Cable Sizing
The process of determining a circuit's cable thickness in square millimetres based on current, run length and the accepted voltage drop. In 12 V systems the governing constraint is usually not heating but voltage drop; that is why the cross-section is often chosen larger than the current table suggests.
The calculation has two steps. First you check whether the cable can safely carry the continuous current. Then you compute the voltage drop over the total there-and-back length: the resistance of copper is roughly 0,0175 Ω·mm²/m, and the drop is the current multiplied by the resistance of the run.
Example: a load drawing 20 A sits 5 m away from the battery. There and back that makes 10 m. In a 4 mm² cable the run resistance is roughly 0,044 Ω and the drop roughly 0,9 V — in a 12 V system that is %7, and that is too much. Increasing the cross-section to 10 mm² brings the drop down to roughly 0,35 V.
In an RV the accepted drop depends on the type of load; for lighting and electronics a figure on the order of %3 is targeted. On motorised loads such as the 12 V DC legs of the KTS200 the drop translates directly into torque and movement, so the cross-section is chosen generously. Cable sizing must always be done by measuring the actual cable route, never by straight-line distance.
The context in which this term is used: RV automatic levelling guide