Twin + Earth - no sleeve on earth

[JohnW2]

But it appears from the patent that the cpc was specifically intended to serve as a ripcord, so it should be able to withstand that (ab)use.

As I've been saying, I imagine that was the intention/implication of the patent, even though it does not seem to actually say that explicitly.

As I've also just written, I have managed to reassure myself that (with my caveat about the importance of an initial 'nick' in the sheath) the 'abuse' represented by this approach does not seem to do any appreciable harm.

Kind Regards, John

 

[JohnW2]

I don't care why it's not already covered but it just wish is was as I hate the fiddlyness of putting sleeving on...

I would personally say that the amount of 'fiddlyness' involved is pretty trivial.

Given the hundreds of kilometres of cable that are manufactured, it could be argued that it is hard to justify the effort, cost, material usage and even environmental impact of insulating the CPC throughout it's length, when only a very tiny proportion of its length actually needs (or may need) to be sleeved.

I do struggle to think of any electrical reason for insulating the CPC. On the contrary, as I've said, the only electrical consideration I can think of would seem to favour leaving it 'bare'.

Kind Regards, John

 

[ebee]

Around here the local Electric Board and Colleges, back in the 60s/70s did teach cutting with a sharp knife, usually a penknife. However there was a lot of practicing for the apprentices to do it right so they could end up doing it in their sleep, it was bred into them. Similarly other trades had stuff hammered (sorry I mean taught) into them and once they got things right each time by habit they were pretty good.
Similarly at schools students had up to 12 x tables hammered/taught . Nowadays they use a calculator and get it completely wrong by a factor of 10 or 100 and don`t even realise their error. oh and three out of every two of them did not understand fractions either

 

[JohnW2]

Around here the local Electric Board and Colleges, back in the 60s/70s did teach cutting with a sharp knife, usually a penknife. However there was a lot of practicing for the apprentices to do it right so they could end up doing it in their sleep, it was bred into them. Similarly other trades had stuff hammered (sorry I mean taught) into them and once they got things right each time by habit they were pretty good.

I'm not quite sure of your point. It's obviously the case that the more one practices something, the better one gets at doing it.

However, I think it goes without saying that, no matter how experienced one is, any techniquie which involves taking a knife/blade rto the sheath of a cable inevitably comes with some eisk of damaging the insultaion of conductors. As I assume most people do, if I take a knife to T+E, I try to keep the blade in the middle (hence over the CPC) and, similarly will orientate flex so that if I damage anything it would be G/Y insulation. Howver, the blade often refuses to follow a totally straight course (particularly with flex), so there is always going to be some 'risk'.

Similarly at schools students had up to 12 x tables hammered/taught . Nowadays they use a calculator and get it completely wrong by a factor of 10 or 100 and don`t even realise their error. ....

Indeed. I was 'brung up' in the pre-calculator days, and what we used instead (slide rules) gave no indication about the 'factors of 10 or 100'. We therefore were taught ('drummed into us'!) to always first undertake (and document) very rough calculations to acertain the ballpark of the answer - and the same process might not be such a bad idea for those using calculators

.... oh and three out of every two of them did not understand fractions either

I think my daughters understand halves and quarters, but I'm not sure about much beyond that! ... but I guess that we now live in a 'digital' (hence largely decimal) world!

Kind Regards, John

 

[pcaouolte]

If you strip the cable by running a sharp knife along the CPC there is still a chance that the knife cuts into the copper reducing it's CSA. I'm with John, a nick in the end of the cable with the cutters and a pull on the CPC as a "rip cord" gets the job done. What do professional electricians do?

 

[Sureitsoff?]

"a nick in the end of the cable with the cutters and a pull on the CPC as a "rip cord" gets the job done."

yep, thats what I do

 

[JohnW2]

If you strip the cable by running a sharp knife along the CPC there is still a chance that the knife cuts into the copper reducing it's CSA.

Unless you somehow managed to remove some copper, or cut across part of the cross section of the CPC (which would be almost impossible), you wouldn't actually reduce the CSA, even if you 'cut a slit' all the way through (longitudinally). That doesn't worry me. However, as I've rcently written, there is a real risk of the blade slipping aeay from the COPC and hence threatening the insulation of one of the live conductors.

I'm with John, a nick in the end of the cable with the cutters and a pull on the CPC as a "rip cord" gets the job done.

Yep, that's how I usually start. However, once one has got a couple of inches of sheath 'ripped', if one wants more one can then grasp all 3 (or four) conductors and pull them, with less risk of 'stretching' any of them

What do professional electricians do?

I'm seen them use almost every approach one can think of. The methods which trend to make me most 'nervous' are those which use new-fangled 'gadgets' to do the stripping.

