It would be interesting to watch (from a bit of a distance) someone using an instrument which created a fault and actually measured the current flowing.
Here's such an instrument being calibrated:
Is moving a light switch in the kitchen allowed/notifiable?
- Thread starter acmedone
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Here's such an instrument being calibrated:
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Indeed - if you hunt out that old thread you'll see that we eventually did discover that at the time. However, IIRC, it was a slightly different type of question - in as much as my interest was in whether the 5% and 3% limits were percentages of the nominal or actual voltage. Even before we found the answer in the (then) BRB, it was pointed out that it would be unworkable for it to be anything other than U0, since whether or not one's VD was compliant could otherwise depend on when one measured the voltage.
As I think I pointed out at the time, they could have avoided that potential confusion by simply stating the VD limits as 11.5V and 6.9V, rather than as 'percentages of 230V'.
As often seems to happen to me here, I am being accused of 'wanting' something ('wanting the regs to say something') when, in fact, I simply introduced a genuine question to which I did not know the answer. A couple of pages back, I wrote:
I obviously do not want, and would not suggest, anything which resulted in figures, and hence potentially compliance/non-compliance, to vary from day to day, according to the prevailing supply voltage. That would obviously be crazy.
However, I can see an argument that, for some purposes, it might make sense to apply normal engineering 'safety' principles and look at worst (or, at least, 'bad') case scenarios. In the case of determining circuit design currents, particularly for fixed loads, that would mean considering the maximum possible supply voltage. For example, I cannot remember ever having seen a supply voltage less than 245V (rarely much less than 247V, and often nearer 250V) in this house. That means that, if I calculate the design current on the assumption of a 230V supply, the answers I get will nearly always be of the order of roughly (assuming linearity, which won't be quite the case) 6.5% to 8.7% less than the actual currents. Hence, if the current estimated for a 230V supply was 30A, the actual current would nearly always be in the range 32A - 32.6A. That's a fairly small, but not insignificant difference. If I told you that I had a cable whose design current was 'only 8.7% above the cables rated maximum CCC' I don't think you would accept that as compliant, and might even describe it as 'potentially dangerous' (and would probably 'code' it on an EICR). I could therefore easily understand if the recommended way of calculating design current did consdier worst (or, at least, 'bad') case scenarios - but you are telling me that it doesn't. If that can be confirmed, then fair enough.
Kind Regards, John.
There's a huge difference, and you are completely failing to see it.
The similarity you are striving to establish would be the banning of car ownership, lest one did something stupid with one.
Or the banning of the sale of alcohol lest one did something stupid with it.
The law does neither - it says, basically, if you want to drive a car you mustn't drink too much, or conversely if you've drunk too much you mustn't drive a car.
It is the errant behaviour which we make illegal, not the possession of items which could potentially be used in an errant way.
Driving a car is not illegal, per se.
Drinking alcohol is not illegal per se.
It's the inappropriate combining of the two which is illegal.
There are responsible ways in which to drive, and there are responsible ways in which to drink.
There's no responsible way to drive whilst intoxicated, and it is prohibited.
Before the most recent restrictions on gun ownership it was already illegal to use them irresponsibly (e.g. by shooting people).
There were (and indeed still are) ways to own and use guns responsibly.
But that option was taken away - it is now illegal to own a handgun no matter how you use it.
The analogy is not the banning of drink-driving, it is the banning of all drinking, lest you drive having done it or the banning of all driving lest you do it having been drinking.
Responsible driving is not prohibited.
Responsible drinking is not prohibited.
Responsible handgun ownership is.
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Fair enough; I take your point.
I suspect the anomoly you describe is at least partially down to risk/benefit (or risk/'need') considerations. If the 'need' for people to have handguns was considered to be as great as the need to have cars (or the inconvenience of not having cars), then maybe the risk associated with personal handgun ownership would be regarded as being outweighed by the benefits. ... as perhaps in the case of kitchen knives, axes, screwdrivers, chisels etc. - since, just as for cars, the benefits of their being allowed ('need') far outweigh the risks - despite the fact that such objects have probably, between them, always been responsible for more murders and serious assaults in the UK than have handguns.
Kind Regards, John.
A healthy society needs to be free from tabloid-induced knee-jerk legislation introduced in panic by stupid and ignorant legislators to destroy businesses, leisure pursuits and sporting activities because the people charged with implementing the existing, and perfectly adequate, legislation were grossly negligent.
I recently wrote:
Although there was a question sort-of implicit in that, I didn't actually ask it. If, with my installation's figures, you were completing an EIC, EICR or other form, would you record the PSC as what your meter said (685A) or, since you believe that all currents should be calculated using U0, would you manually calculate the figure using 230V and hence record 638.9A ?
Kind Regards, John.
As a general concept, I agree totally with what you say, but I think that the sort of risk-benefit/need issues (for society as a whole) I mentioned do sometimes warrant consideration (in a rational and responsible way, not as a knee-jerk or in response to media pressures etc.), particularly when the 'need/benefit' (or even just 'desire') relates to a very small minority, yet the risk relates to the whole of society - something which is probably applicable in the case of hand gun ownership.
