The table Bluejets quoted above is correct according to International (IEE Regulations) & UK standards.dunroaming wrote: ↑August 23, 2020, 2:34 pmSo other countries have their own standards of safety regulations and don't actually follow the SAA requirements, always been told it's better to be safe than sorry and the difference in price between 4mm and 6 mm is minimal. Sorry forgot to mention I'm an electrical procurement professional with 35 years experience and have never seen 4 mm used for water heaters or showers but you live and learn.
The original question was about Earthing for hot water showers.
It totally depends on the size of the water heater/shower.
Some are 4Kw some 6Kw and even 8kw.
The earth wire only carries fault current for milli seconds if you have the correct sized Circuit Breaker installed.
The cable supplying the heater is rated for continuous current not fault current.
If you buy 4mm cable Twin & Earth the earth conductor is 2.5 mm.
If you buy 6mm twin & Earth the earth conductor is still 2.5mm .
If you want to buy 3 core cable (for 3 phase circuits). you are wasting your money
.
This is an International Standard not just Australia.