Mira Jump Shower / Cable Size Correct?

13 Oct 2020
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United Kingdom
Hoping for some sound info on cabling for a Mira shower.

About nine years back we had a professionally revamped bathroom installation.
A Mira Sprint 9.5 kW electric shower was installed along with the appropriate isolation switch (string pull) and a RCD box to replace ye olde 1970s fuse box.

This shower unit packed up last year and we had a Mira engineer install a Mira Jump 9.5 kW unit in place (the Sprint we had having been discontinued and no longer available). We did explore the possibility of upgrading to a 10.5 kW unit but apparently that was off the table as our water pressure couldn't quite meet the prerequisite pressure.

Anyhow ... a few months back we noticed water had leaked behind the shower tiles. It had obviously been going on for quite some time as mould had developed. We had to pull the entire shower fixture, remove a lot of tiling, and chop out extensive plasterwork. The walls behind are drying as I type.

We've gone off the idea of a tiled cubicle that can leak into walls and want to switch to an enclosed pod quadrant. We want to continue using the Mira Jump unit and swap it over to the new pod.

The existing wiring has been chased into the wall. The only modification we planned to make is a longer length of cable from the switch to the unit in the shower pod.

The existing wiring is 6mm twin core + earth (for cookers and showers)
The RCD in this application is an MK B40
The shower is located on the other side of the wall to the RCD box (in the garage, so quite a short run of cable).

My question is should the cabling have been 10mm originally and ought we to change it whilst it is exposed? I only ask as some have said it ought to be 10mm for this unit.

I'm in two minds as to whether it needs to be. We already know the shower cannot be upgraded to a 10 kW electric shower as our cold water pressure cannot quite match the prerequisites. So future-proofing isn't really a consideration here.

The existing wire is all in excellent condition and as far as I can recall the RCD for the shower has never tripped in the nine years we've had a Mira - and we have really long showers. No electrical issues at all.

As I said this was a professionally installed package so I would assume moving the shower unit a few meters should just require me having a longer piece of 6mm cabling installed from the switch to unit side.

Am I right?
Thanks in advance.


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