Updated May 2017
Circuit breakers and fuses in caravans both cut the current, but in different ways. Here’s how to know which best suits circuits and appliances protected. Those for 230 volt grid or inverter supplied circuits must be specified and installed by a certified electrician – who will install circuit breakers etc anyway. Circuit breakers and fuses for RVs (for 12/24 volt circuits) can be self-installed by those familiar with such work.
Circuit breakers and fuses in caravans – the problem with fuses
A fuse is a short piece of wire that heats up and melts when current flow exceeds the fuse’s melting point. Fuses are cheap and simple. They respond very fast to excess current. Fuses usefully safeguard sensitive and costly electronics – such as computers. Many such devices have fuses inbuilt.
A fuse’s downside is that it will not cut the current quickly. This is a drawback with water pumps, fridges and electric motors etc. Some draw up to five times their working current whilst starting. A fuse must thus be oversized to cope. Whilst slow blow fuses overcome this, few RV owners know they exist. Let alone know why they are needed. Further, only the most costly can be relied to blow at their intended current. Another failing is that a fuse must be replaced by when it blows. If that which caused it to blow remains, the replacement also will blow. On the plus side, fuses are cheap. They are stocked by most hardware stores.
A further issue with fuses is that there are known problems with some blade fuses and fuse holders. These are mostly over 10 amps or so. See Blade Fuse Problems in Caravans. Fuses and fuse holders tend to corrode. This causes heat to be generated to the point where they may melt. They may catch fire – yet not necessarily blowing the fuse.
Circuit breakers and fuses in caravans – how circuit breakers work
Circuit breakers are a type of switch that turn off when they detect excess current. They are then manually reset. Some automatically reset, however better avoided – because the cause of such tripping may still remain.
The better-made circuit breakers operate more reliably at their rated current. This is a plus with loads with high starting current. They also double as manual on/off switches.
Fusible link – the material above and below the fusible link dampens the explosive forces if/when the fuse link blows. Pic: Blue Seas.
Circuit breakers should be located close to the battery as possible. This protects the cable in the event of short circuits downstream from the circuit breaker. In some instances, fuses are used in place of circuit breakers, but usually to save cost. It is not good electrical practice to do so. If funds are really low, so-called fusible links (below) can be substituted for circuit breakers. This can be done in (say) the feed to a large inverter that may carry 200 amps or more.
High current fusible links go off like fireworks if/when they blow. They need locating so that any such debris is contained.
This high quality circuit breaker doubles as an on/off switch. Pic: 12-volt shop.
Circuit breakers and fuses in caravans – which to use and why
An RV may have multiple cables that each feed a specific item – e.g, fridge, water pump, TV, computer etc. Here, the current flowing through that cable is reasonably constant, and thus readily known. This is the usage where suitably rated fuses work fine. Each fuse is installed as close to the battery as feasible – yet accessible. It needs to so located as it thus also protects the supply cable if it is shorted out.
Many caravans and motor homes have several main cable feeds. Each serves a number of different items that may or may not be used simultaneously. Here, the fuse rating must cope with the maximum load. It may blow slowly (or not at all) if a fault occurs when only one item is switched on. Circuit breakers, that accommodate the cable’s total load, need locating as above. This protects the supply cable, but as the breaker must cope with the total load it may not act fast enough to adequately safeguard. Any connected appliance thus also needs an appropriately rated fuse. Locate that fuse as close as possible to the appliance.
A typical caravan or motor home is thus likely to need one or more circuit breakers as close as feasible to the battery. Plus an individual fuse adjacent to each appliance.
There are major differences in circuit breaker quality. Good ones are not cheap but well worth the price.Make sure the ones you buy are designed for 12/24 volt dc. The best are stocked by marine suppliers, but there are many other sources.
Circuit breakers and fuses in caravans – other information
If you liked this article, you will also like my books. All are technically correct yet written in everyday down-to-earth plain English.
Full details of every aspect of RV electrics and their installation is covered in my totally current Caravan & Motorhome Electrics. Solar That Really Works covers solar in RVs. Solar Success covers home and property systems.
Caravan & Motorhome Book is a comprehensive guide to every aspect of caravans and motor homes. Likewise, all related issues are covered in the Camper Trailer Book. For information about the author please Click on Bio.