Advice sought on shower power supply

[jal]

Hello all,

Our shower is a Mira Sport, installed about 12(?) years ago, fed direct from the cold water supply. I *think* it is the 7.5KW model, though I cannot for the life of me find anywhere on case or in leaflet which model it is.

It's recently started squealing madly when we turn it on, so I'm thinking about replacing it with a more powerful one (in the hope that we'll get a stronger shower: something I've thought about for a while).

The cable is about 13mm across the width, which, from reading old posts in this group I take to be 6mm^2 / 10.5 KW (I'm afraid that means nothing to me); the RCD is 40amp; the run from CU to shower is approximately 11 meters.

I also saw the term "clipped direct" in the discussion, but couldn't work out what this meant (apart from the bleeding obvious). My cable is clipped to ceiling joists as far as the cavity wall, then it drops down the cavity for the rest of its run to the CU.

(1) Am I currently living with a fire hazard?

(2) If I replace the shower with a stronger one (say, the Mira Sport

9.0KW), I'd better replace the cable and the RCD, yes? What with?

TIA for any advice. John

[John Rumm]

It means you can fit a more powerful shower with the cable you currently have.

ITYM the MCB is 40A. 40A at a nominal 230V, suggests a 9kW shower would be ok. If you changed the MCB for a 45A then a 10kW shower would be ok.

It refers to how the cable is fixed. The current carrying capacity of a cable is dictated by how hot it can get before the insulation is damaged. Normally PVC clad cables have a maximum conductor temperature of 70 degrees C - so once this temperature is reached that dictates the maximum current. Needless to say any extra lagging on the cable will mean it reaches maximum temperature at a lower current.

So cables "clipped direct" i.e. run on the surface and fixed with cable clips, or for that matter buried in normal building materials like plaster will have the highest rating (47A for a 6mm^2 T&E. This sounds like what you have.

more detail here:

clipped to ceiling joists as far as the cavity wall, then it drops down

As long as you have not got the cavity filled with insulation then you can treat the cable as "clipped direct" or "method 1" as described in the wiring regs.

no, just a feeble shower.

9kW is ok on the existing MCB. If you want bigger than that then change it for a 45A one. No need to change the RCD at all (if you have one)