Dave, what is your recommendation for protecting this fuse please? We don't seem to have a consensus view on this thread. I assume / hope that failure of the main fuse is rare. Cain's experience sounds alarming!
I don't think there can be one size fits all answer to fuse issues Tom. This due to variation on location of main fuse if one is fitted at all. All the latest cars have this fuse located close to the battery which makes sense as it offers protection to the cable as a whole. Ironic that there is a similar cable direct to starter with no fuse at all, although this is the norm. Fusing for the stater circuit would require a very large fuse in the order of 100's of amps and add unreliability. Fortunately the physical size hence rigidity and thickness of insulation on such cables, together with care in routing makes them less vulnerable.
It should be noted that only in the past few decades battery located fuses were added to cars in general. The fuse is there to protect the cable and attached equipment assuming as with most, they don't have their own internal fuse.
Careful routing and physical protection of cables is just as important as fusing them. Interesting to note my 55 year old Land Rover managed with just two 30 amp fuses and still retains the original loom although past its sell by date
Since the 90's most cars use blade type fuses which come in a range of physical sizes. Current Morgans use the mini
type with the exception of the maxi
battery fuse. Although blade fuses fair better long term than the various earlier types, they do benefit from simply being removed and replaced as the method of contact offers a self cleaning action. If the fuse slides in too easily its socket is worn or damaged. It may be possible to very carefully bend the socket contacts but otherwise replacement required. Dave's issue mentioned above springs to mind.
Finally be wary of squirting any product in the direction of fuse contacts if it has insulating properties.