Shower circuit design.

This is an interesting point, it comes back to the whole idea of standards for everything, and how these are made. BS7671 is in many ways good, it offers minimum standards for many areas of electrical installations, and these must all be different as very few situations are exactly the same. Without it, we would obviously find many “strange” installation practices, some of which would be decidedly unsafe, and no instructions as to how to criticise them.

I don't have easy access to the standards for switchgear, but the one thing I would expect to be absent is a requirement that all components come from a single manufacturer, which would make manufacture very difficult. Such does not apply to anything else I can think of, not planes ships, cars, or any piece of technology. They all have parts meeting particular standards, but none have this single source requirement, made by BS7671. Planes for example are type-tested, but many parts may come from more than one manufacturer.

It is also interesting that BS60898 does not appear to describe mechanical dimensions, and whilst all devices are superficially the same size there are subtle changes obviously designed to PREVENT mechanical interchangeability. This is the opposite of standardisation, and undoubtedly comes from manufacturers, as most standards do. I can see no reason for it, and the reason is far from clear, at least in Engineering terms.

This is an interesting point, it comes back to the whole idea of standards for everything, and how these are made. BS7671 is in many ways good, it offers minimum standards for many areas of electrical installations, and these must all be different as very few situations are exactly the same. Without it, we would obviously find many “strange” installation practices, some of which would be decidedly unsafe, and no instructions as to how to criticise them.

I don't have easy access to the standards for switchgear, but the one thing I would expect to be absent is a requirement that all components come from a single manufacturer, which would make manufacture very difficult. Such does not apply to anything else I can think of, not planes ships, cars, or any piece of technology. They all have parts meeting particular standards, but none have this single source requirement, made by BS7671. Planes for example are type-tested, but many parts may come from more than one manufacturer.

It is also interesting that BS60898 does not appear to describe mechanical dimensions, and whilst all devices are superficially the same size there are subtle changes obviously designed to PREVENT mechanical interchangeability. This is the opposite of standardisation, and undoubtedly comes from manufacturers, as most standards do. I can see no reason for it, and the reason is far from clear, at least in Engineering terms.