Use this calculator to determine the voltage drop across a conductor, ensuring your electrical system operates efficiently and safely. Excessive voltage drop can lead to poor equipment performance, overheating, and energy waste.
Voltage drop is the reduction in electrical potential along the length of a conductor carrying current. It's a natural phenomenon that occurs due to the resistance of the wire. As current flows through a wire, some of the electrical energy is converted into heat, causing the voltage to decrease from the source to the load.
Why is Voltage Drop Important?
Equipment Performance: Many electrical devices are designed to operate within a specific voltage range. Excessive voltage drop can cause motors to run hotter and less efficiently, lights to dim, and electronic equipment to malfunction or fail prematurely.
Energy Efficiency: The energy lost due to voltage drop is dissipated as heat, representing wasted energy and higher electricity bills.
Safety: While less common, extreme voltage drop can sometimes lead to overheating of conductors, posing a fire hazard, especially if the wiring is undersized for the load.
Factors Affecting Voltage Drop
Several key factors influence the amount of voltage drop in a circuit:
Current (Amperes): Higher current draws lead to greater voltage drop.
Conductor Length (Feet/Meters): The longer the wire, the more resistance it presents, and thus, the greater the voltage drop.
Wire Gauge (AWG/kcmil): Thicker wires (smaller AWG numbers, or higher kcmil values) have lower resistance and therefore less voltage drop.
Conductor Material (Copper/Aluminum): Copper has lower resistivity than aluminum, meaning it offers less resistance for the same size wire, resulting in less voltage drop.
System Type (Single Phase/Three Phase): The calculation constant differs between single-phase and three-phase systems.
Recommended Voltage Drop Limits
The National Electrical Code (NEC) and other standards recommend limiting voltage drop to ensure efficient and safe operation. A common guideline suggests:
3% maximum voltage drop for feeders and branch circuits to the farthest outlet of power, heating, and lighting loads.
5% total maximum voltage drop for the combined feeder and branch circuit to the farthest outlet.
Adhering to these recommendations helps prevent issues and prolongs the life of electrical equipment.
How to Use This Calculator
Source Voltage: Enter the voltage supplied by your source (e.g., 120V, 240V, 480V).
Load Current: Input the total current (in Amperes) that the load will draw.
Conductor Length: Enter the one-way length of the wire run in feet. For a circuit that goes out and back, this is just the length of one leg.
Wire Gauge: Select the AWG or kcmil size of your conductor from the dropdown.
Conductor Material: Choose between Copper and Aluminum.
System Type: Select whether your system is Single Phase or Three Phase.
Click "Calculate Voltage Drop" to see the results.
The calculator will display the calculated voltage drop in Volts and as a percentage of the source voltage, helping you assess if your circuit meets recommended standards.
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function calculateVoltageDrop() {
var sourceVoltage = parseFloat(document.getElementById("sourceVoltage").value);
var loadCurrent = parseFloat(document.getElementById("loadCurrent").value);
var conductorLength = parseFloat(document.getElementById("conductorLength").value);
var wireGauge = document.getElementById("wireGauge").value;
var conductorMaterial = document.getElementById("conductorMaterial").value;
var systemType = document.getElementById("systemType").value;
var resultDiv = document.getElementById("result");
// Input validation
if (isNaN(sourceVoltage) || sourceVoltage <= 0) {
resultDiv.innerHTML = "Please enter a valid Source Voltage (must be a positive number).";
return;
}
if (isNaN(loadCurrent) || loadCurrent <= 0) {
resultDiv.innerHTML = "Please enter a valid Load Current (must be a positive number).";
return;
}
if (isNaN(conductorLength) || conductorLength <= 0) {
resultDiv.innerHTML = "Please enter a valid Conductor Length (must be a positive number).";
return;
}
// AWG to Circular Mils lookup table
var circularMils = {
"14": 4107,
"12": 6530,
"10": 10380,
"8": 16510,
"6": 26240,
"4": 41740,
"3": 52620,
"2": 66360,
"1": 83690,
"1/0": 105600,
"2/0": 133100,
"3/0": 167800,
"4/0": 211600,
"250": 250000, // kcmil
"300": 300000,
"350": 350000,
"400": 400000,
"500": 500000
};
var cmil = circularMils[wireGauge];
if (!cmil) {
resultDiv.innerHTML = "Invalid Wire Gauge selected.";
return;
}
// Resistivity constant (K) in Ohm-circular mil per foot at 75°C (common for general purpose)
var K;
if (conductorMaterial === "copper") {
K = 12.9; // Copper resistivity
} else if (conductorMaterial === "aluminum") {
K = 21.2; // Aluminum resistivity
} else {
resultDiv.innerHTML = "Invalid Conductor Material selected.";
return;
}
var voltageDrop;
if (systemType === "singlePhase") {
// VD = (2 * K * I * L) / CM
voltageDrop = (2 * K * loadCurrent * conductorLength) / cmil;
} else if (systemType === "threePhase") {
// VD = (sqrt(3) * K * I * L) / CM
voltageDrop = (Math.sqrt(3) * K * loadCurrent * conductorLength) / cmil;
} else {
resultDiv.innerHTML = "Invalid System Type selected.";
return;
}
var percentageVoltageDrop = (voltageDrop / sourceVoltage) * 100;
var recommendation = "";
if (percentageVoltageDrop <= 3) {
recommendation = "This is within the recommended 3% limit for feeders and branch circuits.";
} else if (percentageVoltageDrop <= 5) {
recommendation = "This is acceptable for total voltage drop (feeder + branch), but consider reducing for optimal performance.";
} else {
recommendation = "This exceeds the recommended 5% total voltage drop. Consider increasing wire gauge, reducing length, or increasing source voltage.";
}
resultDiv.innerHTML =
"Calculated Voltage Drop: " + voltageDrop.toFixed(2) + " V" +
"Percentage Voltage Drop: " + percentageVoltageDrop.toFixed(2) + "%" +
"" + recommendation + "";
}