Voltage Drop Calculator
Use this calculator to determine the voltage drop in an electrical circuit, ensuring your wiring meets safety and performance standards.
Enter the total current (in Amperes) expected to flow through the conductor.
Enter the one-way distance (in feet) from the power source to the load.
Enter the nominal voltage of the power source (e.g., 120V, 240V).
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 AWGSelect the American Wire Gauge (AWG) of the conductor.
Copper AluminumChoose the material of the electrical wire.
Calculation Results:
Please enter valid positive numbers for Current, Length, and Source Voltage.
';
return;
}
// Resistivity constant K (Ohms per circular mil-foot at 20°C)
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;
}
// Circular Mils (CM) lookup table for common AWG sizes
var circularMils;
switch (wireGauge) {
case '14': circularMils = 4110; break;
case '12': circularMils = 6530; break;
case '10': circularMils = 10380; break;
case '8': circularMils = 16510; break;
case '6': circularMils = 26240; break;
case '4': circularMils = 41740; break;
case '2': circularMils = 66360; break;
case '1': circularMils = 83690; break;
case '0': circularMils = 105600; break; // 1/0 AWG
case '00': circularMils = 133100; break; // 2/0 AWG
case '000': circularMils = 167800; break; // 3/0 AWG
case '0000': circularMils = 211600; break; // 4/0 AWG
default:
resultDiv.innerHTML = 'Invalid wire gauge selected.
';
return;
}
// Voltage Drop Formula: Vd = (2 * K * I * L) / A
// Note: L is one-way length, so we multiply by 2 for total circuit length (out and back)
var voltageDrop = (2 * K * currentAmps * conductorLength) / circularMils;
var percentageVoltageDrop = (voltageDrop / sourceVoltage) * 100;
var recommendation = ";
if (percentageVoltageDrop <= 3) {
recommendation = 'This is generally acceptable for most applications.';
} else if (percentageVoltageDrop > 3 && percentageVoltageDrop <= 5) {
recommendation = 'This is acceptable for some applications, but consider reducing the drop.';
} else {
recommendation = 'This is excessive and should be corrected to prevent issues.';
}
resultDiv.innerHTML =
'Calculated Voltage Drop: ' + voltageDrop.toFixed(2) + ' Volts' +
'Percentage Voltage Drop: ' + percentageVoltageDrop.toFixed(2) + '%' +
'Recommendation: ' + recommendation + ";
}
Understanding Voltage Drop
Voltage drop is the reduction in electrical potential along the length of a conductor carrying current. It's a natural phenomenon that occurs in all electrical circuits due to the resistance of the wire. As current flows through a wire, some of the electrical energy is converted into heat, leading to a decrease in voltage available at the load (the device using the electricity).
Why is Voltage Drop Important?
- Performance Issues: Excessive voltage drop can cause motors to run hotter and less efficiently, lights to dim, and electronic equipment to malfunction or not operate at all.
- Energy Waste: The energy lost as heat due to voltage drop is wasted, leading to higher electricity bills.
- Safety Concerns: While not always a direct safety hazard, consistently high voltage drop can indicate an undersized wiring system, which could lead to overheating under certain fault conditions.
- Compliance: Electrical codes (like the National Electrical Code in the US) recommend limits for voltage drop to ensure efficient and safe operation of electrical systems.
Factors Affecting Voltage Drop
The amount of voltage drop in a circuit is influenced by several key factors:- Current (Amps): Higher current draws lead to greater voltage drop.
- Length of Conductor (Feet): The longer the wire, the more resistance it presents, and thus the greater the voltage drop.
- Wire Gauge (AWG): Thinner wires (higher AWG numbers like 14 AWG) have higher resistance per foot than thicker wires (lower AWG numbers like 6 AWG), resulting in more voltage drop.
- Conductor Material: Different materials have different electrical resistivities. Copper has lower resistivity than aluminum, meaning copper wires will have less voltage drop for the same gauge and length.
The Voltage Drop Formula
The most common formula for calculating voltage drop in a single-phase AC or DC circuit is:Voltage Drop (Vd) = (2 * K * I * L) / A
- K: The resistivity constant of the conductor material. For copper, it's typically around 12.9 (Ohms per circular mil-foot at 20°C). For aluminum, it's about 21.2.
- I: The current in Amperes (A).
- L: The one-way length of the conductor in feet. The formula uses '2 * L' because current travels out to the load and back to the source.
- A: The cross-sectional area of the conductor in circular mils (CM). This value is specific to each wire gauge.
Recommended Voltage Drop Limits
The National Electrical Code (NEC) recommends that the total voltage drop for feeders and branch circuits combined should not exceed 5%. For feeders alone, a 3% drop is recommended, and for branch circuits alone, another 3% drop is recommended. Keeping voltage drop within these limits ensures optimal performance and longevity of electrical equipment.How to Mitigate Voltage Drop
If your calculations show excessive voltage drop, here are ways to reduce it:- Increase Wire Gauge: Use a larger (lower AWG number) wire. A thicker wire has less resistance.
- Reduce Circuit Length: If possible, shorten the distance between the power source and the load.
- Reduce Current: Distribute loads across multiple circuits or use more efficient appliances to lower the total current draw.
- Use Copper Wire: If currently using aluminum, switching to copper can reduce voltage drop due to its lower resistivity.