cable/kw

[bcafg1]

Ive been reading threads regarding shower cable size etc and have found differing opinion on certain areas regarding what kw shower can go on what cable.
Was led to believe 6mm cable would take up to a 8.5kw shower but a council plumber i know says they wouldnt go over 7.5kw. Just done a couple of bathrooms with an electrician who put an 8.5kw shower on 6mm cable. this was in a downstairs flat where the cable was run in conduit with other cable for around 8 metres. On another job i did with him he replaced a 7kw with a 7.5 kw shower on 6mm cable with a 30 amp wired fuse but no rcd (old wylex board) Are the two instances safe practice as information ive read on this site gives varying answers on what is right or wrong.

 

[luminaire]

As we now come under 17th edition of the wiring regs any cable now virtually has to be RCD protected. Good practice under 16th ed as well.
As to what size will depend on various rating factors, not least is if it will be enclosed in insulation.
As general rule of thumb, most electricians wouldn't consider using anything less than 10mm² because even it was for say an 8kW shower today, someone might want to upgrade it to a larger size later on, and save having to replace it all again at a later date.