Shower upgrade, MCB rating?

[zorgan]

I'm not a fan of what bas's recent behaviour and if I was a moderator he would have been warned multiple times and probably banned by now

BAS you have absolutely no tact whatsoever when talking to people, what kind of response do you expect from a guy when your shouting in big red ink NO NO NO

 

[ban-all-sheds]

It doesn't and it's a poor choice of wording. I was only trying to show that taking 9.8 as the starting point, dividing by 230 is going to increase the figure.

OK - so how does telling the OP to use the same power rating at 230V as 240V keep it simple for him?

 

[ban-all-sheds]

Firstly, they no longer give guidance on the size of the cable required because of a lack of knowledge of local conditions - fair enough.

They could easily quote a minimum adjusted CCC.

Although not mentioned in the installation instructions they expect the 'Part P' electrician to take voltage reading of the installation and use this to calculate the size of the MCB/cable size.

Interesting.

Using what data for power or load resistance to do that, I wonder?

The 230/240v kw and MCB ratings are for guidance only.

That's OK - anybody who is competent to design and install the circuit will know what voltage he's supposed to use for the calculations.

In the scenario the OP has outlined, their view is that you go up (definitely not down) to the next available MCB size - which in this case is 50Amp - and this variation in the manufacturers instructions will not invalidate the shower guarantee.

I thought that they didn't have "instructions", only "guidance"?

Hello all,
We're upgrading our shower from an 7.8kW to a 9kW (@230v). Consumer unit currently uses a 40A Crabtree MCB (61/B40) and wiring is 10mm with no more than a 6m run, surface clipped.

and that no breaker rating was specified in the MI.

Uo is 230V. I don't care what the supply voltage actually is when measured, nor does it matter for its upper bound is no higher than it always was (actually slightly less).

So, in the postulated scenario we would be replacing a 34A load with a 39A one, and everybody would have been happy with the 40A breaker, and this topic would have been finished on page 1.

The shower would be the same item, with the same potential current draw of 43A (which is below I1 for a B40 ).

Nobody would have said "Oh no - you have to work out what the current draw would be at a higher voltage".

 

[scousespark]

It doesn't and it's a poor choice of wording. I was only trying to show that taking 9.8 as the starting point, dividing by 230 is going to increase the figure.

OK - so how does telling the OP to use the same power rating at 230V as 240V keep it simple for him?

What exactly do you want? I have admitted I was wrong. Have I done something to offend you in some way?