Given that you have introduced 'leisure pursuits and sporting activities', one might suggest that there are at least some parallels with fox hunting (a topic about which we can easily predict your views - with which I would agree). In that case, the feeling of a small minority that they have a need to be able to pursue such activities have (I would say correctly) been over-ridden by 'restrictive' legislation which is considered to be a benefit to society (in the widest sense) as a whole.
Kind Regards, John.
You would record your meter reading - assuming its calibrated and you have used it for recording all the other test results. But for the example given it doesn't really matter does it?
That's what I assumed.
Obviously not - provided the PSC is less than 6,000A, the actual value is pretty irrelevant. If (way out of my zone of experience) the recorded meter reading were fractionally over 6,000A, the OPD rated at 6kA and the PSC calculated using 230V a little below 6,000A, then the difference clearly could matter.
However, as I'm sure you realise, I only used PSC calculation as an example. EFLI seems to feel that, because nominal supply voltage (230V) is mentioned in many of the Tables in the BGB, this means that all calculations of currents based on votage and resistance/impedance should utilise U0 (i.e. 230V), not the actual voltage - and I was citing PSC as one case in which we (and presumably he) don't actually normally do that. That leaves my question about the calculation of circuit design currents still not really ('officially') answered.
Kind Regards, John.
So it's OK to oppress minorities, just because they are a minority?
And regarding handguns we did get what I described - the "rational and responsible consideration" you talk of, i.e. the Cullen enquiry did not conclude that a ban was warranted. The Home Affairs Select Committee said that a ban would be panic legislation.
I would have loved the IOC to have refused to allow us to even bid for the Olympics on the grounds that some events were illegal here, and that no country should ever be allowed to host them if they prohibited their own people from participating in the sport.
You seem determined to introduce daft "analogies".
The whole concept of fox hunting is that of organised animal cruelty. It's hard to see what is objectionable about making holes in a piece of paper.
It's also hard to see how much further off-topic this can get. I only brought it up to prove my assertion that we don't just legislate against stupid behaviour, we also legislate against things which are not stupid or wrong.
I have always calculated PFC myself - not specifically for the reason you state (probably just a remnant from having meters which did not do it ).
That is why I did not know what value the meter used - I have never checked.
I still maintain that using the same value of Uo for all calculations would seem logical.
Otherwise what is the purpose of a box on the EIC for nominal voltage.
Also, if you disagree, then what IS nominal voltage other than a meaningless, useless number thought up for no reason?
Fair enough - so, when you calculate it, do you use 230V for the calculation, and hence record a value for PFC or PSCC different from that displayed by your meter, or do you calculate on the basis of the voltage measured by the meter?
If you use 230V for those calcs, and if you ever enounter very high PFCs (6kA or more), what would you do in the situation I recently mentioned ... if your calculation using 230V was below 6kA, but the value displayed by the meter (calculated from actual voltage) was above 6kA, would you regard a 6kA OPD as being OK or not?
For many calculations, and in the interests of consistency/practicality, I would agree. However, I don't believe that one should necessarily always use U0,'as a metter of principle', without any thought.
Well, as I think you've pointed out yourself, it is an arbitrary (essentially 'political') number, used essentially for convenience. The fact that it is essentially 'meaningless' in engineering terms is illustrated by the fact that, in the UK, it changed from 240V to 230V without any change in supply voltages and, AFAIAA, no changes in any of the tabulated figures/limits etc. in documents like BS7671. The current drawn by, say, a particular shower did not suddenly change on the day that 'political' change occurred but, per your views, the design current of the circuit did change on that day. Whatever else that is, it's not engineering
Kind Regards, John.
I use 230 as that is what I think is meant by Uo/Ze (or Zs).
I never have - that would mean a Ze of 0.03833Ω
What if you had enquired the Ze from the supplier and they had told you 0.35Ω or 0.8Ω ?
I would not - but that would be because the measurement is proving something amiss.
The same as 'my calculation' resulting in 5999A.
Perhaps not in a special installation where it would be necessary but in 'normal service' I think that is what we are told to do.
Yes, but as there is only provision for the value to be recorded once.
It would seem to me that this figure should be regarded as having been used for the all readings on the certificate.
The tables for maximum Zs, for example, were all adjusted by a factor of 23/24 so that the results are the same as before.
I admit that MCBs do not appear to have been altered to allow for the change but, surely, the powers that be must have deemed this acceptable.
No it didn't because, as I have previously said, it is not necessary to calculate for a shower circuit because the MIs state what CPD to use.
True. It's not 'engineering' being told to use a particular CPD and CSA of cable (obviously allowing for the method of installation) but that's what we have to do.
As long as the MIs are followed the circuit for a shower cannot be overloaded.
Fixed load circuits do not take much engineering.
A cooker demand, for example, may take some engineering but then we are allowed to drastically reduce all the results because of diversity.
The only common circuits in a normal house which do require engineering are the Ring FC and Radial FC but these are allowed to be installed as per standard format with no thought by anyone.
I do not mean that I would ignore any regulations but it would seem, as is apparent in many topics which you raise, that house circuits in general are greatly over-engineered and very safe.
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