Tech: Motorhome electrics
We take a look at RV electrical systems – this time at the inner workings of a motorhome.
I'VE PREVIOUSLY TAKEN
a more detailed look at the complicated installation of RV electrics, mostly in caravans. It has since been mentioned to me that, although the same standards largely apply, some aspects of electrics are different in motorhomes.
There are often fundamentally different structural requirements between units. For example, a motorhome carries people as it travels, while a caravan (or fifth wheeler) does not. In addition to a motorhome’s ‘house’ 240V AC and 12V DC supplies, there is also the 12V or 24V DC supply for the ‘motor’ part of the vehicle. Generally speaking, it’s considered good practice to keep the respective 12V systems separate from each other, although the vehicle alternator can be used to charge both the vehicle and house batteries.
Many caravans use Thermo Plastic Sheathed for 240V cabling, but a number of manufacturers in the motorhome and campervan world prefer to use 15A flexible power supply cord.
The key word here is flexibility. Although it doesn’t require as much flexibility as a power cable extension cord, the multi-strand cored cable is better suited to the inherent vibrations of a motor vehicle.
Although the power cord does have a degree of mechanical protection from its outer sheath, many manufacturers run it in flexible conduit to reduce the risk of mechanical abrasion in places like engine bays and through bulkheads or frames.
Using flexible conduit for the power supply cord not only provides mechanical protection, but also electrical separation from 12V circuits where they unavoidably come close together around batteries and chargers, or three-way fridges.
A problem with using multi-strand conductors is the fact that the conductors have to be twisted together at connection points and there is always the risk of some breaking off. A good way to avoid that problem, and ensure a good connection every time, is to use bootlace crimps.
In any installation, good connections matter. A bad joint/connection can often get hot if a high current device is being used, and this then becomes a problem in itself.
To get momentarily scientific: as the temperature of the conductor increases, so does the circuit resistance, which increases the heating even more. The risk of fire is then not far away.
In any RV, electrical safety is a prime concern. The risk of electrical shorts and fire has to be negated not only by correct installation, but also by 16A breakers to protect the 240V circuits, as well as appropriately rated fuses to protect the 12V circuits.
While you, the RV owner, are obviously unable to check everything you can’t see, it’s still possible to do a regular physical inspection of everything you can see: power cords, powerpoints, plugs, sockets, appliances and even exposed cables, to ensure that everything is in tip top condition before you take to the road.
WORDS AND PICS Malcolm Street
Source: Caravan World Jul 2011