Negative Chassis Return
Returning the negative end of the circuit to the battery through the vehicle's metal body instead of a separate cable. It saves cable, but because the resistance of the return path depends on bolted contacts and corrosion, its reliability is limited in high-current RV circuits.
In chassis return the current passes from the device's body connection into the metal structure and from there reaches the battery negative terminal. Because the metal cross-section is large, the resistance of the body itself is small; the problem is the contact points the current passes through. A painted surface, an oxidised bolt or a loosened nut produces resistance on the order of milliohms, and at high current that resistance turns into a visible voltage loss.
The second problem is corrosion. In an RV body, different metals and moisture are present together; galvanic corrosion at the contact point increases the resistance over time. The fault progresses insidiously: the device first works intermittently, then not at all, and measurement finds no problem on the positive side.
For this reason the common practice in RV living area wiring is a two-wire system: the negative end of each load returns to the battery by its own cable via a common busbar. On loads with high instantaneous current, such as levelling legs, the negative line is chosen with the same cross-section as the positive. If chassis return is used, the contact point must be cleaned back from the paint and protected against corrosion.
The context in which this term is used: RV automatic levelling guide