These plastic covers served one primary purpose - to prevent molten metal spraying out of the fusebox when a fuse fails.
This example is made from cream coloured plastic. On the inside view, the black mark near the fixing screw is where a fuse has failed, burning the cover.
The interior has space to indicate the purpose of each circuit. In many installations this was not done, resulting in the homeowner having to remove several fuses in order to locate a blown one.
These covers are typically lost or broken, with the fuses being exposed in full view. This also leaves a sizeable gap around the edges of the fuseholders, with live parts just inside the gap.
The fusewire is easy to replace, provided people know how to do it. The correct installation method is shown here.
The wire passes through the centre ceramic section, and is secured at each end under the brass screw. The wire must be wrapped clockwise around each screw, otherwise the wire will loosen as the screw is tightened.
Unfortunately, such a simple procedure is completely overlooked by some people, with the results including fusewire outside of the ceramic section, randomly twisted around the brass pins, or replaced with any old piece of wire which happened to by lying around.
A plastic shield is required, which both covers the live busbar and serves to identify the rating of fuse which can be inserted. The most popular types were 5A white, 15A blue and 30A red. There was a 20A model which was yellow, although this was uncommon, and cards of fusewire sold in hardware shops did not usually include 20A wire.
Higher fuse ratings were available, but they were enclosed cartridge fuses. Ratings above 30A could only be fitted to a few specific models, which were generally metalclad and had one or more completely separate ways for high current circuits.
The holes in the plastic shield are slightly different for each rating, to prevent the wrong fuse being inserted.
Pictures here show the older type shield with a painted edge, and the newer type where the whole shield is made from coloured plastic. Both are blue 15A types.
The small recess in the centre of the shield was sometimes fitted with a small asbestos or other pad, to absorb some of the energy released when the fuse fails.
The older type fuseboxes were completely open at the back - just a wooden frame with the switch and busbars screwed to it. The backplate was a separate item, with the result that most installations did not include one.
Pictures show the backplate, and a 6 way wooden fusebox with the backplate behind. The plate is slightly shorter than the box, to allow a space for cables to enter without cutting the plate.
The vast majority of these fuseboxes are rated to 30A per way, and in many instances only 60A for the whole box. Of course this does not stop people connecting completely imappropriate loads to them.
In this instance, someone had connected a 9.5kW electric shower, which has a load current of nearly 40A. The fusewire had been replaced with a much thicker piece of wire, probably because the original 30A wire failed on a regular basis.
The fuse has overheated, causing damage to the contacts. This would have got much worse over time, as the continual overheating will weaken the metal and result in a loose connection.
