Do only electronic RCD's/RCBO's have functional earths?

[JohnW2]

If you accept that the concept of 'probability is fairly high', then I would have thought that you would also accept the concept of 'probability is fairly low' (or even 'very/extremely low').

It depends how low, I refer the honourable gentleman to the earlier post which prompted my initial comment,

I think that's where the/your problem arises. If, as you seem to have indicated, you do understand the true/correct meaning of "probability", you should also understand that it does not matter "how low?". Probability is a quantity that can have any value between 0 and 1 (0% and 100% if you prefer), corresponding to the spectrum between 'impossible' and 'inevitable' - so that low, very low or extremely low (even 'vanishingly low') probabilities are are all perfectly valid concepts.

.... which is not a probability. It may never have happened before; it is a possibility.

Everything that is 'possible' (i.e. has a non-zero probability) will have a probability - even if, as is often the case, we don't know what that probability is. Unlike probability, 'possibility' is not a quantification - it is merely an indication that something is 'not impossible'.

Kind Regards, John

 

[EFLImpudence]

I think that's where the/your problem arises. If, as you seem to have indicated, you do understand the true/correct meaning of "probability", you should also understand that it does not matter "how low?". Probability is a quantity that can have any value between 0 and 1 (0% and 100% if you prefer), corresponding to the spectrum between 'impossible' and 'inevitable' - so that low, very low or extremely low (even 'vanishingly low') probabilities are are all perfectly valid concepts.

Yes, but I've accepted several times that that is the Probability Theorists speaking; not what the word means.

As I mentioned earlier, it is the same as economists and negative growth.
They and we know what they mean but it is an oxymoron as you cannot have negative growth. It is shrinking or lessening.

Everything that is 'possible' (i.e. has a non-zero probability) will have a probability - even if, as is often the case, we don't know what that probability is. Unlike probability, 'possibility' is not a quantification - it is merely an indication that something is 'not impossible'.

As above.

 

[JohnW2]

Yes, but I've accepted several times that that is the Probability Theorists speaking; not what the word means.

I don't really understand what you mean when you say "what the word means". As I pointed out before, (and in the primary, general, definition, not the subsequent 'mathematical' definition) the Oxford Dictionary defines "probability" as meaning "...the extent to which something is likely to happen or be the case" - which is essentially the same as the meaning used by "Probability Theorists". The dictionary talks of "extent" and those "Theorists" quantify that extent by a number between 0 and 1 (inclusive). ... so what do you think that "probability" actually ('correctly') 'means'??

As I mentioned earlier, it is the same as economists and negative growth. They and we know what they mean but it is an oxymoron as you cannot have negative growth. It is shrinking or lessening.

There are countless examples of 'directional' quantities for which the accepted convention is to use the same word for both directions, but to use 'positive' and 'negative' (either as words or signs) to indicate direction. Even my bank account has a 'balance' with a positive or negative sign to indicate whether it is an actual balance (of money which is mine) or the amount I am overdrawn.

Kind Regards, John

 

[EFLImpudence]

I don't really understand what you mean when you say "what the word means". As I pointed out before, (and in the primary, general, definition, not the subsequent 'mathematical' definition) the Oxford Dictionary defines "probability" as meaning "...the extent to which something is likely to happen or be the case"
- which is essentially the same as the meaning used by "Probability Theorists". The dictionary talks of "extent" and those "Theorists" quantify that extent by a number between 0 and 1 (inclusive). ... so what do you think that "probability" actually ('correctly') 'means'??

I've said it all before.
If you think something has a probability when it is not probable, I don't know what else to say.

There are countless examples of 'directional' quantities for which the accepted convention is to use the same word for both directions, but to use 'positive' and 'negative' (either as words or signs) to indicate direction.

That they do and say these things does not make them linguistically correct.
It is just business jargon.

Even my bank account has a 'balance' with a positive or negative sign to indicate whether it is an actual balance (of money which is mine) or the amount I am overdrawn.

That's a bit different, isn't it?
A mathematical income minus expenditure - could just as easily be black or red figures.
An equivalent may be them saying you were negatively overdrawn when in credit - or you had a negative surplus when in debit.

