Wiring Calculator

Electrical Wiring Voltage Drop Calculator

14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 2 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG
Single Phase Three Phase
function calculateVoltageDrop() { var sourceVoltage = parseFloat(document.getElementById("sourceVoltage").value); var loadCurrent = parseFloat(document.getElementById("loadCurrent").value); var circuitLength = parseFloat(document.getElementById("circuitLength").value); var wireResistancePerFoot = parseFloat(document.getElementById("wireGauge").value); var systemType = document.getElementById("systemType").value; if (isNaN(sourceVoltage) || isNaN(loadCurrent) || isNaN(circuitLength) || isNaN(wireResistancePerFoot) || sourceVoltage <= 0 || loadCurrent <= 0 || circuitLength <= 0) { document.getElementById("result").innerHTML = "Please enter valid positive numbers for all input fields."; return; } var voltageDrop; if (systemType === "single") { // For single phase, voltage drop = 2 * Current * Length * Resistance_per_foot voltageDrop = 2 * loadCurrent * circuitLength * wireResistancePerFoot; } else { // three phase // For three phase, voltage drop = sqrt(3) * Current * Length * Resistance_per_foot voltageDrop = Math.sqrt(3) * loadCurrent * circuitLength * wireResistancePerFoot; } var percentageDrop = (voltageDrop / sourceVoltage) * 100; var recommendation = ""; var recommendationColor = ""; if (percentageDrop <= 3) { recommendation = "Excellent: Voltage drop is within acceptable limits (typically <3% recommended by NEC for feeders and branch circuits)."; recommendationColor = "#28a745"; // Green } else if (percentageDrop <= 5) { recommendation = "Acceptable: Voltage drop is slightly above ideal, but may be acceptable for some applications. Consider a larger wire gauge for better efficiency."; recommendationColor = "#ffc107"; // Yellow/Orange } else { recommendation = "Excessive: Voltage drop is too high. This can lead to poor equipment performance, overheating, and energy waste. A larger wire gauge is strongly recommended."; recommendationColor = "#dc3545"; // Red } document.getElementById("result").innerHTML = "

Calculation Results:

" + "Calculated Voltage Drop: " + voltageDrop.toFixed(2) + " Volts" + "Percentage Voltage Drop: " + percentageDrop.toFixed(2) + "%" + "Recommendation: " + recommendation + ""; }

Understanding Voltage Drop in Electrical Wiring

Voltage drop is a critical factor in electrical system design and safety. It refers to the reduction in electrical potential along the length of a conductor 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 available at the load (e.g., an appliance or motor) to be less than the voltage at the source.

Why is Voltage Drop Important?

  • Equipment Performance: Appliances and motors are designed to operate within a specific voltage range. Excessive voltage drop can cause them to run inefficiently, overheat, or even fail prematurely. Motors, for instance, draw more current when voltage is low, leading to increased heat and reduced lifespan.
  • Energy Efficiency: The energy lost due to voltage drop is dissipated as heat in the wires, representing wasted energy. Minimizing voltage drop improves the overall efficiency of your electrical system.
  • Safety: While not always a direct safety hazard in itself, excessive voltage drop can contribute to conditions that might lead to safety issues, such as overheating wires or malfunctioning safety devices.
  • Lighting Quality: For lighting circuits, significant voltage drop can result in dim or flickering lights.

Factors Affecting Voltage Drop

Several key factors influence the amount of voltage drop in a circuit:

  1. Current (Amperes): Higher current draws lead to greater voltage drop.
  2. Length of Wire (Feet): The longer the wire, the more resistance it presents, and thus, the greater the voltage drop. This calculator uses the one-way length, but the current travels the full round trip.
  3. Wire Gauge (AWG): Thicker wires (smaller AWG numbers) have lower resistance per foot and therefore less voltage drop. This is often the most practical factor to adjust to control voltage drop.
  4. Conductor Material: Copper has lower resistance than aluminum for the same gauge, resulting in less voltage drop. This calculator assumes copper wire.
  5. System Type (Single vs. Three Phase): Three-phase systems inherently distribute current more efficiently, leading to less voltage drop compared to single-phase systems for the same power delivery.

National Electrical Code (NEC) Recommendations

While the NEC does not mandate specific voltage drop limits, it provides recommendations in Section 210.19(A)(1) FPN No. 4 and 215.2(A)(1) FPN No. 2. These suggest that for feeders and branch circuits, a voltage drop of no more than 3% at the farthest outlet is desirable to provide reasonable efficiency of operation. The total voltage drop for both feeders and branch circuits combined should ideally not exceed 5%.

How to Use This Calculator

Our Voltage Drop Calculator helps you quickly determine the voltage drop for your specific wiring scenario:

  1. Source Voltage: Enter the voltage supplied by your power source (e.g., 120V, 240V, 480V).
  2. Load Current: Input the total current (in Amperes) that the circuit will carry. This is the sum of all loads connected to the circuit.
  3. One-Way Circuit Length: Provide the distance (in feet) from the power source to the load.
  4. Wire Gauge (AWG): Select the American Wire Gauge (AWG) of the conductor you are using. The calculator uses standard resistance values for copper wire at 75°C.
  5. System Type: Choose whether your system is Single Phase or Three Phase.

Click "Calculate Voltage Drop" to see the results, including the calculated voltage drop in volts, the percentage of voltage drop, and a recommendation based on common electrical standards.

Example Scenario:

Imagine you have a 120V circuit powering a 15 Amp load, located 100 feet away, using 14 AWG copper wire (single phase). Using the calculator:

  • Source Voltage: 120V
  • Load Current: 15A
  • One-Way Circuit Length: 100 ft
  • Wire Gauge: 14 AWG (resistance per foot approx. 0.0031 Ohms/ft)
  • System Type: Single Phase

The calculator would show a voltage drop of approximately 9.30 Volts, which is 7.75% of the source voltage. This is considered excessive, indicating that a larger wire gauge (e.g., 12 AWG or 10 AWG) should be used to reduce the voltage drop to an acceptable level.

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