Voltage Drop Calculator

Modern online calculator for calculating voltage drop in wires

Calculation

V
A
m
*) Calculation uses double wire length (forward and return wire)
mm²
-
1 = resistive load, <1 = inductive load
Result
Voltage drop:
Usable voltage:
Voltage loss:
Wire resistance:

Good to know

What is voltage drop?

Voltage drop refers to the reduction in electrical voltage along a conductor when current flows through it. This happens due to the resistance of the conductor.

Specific conductance values
Material Conductance (S)
Silver 62.5
Copper 56.0
Aluminum 35.0
→ More specific values
Basic formula
\[\Delta U = I \times R\]
Voltage drop = Current × Resistance
Power factor (cos φ)

Cos φ = 1: Resistive load (heating, incandescent bulb)
Cos φ < 1: Inductive load (motor, transformer)

Description of voltage drop

The term "voltage drop" refers to the reduction in electrical voltage along an electrical conductor when current flows through it. This happens due to the resistance of the conductor, causing energy to be lost in the form of heat. The voltage drop is directly proportional to the resistance of the conductor and the current flowing through it.

Basic principle

The formula describing voltage drop is based on Ohm's law:

\[\Delta U = I \times R\]
  • \(\Delta U\): Voltage drop (V)
  • \(I\): Current (A)
  • \(R\): Wire resistance (Ω)

High resistance or large current leads to greater voltage drop. In electrical systems, it is important to minimize voltage drop to ensure efficient energy transmission and safe operation of equipment.

Formulas for voltage drop

Single wire length:
\[R = \frac{\rho \times l}{A} = \frac{l}{\sigma \times A}\]
Double wire length:
\[R = 2 \times \frac{\rho \times l}{A} = 2 \times \frac{l}{\sigma \times A}\]
Voltage drop:
\[\Delta U = 2 \times \frac{l}{\sigma \times A} \times I \times \cos(\phi)\]
Voltage drop in %:
\[\Delta U [\%] = \frac{\Delta U}{U_n} \times 100\%\]

Variable legend

  • \(A\): Cross-section (mm²)
  • \(l\): Length (m)
  • \(R\): Wire resistance (Ω)
  • \(\rho\): Specific resistance (Ω)
  • \(\sigma\): Specific conductance (S)
  • \(U_n\): Applied voltage (V)
  • \(\Delta U\): Voltage drop (V)
  • \(\phi\): Phase angle (cos φ)

Practical application

Calculator functionality

This page calculates the voltage drop of an electrical wire. The input voltage, current, single cable length and wire cross-section must be specified.

Optionally, a phase shift for inductive loads can be specified. For resistive loads and DC, a value of 1 is preset for cos φ.

Important notes
  • Calculation uses double wire length (forward and return wire)
  • Voltage drop reduces the available usable voltage
  • Larger cross-sections reduce voltage drop
  • For inductive loads, cos φ < 1 must be considered
Allowable voltage drops according to DIN VDE
Application Allowable voltage drop Note
Lighting 3% Avoiding brightness fluctuations
Power/Motors 5% Starting problems with excessive voltage drop
Household appliances 3-5% Depending on device type and sensitivity
Heating 5% Less critical with purely resistive load
Example calculation
Example: House installation

Given: 230V mains voltage, 16A current, 25m cable length, 2.5mm² copper cable (σ = 56)

Calculation:

\[\Delta U = 2 \times \frac{25}{56 \times 2.5} \times 16 \times 1\] \[\Delta U = 2 \times \frac{25}{140} \times 16 = 5.7 \text{ V}\]

Result:

Voltage drop: 5.7 V
Usable voltage: 224.3 V
Voltage loss: 2.5%

✓ Below 3% (limit for house installation)

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