Wiki article on T&E cable dimensions

[JohnW2]

A comment in another thread has caused me to just look at the wiki article of T&E dimensions and I find that it seems to contain one incorrect/potentially misleading statement.

An asterisk in the heading of the "Diameter of Live/Neutral Cores" column leads to a footnote which says "Total diameter for stranded cores". I presume that most people will take that to mean the figure one gets of adding up the diameters of the individual strands - which is totally incorrect in terms of what is tabulated. In fact, what appears in that column for stranded cables is the diameter of the equivalent solid core conductor.

Consider an example. 4mm² T&E usually has L/N conductors which each have 7 strands of approximately 0.853mm each. If, as suggested by the table, the 'total diameter' of the stands was 2.26mm, this would presumably mean that each of 7 strands would have a diameter of about 0.323mm (2.26 divided by 7). A conductor with 7 strands, each of 0.323mm diameter, would have a CSA of about 0.57mm², not 4mm². The 2.26mm figure tabulated is the correct one for the "diameter of the equivalent solid core conductor" for a 4mm² conductor.

Kind Regards, John

 

[DetlefSchmitz]

"Total diameter for stranded cores". I presume that most people will take that to mean the figure one gets of adding up the diameters of the individual strands

Must admit I wouldn't. But you're right in that in should probably say "Combined diameter for twisted stranded cores".

It is however a "Wiki". So feel free to correct it!

 

[JohnW2]

"Total diameter for stranded cores". I presume that most people will take that to mean the figure one gets of adding up the diameters of the individual strands

Must admit I wouldn't. But you're right in that in should probably say "Combined diameter for twisted stranded cores".

What would you take that alternative wording to mean? I think I would probably ponder for a good while and yet again conclude that 'combined' probably was intended to mean 'added together'.

I think the real truth is that, for example, the value of 2.26mm really has no useful meaning in relation to real-world (stranded) 4mm² cable (being the diameter of a 4mm² conductor if it were solid - which it virtually never is!), and therefore probably should not be there at all - and the same for all the larger cable sizes. If one includes anything in that column for standed cables (i.e. ≥ 4mm²), it probably should be 'the truth' - e.g. "7 x 0.853mm" for 4mm²

Kind Regards, John

 

[DetlefSchmitz]

It's a Wiki. You can change it to what you like. If anyone disagrees they can change what you wrote. If what you wrote makes sense, it won't get changed. Take your courage in your hands!

 

[JohnW2]

It's a Wiki. You can change it to what you like. If anyone disagrees they can change what you wrote. If what you wrote makes sense, it won't get changed. Take your courage in your hands!

OK. The deed has been done - does anyone have any comments on the revised Wiki?

Kind Regards, John

 

[ban-all-sheds]

I haven't looked at the revised Wiki, so I cannot comment on it.

I can, however, comment on the stuff above which fails to recognise that diameter and area are geometric concepts and that therefore the total of more than one diameter values is not the arithmetic total.

 

[JohnW2]

I haven't looked at the revised Wiki, so I cannot comment on it.

If you have a moment sometime, I'd be grateful for your comments.

I can, however, comment on the stuff above which fails to recognise that diameter and area are geometric concepts and that therefore the total of more than one diameter values is not the arithmetic total.

Although, as I implied in my posts, it wasn't totally clear what the previous version of the article meant by 'total diameter for stranded cores', I really don't understand what you mean by "the total of more than one diameter values is not the arithmetic total". A diameter is simply a linear measurement, and if one wants a 'total' of several of them (although that would be an unusual requirement), then the simple 'arithmetical total' would be totally appropriate. If you think otherwise, I'd be very interested to hear what you think 'a total of more than one diameter' actually is.

What is clear (at least to me ) is that the 'diameter' figures given for stranded cables in the previous version of the Wiki (e.g. 2.26 mm for 4mm² cable) were, at best, of no usefulness and, at worst, potentially confusing/misleading - since they related to what the conductor diameter would be if the cable were solid (which, of course, it is not). I'd like to think that my revision to the Wiki makes it a bit clearer, and possibly a bit more useful for some people, since it simply states the facts (the actual diameters of the cores/strands) - but you may, of course, disagree!

Kind Regards, John.

 

[Robgers]

Can I ask, is this a mine is bigger than yours or a mine is smaller than yours thread

 

[holmslaw]

..

 

[mikhailfaradayski]

probably around the 430 mark, i'd say

http://www.youtube.com/watch?v=Lbg_mq6Y018

 

[JohnW2]

I haven't looked at the revised Wiki, so I cannot comment on it.
I can, however, comment on the stuff above which fails to recognise that diameter and area are geometric concepts and that therefore the total of more than one diameter values is not the arithmetic total.

After a night's sleep, it has dawned on me that the 'total diameter' the Wiki was previously talking about referred to the measurement across the whole bundle of strands, which enables me to understand what BAS was getting at with his comment.

However, the figures quoted in the previous version of the Wiki for stranded cables were not correct, even for 'measurement across the bundle of strands.

Having 7 strands in these cables obviously leads to a very neat geometrical arrangment, with the 6 outer strands all having tangential contact with the central one, as well as those on either side. It follows from this geometry that a measurement 'across the bundle of strands' (which is the closest one can get to a 'diameter' for something which is not a perfect circle) will be equal to 3 times the diameter of each of the strands. For 4mm cable, this is about 2.56mm (0.853mm x 3), rather than the previously tabulated 2.26mm (which would be the diameter if it were a solid core). The reason it's a bit bigger is obviously that there are some small 'air gaps' between the strands.

My revisions to the Wiki remain completely correct, but do you think it would be preferable to include the 'measurement across the bundle of strands' (in addition to, or instead of, the current figures), since that is what people would presumably try to measure? These figures would be 2.56mm for 4mm², 3.13mm for 6mm², 4.05mm for 10mm² and 5.12mm for 16mm².

Kind Regards, John

 

[mikhailfaradayski]

Hi John,

Good point, well put.

-All very cerebral and intelligent of you, but you really need to get out a bit more.

Just a point though, who exactly do you think may have been confused with the discrepancy you have discovered?

(I'm just trying to establish who you think would measure the strands of piece of wire in millimetres to 2 or 3 decimal places as opposed to identifying the cable by some other, probably simpler means)

 

[JohnW2]

(I'm just trying to establish who you think would measure the strands of piece of wire in millimetres to 2 or 3 decimal places as opposed to identifying the cable by some other, probably simpler means)

Very good question. However, the Wiki exists, seemingly as an aid to help (DIY) people in identifying the size of cables, and therefore might as well be correct. You've only got to look at the posts in the recent thread ('Extending cables') which led me to the Wiki to see how confused 'lay' people can be about cable size specification! I've given figures to two decimal places for consistency with the precision (2 DP) of the existing figures in the Wiki.

For completeness, following BAS's comments, I have now added the approximate measurements across the bundle of strands - which is probably the thing which most people would try to measure, if anything.

The most obvious "other, probably simpler, means" for modern cables is that the size is usually embossed on the sheathing!

One source of potential confusion which hadn't even occurred to me until I saw that recent thread is that the diameter of conductor+insulation in mm is, for cable sizes between 1.5mm² and 4mm², not that far off the CSA in mm² - which I suspect is why the op in that thread was talking about "3mm" and "5mm" cables (probably 2.5mm² in the first case and 4 or 6 mm² in the second).

Kind Regards, John