My guess would be that South Africa has uprated them to 16A to line up with the emerging common European standard (the "Schuko" plug common throughout the Continent is rated 16A).
As I have mentioned in another thread, our standard 5, 15 and 30A circuit-breakers have been changed to 6, 16 and 32A in line with this.
The 15A round-pin plug is considered obsolete by the technical committees here, so they probably saw no need to change it, but as it's still the current standard in the RSA I guess they decided to change the rating.
What's SABS? South African British Standards???
On the immersion heater, just about all U.K. domestic types are rated 3kW and run on a 15A (or 16A these days!) branch circuit -- 3000/240 = 12.5 amps.
I've seen many installations dating from around the 1950s where the heater was plug-&-cord connected, but it's rare to find it in a house only 20 years old. As far as the "Regs" go, it's fine so long as the outlet supplying the heater is on its own dedicated circuit and not wired into a general-purpose ring. (A small oversink heater can be on the ring, but a 3kW immersion heater is considered a continuous load and needs its own circuit.)
The only possible problem I can see with the plug-&-cord arrangement would be if the cylinder is located in the ubiquitous airing cupboard with its access door inside the bathroom. You could then get into an argument as to whether it violates the rule about no sockets in a bathroom, and whether being inside the cupboard constitutes being inside the bathroom or not.
The most common problem I see with immersion heater wiring is where somebody has just run the "twin & earth" (NM-style cable) straight into the heater, instead of changing to heat-resistant flex for the final connection.
I know that by law now any residential – non-lighting - outlet rated 13A or less must use the square pin, fused variety.
I'm not aware of any such law, although the rate new rules are being introduced these days I wouldn't be surprised!
But even if the IEE Regs. stopped recognizing the old-style BS546 outlets, that in itself would not make it illegal to install them because there is no legal requirement to follow the Regs. in domestic installations.
Note that this is England & Wales. As I'm sure you're aware, Scottish law sometimes differs from that here and I know that for many years the Scottish
Building Regulations have specified that electrical installations must be in accordance with IEE Regs. Whether they have also added any other specific requirements, I don't know. (Strange, but although I've been halfway across America and around Western Europe, I've never been to Scotland!)
