltage').value); var current = parseFloat(document.getElementById('vol-current').value); var length = parseFloat(document.getElementById('vol-length').value); var wireSize = document.getElementById('vol-wire-size').value; var material = document.getElementById('vol-material').value; var phase = document.getElementById('vol-phase').value;

// --- Validation --- if (!voltage || voltage ⚠ Please enter a valid system voltage greater than 0.'; return; } if (!current || current ⚠ Please enter a valid load current greater than 0.'; return; } if (!length || length ⚠ Please enter a valid one-way wire length greater than 0.'; return; } if (!wireSize) { resultDiv.innerHTML = '⚠ Please select a wire size.'; return; }

// --- Resistivity lookup table (ohms per 1000 ft) at 75°C per NEC Chapter 9 Table 9 --- // Values: { copper, aluminum } var resistivity = { '14': { copper: 3.14, aluminum: 5.17 }, '12': { copper: 1.98, aluminum: 3.25 }, '10': { copper: 1.24, aluminum: 2.04 }, '8': { copper: 0.778, aluminum: 1.28 }, '6': { copper: 0.491, aluminum: 0.808 }, '4': { copper: 0.308, aluminum: 0.508 }, '3': { copper: 0.245, aluminum: 0.403 }, '2': { copper: 0.194, aluminum: 0.319 }, '1': { copper: 0.154, aluminum: 0.253 }, '1/0': { copper: 0.122, aluminum: 0.201 }, '2/0': { copper: 0.0967,aluminum: 0.159 }, '3/0': { copper: 0.0766,aluminum: 0.126 }, '4/0': { copper: 0.0608,aluminum: 0.100 }, '250': { copper: 0.0515,aluminum: 0.0847}, '300': { copper: 0.0429,aluminum: 0.0707}, '350': { copper: 0.0367,aluminum: 0.0605}, '400': { copper: 0.0321,aluminum: 0.0529}, '500': { copper: 0.0258,aluminum: 0.0424} };

var rPer1000ft = resistivity[wireSize][material];

// Resistance of one conductor for the one-way length (ohms) var R_one = (rPer1000ft / 1000) * length;

// Phase multiplier: // Single-phase: VD = 2 * I * R (current travels out and back) // Three-phase: VD = sqrt(3) * I * R var phaseMult = (phase === 'three') ? Math.sqrt(3) : 2;

var voltageDrop = phaseMult * current * R_one; var dropPercent = (voltageDrop / voltage) * 100; var receivingVolt = voltage - voltageDrop;

// NEC recommends max 3% for branch circuits, 5% total (feeder + branch)
var necStatus3 = dropPercent ✓ Within NEC 3% branch-circuit recommendation'
'⚠ Exceeds NEC 3% branch-circuit recommendation';
var necStatus5 = dropPercent ✓ Within NEC 5% total (feeder + branch) recommendation'
'⚠ Exceeds NEC 5% total recommendation — consider larger wire';

var phaseLabel = phase === 'three' ? 'Three-Phase' : 'Single-Phase'; var materialLabel= material.charAt(0).toUpperCase() + material.slice(1);

resultDiv.innerHTML = '### Results ' + '' + 'Voltage Drop' + '' + voltageDrop.toFixed(3) + ' V' + 'Percentage Drop' + '' + dropPercent.toFixed(2) + ' %' + 'Receiving-End Voltage' + '' + receivingVolt.toFixed(2) + ' V' + 'Conductor Resistance (one-way)' + '' + R_one.toFixed(4) + ' Ω' + 'Resistivity Used' + '' + rPer1000ft + ' Ω/1000 ft (' + materialLabel + ')' + 'System' + '' + phaseLabel + '' + '' + '' + necStatus3 + '' + necStatus5 + ''; }

#### Formulas Used

Single-Phase Voltage Drop: VD = 2 × I × Rone-way

Three-Phase Voltage Drop: VD = √3 × I × Rone-way

One-Way Conductor Resistance: Rone-way = (r / 1000) × L

Where: r = resistivity in Ω/1000 ft (from NEC Chapter 9, Table 9 at 75°C), L = one-way length in feet, I = load current in amperes.

Percentage Voltage Drop: VD% = (VD / Vsource) × 100

Receiving-End Voltage: VR = Vsource − VD

#### Assumptions & References

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References

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