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

[JohnD]

everything has a probability, even if it is only 1 in 60 million.

If I was in the business of reducing accidental deaths, I would rank them to find a priority. For example the rating of the risk in the UK might be

Severity 1 death
Probability 1 in 60 millions
Multiplied by UK population about 60 million
so rate it at "1" on my example scale

If compared to, say riding a motorcycle, severity would be the same but the probability would be much higher, so on my fantasy risk chart, it would come at the top, and the RCBO would come at the bottom.

I would then look at the cost (to me) of reducing risks, and I would start with the ones where I could save the most lives at the least cost.

Socks would probably get more priority than RCBOs.

 

[EFLImpudence]

I am talking English.

Yes, I realise that there is "Probability Theory" which may, of necessity, include all from 0% to 100%.

However, 1 in 60 million is not "probable".

 

[JohnD]

When preparing risk registers, I (we) used to laughingly put the risk that a 747 might crash into the building, destroying all the equipment and infrastructure, incinerating the plans and records, and killing all the trained staff as "Severity, total, probability, zero"

After 9/11 we stopped doing that.

My last major project was not far from a nuclear submarine base, so we set up a standby site far enough away to be outside the devastation area.

 

[JohnD]

However, 1 in 60 million is not "probable".

If one person a year in the UK was killed by a known fault in a tumble drier design, I think you'll find that the probability was considered severe enough for the manufacturer to be forced to correct it.

The Ford Motor Company knew that the position of the petrol tank in the Pinto would occasionally cause it to burst into flames in an accident, and burn the passengers to death. It would have cost $11 per car to change the design. They thought the probability was small enough to ignore.
When this became public knowledge, they were slaughtered.

https://philosophia.uncg.edu/phi361...oes-business-need-ethics/case-the-ford-pinto/

1 in 60 million might not matter to you, but it does to others.

 

[JohnW2]

I am talking English. Yes, I realise that there is "Probability Theory" which may, of necessity, include all from 0% to 100%.

Indeed there is, and I would have thought that it was clear that that is the sort of probability that I was talking about. (statistical) "probability" is an ever-present part of my working life

However, 1 in 60 million is not "probable".

I'm not sure that you are right even in terms of English. I agree that "probable" and "possible" (and "not probable" and "not possible") are commonly used to refer to different levels of 'likelihood' but I think that "probability" generally still has the statistical meaning.

Kind Regards, John

 

[JohnW2]

If one person a year was killed by a known fault in a tumble drier design, I think you'll find that thew probability was considered severe enough for the manufacturer to be forced to correct it.

Any such decisions obviously involve risk-benefit considerations, and I'm far from convinced that the decision would necessarily be as you suggest in the situation you describe.

The vast majority of 'activities' (even mundane ones, like eating, getting dressed and going up stairs!!) are associated with at least one death per year in the UK but (sensibly!!) we don't ban everyone from doing everything!

Kind Regards, John

 

[EFLImpudence]

Yes, but I am not talking about "Probability Theory" where, obviously, the name would not be changed below a certain value.

I was commenting on:

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

where, as we know, Bernard worries about things which are not probable.

 

[JohnW2]

where, as we know, Bernard worries about things which are not probable.

Indeed, but when he says (or thinks) that, what he is talking about are things which have a very low (statistical) probability.

To a Statistician, or anyone who has to make use of statistics, "not probable" is meaningless - to them, Probability (with a capital 'P' if you wish) is a measure which only really has meaning when quantified. However, depending on context, it might be sufficient to talk about things such as "very high probability", "extremely low probability" or, even "vanishingly small probability".

Kind Regards, John

 

[EFLImpudence]

"vanishingly small probability".

They may say that but:

"vanishingly small probability" means unlikely to happen therefore, by definition, improbable.

Why are you arguing that using the wrong word changes the definition of that word?

 

[JohnW2]

"vanishingly small probability" means unlikely to happen therefore, by definition, improbable.

Indeed it does (albeit extremely {or similar word} unlikely). "Improbable" is a non-technical (and non-quantified) English word. Would you be happier if, instead of "vanishingly small probability" I said "incredibly improbable"??

