Here is the scenario: you climb in the roof and it is wired in pvc cleated wiring running into metal downpipes.
The older installation has earth wires attached to the exposed portion of the metal downpipes, in the roof.
On the older installation there are no earth wires running down into the pipes, to the light switches or plugs.
There have been some additional plugs and lights and they have been wired using pvc pipe and pvc wires which are tapped of the older installation.
The new additions have all got the required earthing which is also tapped of the older installation
SANS says "If an existing
installation is extended or altered, such extension or alteration has to comply
with the provisions of this part of SANS 10142 that were applicable at the
time of the erection of the extension or alteration."
I take this to mean that only the new portion of the circuit has to comply with the latest regs.
In a recent statement in the media it was said that "changing a plug socket or light switch does not constitute an alteration therefore you must not upgrade the older installation when changing a plug socket or light switch."
In my given example if you change a plugsocket or light switch then you must upgrade the effected circuit to the latest regs because the new sockets and light switches have different requirements to the older ones. For example the new plugs need an earth wire connection, and connecting a wire from the earthing terminal to a screw on the metal housing is "using the pipework as an earth continuity path" which is no longer legal.
Another thing is, by installing the new plugs an earth leakage now has to be added to the circuit. After that is done EVERY plug has to have an earth wire as required by the earth leakage.