How is cable cross-section chosen in a levelling system, and why does voltage drop matter?
In 12V DC systems the current for the same power is much higher than at 230V; that is why the voltage drop across the cable resistance becomes decisive. KTS200 jacks run on 12V DC, and as the voltage reaching the jack drops, the motor slows down, current draw rises and the control unit's current protection can trip early. The cross-section is chosen according to the current drawn and the total out-and-back length of the cable.
Two things are separate in cable selection: the heating limit and the voltage drop limit. In 12V systems the second is almost always decisive. A loss of 0,5 V on a 12V run takes away more than four percent of the supply voltage; the same loss would not even be noticed at 230V.
In practice:
- Include the total length of the outgoing and return conductor in the calculation, not just the distance from the battery to the jack.
- Increase the cross-section for every added metre. A thin cable over a long distance loses far more than the same cable over a short distance.
- When the voltage drops, a DC motor draws more current to do the same work; this both heats the cable more and brings it closer to the protection threshold.
- Looseness at terminals, lugs and joints is also a source of voltage drop; tightening and contact surface are as important as cross-section.
The KTS200 kit comes with its own power and data cables; in a standard layout these cables are sufficient. However, if you need to extend the run because of the chassis geometry, do not do the extension on your own judgement; consult installation support for the cross-section and the route. Since a cable cross-section table is not separately published in the product documentation, confirmation of values must be obtained from technical support.
Full coverage of the topic: Guide to automatic RV levelling