Estimate the voltage lost over a conductor run so you can size cable correctly.
Load current the conductor must carry (A). From your load spec, not the breaker rating.
One-way cable length in meters. The loop (out+back) is accounted for in the formula.
Copper has lower resistivity than aluminum — same size, lower drop.
Cross-sectional area in mm². Larger means lower resistance and lower drop.
Voltage Drop
6.88 V
Voltage lost along the conductor run — what the load does not receive.
Conductor Resistance
0.1720 Ω
Total two-way resistance of the installed conductor.
What this means
Sizing check for low-voltage runs. Many codes target ≤3% on feeders and ≤5% total, but verify your local standard.
Voltage drop is the reduction in voltage a conductor produces as current flows through its resistance. It is the key input for sizing cable runs so connected equipment still receives enough voltage to operate.
Formula
Vd = 2 × L × I × (ρ ÷ A)
Worked examples
FAQ
How do I account for the return conductor?
This calculator already does. The factor of 2 in the formula represents current flowing out on one conductor and back on the other.
What is a typical acceptable voltage drop?
Many guidelines allow up to 3% for feeders and 5% total for branch circuits, though requirements vary by code and installation.
Important assumptions