David,
Seeing you’re a Scottish electrician, I wonder if you could answer a Scottish inquiry. My brother-in-law’s house in Glenfarg, Perthshire has an immersion heater in a closet off the landing which uses an old round-pin 15A plug as a disconnect. The house must be around 1970’s vintage. Is this normal as the set-ups I’ve known in England and South Africa are hard-wired into a double-pole isolator?
What struck me as unusual in this case was that South African immersion heaters that I am familiar with are on dedicated 30A circuits which would exceed the capacity of this connector. PaulUK said that standard UK heaters pulled about 13A. Sorry for being so far off-topic!
