We also see locs made out of a shiny unpainted material, stainless steel I assume, with louvred doors as mentioned above. Some also have a second top above the main one, presumably so that can take the heat from the sun without conducting it through to the inside of the cabinet.
In the area where I worked, there are various designs / types of location cupboard.
Western Region originally used silver paint for signal posts, with matt black paint for the top where the arm or the signal head was. This was for visibility reasons. So the S&T location cupboards and dis-boxes were also painted silver with the top being painted matt black.
The location cupboard came in three sizes, I can't remember the official name for the small one, or the middle sized ones ("medium narrow" maybe), but the type used for most late 1960s and 1970s MAS signalling schemes was the "large" size.
The later versions of these, the medium and large sizes did include various vents to allow some air flow.
This was fine for location cupboards that only housed cables, transformers and relays. But it was found to be unsuitable for cupboards that contained ASTER track circuit transmitter or receiver modules (audio frequency track circuits and hence the modules use electronic circuitry). Hence instead the painting teams painted the whole thing silver.
Even then, on a hot sunny summer day, you could fry an egg on the top of a cupboard that had equipment in it... As an S&T technician, you quickly learnt not to lean on them with your bare arm!
At one stage, special heat reflective paint was tried.
Note that the original Western Region location cupboards are actually made of a wood frame, then horizontal wood planks forming a backboard. Then galvanised sheet steel was formed to form the outer shell.
The original doors (which lift off) also used galvanised sheet steel, but were very heavy, so a lighter metal was used instead (I don't know what).
BR did come up with a standard design, in two sizes: "half width" (single door each side) and "full width" (double doors each side). These were made of mild steel and painted grey.
The basic design has changed slightly over the years.
These are still made as far as I know, but there are now some other designs. They look similar but there are some differences. It may be because a different manufacturer makes them.
Similarly, the grey colour paint is a lighter shade on some compared to others.
Sometimes S&T equipment used stainless steel cases. The GWML ATP scheme used stainless steel cases that were never painted.
In places, you will see stainless steel cases that houses the 650V power distribution equipment for the signalling. These are now the responsibility of the sparks (railway electricians). But in other places, they use the same cases/cupboards as the S&T.
The new signalling controlled by TVSC that was installed in the former Swindon and Bristol PSB areas used the standard location cases, but many do have the "extra" roof.
Even so, at one place (near Bristol Parkway), we did experience heat related issues in a location case that did not have the extra roof on it. So my colleagues had to fit an extra roof to it.
