Voltage drop
Enter the design current, one-way route length and the appropriate tabulated mV/A/m value for the cable and circuit you are checking. The calculator shows the circuit drop, percentage, total allowance including any upstream drop and the maximum route length within the selected budget.
Circuit voltage drop
Circuit drop
Total incl. upstream
Budget margin
Maximum one-way route length within remaining budget
The calculator does not choose the cable.The mV/A/m input must come from the cable data or table appropriate to the selected cable, circuit arrangement and design conditions.
Include the whole installation path.If an upstream submain has already used part of the voltage-drop allowance, enter that percentage so the remaining circuit budget is shown.
Use and limitations: This is a design aid, not a cable-selection or compliance tool. It does not apply current-carrying-capacity factors, operating-temperature corrections, reactive components, harmonics, starting conditions, fault protection or equipment-specific voltage requirements. Check the selected mV/A/m value and complete the project-specific design using the current standards and manufacturer information.
Reference: IET Wiring Matters describes the BS 7671 Appendix 4 recommended maximum voltage-drop values of 3% for lighting and 5% for other uses for low-voltage installations supplied directly from a public low-voltage distribution system, and gives the voltage-drop calculation in the form (mV/A/m) × Ib × length. IET: Amps per Pound · IET: Appendix 4 overview