Zoltrix77
Member
4mm is probably fine.
I've seen conflicting reports about the breaker size. There is definitely a rule in the US where breakers need to be oversized by 20%, but despite numerous people saying the same in Australia, I haven't seen any documented proof of such a requirement. My electrician also installed mine with a 32A breaker, and I have been charging for about a year without issue.
An undersized breaker shouldn't cause any safety issues as it will just trip earlier.
Disclaimer: Not an electrician, don't use anything I say as advice.
4mm2 is probably fine depends of how the cable is installed, in a wiring enlcosure (eg conduit), v75 TPS at 40C is only good for 30A, and thats without any kind of derating for multiple circuits etc. In a continual load situation like this, I would definately use 6mm2 even just for voltage drop regardless of distance. 6mm2 TPS in a wiring elcosure is rated at 38A, again without any kind of derating, so I would stick with a 32A RCBO, even at 32A continual, I wouldn't expect the RCO to trip. It just doesn't cost that much extra to have peice of mind.
Your right, no such rule on oversized breakers.