Actual KW Rating of Electric Shower

There's a reason why all the showers sold in the UK have power ratings ending in ".5": 7.5, 8.5, 9.5 or 10.5kW.  They are using elements rated at 7, 8, 9 or 10kW at 220V, recalculating the draw when connected to 240V, and rounding it to the nearest 0.5kW.

I must admit I`d never heard that one before. Never considered it. I was perhaps in Middle Britain mode. Anyone else heard that ?

7 becomes 8.33,

8 becomes 9.52,

9 becomes 10.71,

10 becomes 11.9,

therefore rounded gives 8.5, 9.5, 10.5, and 12 ? 

Now that is interesting.

I bet the tolerances beggar that up quite a bit and, perhaps to a small extent though, the new running temperatures from those extra KWs tweek it a bit too!

I must admit I`d never heard that one before. Never considered it. I was perhaps in Middle Britain mode. Anyone else heard that ?

7 becomes 8.33,

8 becomes 9.52,

9 becomes 10.71,

10 becomes 11.9,

therefore rounded gives 8.5, 9.5, 10.5, and 12 ? 

Now that is interesting.

I bet the tolerances beggar that up quite a bit and, perhaps to a small extent though, the new running temperatures from those extra KWs tweek it a bit too!

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

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.