DB earth fed direct from HRC fused cutout or from external MET first?

[ban-all-sheds]

It is, so I was right and wrong at the same time, dependent on how separate.

I would say that "separate" or not was binary, and that there can be no concept of "how separate", any more than there can be any concept of "how dead", or "how pregnant".

If the main earthing terminal is not part of the "main switchgear" then it is separate, whether the distance of separation is 1mm or 1m or 10m or...

 

[ban-all-sheds]

An image showing cable tray/strut whose function is hard to determine.

 

[JohnW2]

I would say that "separate" or not was binary, and that there can be no concept of "how separate", any more than there can be any concept of "how dead", or "how pregnant".

As you go on to illustrate, "separation" is certainly not binary.

Kind Regards, John

 

[ban-all-sheds]

The state of being separate or not is.

The distance of separation is of no relevance to the state of separation.

 

[JohnW2]

I take it that you feel we should take "Jobsworth" approach to the regulation, rather than daring to apply common sense?

We were shown a photo with an earth block about an inch below a CU. and clearly connected to the CU with a G/Y cable. If the block had been moved up an inch and bolted to the outside of the CU case, I presume you would accept that as 'not separate' (the reg says nothing about it having to be 'inside' the switchgear), and therefore not required to have a label, whereas in its present position it does require a label. Is that correct?

Kind Regards, John

 

[ban-all-sheds]

I have only commented on what the regulation clearly says.

What if that "about an inch" became "about 2 inches"? Or 3 inches? Or... Or... Or...

At what distance does your "common sense" say it becomes "separate"?

Having answered that, please then move the earth block back by 1mm closer to the CU, and explain how "common sense" says that is not separate then, but it was when it was 1mm further away.

This is the sort of problem that you encounter (and have encountered in relation to other issues) when you decide that what you should do is to try to use what you call "common sense" to do what you call "interpretation" of a regulation rather than simply read what it says.

"Jobsworth" is a pejorative term.

Separate is separate no matter what the gap, and not separate is not separate.

Binary.

Applying a label is not onerous in time, effort or expense, so what is your real motive in deciding that you should pretend that the regulation really means "the main earthing terminal, when separate by a distance of more than X from the main switchgear"?

 

[JohnW2]

Applying a label is not onerous in time, effort or expense, so what is your real motive in deciding that you should pretend that the regulation really means "the main earthing terminal, when separate by a distance of more than X from the main switchgear"?

As I said, 'common sense'. Whilst I agree that there is scope for debate about what separation distance should represent a threshold, when it is only an inch or so, with an obvious electrical connection to the CU, I am quite satisfied that we are below 'my common sense threshold'.

"Jobsworth" is a pejorative term.

It is.

Kind Regards, John

 

[ban-all-sheds]

As I said, 'common sense'. Whilst I agree that there is scope for debate about what separation distance should represent a threshold, when it is only an inch or so, with an obvious electrical connection to the CU, I am quite satisfied that we are below 'my common sense threshold'.

Fine.

Then please tell us what your "common sense threshold" is, and explain with reason and logic why at that point an earth terminal is separate but at 1mm below it it is not. I won't argue about the value of the threshold, as that doesn't matter, but a threshold is a threshold, and over/under it is binary, so I am keen to understand why you are unhappy with a binary over/under a threshold of zero but say it is common sense to have a threshold of X even though that does nothing to resolve the "it is either separate or it is not" problem - all it does is to move it X away.

There may be "scope" for debate about what separation distance should represent a threshold, but I see no point, for as soon as that threshold is decided you immediately run into the problem of explaining, with reason and logic, why a movement of 1mm either side of that arbitrary line is "common sense" a change between not separate and separate.

 

[JohnW2]

There may be "scope" for debate about what separation distance should represent a threshold, but I see no point, for as soon as that threshold is decided you immediately run into the problem of explaining, with reason and logic, why a movement of 1mm either side of that arbitrary line is "common sense" a change between not separate and separate.

Dichotomisation of a continuum by imposition of a 'threshold' (quite often fairly arbitrary) always produces that problem, but we often have to live with that ...

If our Tables say that the maximum safe current for a cable is 27A, will it really become unsafe at 27.1A ?
If some regulation refers to a maximum cable length of 3 m, would there really be a problem with 3.01 m ?
If it is deemed acceptable ('safe') to drive at 30 mph on a certain road, is it 'unsafe' at 30.1 mph ?
If the pass mark of an exam is 60%, is it 'fair' that someone with 59.9% fails ?

In all of those cases, it is impossible "to explain, with reason and logic" why crossing the threshold has such a profound effect (toggling a binary change), but we have to live with that problem. This is therefore not, in itself, a compelling reason for not having a 'threshold' in the situation we are discussing.

