230V/240V Question

[ban-all-sheds]

I said nominal, not average.

I know you did, but, as I said in several posts, the 'on paper harmonisation' of nominal voltage would only really make much sense if the hope/expectation/intent that what would follow would be a gradual movement of average voltages towards that arbitrarily declared 'nominal' value.

No - it would also make sense if it were a nominal value which fell within the range which would be encountered IRL.

But you don't need that.

Of course you do.

Depending on the nature of your calculations, what you do need is the minimum, maximum or average weight

But if all of those differ from one location to another you are forced to do multiple calculations, each one specific to one location.

an arbitrarily defined 'nominal weight' which does not correspond to any of those is bound to cause the calculations to give inaccurate and/or unhelpful results.

On the contrary, it is going to give results which are authoratitive.

As I wrote fairly recently, in virtually all; engineering contexts, a 'nominal' measurement is the expected/intended/average value.

Maybe. Even if the documents do not redefine the meaning of "nominal", it could still be "maybe". But that would be because of the choice of the nominal value, not because nominal means or implies expected/intended/average.

 

[JohnW2]

Depending on the nature of your calculations, what you do need is the minimum, maximum or average weight

But if all of those differ from one location to another you are forced to do multiple calculations, each one specific to one location.

You misunderstood. I was talking of the minimum or maximum permitted (at any location) or (rarely appropriate for safety-related calculations) the average across all locations.

A safety-related calculation can only be guaranteed to be 'safe' for a particular location is it is based on the minimum (or maximum) possible supply voltage at that location. As discussed, after decades of specifying 'maximum Zs' figures based on nominal voltage (hence 'unsafe' for any location with a supply voltage lower than that arbitrary nominal figure), in 2015 BS7671 went a long way to making the figures 'safe' with any permitted supply voltage.

As I wrote fairly recently, in virtually all; engineering contexts, a 'nominal' measurement is the expected/intended/average value.

Maybe. Even if the documents do not redefine the meaning of "nominal", it could still be "maybe". But that would be because of the choice of the nominal value, not because nominal means or implies expected/intended/average.

In engineering contexts, 'nominal' will usually be defined (and usually in a manner which corresponds with common sense and usefulness). As I've said, think of a range of screws, drills or whatever with 'nominal' diameters of 3, 4, 5, 6, 8. 10 mm. Is not the meaning of 'nominal' (which I feel sure will be defined in relevant Standards or other documents) in that context fairly obvious? (and not a figure which has been chosen arbitrarily from within the range of possible/permitted actual values).

Kind Regards, John

 

[ban-all-sheds]

Depending on the nature of your calculations, what you do need is the minimum, maximum or average weight

But if all of those differ from one location to another you are forced to do multiple calculations, each one specific to one location.

You misunderstood. I was talking of the minimum or maximum permitted (at any location) or (rarely appropriate for safety-related calculations) the average across all locations.

If those permitted minima/maxima differ from one location to another you are forced to do multiple calculations, each one specific to one location.

As I've said, think of a range of screws, drills or whatever with 'nominal' diameters of 3, 4, 5, 6, 8. 10 mm. Is not the meaning of 'nominal' (which I feel sure will be defined in relevant Standards or other documents) in that context fairly obvious? (and not a figure which has been chosen arbitrarily from within the range of possible/permitted actual values).

I'm not sure that an example with discrete values is useful.

 

[JohnW2]

If those permitted minima/maxima differ from one location to another you are forced to do multiple calculations, each one specific to one location.

They surely don't differ? Where in the UK is the supply voltage allowed to be below 216.2V or above 253V (10 min averages, for more than 5% of the time) ?

I'm not sure that an example with discrete values is useful.

I don't understand your point - what is the conceptual difference between a screw with a nominal diameter of 8 mm and an electricity supply with a nominal voltage of 230V?

Kind Regards, John

 

[ban-all-sheds]

They surely don't differ? Where in the UK is the supply voltage allowed to be below 216.2V or above 253V (10 min averages, for more than 5% of the time) ?

