What sort of calculations did you have in mind? As I said, for most calculations the only safe approach is to utilise the 'worst case scenario' (i.e. the minimum or maximum permitted supply voltage, as appropriate).
Kind Regards, John
If the UK leaves the EU, will the nominal voltage be changed back to 240v?
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Kind Regards, John
I'm not sure that those two NOs are compatible, are they? - or are you perhaps suggesting that, by pure chance, at the very moment 'harmonisation' came into being the UK legislation "co-incidentally" changed to correspond with the transitional limits for the UK specified by the harmonisation?
Kind Regards, John
That's what one calls them. However, are you saying that the "12V" bears no relationship to the 'usual'/'expected' (or average, or whatever) voltage of such a battery.
Look at the distribution of voltages of "nominal 12V batteries" and see where 12V comes relative to that distribution. Then look at the distribution of "nominal 230V electricity supplies" supplied to UK installations and see where 230V comes relative to that distribution.
Kind Regards, John
The Electricity Supply (Amendment) (No. 2) Regulations 1994, coming into effect 1st January 1995:
http://www.legislation.gov.uk/uksi/1994/3021/contents/made
http://www.legislation.gov.uk/uksi/1994/3021/contents/made
You know perfectly well.
For a simple example a 10kW @ 240V quoted shower can be installed with a 40A MCB.
There's a big difference between winston and myself. Although it's undoubtedly closer to actual supply voltages in the UK, I do not think that 240V is any more appropriate a figure to use 'safely' for most calculations than is 230V, or any other arbitrary figure. Particularly if it's near the end of part of the network, even if the observed voltage is around 240V at a particular time of day, that in no way proves that it might not be <220V or >250V at some other time of day.
Kind Regards, John
And that's another example of the lowering of standards: At one time the regs. stipulated voltage drop within the installation to be no more than 2.5%.
Fair enough. Whatever, it's the same figure one would get by allowing for the BS7671 guidance of maximum 5% (of nominal) within-installation VD on top of a -10% (of nominal) supply tolerance.
Kind Regards, John
Although I confess that, like you and others, I do advise people on that basis, it is reg-compliant rather than necessarily 'safe'. When we tell someone that it is 'OK' to install a 10kW (at 240V) shower on a 40A MCB, for all we know the installation in question might have a voltage which hovers around 250V for much of the time, in which case that shower might draw around 43.4A in that particular installation.
This does illustrate the problem of arbitrary on-paper changes in 'nominal voltage'. Consider the situation the day before harmonisation (i.e. when nominal voltage was 240V). That shower (~41.67A at nominal 240V) would presumably not be regarded as acceptable/ compliant/ 'safe' on a 40A MCB. At midnight the nominal voltage becomes 230V, with obviously no actual change in supply voltage. Has that unacceptable/ non-compliant/ 'unsafe' 40A MCB then suddenly become acceptable/'safe' (even if now 'compliant') as a result on that on-paper change?
Kind Regards, John
Or - 'we' were unnecessarily cautious prior to the change.
Obviously there's a fair amount of leeway built into cable ratings, maximum loop impedance values etc. to allow for variations around the nominal values. Or at least there certainly used to be, so I would hope it's not been abandoned.
I still haven't unpacked my copy from last year's move in order to check, but if you look back at the 14th edition before 240V became the standard supply voltage, I seem to recall that for some calculations it said to use the tabulated figures for nominal supply voltages of 220 to 240 (or maybe it was 230 to 250, or even 220 to 250), and to apply an adjustment factor for supplies of other declared nominal voltages.
I still haven't unpacked my copy from last year's move in order to check, but if you look back at the 14th edition before 240V became the standard supply voltage, I seem to recall that for some calculations it said to use the tabulated figures for nominal supply voltages of 220 to 240 (or maybe it was 230 to 250, or even 220 to 250), and to apply an adjustment factor for supplies of other declared nominal voltages.
I think it's more a question of guessing/gambling than 'being cautious'. Of course, we all know that there are plenty of built-in 'safety margins', but we should not use that as an excuse for 'pushing' things, particularly not when advising others.
What would you say if someone came here proposing to run a 10.75 kW (at 240V) shower (~42.9A at 230V) on a 40A MCB?
If you would not be happy with that, how does it differ from your advising someone that a 10 kW (at 240V) shower would be OK on a 40A MCB, although you didn't know/realise that the OP's normal supply voltage was around 250V (shower current ~43.4A at 250V). Can an (arbitrarily calculated) 42.9A be less acceptable than a (possible) 43.4A?
Kind Regards, John
Towards the lower end, in both cases.
Yes, that's what one calls them. That's what "nominal" means.
The way you keep saying that it is a problem. Or wrong.
Whoops - my arithmetic went a bit awry there. However, I'm sure you understand my point, and I will correct the original post.
[I presume you mean 216V]
No - I did mean 240V - 6%
So that will be equipment which they could never have sold to countries with a nominal 220V supply.
According to the requirements it is not allowed.
It wasn't a proposal on my part.
That's how we are supposed to do it. If not, there should be a Cmax.
I do realise the point you are making.
It's not advice on my part.
That's how we are supposed to do it. If not, there should be a Cmax.
Are you saying 9.2kW @ 230V should not be on a 40A MCB?
I can but presume that the rules we are told to follow account for the possible increase, whereas a rating above the allowed would obviously be excessive should the same occur.