Amps

[skotl]

How about trying to make a given point just once per thread

Can you persuade eveybody else to only make theirs once?

Aye - good point... Must admit that "nominal" always suggests "roughly" to me...
Anyway, you're my life's mission, B-A-S, not the rest

 

[EFLImpudence]

As our voltage is allowed, and has always been allowed, to vary by a certain amount above or below a nominal value, the ONLY way that a statement of what our voltage IS can be correct is for it to quote our nominal voltage.

And our nominal voltage is 230V, not 240V.

Whilst everyone knows that is correct -

How many times have you berated someone for using 230V when calculating a shower current stating the manufacturer will have used 240V - which is what was being done in the post to which winston1 was responding?

 

[winston1]

Sorry, don't agree. That is what the eurocrats and arse sitters quote, but it is not what happens in practice.

 

[JohnW2]

And our nominal voltage is 230V, not 240V.

Very true - and, as you correctly say, for that reason the regulations require us to use 230V for many calculations.

However, I'm sure that winston1 would be right in saying that the average actual UK supply voltage is nearer to 240V (probably a bit over) than to 230V - which, as you've also said, is well within the premit tolerance around the 'nominal' value.

There's often something to be said for true 'harmonisation'. However, to create so-called 'harmonisation' in the way which was done for 'nominal' EU electricity supply voltages is, IMO, quite bizarre - and I'm not really sure what it has achieved.

Kind Regards, John

 

[skotl]

A new can of worms, then...

If we talk about EU harmonisation, I thought that most of Europe had settled on 220V?
Is that my over-fevered imagination? If not, how does the UK being on 230 or 240 achieve EU harmonisation?

 

[EFLImpudence]

And our nominal voltage is 230V, not 240V.

Sorry, don't agree. That is what the eurocrats and a**e sitters quote, but it is not what happens in practice.

You can't disagree. The nominal voltage is 230V.

It just has no bearing on what the actual voltage may be (apart from the percentage limits allowed).

 

[JohnW2]

Now your stretching semantics for the sake of it.

No, not really. Everything else he wrote was totally correct and very pertinent. Unnecessarily adding "Ohms law applies" just slightly spoiled it.

Now we will have to also compensate for a reduced resistance while the kettle warms more slowly. ... However, the water does not know any of this and will boil at the same 100°C so is the resistance of the element any different?

If, as seems reasonable, one assumes that the element always remains at the same temperature as the water then, yes, the resistance should be the same when the water reaches 100°C, regardless of the voltage - hence 'Ohms law would apply' at that point in time. However, as you say, a lower voltage would mean that the kettle would spend more time at lower temperatures (hence lower resistances) - so that the average current and average power over the full heating cycle would presumably be a little higher than one would have predicted by applying Ohm's Law with an assumption of constant resistance.

Kind Regards, John

 

[JohnW2]

If we talk about EU harmonisation, I thought that most of Europe had settled on 220V? Is that my over-fevered imagination? If not, how does the UK being on 230 or 240 achieve EU harmonisation?

I'm pretty certain that no EU country changed anything when 'harmonisation' occurred - for example, as winston1 said, the 'usual' UK supply voltage remains in the range of roughly 240-245V post-harmonisation, just as it had been for many decades prior to that. 'Harmonisation' was, AFAICS, a purely paper exercise which created a permitted range of 'acceptable voltages' which encompassed all the voltages which were actually being used in Europe. As I said, I'm not really sure what it is meant to have achieved, except in the minds of bureaucrats! Maybe some of them were naive enough to believe that the various Member States would gradually change their actual supply voltages to 230V!!

Kind Regards, John

 

[EFLImpudence]

Of course water boils at 100°C only at sea level so you would also have to allow for the altitude of your worktop.

 

[ban-all-sheds]

How many times have you berated someone for using 230V when calculating a shower current stating the manufacturer will have used 240V - which is what was being done in the post to which winston1 was responding?

Never - I've berated them for using a 240V rating with 230V.

But if it is a 240V rating then you're not to use it in calculations, because our nominal voltage is 230V.

 

[ban-all-sheds]

And our nominal voltage is 230V, not 240V.

Sorry, don't agree. That is what the eurocrats and a**e sitters quote, but it is not what happens in practice.

That really does make as much sense as not agreeing that the cover of the current edition of BS 7671 is green.

Edited to correct malformed quotes

 

[DetlefSchmitz]

the element always remains at the same temperature as the water t

This is nonsense. If the element and the water were the same temperature then the element would never be able to raise the temperature of the water. That's basic thermodynamics.

 

[JohnW2]

the element always remains at the same temperature as the water

This is nonsense. If the element and the water were the same temperature then the element would never be able to raise the temperature of the water. That's basic thermodynamics.

True - but I woiuld say probably quibbling. If (as is obvioulsy desirable) the element is in close thermal contact with the water, the temperature differential between them will always be small - although, as you say, obviously not zero.

Kind Regards, John

 

[ericmark]

How does all this help the guy with his question?

It is rather simple if a 13A fuse is used and then more than 13A is drawn over an extended time the fuse will blow and so fail safe.

There is a curve so likely you can draw 26A for 100 seconds without it blowing.

There is really no danger in trying to use the circuit and see if the fuse blows. If it does no great problem renewing and no harm done as long as you allow things to cool before renewing.

All this ohms law and calculations with talk about if the UK is 230 or 240 volts does not help the poster of the thread.

The simple fact is the fuse will blow before the cable is damaged so everything should fail safe.

Keep it simple 3kW = 3000W = 13A there is no need to argue to if 2800W or 3100W it does not really matter with a 13A fuse.

 

[ban-all-sheds]

True - but I woiuld say probably quibbling. If (as is obvioulsy desirable) the element is in close thermal contact with the water, the temperature differential between them will always be small - although, as you say, obviously not zero.

I have another experiment for you.

Fill your kettle, switch it on, and before the water is too hot to injure you put your hand in and touch the element, then report back your findings.