Shed straight concentric supply query

[ban-all-sheds]

One can but presume that he has found some definition of "sheathed" but, although I have asked, he has yet to share it with us.

And I've asked you, twice, do do your bit and look for one.

But it seems that you and EFLI would rather decide what it must mean and close your minds to the possibility that you might be wrong, close your minds to the possibility that other relevant standard(s) do define it, and close your minds to the possibility that other relevant standard(s) might prescribe characteristics of it.

 

[JohnW2]

And I've asked you, twice, do do your bit and look for one.

I shouldn't need to. Given you laudable insistence on truth and correctness, you surely would not have written something as clear as ....

That is not a metal sheathed cable.

... unless you knew the relevant definition?

Kind Regards, John

 

[ban-all-sheds]

Maybe. Perhaps you could let us know what definition of "sheath" or "sheathed" it has inherited. ... or are you perhaps just guessing, then arguing on the basis of your guess?

I am not the one who is guessing - that will be you and EFLI, that will.

My position is that if you wish to claim that a particular cable has armour, or has a metal sheath, then you need corroboration, you need to prove that it is officially so.

I shouldn't need to.

Really?

You shouldn't have to show that your claims are true?

Given you laudable insistence on truth and correctness, you surely would not have written something as clear as .... ... unless you knew the relevant definition?

You're claiming that it is metal sheathed. Are you doing so without knowing the relevant definition of that? Are you happy not to care about truth and correctness?

I don't need to know what the definition of "metal sheathed" is to point out that a cable which is not described as "metal sheathed" isn't.

That foil layer is a screen, not a sheath.

 

[ban-all-sheds]

Ah, another worm crawling out of the can. If it says "adequate as a CPC" then it's debatable whether that should be read as "adequate as the CPC on it's own".

It's only debatable amongst people who think they should pretend that the people who wrote it meant to write other words as well but for some reason failed to do so.

As you've pointed out, without being able to read the minds of those who wrote the reg, it's hard to know what they intended.

It is not at all hard to know what they intended if you accept that they intended what they wrote, and wrote what they intended.

Any difficulties which arise because you think you should pretend that the people who wrote it meant to write other words as well but for some reason failed to do so are difficulties which you have invented.

 

[EFLImpudence]

I think you will find that I have been asking about things, as with -

That is not a metal sheathed cable.

Why not?

A question, not a disagreement.

It would be better in such instances if you explained why it is not, if you know and we don't, rather than berate and accuse us of trying to contort the regulations.

Are you also saying that cables with such a screen are not suitable for burying without RCD coverage in walls either?

 

[JohnW2]

It would be better in such instances if you explained why it is not, if you know and we don't, rather than berate and accuse us of trying to contort the regulations.

Quite so. He clearly doesn't actually know, since he has asked me to find out for him, but he nevertheless makes this assertive "is not" statement, as if he did know.

Kind Regards, John

 

[JohnW2]

{Details of a method which seems an awful lot of work for the sake of improved accuracy to the values of fractions of microns when compared to 30 seconds work with a calculator}

Since I couldn't be bothered to solve that for T, I just threw it into a spreadsheet....

Although I was hesitant to try at the time (in the middle of the night), having just had a few spare moments, I have discovered that solving the equation was essentially painless. Given an outside diameter of D, the exact thickness of covering,T, required to achieve any particular CSA is simply given by ...

T = (D - sqrt(D^2 - 4*CSA/pi))/2

... armed with which, one can get a precise answer almost as quickly as you got an answer with your 'approximation' - a trivial difference when T is small, but not if T was much greater.

Kind Regards, John

 

[ban-all-sheds]

I think you will find that I have been asking about things, as with -


A question, not a disagreement.

Fair enough.

It would be better in such instances if you explained why it is not, if you know and we don't, rather than berate and accuse us of trying to contort the regulations.

Again, fair enough, but I do stand by the general thrust of what I said, in that there does seem to be a great unwillingness to consider that I might be right, and that the certainty with which people are claiming that any cables can be buried might be misplaced.

Are you also saying that cables with such a screen are not suitable for burying without RCD coverage in walls either?

No. BS 8436 cables are specifically allowed to be used like that.

 

[ban-all-sheds]

Quite so. He clearly doesn't actually know, since he has asked me to find out for him, but he nevertheless makes this assertive "is not" statement, as if he did know.

I also know that there are no herds of invisible unicorns living in the Arctic, and am confident in asserting that there are none.

 

[JohnW2]

I also know that there are no herds of invisible unicorns living in the Arctic, and am confident in asserting that there are none.

Fair enough - but if that's the case (in relation to the matter in question) why have you been asking me to find out for you (whether or not you are correct in your assertion)?

