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 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.
Pressing the larger button closes the circuit. The smaller red button below will release the large one, opening the circuit and disconnecting power.
The small red buttons are very easy to accidentally press, such as where items have been hung up above the fusebox or the understairs cupboard where these were often located is stuffed out with unwanted junk. The transparent plastic cover will prevent this problem, however these covers were rarely used.
From left to right, the larger image shows a blanking plate, two white 5 amp MCBs, two red 30A MCBs and a green 45A MCB.
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.
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.
Note the different construction of the terminals in the rightmost position, with the metal being substantially thicker, and a separate contact spring screwed to the terminal block.
The brown plastic backplate has a small cutout to the right of the top terminal. The fuse shield had a corresponding tab which fitted into this hole - this was intended to prevent the larger size shield being fitted into the other positions. Unfortunately the tab was easily broken off by people who thought it appropriate to shove a 45A device into another position, or even fit two of them into the same fusebox.
In some boxes, the 45A way was totally separate, and located on the other side of the main switch. These high rated circuits were intended for large cookers or submains to other fuseboxes.