But we are talking about a wider area than just the UK.

But even within the UK, you cannot use the "average" value, as that does vary from place to place, even within the space of a few streets. If you pick a number which is never the mean, the median nor the mode seen in some places what you are really doing is defining a nominal value.

I don't understand your point - what is the conceptual difference between a screw with a nominal diameter of 8 mm and an electricity supply with a nominal voltage of 230V?

If you have an 8mm hole and an 8.1mm thing to fit into it you have a major problem.

If you have a 230V supply and a 232.9V appliance you don't have a problem at all.

If you have something where the sizes of the holes in it vary all the time, or if you have a box of drills and you never know what diameter they will be when you come to use one because they change all of the time you have a problem.

If you have a voltage which ranges between defined limits either side of 230V you do not have a problem.

 

[JohnW2]

I did not realise that you hadn't spotted that we are talking about a wider area than just the UK.

Well, for a start, that illustrates another flaw in the so-called 'harmonisation'. There's no real point in harmonising the 'nominal voltage' if one does not also harmonise the permitted tolerances around that nominal value.

Whatever, I would expect/hope that, if done properly, the 'limits' (e.g. 'maximum Zs') associated with calculations will vary between countries to reflect their local 'permitted tolerance', and I was talking about the limits imposed by BS7671 in relation to the the UK (where the permitted tolerance is -6%/+10%). If some country allows lower voltages than 230V - 6%, then 'safe' levels of 'maximum Zs' would be lower than those in the UK.

But even within the UK, you cannot use the "average" value, as that does vary from place to place, even within the space of a few streets. If you pick a number which is never the mean, the median nor the mode seen in some places what you are really doing is defining a nominal value.

As I said, no sort of average is ever really going to be a safe basis for safety-critical calculations. One needs to base calculations on 'worst possible case' scenarios - e.g. the minimum permitted supply voltage for 'maximum Zs' or the maximum permitted supply voltage for most adiabatic calculations.

If you have an 8mm hole and an 8.1mm thing to fit into it you have a major problem.

True - and, in some situations, if you have an 8.1mm hole into which a 8.0mm (or 7.99mm) thing is meant to be a very tight fit, then again you could again have a major problem. Manufacturers of drills do not know whether the user's application will be more tolerant to over-size than to under-size, so they have no sensible choice but to quote a nominal size that is equal to the average of their drills (the 'intended' size), with a specified (usually symmetrical) tolerance around that nominal figure. It would make absolutely no sense, and would be totally unhelpful, to specify a 'nominal' size of, say, 7.95mm or 8.05mm for a drill intended to be (and on average being) 8mm in diameter.

If you have a 230V supply and a 232.9V appliance you don't have a problem at all.

Sure, but that's merely because variations in electricity supply voltage are less critical than variations in sizes of holes into which things are to be inserted.

If you have a voltage which ranges between defined limits either side of 230V you do not have a problem.

Indeed not - provided that you undertake your safety-related calculations on the basis of the lower or upper (as appropriate) of those 'defined limits', and ignore the 230V, which is an irrelevance in such a context. If, unlike the (irrelevant) 'nominal' voltage, those 'defined limits' are not also harmonised, then the whole concept of 'harmonisation' would seem to be fatally flawed.

Kind Regards, John

 

[stillp]

There's no real point in harmonising the 'nominal voltage' if one does not also harmonise the permitted tolerances around that nominal value.

But they are harmonised, in EN 50160!

 

[JohnW2]

There's no real point in harmonising the 'nominal voltage' if one does not also harmonise the permitted tolerances around that nominal value.

But they are harmonised, in EN 50160!

Well, if that's true, then BAS's point was invalid. However, not being blessed with easy access to relevant Standards, I'm rather confused, so perhaps you can help ...

... my only immediate source of information is the Wikipedia, and that says that supplies throughout the EU were harmonised to 230V ±10%, but that for a transition period ("1995-2008") some member states (like the UK) would use 230V -6%/+10% and others would use 230V -10%/+6%. However, now 8 years after 2008, at least in the UK we still seem to think we are using 230V -6%/+10%.

