shower flow rate/installation costs/regulations etc

paulmapp8306

bit of a long one this, with many "what ifs" but if you'll indulge me.

I have recently moved into a new house (for me) and plan to re-do the bathroom in the next few months. the issue is the shower.

the current electric one is OK, but the flow rate is terrible - though that doesn't surprise me. Its fed by a standard 6mm cable but the braker is only a 32 Amp one. That means the show is at most a 7.5KW shower - provided 240v rather than 230v was used for the calculation for the install. If it was 230v then its at most 7.2Kw.

The most economical shower to fit - and run to get the best flow rate would be either a 9KW (if 230v is used for calculations) or 9.5KW (if 240v used). Either required the braker to be uprated to 40Amp, BUT the 6mm cable will take the load (41 Amp directly clipped as it is - with the draws being 39.1 Amp for a 9KW shower using 230v, and 39.6 Amp for 9.5Kw using 240v). This means a lower running cost and no Part P required for the install as its minor works.

the other option is to uprate the cable to 10mm and the braker to 50 Amp (providing thats possible on my consumer board - which is a Wylex). This will allow for the most powerful shower available at present.

so - the conundrums.

1. Is 230v or 240v used for install calculations. 230v is obviously the current rated supply - but in practice its still 240v - with the nominal 230v coming from a compromise with the rest of the EU whos supply is actually 220v. Were all "rated" at 230v despite them still having 220v and us still 240v.

2. Would an electrician fir a 9.5Kw shower to existing 6mm cable (my instructor on my recent 17th edition course said most working electricians would, but wouldn't go higher).

3. How much better is the flow rate of a 10.5KW shower over a 9Kw shower - and how much better is a 9KW over my existing shower.

4. is my existing shower more likely a 7Kw or 7.5Kw.

5. How much is the cost of running 10mm cable and issuing Part P if I go that route. if it was shower alone it would be a big consideration - as its a complete bathroom re-fit Im guessing the extra cost isnt actually that great compared to the whole cost.

tlh858

1. 230v. However this is of no use, since the rating of most showers is that when they are used at 240v. In a house, the actual differences in calculations between 230 and 240 are largely irrelevant and can be ignored. You can't change the incoming voltage anyway.
2. Possibly, although changing the protective device for a circuit is NOT 'minor works' and would be notifiable anyway. Also note that 'minor works' is where a less detailed certificate is used for smaller jobs such as just adding a single socket - but even that could still be notifiable work.
3. Tiny difference, most people wouldn't even notice it had been changed.
4. It should be 7.5kw or less with a 32A circuit, but that doesn't stop idiots fitting higher rated items.
5. Depends on a variety of other factors.

Ultimately, you are wasting your time and money - all electric showers have poor flow rates, and they are worse in the winter, as the incoming water is cooler.

If replacing the whole bathroom, ditch the electric shower and get a proper one installed.

cajef

tlh858 wrote: »

all electric showers have poor flow rates

Rather a sweeping statement, we have just replaced a Triton electric shower with a Mira after a bathroom refit and have never had a problem with flow rates even in the depths of winter.

paulmapp8306

Ive been in forces rented for 15 years, and all without exception have used electric showers, not pumped power showers. they dont have the flow rate of power showers obviously - but in comparison the one we have at present is a trickle. The stream barely gets over the edge of the bath.

Ultimately, our boiler will need replacing in a year or 3, and well almost certainly end up with a sealed combi at that point (the only hot water we use is the odd bit of hot when cleaning the kitchen and a bath once a week, so heating a whole tank every day is really wasteful) - which means I couldnt fit a pump if I wanted too.

I dont however know what the pressure of the cold water is. i had a look and have a feeling it has not been fitted to a cold riser, but is being gravity fed from the water tank - which is barely 1 meter above the shower.

So - as for Part P stuff. If Im going to need one whatever happens as the CB needs uprating - am i as well having 10mm cable fitted regardless of what shower I actually fit? future proofing if you like.

Seriously thinking of a 50amp breaker and 10mm cable even if I only put a 9KW shower in.

Also, if the power rating of showers is at 240v, then a 9.5Kw shower is in fact - using 230v - only 9.1KW meaning I would only need a 40Amp breaker? so to get a 50 amp fitted Id need a 10Kw shower or over?