Thank you everyone! My dayjob and loadshedding kept me from replying sooner.

All of you basically confirmed my suspicions that all is not right. In particular, there is a lack of overload protection. I don't really trust the MCB's tripping-ability any more, since they are as old as the previous ELCB (at least 40 years old), which was old enough to not work correctly anymore. So the MCB's may or may not work.

So as a minimum (as I suspected) it appears the MCB's need replacement and a circuit breaker needs to be installed in the meterbox (our own, not the municipal box). A proper investigation will probably reveal more.