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⚡ Voltage Drop Calculator

Calculate the voltage drop in an electrical circuit based on wire size, distance, and load current.

⚡ Voltage Drop Calculator

Calculate the voltage drop in an electrical circuit based on wire size, distance, and load current.

A
m
mm²

✅ Calculation Result

Voltage Drop (V_drop)- V
Percentage Drop (%)- %
End Voltage (V_end)- V

Voltage Drop Diagram

SRC220V
- ? V
50 m
LOAD?V

* A voltage drop of less than 3% to 5% is generally recommended for optimal performance.

Calculator Description

Voltage drop is the reduction of voltage at the load below the supply voltage due to wire resistance. If too large it causes malfunction, heating and poor efficiency, so wiring design must keep it within an allowable range.

What this calculator finds

Enter the wire material (Cu/Al), phase (single/three), system voltage, load current, cable distance and conductor cross-section to obtain the voltage drop (V), percentage drop and load-end voltage.

Why it matters

  • Selecting adequate conductor size (cost vs drop limit)
  • Checking the allowable drop (typically 3–5%) for stable operation
  • Long-distance supply and emergency backup circuit design

Formula

Voltage Drop Formula (Ohm's law)

The one-way resistance is R = ρ·L/A; single-phase uses the round-trip (factor 2) and three-phase multiplies by √3 for the phase relationship.

단상:  Vdrop=2IR\text{단상:}\; V_{drop} = 2 I R
삼상:  Vdrop=3 IR\text{삼상:}\; V_{drop} = \sqrt{3}\,I R
R=ρLAR = \dfrac{\rho L}{A}
  • V_drop — Voltage drop [V]
  • I — Load current [A]
  • R — One-way wire resistance (not round-trip) [Ω]
  • L — One-way circuit distance [m or ft]
  • A, ρ — Conductor area [mm²] and resistivity (Cu 0.0168, Al 0.0282 Ω·mm²/m)

Imperial form (K-factor)

In the US form, using circular-mil area and K (copper 12.9, aluminum 21.2 ohm·cmil/ft): V_drop = (factor × K × I × L) / cmil.

How the formula works

  • Larger current I or longer distance L increases the drop proportionally.
  • A larger area A lowers resistance and thus the drop (inverse proportionality).
  • Aluminum has higher resistivity than copper, giving a larger drop for the same area.

Worked example

For 220 V single-phase, copper A=4 mm², 50 m, 20 A: R = 0.0168×50/4 = 0.21 Ω, V_drop = 2×20×0.21 = 8.4 V, drop = 8.4/220 ≈ 3.8% (within the recommended 3–5%).

Useful Tips

Practical tips

  • If drop is large, enlarge the conductor, raise the voltage, or shorten the run.
  • Three-phase loads have less drop for the same conductor — more economical.
  • Resistivity rises with temperature, slightly increasing the drop.

Limitations & cautions

  • This covers only the resistive (Ohmic) drop; power-factor and reactance effects are excluded.
  • L is the one-way distance; using the round-trip length doubles the error.
  • Code-allowable drops (e.g., NEC recommendations) vary by region and use — check the applicable standard.