I work on the Underground. Mostly done metal work conduit trunking tray ladder rack. Only recently out of my time. Believe it or not I have my inspection and testing qualification aswell. But just not done much of it that’s all.I don't wish to be harsh, and I'll happily admit to having many gaps in my knowledge and experience, but I was wondering what area of electrical work you work in as you seem to have some slightly skewed ideas regarding OCPD's (or lack of) and RCD's providing additional protection.