Engineering CalculationVoltage Drop Calculator for LT Cables (3-phase and 1-phase)
Check the voltage drop of a cable run in volts and percent, and see whether it meets your limit before you lay the cable.
Open the calculator →Formula
ΔV = √3 × I × L × (R cosφ + X sinφ) / 1000 (3-phase)
ΔV = 2 × I × L × (R cosφ + X sinφ) / 1000 (1-phase)
I in A, L in m, R and X in Ω/km from the cable data sheet
Worked example
100 A, 150 m run, R = 0.32 Ω/km, X = 0.08 Ω/km (example values - take yours from the cable data sheet), power factor 0.85, 415 V
ΔV = 1.732 × 100 × 150 × (0.32×0.85 + 0.08×0.527) / 1000 = 8.16 V = 1.97 %
Where engineers use it
- Long feeders to pumps, cooling towers and remote panels
- Street and yard lighting circuits
- Solar DC and AC cable runs
How to use
- Click Open the calculator. It runs free in your browser, on desktop or phone.
- Enter your values. Units and typical ranges are shown next to each input.
- Read the result and the step-by-step working, then print or add it to your Project BOQ.
Questions
What is an acceptable voltage drop?
It depends on the code and your design basis; many designs use limits of a few percent from source to load. The suite lets you enter your own limit.
Can I solve for the cable size instead?
Yes, the Cable Sizing guided check picks the smallest size that meets both current and voltage-drop limits.