Kind Regards, John

 

[ban-all-sheds]

But you are not arguing in favour of having a threshold or not. You are arguing in favour of having a non-zero threshold instead of a zero one, and claiming that that is common sense.

 

[JohnW2]

But you are not arguing in favour of having a threshold or not. You are arguing in favour of having a non-zero threshold instead of a zero one, and claiming that that is common sense.

I am, and I do claim that.

However, I accept that whatever non-zero threshold were chosen, you could always ask why that figure represented a fundamentally different situation as compared with 1 mm more. I couldn't answer that - but, as I've just said, such problems with dichotomisation are a fact of life.

One could equally turn the argument on its head and ask, if the current threshold is zero, what changes dramatically if that is increased to 1 mm.

Kind Regards, John

 

[ban-all-sheds]

If our Tables say that the maximum safe current for a cable is 27A, will it really become unsafe at 27.1A ?

Do you think that it would be common sense to have a design load of over the tabulated maximum safe current because of that? Where does your common sense say you should stop? 27.2A? 27.3A? 29.7A? What if somebody elses "common sense" stops at a different point? Who authoritatively decides which common sense is right and which one is not?

If some regulation refers to a maximum cable length of 3 m, would there really be a problem with 3.01 m ?

Ditto for 3.02m? 3.03m? 3.3m?

If it is deemed acceptable ('safe') to drive at 30 mph on a certain road, is it 'unsafe' at 30.1 mph ?

In reality, of course, the threshold for official sanctions is >30mph, but in principle the same type of ditto questions should be asked.

If the pass mark of an exam is 60%, is it 'fair' that someone with 59.9% fails ?

If you say it isn't, then what you have done is to say that you think the threshold should be 59.9%.

And then, inevitably, you have to turn your attention to the fairness of failing someone with 59.8%.

And so it goes on, unless you can explain why your common-sense threshold of X% is where the threshold should be, until you get down to 0%.

Do you not see?

In all of those cases, it is impossible "to explain, with reason and logic" why crossing the threshold has such a profound effect (toggling a binary change), but we have to live with that problem.

But you won't live with it.

You are given a threshold of zero, and will not accept it, and want to use what you term "common sense" to argue for a non-zero threshold.

Do you really not see that even if you do that then at some point you are going to bang up against your threshold, and will have resolved absolutely nothing, for you will still have the profound effect of crossing it.

What is your real motive in proposing that the threshold should be what you think rather than what the regulations prescribe?

This is therefore not, in itself, a compelling reason for not having a 'threshold' in the situation we are discussing.

We do have a threshold.

What is the compelling reason for saying it is wrong, and should be different?

 

[ban-all-sheds]

But you are not arguing in favour of having a threshold or not. You are arguing in favour of having a non-zero threshold instead of a zero one...

I am

You are what?

Arguing in favour of having a threshold, or in favour of it being non-zero?

However, I accept that whatever non-zero threshold were chosen, you could always ask why that figure represented a fundamentally different situation as compared with 1 mm more. I couldn't answer that - but, as I've just said, such problems with dichotomisation are a fact of life.

You could ask that, and I too would struggle to answer it, except, e.g., in the context of clearances of moving parts.

But do you really not see? If you move the threshold you have not removed the problem of dichotomisation, all you have done is to move it.

One could equally turn the argument on its head and ask, if the current threshold is zero, what changes dramatically if that is increased to 1 mm.

Let's do that then.

What changes dramatically if it is increased to 1mm? Or 1cm? Or 10cm? Or{insert value of choice}?

If the answer is "nothing", why do it?

"Common sense" doesn't work as a reason, because as soon as you claim that it does, and that it leads to a "common sense" threshold T > 0, how can you abandon the logic of your common sense which you used to arrive at T when someone says "what about T + small increment"?

 

[ban-all-sheds]

If our Tables say that the maximum safe current for a cable is 27A, will it really become unsafe at 27.1A ?
If some regulation refers to a maximum cable length of 3 m, would there really be a problem with 3.01 m ?
If it is deemed acceptable ('safe') to drive at 30 mph on a certain road, is it 'unsafe' at 30.1 mph ?
If the pass mark of an exam is 60%, is it 'fair' that someone with 59.9% fails ?

In reality common sense says that if the tabulated maximum is 27A, you use that as the maximum.

In reality common sense says that if a regulation says the maximum cable length is 3m, you use that as the maximum.

In reality common sense says that if the speed limit is 30mph you drive as if the speed limit were 30mph.

In reality common sense says that if the pass mark is 60% then you need to get at least 60% to pass.