Cable Voltage Drop Guide

Let's use 6 B&S as an example.


Voltage Drop for 6 B&S Cable: 

To calculate the voltage drop of 6 B&S copper cable, use the following formula:


Voltage Drop = Length x Current x 0.017
                                      Area (13.50)


Length = Total length of cable in metres.

Current = Current draw (amps) through the cable.

Area = Cross sectional area of the copper (in this case 13.50mm²)



  • Formula only applies to copper at 25°C, voltage drop increases with both ambient and cable temperature, at approx 0.4% per °C.

  • 0.017 - This multiplication factor only applies to copper


Example for 6 B&S:

How much voltage drop over 10m of 6 B&S with a current draw of 103A?


  • 10m x 103A x 0.017 = 17.51


Divide this by 13.50 (cross sectional area of 6 B&S - mm²)


  • 17.51/13.50 = 1.297V


You will have a drop of approximately 1.3 Volts over the 10m length