unusual cable - can anyone tell me what it is please

[westie101]

I don't think anyone could really argue that the outer conductors constituted a 'earthed metal sheath' (indeed, with split con, it would be incomplete).

I would suggest that if you argued that with the regulatory bodies governig my part of the industry you would fail!
We have the same requirements for earthed metallic sheaths, so if we are seen to be complying with that - why do you think the same design of cable does ot comply on the customer side of the meter?
Don't forget, either, that we are using 3 core cables of the same basic design with 300mm2 cores

(hint the neutral is bonded to earth)

522.8.10 (page 101) : “Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both”.

So where does this state that a cable buried directly must have an earthed armour?

Concentric cables compy with ESQCR by having an earthed metallic sheath so why does it not comply with BS7671

 

[JohnW2]

I don't think anyone could really argue that the outer conductors constituted a 'earthed metal sheath' (indeed, with split con, it would be incomplete).

I would suggest that if you argued that with the regulatory bodies governig my part of the industry you would fail!

That might be true, but we were talking specifically about BS7671 compliance. We know that some things permitted by the regs on your side of the cutout/meter would not be acceptable (to BS7671) within an installation - and probably also vice versa.

We have the same requirements for earthed metallic sheaths, so if we are seen to be complying with that - why do you think the same design of cable does ot comply on the customer side of the meter? Don't forget, either, that we are using 3 core cables of the same basic design with 300mm2 cores.

I suppose you could be right, but I personally very much doubt that is what BS7671 intended. For a start, I'm not sure that a number of separate conductors, some of which are individually insulated, actually constitutes 'a sheath' in the mind of BS7671- that does, after all, leave it theoretically possible that one could penetrate the cable with something fine (e,g, a pin, wire, or even a very small screw/drill and hit the centre conductor without coming nto contact with any of the outer conductors.
i

(hint the neutral is bonded to earth)

Whilst it is obviously true that neutral is connected to earth somewhere, I really don't think that one could satisfy BS7671's requirements for 'earthing' (in any context) by connection to the installation's neutral. That means that, in the case of split con, part of the 'metallic sheath' would not be properly 'earthed' in the sense that BS7671 usually means.

I guess that the BS7671 regulation which prohibits this (clearly very different from things 'on your side' is that which forbids CNE conductors within installations. One could not, for example, use straight con within an installation and argue that the outer neutral was fulfilling the function of a CPC.

However, as we discuss so often, there's really no telling what was in the minds of those who wrote the less-than-fully-explicit regulations!

Kind Regards, John.

 

[JohnW2]

522.8.10 (page 101) : “Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both”.

So where does this state that a cable buried directly must have an earthed armour? Concentric cables compy with ESQCR by having an earthed metallic sheath so why does it not comply with BS7671

You slipped this bit in whilst I was typing my reply

No-one said that it had to have earthed armour - as you quote, it has to have earthed armour or an earthed metallic sheath. The question is whether (in the 'mind' of BS7671), outer conductors of concentric cable which are connected to the installation's neutral constitute an 'earthed metallic sheath' - and, as I have said, I personally very much doubt that, particularly in the case of split con (and BS7671 effectively bans straight con within installations).

Kind Regards, John.

 

[westie101]

No one doubts that plain con is not allowed to be used other than on the supply network.

I ask again, as split con complies with the metallic sheath requirements of ESQCR, why does it not comply with BS7671?

From ESQCR: -

. . . Underground cables and associated equipment which contain conductors not connected with earth shall be protected . . . .

(a) in respect of joints or terminations of a conductor in a low voltage system, some form of mechanical protection; and

(b) in respect of any other part of any conductor, an electrically continuous metallic screen connected with earth,

so placed as to ensure that, so far as is reasonably practicable, any tool or device likely to be used in the vicinity will make contact with that protection or screen before it can make contact with any conductors not connected with earth.

All concetric cable comply with this, if you doubt it I suggest you report the whole of the supply industry to the appropriate government department for non compliance!

 

[westie101]

No-one said that it had to have earthed armour

Read the thread there are at least 2 or 3 posters suggesting just that.

You can argue sementics and cable design, I am quite prepared to stand up in court and confirm it does comply!

 

[JohnW2]

No one doubts that plain con is not allowed to be used other than on the supply network. I ask again, as split con complies with the metallic sheath requirements of ESQCR, why does it not comply with BS7671?

As I've said, one can only guess what was in the minds of those who wrote BS7671. The main issue, I think, is the different ways in which ESQCR and BS7671 view 'earthing', partially because of the fact that ESQCR regards 'earth' and 'neutral' as being far more 'similar' than does BS7671.

My turn to ask you a question .... In any other context, BS7671 would not accept connection to an installation's neutral as constituting 'earthing'. That being the case, why do you think it should regard something as a 'continuous earthed metallic sheath' if some components of that 'sheath'were connected to the installation's neutral, not 'earth'?

Is it not this differing attitude to 'earthing' the main thing which results in BS7671's requirement for CPCs in a TN-C-S installation?

It's not primarily an engineering issue (as you have said, neutral and earth must be joined somewhere) but a 'regulations' one.

