Cable Capacity Calculator

Cable Capacity & Voltage Drop Calculator

Copper Aluminum
14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG
60°C 75°C 90°C

Calculation Results:

Maximum Ampacity: —

Calculated Voltage Drop: —

Voltage Drop Percentage: —

Recommendation: —

Understanding Cable Capacity and Voltage Drop

When designing or installing electrical systems, two critical factors must be considered for every cable run: its current-carrying capacity (ampacity) and the voltage drop that will occur along its length. Failing to account for these can lead to overheating, fire hazards, equipment malfunction, and inefficient operation.

What is Cable Ampacity?

Cable ampacity refers to the maximum amount of electrical current (measured in Amperes, or Amps) a conductor can continuously carry without exceeding its temperature rating. Exceeding this limit causes the cable to overheat, which can damage the insulation, lead to short circuits, and even start fires. Ampacity is determined by several factors:

  • Conductor Material: Copper generally has higher ampacity than aluminum for the same gauge due to its lower resistivity.
  • Cable Gauge (AWG/mm²): Thicker wires (smaller AWG numbers) have a larger cross-sectional area, allowing them to carry more current.
  • Insulation Temperature Rating: The type of insulation material dictates how much heat the cable can withstand before degrading. Common ratings are 60°C, 75°C, and 90°C. Higher temperature ratings generally allow for higher ampacities.
  • Installation Method: Cables installed in free air dissipate heat more effectively than those bundled together or enclosed in conduit, which can reduce their effective ampacity (derating).
  • Ambient Temperature: Higher surrounding temperatures reduce the cable's ability to dissipate heat, thus lowering its ampacity.

What is Voltage Drop?

Voltage drop is the reduction in electrical potential along the length of a conductor due to its resistance. As current flows through a wire, some of the electrical energy is converted into heat, resulting in a lower voltage at the load end compared to the source end. Excessive voltage drop can lead to:

  • Dim Lights: Incandescent bulbs will appear dimmer.
  • Motor Damage: Motors may run hotter, draw more current, and have a reduced lifespan.
  • Equipment Malfunction: Sensitive electronics may not operate correctly or at all.
  • Energy Waste: The lost voltage represents wasted energy in the form of heat.

The National Electrical Code (NEC) generally recommends a maximum voltage drop of 3% for feeders and branch circuits to the farthest outlet, and a total of 5% for the combined feeder and branch circuit. Our calculator uses the following formula for voltage drop (for single-phase AC or DC circuits):

VD = (2 * K * I * L) / CM

Where:

  • VD = Voltage Drop (Volts)
  • K = Resistivity of the conductor material (12.9 for Copper, 21.2 for Aluminum at 75°C, in Ω·CM/ft)
  • I = Load Current (Amps)
  • L = One-way Length of the cable (Feet)
  • CM = Circular Mils of the conductor (cross-sectional area)

How to Use This Calculator:

  1. Select Conductor Material: Choose between Copper or Aluminum.
  2. Select Cable Gauge: Pick the AWG size of your cable.
  3. Enter Cable Length: Input the one-way length of your cable run in feet.
  4. Enter System Voltage: Provide the nominal voltage of your electrical system (e.g., 120V, 240V).
  5. Enter Expected Load Current: Input the maximum current (in Amps) that your connected load is expected to draw.
  6. Select Insulation Temperature Rating: Choose the temperature rating of your cable's insulation (found on the cable jacket).
  7. Enter Max Desired Voltage Drop (%): Specify the maximum percentage of voltage drop you are willing to tolerate (e.g., 3% for general circuits).
  8. Click "Calculate": The calculator will display the maximum safe ampacity for your chosen cable, the actual voltage drop for your specified load, and a recommendation based on your inputs.

Disclaimer: This calculator provides estimates based on common electrical engineering principles and simplified NEC ampacity tables (for 3 current-carrying conductors in raceway/cable at 30°C ambient). It should be used for preliminary planning and educational purposes only. Always consult the latest National Electrical Code (NEC) or local electrical codes, and a qualified electrician for specific installation requirements and safety compliance.

