Choosing the correct automotive cable / wire size to suit your application when installing an accessory into your RV, Caravan or Motorhome is critical. To find out the correct cable / wire size to use or to determine whether you are using the right cable / wire size, please use this voltage drop calculator tool below. At absolute minimum, an acceptable DC voltage drop of 5% of your nominal battery voltage would be acceptable for most devices. In saying this, you should be aiming for less than 3% Voltage Drop or even lower if you can. Note: This DC Voltage Drop Calculator is suitable for 12 Volt and 24 Volt DC systems only.