Blade fuse problems in caravans – they may burn or melt

by Collyn Rivers

The blade fuse problems in caravans and motorhomes (and particularly boats and 4WDs used on beaches and camper trailers) are mostly caused by exposure or partial exposure to damp air, dirt and water. This corrodes the fuse holder and fuse contact surfaces.

Typical burnt blade fuse and holder. The fuse and fuse holder have melded into a solid lump. Pic: redarc.com.au

Blade fuse problems in caravans – fuse holder sizes

There are two main sizes of blade fuses and blade fuse holders. Most blade fuse problems in caravans arise if the smaller size fuses and fuse holders are used at currents greater than 15 amps. Some auto-electricians suggest 10 amps. All need protecting against damp or salty water, or atmospheres.

As can be seen, the larger size has substantially more contact area.

Blade fuse problems in caravans – quality issues

There can also be blade fuse problems in caravans with poor quality versions of the larger sizes fuses and holders. Some have next to no protection against even mild corrosion. This causes them to resist current flow, usually partially melting the holder but not necessarily the fuse. This results in a major risk of fire – especially if the wiring’s insulation is also burned. It may expose current-carrying copper that, then allows full battery current to flow – possibly to earth. This can and does cause fires.
Long term blade fuse problems in caravans are also indirectly caused by badly crimped cable lugs. The resultant poor contact eventually allows corrosion between the copper and the lug. Heat builds up, in turn heating up the blade fuse holder.

This cable is only barely in contact with the crimp lug. Pic: original source unknown

A correctly formed crimp creates a cold weld. To achieve this it is 100% essential to use a proper crimping tool (as shown). Never use pliers or plier-like cheap crimping tools. A good ratchet type crimping tool, as shown below, forms that cold weld (i.e. an inter-molecular bond).

Use only a crimping tool like that shown: they are not cheap, but a badly crimped lug can set a caravan on fire! Pic: RV Books.

Blade fuse problems – the need for larger holders

Blade fuses. That most typically used is shown on the right. Use the Maxi version (left) for fuses of 10-15 amps and over.

The above fuses typically blow within 0.1-02 of a second at 600% of their rated value, and 1.0-2.0 seconds at 350% of their rated value. This is fine for protecting correctly specified cabling. Don’t, however, use any fuse that is higher rated than necessary.

Blade fuse problems in caravans – circuit breakers preferred

Ideally, replace high current blade fuse holders and fuse by manually re-settable dc circuit breakers. Those of totally reliable quality are stocked by marine electrical suppliers. Cheaper versions are available but are very temperature sensitive. This, in particular, is not an area to cut costs via eBay specials.

This a high-quality double pole dc circuit breaker. It protects both positive and negative cables. Pic: Carling Inc.

See also Circuit-Breakers-and-Fuses-in-RVs

Blade fuse problems in caravans – further information

Every aspect of RV electrics is covered in detail in my Caravan & Motorhome Electrics. Solar That Really Works is for cabins and RVs. Solar Success is for homes and properties. My other books are the Camper Trailer Book and the Caravan & Motorhome Book. For info more about the author Click on Bio.

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