Electric Shower, Fuse and Cable?

busterjones

Hi -

Getting an electric shower installed. While I'm not doing it myself, I still wanted to understand what cable and fuse are needed and why.

We've a 3 phase supply. The shower is 9.8KW. Shower will be approx 5m from sub-board.

Should he be using 10mm and a 40 amp RCBO?

E.g. something like this: https://www.meteorelectrical.com/distribution-control/consumer-units-accessories-1/garo-rcbo-1-n-40a-char-b-6ka-type-a.html?IE&campaignid=17785162035&adgroupid=&keyword=&device=m&gclid=Cj0KCQiAmNeqBhD4ARIsADsYfTcSmy7RkNeZP_123UPmCStZHBpdhhXStkiw-STfmMIzjQEgwYG_VjIaAr7GEALw_wcB

Thanks!

kirk.

The 9.8kw might be the 240v wattage

Have you a link for the shower or a pic of the box showing the rating ?

2011

The fact that you have a 3 phase supply will not change the cabling or protective device. However what phase the shower is added to should be carefully considered so as to balance the phases as much as possible.

A 10 sq. cable would be suitable fed from a 40A B type RCBO with residual operating current of 30 mA.

They’re rated 9kW at 230V.

Bear in mind Irish voltage is historically the same as continental Europe, not the UK

We reclassified 220/380V as 230/400V, while they reclassified 240/415V as 230/400.

The shower manufacturers seem to slightly B/S the kW ratings, marketing them with the 240V rating as it looks bigger.

9kW is the rating at 230V so it’s a bit of a marketing and technical fudge tbh.

There’s always some degree of variation in supplies, with 230V +/-10% being acceptable, but UK supplies will often still deliver above 240V, and plenty of Irish and continental supplies will still very much centre around 220V. More recently installed transformers will aim at 230V however. Oddly NI always had 230V as its spec, so the entire EU and U.K. could be argued to have adopted NI’s old standard.

See this one for example: 9.8 with 9.0 in brackets.

https://www.plumbworld.co.uk/documents/mira-azora-98kw-electric-shower-installation-user-guide.pdf

Just to give the historical context

The UK actually adopted a standardised voltage very late. Until end of the 1960s it varied from 200 to 250V and there were regional and local differences. There was a lot of just laissez faire in the way things had developed and different electricity boards and companies had settled on slightly different norms.

You used to find old audio appliances and with sliding voltage selectors and TVs often had internal circuitry that could be adjusted by the installer. Why they didn’t adopt 220V is probably just island exceptionalism, and ultimately access to the single market in 1993 meant they caused the whole continent to have to do a compromised fudge to 230V.

In Ireland ESB simply adopted the most international standard of 220/380 50Hz in the 1920s, which was the most widespread standard in Northern Europe, and became the default across the continent. It would have given them access to off the shelf equipment much more easily. Those standards were driven by Siemens, AEG, ASEA and loads of companies across Northern Europe. The Brits and also the French (old 127V 50Hz pre WWII system) were outliers.

ESB also defaulted to Schuko plugs for a long time. There wasn’t really a competing harmonised British system to adopt - just a kludge of various sizes of round pin plugs & sockets, none of which were compatible with each other - you might have had large plugs in the kitchen, small ones in the living room, tiny ones in the bedroom and various old UK 2 pin pin types etc etc too. Ireland didn’t enforce a standard, and people didn’t really carry appliances around with them, so the old UK types appear here too. The modern UK system that got introduced after WWII was far more sensible, introduced a lot of safety features and we did adopt it.

kirk.

9kw/230v should be ok for 10sq and 40amp rcbo there

As 2011 said check supply capacity and balancing

Preferably fit a high-quality wall isolator if shower within 2m distance If not a quality pull-cord such as MK or Crabtree

2011

https://www.boards.ie/discussion/comment/121379511#Comment_121379511

Agreed. I generally select a switch with a 45 A rating (or higher) as it is more robust. I have seen many of these isolation switches fail. These will require a deep box (the deeper the better) as 10 mm sq. cables are difficult to bend. It can be a real struggle to screw the switch onto the box.

busterjones

Excuse my ignorance - but what is the gauge of cable in to the sub-board?

If less than 10, does that cause any concern for running a 9.8 KW shower out of the sub-board (with 40 amp rcbo)?

Here's a link to the shower itself: https://www.screwfix.ie/p/mira-elite-se-dual-white-chrome-9-8kw-silent-pumped-electric-shower/949JX?gad_source=1&gclid=CjwKCAiAu9yqBhBmEiwAHTx5p1XNOEvF6fewSgbw3vc9Onz6gGFk6agvREmprtvdueHWHxrsmVpMjBoCu4oQAvD_BwE&gclsrc=aw.ds

The existing mixer shower is fed from the attic so need a gravity fed shower and options are limited.

kirk.

You'll have to get a REC out and see what they say