shower confusion

Hi All

i know this is probably in old threads somewhere but i can't find what i'm looking for so appologies if this is boring basics for most. i was under the impression that all showers circuits should be 10mm cable and 45 amp MCB (or 50 amp if over 10.3 kw) I am now questioning this because our new/first house is supposed to have been rewired professionally about 10 years ago and the circuit is

6mm cable with 32 amp MCB (shower is either 7.5 or 8.5 KW. not sure which as model came in 2 powers and label no longer on shower unit). This came to light because i want to replace the battered old wall mounted shower switch located in hallway outside bathroom. Questions are:

1) are cable and mcb ok / comply as they stand?

2) if existing set up is ok but i replaced the shower in future, what would be the maximum kw rating i could fit while retaining 6mm cable?

3) can i double check that wall mounted shower switches are still ok provided they are located outside the bathroom, or will i have to replace with a pull cord switch?

4) am i correct in saying that the amp rating of the new switch i'm fitting should match that of the mcb? (in this case 32 amp, again assuming existing set up is ok)

Thanks in advance for any help and taking the time to read this lot!

Not necessarily...

Without having full details like the length of the cable run and whether there are any factors that would de-rate its current carrying capacity (like runs through insulation etc), one can't answer for certain.

However if you took the 7.5kW shower, that would have a current rating of 7500/240 = 31.25A which is fine on both cable and MCB in most circumstances. Being realistic, even the 8.5kW would be unlikely to trip a 32A MCB, and the cable is unlikely to be overloaded in most circumstances.

The best case current rating for 6mm^2 is about 47A

See column C here:

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the total length is short enough to limit the voltage drop to reasonable limits, that would allow a maximum rating of over 11kW.

Outside the bathroom, a wall mounted switch is fine. Inside a switch needs to be appropriate for the location and zone. There are cases where a wall mounted switch in the room would be ok.

The switch needs to be capable of switching the full load current - it does not have to match exactly in that it can be larger. A 45A switch would be fine for example.