function calculateCableCapacity() { var conductorMaterial = document.getElementById("conductorMaterial").value; var cableGauge = document.getElementById("cableGauge").value; var cableLength = parseFloat(document.getElementById("cableLength").value); var systemVoltage = parseFloat(document.getElementById("systemVoltage").value); var loadCurrent = parseFloat(document.getElementById("loadCurrent").value); var temperatureRating = document.getElementById("temperatureRating").value; var voltageDropTarget = parseFloat(document.getElementById("voltageDropTarget").value); // Input validation if (isNaN(cableLength) || cableLength <= 0) { alert("Please enter a valid cable length (greater than 0)."); return; } if (isNaN(systemVoltage) || systemVoltage <= 0) { alert("Please enter a valid system voltage (greater than 0)."); return; } if (isNaN(loadCurrent) || loadCurrent <= 0) { alert("Please enter a valid load current (greater than 0)."); return; } if (isNaN(voltageDropTarget) || voltageDropTarget 100) { alert("Please enter a valid voltage drop target (between 0.1 and 100)."); return; } // Data tables for AWG to Circular Mils (CM) var awgToCM = { "14": 4107, "12": 6530, "10": 10380, "8": 16510, "6": 26240, "4": 41740, "2": 66360, "1": 83690, "1/0": 105600, "2/0": 133100, "3/0": 167800, "4/0": 211600 }; // Resistivity (K factor) in Ω·CM/ft at 75°C (common for calculations) var K_copper = 12.9; var K_aluminum = 21.2; // Simplified Ampacity Table (NEC Table 310.16, 3 current-carrying conductors in raceway/cable, 30°C ambient) // Values are for Copper and Aluminum at 60°C, 75°C, and 90°C insulation ratings var ampacityTable = { "copper": { "60": {"14": 15, "12": 20, "10": 30, "8": 40, "6": 55, "4": 70, "2": 95, "1": 110, "1/0": 125, "2/0": 145, "3/0": 165, "4/0": 195}, "75": {"14": 20, "12": 25, "10": 35, "8": 50, "6": 65, "4": 85, "2": 115, "1": 130, "1/0": 150, "2/0": 175, "3/0": 200, "4/0": 230}, "90": {"14": 25, "12": 30, "10": 40, "8": 55, "6": 75, "4": 95, "2": 130, "1": 150, "1/0": 170, "2/0": 195, "3/0": 225, "4/0": 260} }, "aluminum": { "60": {"14": null, "12": 15, "10": 25, "8": 30, "6": 40, "4": 55, "2": 75, "1": 85, "1/0": 100, "2/0": 115, "3/0": 130, "4/0": 150}, "75": {"14": null, "12": 20, "10": 30, "8": 40, "6": 50, "4": 65, "2": 90, "1": 100, "1/0": 120, "2/0": 135, "3/0": 155, "4/0": 180}, "90": {"14": null, "12": 25, "10": 35, "8": 45, "6": 60, "4": 75, "2": 100, "1": 115, "1/0": 135, "2/0": 150, "3/0": 175, "4/0": 205} } }; var circularMils = awgToCM[cableGauge]; var K_factor = (conductorMaterial === "copper") ? K_copper : K_aluminum; var maxAmpacity = ampacityTable[conductorMaterial][temperatureRating][cableGauge]; if (!circularMils) { document.getElementById("maxAmpacityResult").innerHTML = "Maximum Ampacity: N/A (Invalid Gauge)"; document.getElementById("voltageDropResult").innerHTML = "Calculated Voltage Drop: N/A"; document.getElementById("voltageDropPercentResult").innerHTML = "Voltage Drop Percentage: N/A"; document.getElementById("recommendation").innerHTML = "Recommendation: Please select a valid cable gauge."; return; } if (maxAmpacity === null) { // For 14 AWG Aluminum, etc. document.getElementById("maxAmpacityResult").innerHTML = "Maximum Ampacity: Not applicable for " + cableGauge + " " + conductorMaterial + " at " + temperatureRating + "°C."; document.getElementById("voltageDropResult").innerHTML = "Calculated Voltage Drop: N/A"; document.getElementById("voltageDropPercentResult").innerHTML = "Voltage Drop Percentage: N/A"; document.getElementById("recommendation").innerHTML = "Recommendation: This combination of material, gauge, and temperature rating is not standard or recommended."; return; } // Calculate Voltage Drop (VD = (2 * K * I * L) / CM) var calculatedVoltageDrop = (2 * K_factor * loadCurrent * cableLength) / circularMils; var voltageDropPercentage = (calculatedVoltageDrop / systemVoltage) * 100; var recommendationText = ""; var recommendationColor = ""; if (loadCurrent > maxAmpacity) { recommendationText += "WARNING: Load current (" + loadCurrent.toFixed(1) + "A) exceeds cable's maximum ampacity (" + maxAmpacity + "A). This is a fire hazard!"; recommendationColor = "red"; } else if (voltageDropPercentage > voltageDropTarget) { recommendationText += "WARNING: Voltage drop (" + voltageDropPercentage.toFixed(2) + "%) exceeds your target (" + voltageDropTarget.toFixed(1) + "%). This can cause equipment malfunction and inefficiency."; recommendationColor = "orange"; } else { recommendationText += "Cable appears suitable for the specified load and length, meeting voltage drop targets."; recommendationColor = "green"; } document.getElementById("maxAmpacityResult").innerHTML = "Maximum Ampacity: " + maxAmpacity + " Amps (based on " + temperatureRating + "°C insulation)"; document.getElementById("voltageDropResult").innerHTML = "Calculated Voltage Drop: " + calculatedVoltageDrop.toFixed(2) + " Volts"; document.getElementById("voltageDropPercentResult").innerHTML = "Voltage Drop Percentage: " + voltageDropPercentage.toFixed(2) + "%"; document.getElementById("recommendation").innerHTML = "Recommendation: " + recommendationText + ""; }

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