Replacement Shower

Firstly you need to differentiate between 'to' , 'too' and' 'two'.
Once done you need to get a good sparks in (not plumbers who have no idea about lecktrickery)
The highly skilled and experienced, handsome, sparks will assess the situation and advise you accordingly as to what is allowable and safe.
RS

 

No probs Cwm....
RS

 

Hmmmm if the cable is say 5 meters long and clipped direct then 6mm would be in....however it does look like 10mm is indicated. If you could say how long the cable is from db to shower, and how it is run (clipped direct, covered with insulation etc etc) then a more accurate assumption as to whether the 6mm is ok would be forthcoming op.

The Crabtree DB - is it a split load Starbreaker? and is the mcb on the rcd protected side if it is op?

 

Starting with the CB, 40A, using a supply voltage of 230v, the current drawn by a 9.5kW shower is a little over 39A, so the breaker is big enough.
That's the easy bit, now for the cable. Clipped direct with no de rating due to ambient or insulation, 6mm will be protected by the 40A CB, BUT we do not know the length of run and we have assumed no de rating or disconnection time calcs.
Most contributors will agree that 6mm is on the 'edge' of being too small, ie it may be OK, or it may not. It needs a qualified spark to check this BEFORE you buy the shower as it may be that a 9.0 kW shower will be OK on your cable but a 9.5 may not.

 

In reality the 6mm2 cable will be okay. The calculations would show a 10mm2 is required.

 

Bob, you need a new calculator. 9.5Kw @ 230v is 41.3amp.
Shower makers tend to quote their shower power ratings not at the nominal 230v figure. Your actual supply voltage is probably more like 240v.

But even being a tad over the actual rating, a 40A MCB will last a lot longer than a 16-year teenager's shower.

So existing circuit and MCB will be fine.

 

Concur with Bazz - run at 3 meters and as above, the 6mm will be ok - not much headroom but its in. Happy days for the op.
Must admit admit in all calcs use 230v ..why? because regulation calcs say you have to use that figure..makes sense actually.

 

When I did my 236 course, a thousand years ago, they always set the cable call examples on the edge. A bit like this one.
I would be asking for a severe ear-bashing (or exam fail) if I allowed ib to be bigger than in.