Unfortunately, English becomes a little inconsistent when one considers "impossible". That word has come to mean "not possible at all" (i.e. statistical probability is zero), not just "unlikely" (or "extremely unlikely", or whatever).

Why are you arguing that using the wrong word changes the definition of that word?

Because in the world in which I live and work, it is not the wrong word. It's like you, as an electrician, telling me that "bulb" is wrong.

Kind Regards, John

 

[EFLImpudence]

Indeed it does (albeit extremely {or similar word} unlikely). "Improbable" is a non-technical (and non-quantified) English word. Would you be happier if, instead of "vanishingly small probability" I said "incredibly improbable"??

No, "vanishingly small possibility".
I am not talking technically.

Unfortunately, English becomes a little inconsistent when one considers "impossible". That word has come to mean "not possible at all" (i.e. statistical probability is zero), not just "unlikely" (or "extremely unlikely", or whatever).

That depends how it is being used. You are introducing another meaning - able to be done/made etc..
What we are talking about is:
A possibility means it could be the case but may not be; impossibility means no possibility of that.
A probability means it is likely to be the case; improbable means it is unlikely but not zero.
"Statistical probability of zero" is what is causing the misuse.

Because in the world in which I live and work, it is not the wrong word. It's like you, as an electrician, telling me that "bulb" is wrong.

Ok. It is a bulb shaped lamp.

I accept that in Probability Theory that will be the usage no matter how low the value.
However, a person cannot say, for example, "The probability of me going to The Moon is zero".

 

[bernardgreen]

where, as we know, Bernard worries about things which are not probable.

I tend to not ignore situations which are extremely unlikely to occur but are also not impossible to occur.

Or in other words if it is possible then it should be considered when planning / designing / preparing systems / equipment / procedures.

Problems happen and planning fails when the environment changes and things that were once extremely unlikely to happen become less unlikely ( or even likely ) to occur.

 

[EFLImpudence]

That's my point.

They may be possible but may not be probable.

 

[JohnW2]

No, "vanishingly small possibility". I am not talking technically.

Interesting. I realise that I am biased by my background and 'the world I work in', but I would have thought that the majority of 'ordinary persons' do (whether they realise it or not) understand, accept and often use the statistical meaning of "probability" - i.e. they do understand (and use) the concept of 'low probability'. Because of the dictionary definitions, you appear to believe that a "probability" always has to relate to a fairly high (statistical) probability - is that the case?

A possibility means it could be the case but may not be; impossibility means no possibility of that. A probability means it is likely to be the case; improbable means it is unlikely but not zero.

As above, I would think that the majority of the general public do understand the (essentially statistical) concept of a "low probability", which you don't seem to regard as a valid concept.

"Statistical probability of zero" is what is causing the misuse.

I'm not quite sure what your point is. As I have said, statistical probability can be zero (or low, or extremely low), albeit usually in relation to silly theoretical cases. For example, the (statistical) probability of a dead person being alive is zero.

However, a person cannot say, for example, "The probability of me going to The Moon is zero".

Well, if you were using 'proper grammar', you would probably say "my", rather than "me" Notwithstanding that, I agree with you, but not for the reason you are presumably thinking of. Although there are situations in which it would be extremely improbable (e.g. if the person was an incapacitated 90 year-old), I suppose one can never say that it is totally impossible that any given person will ever go to the moon - so, in 'my' language, I would be happy for them to say that "The probability of me [my!] going to The Moon is incredibly small" - but you do not accept the concept of incredibly small (or even just small) probabilities.

Kind Regards, John

 

[JohnW2]

I tend to not ignore situations which are extremely unlikely to occur but are also not impossible to occur.

Yes, I understand that's what you are saying but, given that almost nothing is 'totally impossible', I'm not sure how you put that into practice. For example, if one took that viewpoint to its extreme, one would have an EICR undertaken on ones electrical installation at least once every day (since it is "not impossible" that some hazardous fault will have arisen since the previous day)!

Kind Regards, John
Edit: "that" changed to "how" - which is what I had intended to type!