Voltage Drop Calculator

Free voltage drop calculator for single-phase and three-phase circuits. Instantly compute wire size, % voltage drop, and power loss. NEC-compliant and engineer-tested.

Or use custom resistance:

Results

Voltage Drop
0.000 V
Power Loss
0.000 W
0.00% Drop

Formulas Used:

Single Phase: VD = 2 × I × R × L
Three Phase: VD = √3 × I × R × L
Power Loss: P = I² × R × multiplier
Where: I = Current (A), R = Resistance (Ω/ft), L = Distance (ft)

NEC Guidelines:

  • • Branch circuits: Max 3% voltage drop
  • • Feeders: Max 3% voltage drop
  • • Total system: Max 5% voltage drop

Understanding Voltage Drop

Voltage drop is the reduction in voltage along the path of a current-carrying conductor. It occurs naturally due to the resistance of wires and can affect the performance of electrical equipment. Excessive voltage drop may lead to inefficient operation, overheating, or even equipment failure.

Why Calculate Voltage Drop?

Calculating voltage drop is essential for designing safe and efficient electrical circuits. Whether you are working on single-phase or three-phase systems, ensuring that voltage levels remain within acceptable limits helps prevent equipment damage and energy loss. Our calculator instantly computes voltage drop, power loss, and % voltage drop based on your wire size, conductor material, and load.

Key Factors Affecting Voltage Drop

  • Conductor Material: Copper and aluminum wires have different resistances.
  • Wire Length: Longer cables increase voltage drop.
  • Current Load: Higher currents cause larger drops.
  • Temperature: Resistance increases with heat, affecting voltage drop.
  • Number of Phases: Single-phase and three-phase circuits require different calculations.

How to Use This Calculator

  1. Select whether your circuit is single-phase or three-phase.
  2. Enter the voltage, current, and wire length of your circuit.
  3. Choose the conductor type (copper or aluminum).
  4. Click "Calculate" to see voltage drop, % voltage drop, and power loss.

Example Calculation

Suppose you have a single-phase 230V circuit with a 20A load, a 50-meter copper wire, and want to calculate the voltage drop. Using our calculator:

  • Input Voltage: 230V
  • Load Current: 20A
  • Wire Length: 50ft
  • Conductor: Copper

The calculator might show a voltage drop of 4.6V, which is 2% of the supply voltage. This is within the recommended limit for most branch circuits.

NEC Compliance & Best Practices

The National Electrical Code (NEC) recommends keeping voltage drop under 3% for branch circuits and under 5% for total feeders and branch circuits combined. Using our calculator helps ensure your wiring is NEC-compliant, energy-efficient, and safe.

Tips for Reducing Voltage Drop

  • Use larger wire sizes to reduce resistance.
  • Minimize the length of wiring runs.
  • Use copper conductors where possible for lower resistance.
  • Balance loads across three-phase circuits to optimize performance.

Frequently Asked Questions

Q: What is an acceptable voltage drop?
A: For branch circuits, NEC recommends no more than 3%, and for feeders plus branch circuits combined, no more than 5%.

Q: How does wire size affect voltage drop?
A: Larger wire sizes have lower resistance, which reduces voltage drop over the length of the wire.

Q: Can aluminum wires be used instead of copper?
A: Yes, but aluminum has higher resistance than copper, so voltage drop will be higher for the same size conductor.

Q: Does voltage drop affect my electrical devices?
A: Yes, significant voltage drops can reduce the efficiency and lifespan of electrical equipment and motors.

Q: How do I calculate voltage drop for three-phase circuits?
A: Our calculator automatically adjusts the formula based on whether you select single-phase or three-phase, considering line-to-line voltage and current.