.... so what is actually going on, or meant to be going on? Is the current permitted minimum in the UK 216.2V (as virtually everyone seems to believe) or 207V? What is the truth, since I presume that (not for the first time!) the Wikipedia is not correct?

Kind Regards, John

 

[ban-all-sheds]

I think the article is wrong. The full ±10% seems to keep getting kicked down the road.

 

[JohnW2]

I think the article is wrong. The full ±10% seems to keep getting kicked down the road.

Fair enough. From the UK suppliers' point of view, there obviously would be no problem in ±10% being implemented 'tomorrow' (since they are already satisfying it) - indeed, they would probably welcome that extra wiggle room at the lower end. So what is the issue - is there perhaps a suggestion/belief that some equipment in the UK would not function satisfactorily below 216.2V? If that's the case, then the 'kicking down the road' will presumably have to continue for decades, until such a time as all equipment that will not function satisfactorily below 216.2 is assumed to have died?

Kind Regards, John

 

[stillp]

Wish I hadn't mentioned it now, as my copy of 50160 is on one of a large number of uncatalogued DVDs I have! However, it is derived from IEC 60038, which I have the 1997 version of on my hard drive. That contains the following:
"The nominal voltage of existing 220/380 V and 240/415 V systems shall evolve toward the recommended value
of 230/400 V. The transition period should be as short as possible and should not exceed the year 2003. During
this period, as a first step, the electricity supply authorities of countries having 220/380 V systems should bring
the voltage within the range 230/400 V +6 %, –10 % and those of countries having 240/415 V systems should
bring the voltage within the range 230/400 V +10 %, –6 %. At the end of this transition period, the tolerance
of 230/400 V ± 10 % should have been achieved; after this the reduction of this range will be considered. All
the above considerations apply also to the present 380/660 V value with respect to the recommended value
400/690 V."

I'll see if I can find 50160 next week.
Further to the discussions on the voltage range of appliances, in the industrial world, where equipment is specified for use at e.g. 220 - 240V, that refers to a range of nominal voltages, and the equipment will usually (depending on its product standard) be expected to work safely at +10% -15% of those nominal voltages.

 

[JohnW2]

"... The transition period should be as short as possible and should not exceed the year 2003. During this period, as a first step, the electricity supply authorities of countries having 220/380 V systems should bring the voltage within the range 230/400 V +6 %, –10 % and those of countries having 240/415 V systems should bring the voltage within the range 230/400 V +10 %, –6 %. At the end of this transition period, the tolerance of 230/400 V ± 10 % should have been achieved; after this the reduction of this range will be considered.

Thanks. I think I must be missing something pretty basic .... if, during this 'transition period', all countries are working to 230V ± 10%, OR 230V +6%/-10% OR 230V -6%/+10% (the latter two being subsets of the first), then surely all countries are already complying with 230V ± 10% - so why not just say that that is the (truly) harmonised (for all EU countries) 'nominal' voltage and permitted tolerance now???

Kind Regards, John

 

[stillp]

Indeed, why not?

 

[PBC_1966]

Thanks. I think I must be missing something pretty basic .... if, during this 'transition period', all countries are working to 230V ± 10%, OR 230V +6%/-10% OR 230V -6%/+10% (the latter two being subsets of the first), then surely all countries are already complying with 230V ± 10% - so why not just say that that is the (truly) harmonised (for all EU countries) 'nominal' voltage and permitted tolerance now???

No, you're not missing anything, it just makes no sense. As you say, if the aim was to end up with a European standard of 230V +/-10% why the temporary (even if it's turning out to be semi-long term) adoption of 230V +10/-6% when the existing 240V +/6% supplies already fall within the 230V +/-10% range?

 

[JohnW2]

Indeed, why not?

Quite - but, as PBC has said, it's really worse than that - what is going on seems plain daft ... so daft that I can't help but wonder whether we are perhaps not all 'missing something basic'!

Kind Regards, John