Voltage Drop Calculator
Determine the exact voltage loss and percentage drop across electrical cables based on length, current, wire size, and material.
Understanding Voltage Drop
Every electrical conductor has inherent electrical resistance. As current flows through a wire over a given distance, a fraction of electrical power converts into heat, causing a reduction in voltage at the load terminals. Excessive voltage drop reduces energy efficiency, dims lights, and can cause electric motors to overheat or fail.
Voltage Drop Formulas
For Single-Phase AC and DC Systems:
$$V_d = \frac{2 \cdot L \cdot I \cdot \rho}{A}$$For Three-Phase AC Systems:
$$V_d = \frac{\sqrt{3} \cdot L \cdot I \cdot \rho}{A}$$Voltage Drop Percentage Calculation:
$$\% V_d = \left( \frac{V_d}{V_{\text{system}}} \right) \times 100$$Where:
- Vd = Total voltage drop across the run in Volts (V)
- L = One-way length of the cable run in meters
- I = Operating circuit load current in Amps (A)
- ρ = Resistivity of the conductor (Copper ≈ 0.01724, Aluminum ≈ 0.0282 Ω·mm²/m)
- A = Conductor cross-sectional area in mm²
- Vsystem = Nominal supply voltage (V)
Frequently Asked Questions
What is an acceptable voltage drop limit?
Standard electrical guidelines (such as NEC Article 210 and IEC 60364) recommend keeping voltage drop within 3% for lighting or branch circuits, and no more than 5% for overall power distribution circuits from supply to final load.
How can I reduce voltage drop?
You can effectively reduce voltage drop by increasing the conductor size (selecting a larger mm² area), reducing total cable length, splitting load across multiple branch circuits, or choosing copper over aluminum.
Does temperature affect voltage drop?
Yes. As conductor temperature rises, electrical resistance increases. High ambient temperatures or heavily loaded cables experience higher internal resistance, leading to increased total voltage drop.