Kind Regards, John.

 

[JohnW2]

No-one said that it had to have earthed armour

Read the thread there are at least 2 or 3 posters suggesting just that.

That's probably because they have, in context, thought it through and decided that they do not think that the outer conductors of a split con cable constutute an 'earthed metallic sheath'as far as BS7671 is concerned. Given that straight con is not allowed in installations, that only leaves 'armour' or some other complete metallic sheath (maybe pyro) as being permitted for 'bare burying' by BS7671.

You can argue sementics and cable design, I am quite prepared to stand up in court and confirm it does comply!

You could certainly express your opinion (an opinion which I suggest would differ from that of many people/experts 'on the other side of the meter') - but,as I've said, I don't think that anyone other than those who wrote BS7671 could 'confirm' that it complies with BS7671.

...but I'm just a 'DIYer', so who am I to know?

Kind Regards, John.

 

[JohnW2]

Duplicate deleted

 

[westie101]

as I've said, I don't think that anyone other than those who wrote BS7671 could 'confirm' that it complies with BS7671.

On the basis that representatives from "my side of the meter" were among those I would beg to differ.

I would suggest that the only uncertainty about aspects of BS7671 rests on forums like this.

As I keep saying if it constitutes an earthed metallic sheath in one piece of legislation there is no reason why it shouldn't in another document, whilst legislation can often be strange it would be rare and fly in the face of those that are employed to ensure such differences don't occur.

[PEDANT]In fact if I think it through ESCQR is a part of the Electricity Act so is legislation, BS7671 is a set of guidelines to show how legislation could be complied with, so anything acceptable directly under legislation could be said to take precedence of other definitions{/PEDANT]

 

[JohnW2]

as I've said, I don't think that anyone other than those who wrote BS7671 could 'confirm' that it complies with BS7671.

On the basis that representatives from "my side of the meter" were among those I would beg to differ. I would suggest that the only uncertainty about aspects of BS7671 rests on forums like this. As I keep saying if it constitutes an earthed metallic sheath in one piece of legislation there is no reason why it shouldn't in another document, whilst legislation can often be strange it would be rare and fly in the face of those that are employed to ensure such differences don't occur.

As I said, I'm merely an outsider, so it's not really for me to know, or even really to have an opinion. I do, however, suspect that, despite what you say, a substantial proportion of those who do work professionally on the consumer's side of the meter would express the view that split con buried without any protection as part of an installation is not compliant with BS7671 - or, at the very least, 'is not good practice' ... but, as always, maybe I'm wrong in my suspicions about their views. Can we have some views from the electricians?

Anyway, certainly from the perspective of someone like myself, SWA is far more readily available, easier to terminate satisfactorily/neatly, quite possibly (to the likes of me) cheaper, and 'looks/feels' better protected!

Kind Regards, John.

 

[ban-all-sheds]

As I keep saying if it constitutes an earthed metallic sheath in one piece of legislation there is no reason why it shouldn't in another document, whilst legislation can often be strange it would be rare and fly in the face of those that are employed to ensure such differences don't occur.

I think it can, and does, because after the cutout N does not count as an earthed conductor - indeed there are almost universally mandated protective devices which will cut off the supply should you earth it.

So no - for electrical installations within the scope of BS 7671, split-con does not have an earthed metallic sheath.

 

[westie101]

It still does not change the fact that the neutral is connected to earth and is usually at or about earth potential!
So because there is some vague wording and some liability driven thinking it suddenly changes!

Bear in mind that this cable type has been in use for over 40 years and is surrounded by an earthed metallic sheath as is required by law!

You'll be arguing that black is white next.

 

[JohnW2]

It still does not change the fact that the neutral is connected to earth and is usually at or about earth potential!

No, it doesn't change that and, as I said, it is not primarily an engineering issue we are talking about. We're talking about regulations.

However, as I was suggesting before, do you really think that BS7671 would be satisfied if one 'earthed' exposed-conductive-parts to the neutral conductor (and, indeed, perhaps took the next logical step and 'did without' a CPC altogether)?

Where are the electricians? It seems daft that only a couple of non-electricians are having this discussion with you!

Kind Regards, John.

 

[westie101]

However, as I was suggesting before, do you really think that BS7671 would be satisfied if one 'earthed' exposed-conductive-parts to the neutral conductor (and, indeed, perhaps took the next logical step and 'did without' a CPC altogether)?

Electrically I would not disagree!

A definition of earthed that is used is "connected to the greater mass of earth"
If that is accepted then a neutral conductor in an installation is connected to the greater mass of earth by virtue of its connection to the supply network.

(This is assuming that there is no automatic device to disconnect the neutral without disconnecting the live as well)

Face it, on a PME system there is live and neutral/earth, just by calling them neutral and earth/cpc either side of the cut-out doesn't change what is connected to what

 

[westie101]

Or look at it this way.

Do you really think that the electrical engineers that were involved with the writing of BS7671 were that foolish not to see the situation?

One thing about a lot of legislation, particularly in the safety world is that it is deliberately vague to allow users to find their own solutions to comply with that legislation.