Kind Regards, John

 

[ebee]

If you strip the cable by running a sharp knife along the CPC there is still a chance that the knife cuts into the copper reducing it's CSA. I'm with John, a nick in the end of the cable with the cutters and a pull on the CPC as a "rip cord" gets the job done. What do professional electricians do?

nope it is a practice thing. you never nick it once you learn properly. brfore that point you nick it loads. that is the whole point

 

[JohnW2]

nope it is a practice thing. you never nick it once you learn properly. brfore that point you nick it loads. that is the whole point

As I often say, one of the very first things I was taught in my higher education was that, because the real world is such that it is, if a statement (or exam question) contains words like "never", "always", "all", "none" etc., then it is very unlikely to be true.

Having said that, I can immediately offer one pertinent exception to that rule ...

. If you don't use a sharp instrument to strip cable then you will NEVER nick anything

Kind Regards, John

 

[Harry Bloomfield]

I would add that my reason for taking that approach has not been primarily a matter of 'laziness' but, rather, that any other approaches involve the use of a knife/blade/whatever that might damage the insulation of the live conductors. I have therefore tended to regard the 'ripping' approach as probably, 'on balance', being 'safer'

My personal choice, is that of using a Stanley knife, inserted via the cut end of a T&E, and using the earth wire as a guide for the blade to follow. With practice, it becomes second nature, to not damage the insulation of the L or N, if the blade is angled very slightly towards the earth conductor.

 

[Harry Bloomfield]

If you don't use a sharp instrument to strip cable then you will NEVER nick anything

I was taught a blunt blade is a dangerous thing - the more blunt they are, the less predictable they can become

 

[JohnW2]

My personal choice, is that of using a Stanley knife, inserted via the cut end of a T&E, and using the earth wire as a guide for the blade to follow. With practice, it becomes second nature, to not damage the insulation of the L or N, if the blade is angled very slightly towards the earth conductor.

Again, it's really a question of what one has had a lot of experience ('practice') of doing - so it's really a case of 'every man to his own thing'.

I have tried what you describe, but not often enough for it to have 'become second nature'. When one hasn't reached that stage, it's pretty easy to shave a bit of insulation off the side of the adjacent live conductor.

Kind Regards, John

 

[JohnW2]

I was taught a blunt blade is a dangerous thing - the more blunt they are, the less predictable they can become

That's very true. As I imagine you actually will have understood, when I wrote "a sharp instrument", I really meant "a cutting instrument" - and, as you say, a blunt cutting instrument is, in many contexts, 'more dangerous' than a sharp one. However, if one doesn't use a cutting instrument at all, then the issue of sharpness/bluntness doesn't arise!

Kind Regards, John

 

[FrodoOne]

It is, perhaps. a pity that the following Video was only an April Fools Day "joke".

"Twin and Earth" cables, in almost any OECD country, other than the UK
(and North America - where the Ground/Earth is not [usually] mentioned),
are now REQUIRED to have the "Earth" conductor insulated - to the same standard as the "current carrying" conductors.

https://en.wikipedia.org/wiki/Electrical_wiring is "interesting"
in that it indicates (in "Color codes") - for
"United Kingdom from April 2004 (BS 7671)"
"the Protective earth/ground (PE)" - shall be insulated "Green/Yellow".
(Perhaps this Wikipedia item needs "correction"?)

https://en.wikipedia.org/wiki/Twin_and_earth may also be of interest.

To add another "comparison": -
In Australia (and NZ),
while cables with "solid" conductors of 1.5 mm² (CSA) and 2.5 mm² (CSA) ARE available
(in 100 m Rolls, from Electrical Suppliers)
these are hardly ever used.
Virtually all cables sold in these sizes use stranded conductors, because such cables are much easier to work with.

1.0 mm² (CSA) Twin and Earth cable has solid "current carrying" conductors but
the "Insulated Protective Earth" conductor is stranded.

 

[JohnW2]

It is, perhaps. a pity that the following Video was only an April Fools Day "joke". ..... Twin and Earth" cables, in almost any OECD country, other than the UK
(and North America - where the Ground/Earth is not [usually] mentioned), are now REQUIRED to have the "Earth" conductor insulated - to the same standard as the "current carrying" conductors.

True - but, as I keep asking, "why?".

As I've said, the only real electrical argument (albeit a pretty 'weak' one) I can think of actually favours having the CPC not insulated. Beyond that, the only real differences I can see are a bit more plastic (hence presumably a bit more cost) and slightly larger cables.

You clearly feel that CPCs should be insulated 'everywhere' (including UK and North America) so perhaps you could help me understand by explaining why (in terms of electrical considerations) you hold that personal opinion?

Kind Regards, John