Can I use a live or neutral coloured cable with earth sleeving?

[DetlefSchmitz]

Just had a quick look at some parts of BS EN 60811 which appears to cover the sheathing (or insulation) requirements for, e.g, twin and earth. In my rapid scan, it looked as though the emphasis is on thickness, strength and chemical resistance. Although the word electrical occasionally appears I couldn't see any specific electrical measurement tests. I may easily have missed the critical part of course.

I suppose that for cables this is really the point. They just don't want the first insulation layer to be jeopardised by sheathing scraping off.

 

[JohnW2]

Just had a quick look at some parts of BS EN 60811 which appears to cover the sheathing (or insulation) requirements for, e.g, twin and earth. In my rapid scan, it looked as though the emphasis is on thickness, strength and chemical resistance. Although the word electrical occasionally appears I couldn't see any specific electrical measurement tests. I may easily have missed the critical part of course.

Yes, that's much the same as previous 'searching' achieved - i.e. we were not able to find anything about 'insulation' requirements of the sheathing.

I suppose that for cables this is really the point. They just don't want the first insulation layer to be jeopardised by sheathing scraping off.

Maybe, but I still find it hard to believe that there are not some requirements for it to be 'non-conductive' (unless earthed). Let's face it, single insulated conductors inside unearthed metal conduct would not be allowed, and that's a situation in which flexing and movement of the conductor/insulation is not an issue.

Kind Regards, John

 

[JohnW2]

Typically it would be an impulse voltage test and a power-frequency test between the conductors of the EUT and a layer of foil wrapped around the enclosure. No requirements at all for the materials used.

What's "the EUT"?

When I talked about the materials, I thought it was clear (maybe not!) that I was referring to the insulating properties of the material, and I would think that the tests you mention could be said to be addressing that.

Acceptable to whom, and for what purpose? In some documents a single layer is sufficient, if it meets the provisions of the relevant standard.

The context of this discussion is that of wiring cables in electrical installations. Are there any relevant standards which would render a single layer of covering of a conductor adequate in that situation?

Kind Regards, John

 

[ban-all-sheds]

What's "the EUT"?

My educated guess is Equipment Under Test.

 

[JohnW2]

My educated guess is Equipment Under Test.

Sounds credible.

Kind Regards, John

 

[securespark]

PVC...strippability...

Ooh...reminds me of Mrs Secure in that PVC catsuit...

 

[ban-all-sheds]

Not in recent weather, I hope.

 

[stillp]

My educated guess is Equipment Under Test.

Correct!

 

[stillp]

When I talked about the materials, I thought it was clear (maybe not!) that I was referring to the insulating properties of the material, and I would think that the tests you mention could be said to be addressing that.

No, those tests are not tests of the insulation properties of the material, but of the EUT. Tests on the material would use a standard size sample of that material.

The context of this discussion is that of wiring cables in electrical installations. Are there any relevant standards which would render a single layer of covering of a conductor adequate in that situation?

I don't know, I don't generally deal with installation standards, but I don't see why not, if that single layer met the relevant requirements. Have you ever tried to strip (calm down Secure!) Kevlar-insulated singles?

 

[JohnW2]

No, those tests are not tests of the insulation properties of the material, but of the EUT. Tests on the material would use a standard size sample of that material.

Fair enough - I can understand that. I suppose I was really thinking of what you call "a test of the EUT" (i.e. a test of the entire cable), not a test of just the material.

If, as seems probable, the insulation around the core was enough to enable the EUT/cable to pass an 'insulation' test, then it presumably would also pass that test if that insulation was surrounded by a frankly conductive sheath. Are you suggesting that, if that sheath satisfied the mechanical etc. requirements for a sheath, that such a cable would, or might, be acceptable in terms of the relevant Standards (despite having an external conductive covering that was not required to be earthed)?

Kind Regards, John

 

[stillp]

Are you suggesting that, if that sheath satisfied the mechanical etc. requirements for a sheath, that such a cable would, or might, be acceptable in terms of the relevant Standards (despite having an external conductive covering that was not required to be earthed)?

If the cable met the relevant Standard's requirements, and passed the specified tests, then it would conform to the Standard, however it was constructed.

 

[JohnW2]

If the cable met the relevant Standard's requirements, and passed the specified tests, then it would conform to the Standard, however it was constructed.

Well, yes

I was really asking for you opinion as to whether a cable which passed the specified tests would be likely to meet the relevant Standard's requirements if the outer covering were conductive (and not intended to be earthed).

Although it's not a Standard for cables, my understanding (which, as always, may be wrong!) is that a 'single-insulated' conductor inside something conductive and unearthed (e.g. unearthed conduit, armour or sheathing) would not be compliant with BS7671.

Kind Regards, John

 

[stillp]

I was really asking for you opinion as to whether a cable which passed the specified tests would be likely to meet the relevant Standard's requirements if the outer covering were conductive (and not intended to be earthed).

That would depend on the relevant Standard, not my (or your) opinion.

Although it's not a Standard for cables, my understanding (which, as always, may be wrong!) is that a 'single-insulated' conductor inside something conductive and unearthed (e.g. unearthed conduit, armour or sheathing) would not be compliant with BS7671.

Quite possibly. BS7671 can be selective as to which cables are permitted to be used in a UK installation, regardless of any cable standards to which a cable conforms.
Would you still think that a 'single-insulated' conductor inside something conductive and unearthed would not be compliant with BS7671 if the core was insulated with something that met the requirements for double or reinforced insulation?

 

[JohnW2]

That would depend on the relevant Standard, not my (or your) opinion.

I should not have used the word "opinion" - really meant "your expert advice" - i.e. I wondered whether you had knowledge of the requirements of the relevant Standard which would enable you to say whether what I described would satisfy those requirements - but, from what you have said, I presume that you do not have that knowledge.

Would you still think that a 'single-insulated' conductor inside something conductive and unearthed would not be compliant with BS7671 if the core was insulated with something that met the requirements for double or reinforced insulation?

Probably not, any more than I would think that a piece of Class II equipment suddenly becomes unacceptable if one places it in a metal box. However, that is primarily because you are talking about double (or reinforced) insulation.

As I've said before, there seems to be a difference between how conductors within enclosures and conductors within cables are treated. In the former case, unless there is an outer earthed metal casing, there is a requirement for double (or 'reinforced') insulation. With cables (in the absence of an outer earthed layer), there is still a requirement for 'two layers', but there seems doubt as to whether or not the second one has to be 'insulation'.

Kind Regards, John

 

[stillp]

I should not have used the word "opinion" - really meant "your expert advice" - i.e. I wondered whether you had knowledge of the requirements of the relevant Standard which would enable you to say whether what I described would satisfy those requirements - but, from what you have said, I presume that you do not have that knowledge.

My usual rate for "expert opinion" is £60 per hour or part thereof! I do know some Standards that would be satisfied by what you described, but you hadn't specified which Standard(s) you meant. If you meant BS7671, then no, I don't have sufficient knowledge of that Standard.

In the former case, unless there is an outer earthed metal casing, there is a requirement for double (or 'reinforced') insulation.

Where did you find that?