 

[JohnW2]

I've said it all before. If you think something has a probability when it is not probable, I don't know what else to say.

I've also said it all before If you believe that something does not "have a probability" if it is not probable, what definition of "probability" are you using - since, as I've said several times, it doesn't seem to correspond to the dictionary definition. The whole point is that, as defined by both dictionaries and 'Probability Theorists', "having a probability" does not require that something is "probable". Despite the similarity, and probably also etymological derivation, of the two words, they have very different meanings. Something which is 'very improbable' does have a (very low) probability. You seem to think, probably because of the similarity of the words, that "having a probability" requires something to be "probable" - but that simply is not true (at least, not by any definitions of which I am aware).

That they do and say these things does not make them linguistically correct. It is just business jargon.

You may call it 'jargon' (rather than 'convention'), but I was thinking more about physics and engineering than of business. Do you have the same problem with things like 'negative pressure' and 'negative buoyancy'?

Kind Regards, John

 

[JohnD]

In the same way that you can measure anything...

Every piece of wood has a width. It might be a large width or a small width. You might say it has enormous width, or insignificant width, but these words only have meaning if you and the person you are talking to know whether you are discussing matchsticks or hammer beams. Saying it has width does not tell you.

Every electrical load has a current. Saying that does not give you any idea of how many amps. It might be important for you to know.

Every event has a probability. It might be a high probability or a low probability. It might be unknown. You can say something is improbable, if you want to. In colloquial English "it's probable" suggests something over 50% and "it's unlikely" suggests something less than 50%, and often these rough approximations are adequate for your needs. But there might be a reason why you need to be able to estimate and compare multiple potential events. If you say to your garage "will my car last until the scheduled service" and they say "maybe" that is useless.

If you are comparing two or more potential events, you will need to compare them with more precision.

How probable is rain tomorrow = should I take an umbrella
How probable is a typhoon - should I take shelter

If you are thinking about devoting time, effort or money, you might want to be a bit more precise, but you will also want to know the severity of impact. If you have identified ten potential risks, and you can only afford to prevent or mitigate one of them, you need to decide which.

 

[JohnW2]

In colloquial English "it's probable" suggests something over 50% and "it's unlikely" suggests something less than 50%, and often these rough approximations are adequate for your needs.

I think the 'English' of this word "probable" (and "improbable") which EFLI, not me, introduced into his discussion about "probability", is probably somewhat worse than that. I suspect that many people (maybe including EFLI) require substantially more than a 50% probability for something to be called "probable" and substantially less than a 50% probability for it to be called "improbable" - thereby leaving a big gap in the middle of the spectrum of probabilities for which they have no word!

As you will probably have seen, the thing I'm finding most difficult to understand about EFLI's viewpoint is that he appears to accept that "improbable" means 'low probability', yet he also seems to think that things which are improbable "don't have a probability".

Mind you, this is no new experience for me. Over the years/decades, I have periodically spent a fair bit of time trying to help 'lay' people (albeit highly qualified in their own fields) understand probabilistic concepts, and the sort of things being said by EFLI are very familiar to me from those attempts!

Kind Regards, John

 

[EFLImpudence]

All I have said (starting with Bernard's post) is that things which have a vanishingly small chance of happening are not probabilities.
I have not mentioned 80% or even 50%. Things which do happen regularly and have to be catered for may be defined as probabilities.
Those that do not are not probabilities.

I have given enough examples - lightning, earthquake - but you just keep mentioning Probability Theories where the participants use the word even for zero happenings.

 

[JohnW2]

All I have said (starting with Bernard's post) is that things which have a vanishingly small chance of happening are not probabilities.

You are now introducing a different use/meaning of the word - namely in the sense of something being "a probability". In that sense, it has the same meaning as "probable", and I agree with you that improbable things are not "a probability". However, that is totally different from the quantitative meaning of probability - as in "probability = x%", "probability = zero", "probability is high/large", "probability is low/small" or, even, "probability is vanishingly small".

Things which do happen regularly and have to be catered for may be defined as probabilities. Those that do not are not probabilities.

