Electrical
Voltage Drop Calculator
Calculate voltage drop from current, cable length and tabulated voltage drop values.
Use this calculator for quick cable voltage drop checks for single-phase and three-phase circuits. It is intended for preliminary circuit design using tabulated millivolt-per-amp-per-metre values.
Inputs
Enter the tabulated voltage drop value for the selected cable type, installation method and conductor size.
Result
Voltage Drop
-
Enter values and click calculate.
Method
Voltage drop is calculated from current, route length and tabulated cable voltage drop value:
Vd = (mV/A/m × I × L) ÷ 1000
Percentage voltage drop is then:
Vd% = (Vd ÷ V) × 100
- Vd = voltage drop (V)
- I = design current (A)
- L = cable route length (m)
- mV/A/m = tabulated cable voltage drop value
- V = nominal voltage (V)
- Calculated voltage drop = -
Reference
- This calculator applies the standard tabulated voltage drop method commonly used in electrical design.
- Voltage drop values should be taken from the relevant cable tables for the selected conductor, insulation type and installation method.
- Typical UK nominal voltages are 230 V for single-phase systems and 400 V for three-phase systems.
- Relevant standards and guidance may include BS 7671 and associated cable sizing tables.
Design note: This calculator provides indicative results only. Final design should consider correction factors, harmonics, operating temperature, installation method, circuit arrangement and applicable voltage drop limits for the project.