O.K., first of all this isn't one of my jobs -- I came upon this photo on one of my occasional trawls through a DIY forum for anything of interest.
Apparently the incoming feed which we can't quite see is 3-core SWA (armored) cable, so presumably this isolator was originally used to feed some sort of motor-driven equipment (delta connected, no neutral). The angle of the photo has completely hidden the red conductor entering the left-hand main.
At some point an enterprising DIYer has converted the old 3-ph feeder to single-phase and this is the result. New connections are now line on red, neutral on blue, earth/ground on yellow. The block top left which should be the neutral (if needed) is being used as an earth block, with one red
wire linked down to the proper earth terminal bottom right and another red
wire linking to the top of the central fuseway.
The left-hand T&E cable exiting at the top has its neutral (black) connected directly to the incoming neutral. The line (red) from the cable can be seen dropping down between the first and second fuseways, and although we can't see it any further, I would assume it's connected into the left-hand main so that this cable is not controlled by the switch.
According to the sparks who founds this during an inspection, all three fuse carriers were still fitted with 30A fuses.
I don't know whether the armor of the supply cable was still grounded or not. If so, then the central switch-pole and fuse would be bypassed, but if not, then we have not only a fused neutral but also a switched and fused earth!
I can't find the original thread in which this appeared, but I'll try again and post the link if I can locate it.
For our North American friends, here are some pics of a similar MEM isolator that I removed recently: https://www.electrical-contractor.net/PC/MEMiso1.JPG https://www.electrical-contractor.net/PC/MEMiso2.JPG https://www.electrical-contractor.net/PC/MEMiso3.JPG
And in case there is still any confusion about the colors, there are no new "harmonized" cables involved in this instance. The colors you would expect to find in a unit like this are:
Phase A = Red
Phase B = Yellow (or white if pre-1965)
Phase C = Blue
Neutral = Black
Ground = Green or green/yellow