Agreed, in terms of the meaning you are now using. Rare events are not "probabilities" (in the sense of "being probable"). However, they do have a (quantitative) probability, even if it is very small and/or one does not know what it is. Winning the UK lottery is certainly not "a probability" (in the sense of "being probable"), but it is perfectly valid and correct to say that the probability of a ticket winning is around 1 in 14 million (express it as a percentage if you wish!).

Kind Regards, John

 

[EFLImpudence]

You are now introducing a different use/meaning of the word

No I'm not.

My first comment in response to Bernard's post about/with which you started arguing was:

Surely that which is vanishingly small cannot be a probability.

namely in the sense of something being "a probability". In that sense, it has the same meaning as "probable", and I agree with you that improbable things are not "a probability".

Thank you.

However, that is totally different from the quantitative meaning of probability - as in "probability = x%", "probability = zero", "probability is high/large", "probability is low/small" or, even, "probability is vanishingly small".

Do you mean what I have been calling "probability-theorist-speak" (jargon) and misuse of words?

You may as well argue that growing means getting smaller (as in negative growth).

 

[bernardgreen]

repeating the quote from the Eaton document

The probability of losing the neutral and having an earth fault at the same time, a double fault condition, is vanishingly small – certainly so small that there is no reason to take it into account when specifying protection devices

The probablity is so small there is no reason to take it into account. The probablity does exist. Eaton accept it does exist but it is small enough to not take it into account.

To be vanishing the item must have been visible, invisible and non existant items cannot vanish.

And if you distance your self far enough away from a hazardous item then that item can appear to have vanished ( in the distance ). But for people close the the item the hazard is there

 

[securespark]

How much of your time and money do you spend on precautions against sock accidents?

My socks are RCBO- protected.

 

[securespark]

They use an FE on the A100HE.

 

[JohnW2]

No I'm not. My first comment in response to Bernard's post about/with which you started arguing was:

Surely that which is vanishingly small cannot be a probability.

Ahhhh! At long last, I think I now understand the 'problem' which has led to all this discussion and disagreement, and I suppose it is largely my fault for not looking carefully enough at what you had written - which related to a different use of the word "probability" from that which Bernard had used in the post to which you were responding:

I am never happy when probabilities are dismissed simply because they are vanishly small.

The word "possibility" can be used in two different senses, both of which are documented in dictionaries ....

Firstly, as I now realise was probably what you were thinking about (and have been talking about all the time), it can be used to mean "probable" - as in "such an event is a probability". In that sense, it is analogous to such statements as "such an even is a certainty", "such an event is an impossibility" etc.

The second sense it which the word can be used [as in bernard's post to which you were responding, Eaton's document and everything I and JohnD have been saying (and, indeed, IMO by far the most common way one sees the word used)] - refers to an indication of the 'extent to which something is likely to happen'. It is therefore used as "the probabilty is X" (or, per bernard's post, "the probabilities are X"), where X can be a number, percentage, or some descriptive words such as high/large, low/small or, even, 'vanishingly small'. Although you call that use of the word "probability-theorist-speak", it is also, as I have indicated, the first definition in the Oxford Dictionary.

If you accept that, do you agree that "being a probability" (which is what you have seemingly been talking about throughout) is totally different from "having a probability of X" (which is what bernard, Eaton, JohnD and I have been talking about)? If so, do you also accept that although a rare event "is not a probability", it does "have a probability ('of X')" (second sense) - where X can be a number, or even such things "vanishingly small"?

If your answers to both those questions are 'yes', then I think that this discussion has (eventually!) reached a fairly conclusion, and I apologise for not having realised earlier that you were talking about a different use/meaning of the word from that which the rest of us were talking about.

Kind Regards, John

 

[JohnW2]

The probability is so small there is no reason to take it into account. The probablity does exist. Eaton accept it does exist but it is small enough to not take it into account.

Indeed. As I've just realised, EFLI has probably all along being saying that a rare event is "not a probability" (i.e. " not probable"), not that it does not have a (numerical) probability associated with it.

To be vanishing the item must have been visible, invisible and non existant items cannot vanish.

You are probably right to criticise this use of the word "vanishingly", but over the last decade or so it has become fashionable to use the word in this way, particularly in the context we are talking about (extremely small probabilities).

Kind Regards, John