Max Draw on 20A circuit

[molc]

The age old question, looking for an electricians input on code etc.

Assuming a 20A modern fuse with new wiring, what is the max draw. I've worked it out to 4500/240 = 18.75, but I'm considering other points of failure. I'm assuming that a domestic plug socket is only rated upto 10A, so you need to swap that with a high voltage socket. Assuming that, what diameter cable is then required from there to the fusebox to be safe? IS there other areas of weakness in a domestic circuit that would require wiring upto the main fuseboard?

The current setup is draw 2x 2kW elements on a single circuit, with different sockets and then a 2.5kW element on a separate circuit. There is a also a short window of time where all three could run concurrently, during the sparge, so say for 30 mins. However, I'd like to upgrade to 2x 4-4.5kW elements and run each off separate 20A circuits.

[neoanto]

The voltage in your house can dip as low as 220V, which would result in just over 20A for a 4.5kW load.
So if they were on the same fuse at the board that could be an issue.
Also the wiring might not be up for taking that kind of current for long periods of time.
Even a lower current than the 20A could break down the insulation in the wiring if it draws current for long enough.

I'm sure any electricians here could help you out more than me.
As usual, if in doubt get an electrician to help!