An example of a rolling chassis

Chassis, Earth, Earth Return

The chassis of a vehicle is the basic framework of the vehicle, and all other components are mounted on to the chassis.

The chassis is normally of metal construction, and, as such, can be incorporated into the vehicle electrical system.

Nowadays, we bolt the negative terminal of the battery directly on to the chassis. We then use this pathway to return electricity from electrical components back to the battery, in order to complete the electrical circuit. This arrangement is known as a 'negative earth return' system.

This system simplifies the wiring of a vehicle as it means we only need half the amount of wires to complete circuits.

An alternative system used on vehicles such as fuel tankers, may have 'insulated earth return' - we do not return the electrons to the battery via the chassis, we use a dedicated insulated wire to do so. For the likes of fuel tankers, in the event of an accident, this is a safer electrical system.

It complicates the wiring system because we now need twice as much wiring to wire the vehicle, but in the event of a live wire coming into contact with the chassis (say, after an accident), no short-circuit will occur, making this arrangement safer.

A rolling chassis is a chassis that has been fitted with wheel hubs and wheels, which is capable of rolling. When a vehicle is described as a rolling chassis, few, if any other components are fitted.

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