The warning notices go along with my comments elsewhere about the IEE's views on anything over 250V.
If you go into a restroom here and it has two or more hot-air hand dryers, then you may well see a similar sign "Danger: 415V between" with arrows. That's a requirement if the dryers are on different phases and within arms reach of each other.
John,
The identification of circuits is often sadly lacking in the residential and small commercial environments in which I work. I often spend the first hour just tracing which fuse/MCB feeds what.
I did once see a medium sized shop, full of freezers, lighted display cabinets, and so on, in which somebody had painted the fronts of the sockets red, yellow, and blue!
