Voltage Drop Calculator
Understanding and calculating voltage drop is crucial for ensuring the efficiency, safety, and proper operation of electrical systems. As electricity travels through a conductor, it encounters resistance, which causes a reduction in voltage. This phenomenon, known as voltage drop, can lead to various issues, including dimming lights, overheating wires, and malfunctioning equipment.
What is Voltage Drop?
Voltage drop is the reduction in electrical potential along the length of a conductor carrying current. It's a direct consequence of Ohm's Law (V = I * R), where the resistance (R) of the wire, combined with the current (I) flowing through it, causes a portion of the source voltage to be "dropped" or lost as heat.
Why is it Important to Calculate Voltage Drop?
- 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 be dimmer, and sensitive electronics to malfunction or fail prematurely.
- Energy Efficiency: The voltage lost due to resistance is converted into heat, representing wasted energy. Minimizing voltage drop improves the overall energy efficiency of your electrical system.
- Safety: While less common with typical voltage drops, extreme voltage drop can lead to excessive heat generation in wires, posing a fire hazard. It also ensures that protective devices (like circuit breakers) operate correctly.
- Compliance: Electrical codes, such as the National Electrical Code (NEC) in the U.S., recommend maximum voltage drops (e.g., typically 3% for branch circuits and feeders) to ensure safe and efficient operation.
Factors Affecting Voltage Drop:
- Current (Amperes): Higher current draws lead to greater voltage drop.
- Wire Length (Feet): Longer wires have more resistance, resulting in increased voltage drop.
- Wire Gauge (AWG): Thicker wires (smaller AWG number) have less resistance and thus less voltage drop.
- Wire Material (Copper vs. Aluminum): Copper has lower resistivity than aluminum, meaning it offers less resistance for the same gauge and length, resulting in less voltage drop.
- Source Voltage: While not directly affecting the voltage drop in volts, a higher source voltage means the same voltage drop represents a smaller percentage of the total voltage.
Use the calculator below to determine the voltage drop for your specific electrical circuit parameters.
Amps
Feet
18 AWG
16 AWG
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
Copper
Aluminum
Volts
Please enter a valid positive number for Current (Amperes).
';
return;
}
if (isNaN(wireLengthFeet) || wireLengthFeet < 0) {
resultDiv.innerHTML = 'Please enter a valid positive number for One-Way Wire Length (Feet).
';
return;
}
if (isNaN(sourceVoltage) || sourceVoltage <= 0) {
resultDiv.innerHTML = 'Please enter a valid positive number for Source Voltage (Volts).
';
return;
}
// Resistivity (K) in Ohms-cmil/ft at 75°C (common for NEC calculations)
var K;
if (wireMaterial === 'copper') {
K = 12.9; // Copper resistivity
} else if (wireMaterial === 'aluminum') {
K = 21.2; // Aluminum resistivity
} else {
resultDiv.innerHTML = 'Invalid wire material selected.
';
return;
}
// Circular Mils (A) lookup table based on AWG
var circularMils;
switch (wireGaugeAWG) {
case '18': circularMils = 1624; break;
case '16': circularMils = 2582; break;
case '14': circularMils = 4107; 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 '-1': circularMils = 133100; break; // 2/0 AWG
case '-2': circularMils = 167800; break; // 3/0 AWG
case '-3': circularMils = 211600; break; // 4/0 AWG
default:
resultDiv.innerHTML = 'Invalid wire gauge selected.
';
return;
}
if (circularMils === 0) {
resultDiv.innerHTML = 'Wire gauge selected has zero circular mils, which is not possible for calculation.
';
return;
}
// Voltage Drop Formula: VD = (2 * K * I * L) / A
// 2 is for round trip (out and back)
var voltageDrop = (2 * K * currentAmps * wireLengthFeet) / circularMils;
var percentageDrop = (voltageDrop / sourceVoltage) * 100;
var remainingVoltage = sourceVoltage – voltageDrop;
var resultHTML = '