That was quick.
Edited previous post - 42.5A @ 250V but we have to use 230 so ok.
Edited previous post - 42.5A @ 250V but we have to use 230 so ok.
Shower upgrade, MCB rating?
- Thread starter lasors
- Start date
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I was referring to the calculation based on 9.8Kw, which doesn't drop below 40A. When doing your calcs, you can't round down to fit.
When you said
I was interested to know what you thought the current was at 230v, as you thought it was not suitable for a 40A MCB
The original post quoted 9.8KW.
You used 240 and got 40.8A. Using 230 gives 42.6A.
Both are over 40A, so you can't use that size MCB.
The manufacturer gives the option of 9.8KW @240 or 9KW @230.
This does get below the 40A, but the MI states a 45A minimum size.
You used 240 and got 40.8A. Using 230 gives 42.6A.
Both are over 40A, so you can't use that size MCB.
The manufacturer gives the option of 9.8KW @240 or 9KW @230.
This does get below the 40A, but the MI states a 45A minimum size.
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This is not a difficult maths problem.
9800 / 240 = 40.83A 9800 / 230 = 42.61A Both of these are > 40A.
You can't just ignore the 'bit' over 40A.
Reducing the voltage increases the current drawn.
I am not referring to the manufacturer quoting 9KW at 230V.
Not in a purely resistive load which will not change impedance depending on the voltage applied to it. The impedance / resistance will increase by a percent or two as its operating temperature rises but for calculation purposes it can be considered as constant for all applied voltages when calculating current through it.
Nor is it difficult to grasp that if a shower draws 40.83A at 240V it will not draw 43.61A at 230V.
Or at least it shouldn't be.
No.
No.
No.
FFS.
Call yourself a spark? Please give it up, you haven't the aptitude for it.
No.
Because you don't have the faintest idea why he does that, do you.
I was trying to keep it simple for the sake of the OP. I am fully aware of Ohms' law and it's application, so the 9KW@230 is not actually a mystery.
The original values stated as 9.8KW@240V give a value in excess of 40A, so it's not okay to say go with 40A as it's only a bit over. That was all I was trying to get across.
The manufacturer has stated he should have a 45A breaker, as they err on the side of caution.
Cheers for the vote of confidence BAS, hope your armchair is nice and comfortable.
The original values stated as 9.8KW@240V give a value in excess of 40A, so it's not okay to say go with 40A as it's only a bit over. That was all I was trying to get across.
The manufacturer has stated he should have a 45A breaker, as they err on the side of caution.
Cheers for the vote of confidence BAS, hope your armchair is nice and comfortable.
How on earth is "Reducing the voltage increases the current drawn" keeping it simple for the OP?
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.
Since I am now faced with a similar situation to the OP in that I am fitting a Mira Shower for a customer who currently has a 40Amp MCB I thought I would give Mira technical a ring.
This is what they expect 'Part P' electricians to do when fitting their showers.
Firstly, they no longer give guidance on the size of the cable required because of a lack of knowledge of local conditions - fair enough.
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.
The 230/240v kw and MCB ratings are for guidance only.
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 did mention that there is no such thing as a Part P electrician and tried to explain the competent persons scheme - but this flew over their heads.
IEE Wiring regulations were also mentioned - not really their concern - they followed the BEAB Approved mark scheme.
This is what they expect 'Part P' electricians to do when fitting their showers.
Firstly, they no longer give guidance on the size of the cable required because of a lack of knowledge of local conditions - fair enough.
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.
The 230/240v kw and MCB ratings are for guidance only.
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 did mention that there is no such thing as a Part P electrician and tried to explain the competent persons scheme - but this flew over their heads.
IEE Wiring regulations were also mentioned - not really their concern - they followed the BEAB Approved mark scheme.
And bas is trying to say that noone with a clue about electrics and dealing with a resistive load would do that.
I'm not a fan of what bas's recent behvaiour and if I was a moderator he would have been warned multiple times and probablly banned by now but in this case he is right.
S0 - now the hallowed MIs are for guidance only.
In that case as we have to use a nominal voltage of 230, then a 40A mcb will be sufficient.
Increases in voltage are obviously taken into consideration in the values of CCC and mcb.
FFS I missed the post where lasors referred to the 9Kw figure and went on to post the worst example of electrical nonsense ever seen in the history of electrical installation. I got it wrong.
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