Voltage Drop in a 12V System
The voltage loss seen at the terminal of the load as a result of the cable resistance multiplied by the current. Since carrying the same power at 12 V requires about 19 times more current than at 230 V, the losses are far larger; that is why on long 12 V runs the cross-section is the decisive design decision.
The reason for the loss is simple: the voltage drop is the current multiplied by the line resistance, and the line resistance rises with length and falls with cross-section. When the same power is carried at a low voltage the current is larger, so the drop is larger too; moreover, since the power turned into heat in the cable rises with the square of the current, the loss climbs much faster.
Looking at it as a percentage matters in order not to be misled. A loss of 0.5 V is negligible on a 230 V line, but on a 12 V line it is about 4% and is felt directly. In LED lighting this loss shows up in light intensity, in a water pump in flow rate, and in motor loads in torque.
In a levelling system the effect works in two directions. First, the torque of a DC motor is proportional to the applied voltage; a dropping voltage slows the jack down. Second, as the motor slows it draws more current and the drop grows further. For this reason the jack supply runs are kept short, the cross-section is chosen generously and the negative return path is taken as seriously as the positive line. Measurement must be made at the jack terminal while the load is running.
Context in which this term is used: RV automatic levelling guide