Actual KW Rating of Electric Shower

I must admit my figures don't actually add up, as you've shown.  Perhaps it's not true after all.

In the UK, the declared voltage and tolerance for an electricity supply is 230 volts -6%, +10%. This gives an allowed voltage range of 216.2 volts to 253.0 volts. Sensible then for makers to opt for a 240V rating.

Jaymack

Simon, just because as said I`d never heard of it does not mean I think you are wrong, it just means I had not heard of it. I wonder if we try the 230V notational voltage and compare with 240ish actual UK voltage we get something nearer. 

All I did originally was to get my plastic brain out (well one of apprenticeship teachers call the calculators "plastic brains"  240/220  = the XX= then X= to do the sums (hope a few of you have checked my figures) so lets think OK we will start with 230 declared volts and compare with 240 actual volts and see what happens.

6 becomes 6.53

7 becomes 7.62

8 becomes 8.71

9 becomes 9.80

10 becomes 10.89

That is starting to look near to what you said.

I think I seem to remember when voltage (APPARENTLY) changed some took exception and kicked up a fuss that if 230v is the declared voltage then the KW at the declared voltage should be the one advertised on the package etc.

Then I think some of them also added the figures at 240 real volts for UK showers in slightly smaller letters in an attempt to fight off Trading Standards criticisms etc whilst still claiming some degree of correctness and to not let the showers look like they had become less powerful either. They might have even argued that some European countries should also show a 220V KW rating but I doubt that would be successful.

I can easily visualise some EU manufacturers getting on a high horse and being pedantic about quoting harmonised figures and not letting the UK products  look "better"

I doubt the 220V theory - most of the 220V world doesn't do 100A or even 60A domestic supplies - so things as big as instantaneous electric showers simply aren't going to sell. France for instance usually has a 30A or 45A single phase supply to a home. In Germany 32A-3-phase might be more common so in theory you could do it by spreading across two or three phases (as is commonly done with electric hobs) but I've never seen the option on a shower.

Also the continentals have been using pressurized hot water cylinders for generations - so no problem getting a decent shower from the normal hot water system - unlike the open vented system traditional in the UK - so no need to use the rising main to get enough pressure. In most of the 220V world if you want an electrically heated shower, you'd just use an immersion.

    - Andy.

AJJewsbury said:

unlike the open vented system traditional in the UK

Traditional, may be, but new builds don't have room for the header tanks.

I did eventually get a response to my email from a major manufacturer . Basically it looks like a printed spec probably given in one of their manuals. It gives the given KW at 240V and shows a comparison of a lower KW rating at 230V.

personally, I have no objection to them stating a KW in a product in the UK market being as per our "real" voltage but I do understand the more pedantic taking the view that it must be stated at the harmonised voltage. Showing both and knowing what is what it also gives us a chance  of interpolating for any slightly differing actual voltages we may be working with in practice, to a degree at least.

So, in this case, the stated KW on the box is if you have a (UK) 240V. Same as it was before we redeclared the value for the sake of harmony with Europe

Well on the very new housing estate near us it really is 235 falling to 230 or 220 something at low point, while where I live (late 60s to 1970 built) the original transformers are still going strong and give ~ 250V in the middle of the night, and 240-245 during the day.  So it may be that post harmonisation the transformer out of the box default taps are not quite the same voltages. But as the transformers last for many decades, and at least half a century, it will be a good while before they are all wound down to the new voltage, if at all.

And in the town centre all the pre-war TT overhead fed houses  are still getting more or less 240.

Mike.

That's to save energy.