Kind Regards, John

 

[EFLImpudence]

Again, fair enough, but I do stand by the general thrust of what I said, in that there does seem to be a great unwillingness to consider that I might be right,

On the contrary, but I would like to know the reason.

and that the certainty with which people are claiming that any cables can be buried might be misplaced.

I don't think there was any certainty.
That is what we or, at least, I am trying to determine.

No. BS 8436 cables are specifically allowed to be used like that.

522.6.204 does indeed state that therefore I can conclude that the cable has an earthed metallic covering. (screen more usually used for emf reasons)
The only difference in requirements for being buried in a wall or the ground is that of a covering or a sheath respectively.



It would be difficult to distinguish semantically between these two words, would it not?

 

[JohnW2]

I don't think there was any certainty. That is what we or, at least, I am trying to determine.

Me too.

522.6.204 does indeed state that therefore I can conclude that the cable has an earthed metallic covering. (screen more usually used for emf reasons). The only difference in requirements for being buried in a wall or the ground is that of a covering or a sheath respectively. It would be difficult to distinguish semantically between these two words, would it not?

Very difficult, I would have thought, it terms of standard dictionary definitions. As BAS has been implying, the only real hope of clarity would be if there is, somewhere, some technical definition of those words in the context of cables. I have no more access to any of the possibly relevant Standards than does BAS.

[stillp has been conspicuous by his absence for a while, and was not really 'acting himself' when last seen, so I hope he's OK. I have just taken steps to attempt to find out]

Kind Regards, John

 

[ban-all-sheds]

I don't think there was any certainty.

Did I misunderstand this?

You should have read the end of that back-and-forth, If you had, you will have seen the agreed conclusion that, as far as the regs are concerned, it would seem that any cable with an earthed metal covering is seemingly deemed OK for burying, provided only that the metal covering is "adequate as a CPC", seemingly regardless of the material or mechanical properties of that covering.

522.6.204 does indeed state that therefore I can conclude that the cable has an earthed metallic covering. (screen more usually used for emf reasons)

A strange conclusion, given that the standard describes itself as "Specification for 300/500 V screened electric cables"

The only difference in requirements for being buried in a wall or the ground is that of a covering or a sheath respectively.

It would be difficult to distinguish semantically between these two words, would it not?

A difficulty not helped (again) by sloppy language in the Regulations.

Unless there is a "proper" definition elsewhere of which we are unaware. After all - nowhere does BS 7671 define 'core', or 'multi-core' or 'single-core', but it uses these terms, and generally people know that the top one here is a single core, and that the lower one has 3 cores, not 21.

But returning to BS 8436, the standard describes the use case as "for use in walls, partitions and building voids". Not underground

The table of contents:

Chapters 9 & 10 would indicate that the screen is not a sheath, and that the screen and sheath are different layers.

This is how IDH describe their Guardian cable:

• Plain annealed stranded copper conductor to BS6360
• XLPE insulation to BS6889
• Aluminium screen tube, applies longitudinally.
  
• CPC tinned annealed stranded copper to BS6360.
• LSZH sheath to BS EN 50267-2-1:1999 and BS EN 61034:2005, UV stable.

That's not a metal sheath.

As I said earlier, the only cable I am aware of which says it is metal sheathed is MIMS.

I'm pretty sure that, before this discussion arose, if asked "which part of a cable is the sheath?", probably most people would say "the outer layer",

and that anyone trying to say "no, it's one of the inner layers", would have an uphill struggle.

 

[JohnW2]

Did I misunderstand this?

It looks as if you may have done ....

.... that, as far as the regs are concerned, it would seem that any cable with an earthed metal covering is seemingly deemed OK for burying, provided only that the metal covering is "adequate as a CPC", seemingly regardless of the material or mechanical properties of that covering.

What aspect of "seem" and "seemingly" do you think indicates certainty?

Kind Regards, John

 

[EFLImpudence]

Did I misunderstand this?

John said "it would seem". Does that denote certainty?

A strange conclusion, given that the standard describes itself as "Specification for 300/500 V screened electric cables"

...but 522.6.204 allows that cable while only calling for an earthed metal covering. It does not mention screen.​

A difficulty not helped (again) by sloppy language in the Regulations.

Do you therefore agree a covering is a sheath - and vice versa?

But returning to BS 8436, the standard describes the use case as "for use in walls, partitions and building voids". Not underground

It may be unsuitable underground for different reasons but 522.8.10 only calls for an earthed metal sheath.

Chapters 9 & 10 would indicate that the screen is not a sheath, and that the screen and sheath are different layers.

Is a screen also not a covering and so the cable should not be suitable for burying in walls?
Is the armour (of swa) not a sheath and so not suitable for underground?