A handy guide, but it does not seem to be displaying the tables correctly with the sizes that are a problem in red.

Using SWA as a CPC the guide for your reference. (gadsolutions.biz)

Using SWA as a CPC the guide for your reference. (gadsolutions.biz)

"The use of Jubilee clips to terminate the armour is an absolute bodge"

But what about lighting column cut-outs? https://www.lucyzodion.com/product/thm0028975-titan-single-fuse-cut-out/
Granted it includes a brass tube to support the inside of the armour, but presumably have proved to be satisfactory.

   - Andy.

Graham, yes, I hadnt thought of it that way and had just slavishly followed Chief Examiner comments (and some of the older texts like BD Jenkins who shows calcs to 60 for the wire armour, albeit as an average of initial and final temps). It all becomes  unnecessarily arcane when one considers the current practice of using 218.5v that used to be 240v then 230v to calculate Zs not to mention the uncertainty of the value of Ze. I believe GB and Mike are probably spot on with that micrometer and axe analogy. 

I just spotted a howler in my own Excel calcs regarding some swa values. I have been extracting data from this table from Paul Cooks wonderful commentary on the 17th. 

I couldnt understand why my calculations using old fashioned approach of separate r and x value was just so far apart from the one in the CPEVCEI 5th Edition until I twigged the r value for the 70C swa was significantly different to the value for 90C thermosetting given in IETEIDG. One is 3.9 and the latter 6. There must be significantly less csa of wire armour in the 90C cable?

Be wary of modern cables claiming to be BS6346 (the PVC clad SWA) as that standard was withdrawn over ten years ago, and the XPLE standard ' 5467 is the more common.

Worth a read of this wiring matters article Of course there is plenty of old cable about the place. But the diameter and no of the steel wires is not guaranteed the same and can be a source of confusion.

Except for BATT cables data, where their values are not always quite the same as those tables either. but the variation of armour resistance between their XPLE and PVC offerings is shown side by side, so is easier  to see.

Mike

I am typing this for insertion below GKs post of two days ago. I dont know why the reply rarely gets posted like that and ends up at the foot of the thread. Nor indeed, does the quote button work Windows 11 PC. It does on my Ipad.

the correction should be to 60C and should be 1.18 rather than 1.225

I am convinced that there is a dusty room somewhere in the dungeons of City and Guilds HQ where equally dusty, bespectacled, old men pour over IET publications in search of secreted minutiae to ambush the unsuspecting candidate. Below from current EIDG.

Yes, I think that, assumption is absolutely fine in some cases, hence that hasn't been updated ... but not others, and in particular perhaps shared ducts for EV charging which is the other example quoted.

I agree with your suggestion that some more examples ... perhaps with the various assumptions used noted, as here ... would be of great benefit to everyone concerned.

At the last update, we were trying our best to move the publication on to align with PD IEC/TR 50480 because of a number of issues relating to calculations, and following the update/withdrawal of some of the armoured cable standards, and the data they provided.

I have a copy of a previous EIDG book and I calculated the total loop impedance at C (Zef) using the formula

where 

r=0.0815 ohms

and 

x=0.0597 ohms

Zef=0.1 ohms

Ief=2500 Amps

How does this compare to the latest edition of the book? Is there a significant difference?

Based on the previous calculations that do not apply PD IEC/TR 504801, the final result is marginally higher, which is more conservative. I will adhere to this method because the empirical measurements correspond to the calculations performed using the prior method. So why change This method I have applied repeatedly when the actual measurements have matched  the calculations.? 

Your lack of response implies that you concede to my argument. Furthermore, as I have demonstrated in my calculations, the addition I use is optimal and does not require any alteration. What is the rationale behind proposing a new standard, other than generating revenue from book sales? It seems that the bureaucrats are meddling with the matter without justification.

AMK said:

Your lack of response implies that you concede to my argument.

NONSENSE ... being unable to access the site since you posted does not indicate an agreement! This Forum is not an "answer on demand" service, but a public forum !

AMK said:

will adhere to this method because the empirical measurements correspond to the calculations performed using the prior method.

That is your prerogative.

AMK said:

So why change

As you will have gathered, some research was carried out, that provided a new empirical formula. It's not magic, but engineering.

AMK said:

What is the rationale behind proposing a new standard, other than generating revenue from book sales?

PD IEC/TR 50480:2011 is not a new standard. The IET would otherwise be criticised for not keeping up-to-date with standards. In addition, other publications (as referenced by others earlier in this thread) were already available with the (at the time) newer method, backed up by research.

There's also the issue of precedence of standards vs guidance.

AMK said:

It seems that the bureaucrats are meddling with the matter without justification.

Really? 

Hi Graham. You have mentioned PD IEC/TR 50480:2011, which is a technical report that introduces a new method of calculation and this technical report is not a standard, but a document that offers information and guidance. I would like to know why this technical report has not been developed into a standard yet? How widely is this technical report recognized and applied by the electrical engineering community? Is this technical report still being reviewed or revised by the relevant technical committees? If PD IEC/TR 50480:2011 becomes a standard, would it would most likely belong to the IEC 60364 series ?

Hi Graham. You have mentioned PD IEC/TR 50480:2011, which is a technical report that introduces a new method of calculation and this technical report is not a standard, but a document that offers information and guidance. I would like to know why this technical report has not been developed into a standard yet? How widely is this technical report recognized and applied by the electrical engineering community? Is this technical report still being reviewed or revised by the relevant technical committees? If PD IEC/TR 50480:2011 becomes a standard, would it would most likely belong to the IEC 60364 series ?

AMK said:

I would like to know why this technical report has not been developed into a standard yet?

It is a standard - but of the informative type rather than normative.

The answer to the question (which I guess should be rephrased as "why is it not published as an international standard with a simply IEC number, and BS designation in the UK), is that it provides a methodology rather than a set of requirements for electrical installations.

There are different types of standards.

AMK said:

How widely is this technical report recognized and applied by the electrical engineering community?

I understand it's used by developers of calculation packages.

However, it's a difficult question to answer, since even though SWA is commonly used, my understanding is that calculations for it are not really part of Level 3 courses any more, because the mathematics of complex numbers and phasor calculations are seen as more than "Level 3" these days (although this has not always been the case - I did complex numbers as part of O-level mathematics in the 1980s).

So, if it's not taught, who's using it?

I believe that is changing, though, at least with one of the C&G EV courses, hence the inclusion of the method in the 5th Edition EV CoP.

And as we discussed above the experimental evidence for some of  it is a bit thin - much being based on tests on two sizes of cable that are to be polite, both in the 'large' category,  It is not so clear if the empirical fitted  formulae can be safely extrapolated to cover say 4mm SWA. So it is better that it is informative data rather than binding. It might be more solid if there was EM modelling that matched the observations, or experimental results over a larger (and probably unfeasible to gather) range of armour and side cable sizes.

Also when trying to make universal  rules It is not helped by the multitude of ways that steels made to the same specs may  not be identical - steel simply made to the same nominal approximate chemical composition and a given mechanical spec can have an electrical  resistivity anywhere in a range of perhaps 2:1, depending on crystalline re-alignment that occurs during the drawing process while steels made to a given electrical spec are far better in that regard, but may be much more variable in magnetic properties and mechanical performance

And to use wires drawn from transformer grade  steels, with both well defined electrical and magnetic properties would make the cables more expensive to make than it would be to have copper armour instead...

.So SWA makers aim for a given DC resistance, and the magnetic properties vary.

No free lunch ;-)

Mike.

.

gkenyon said:

AMK said:

I would like to know why this technical report has not been developed into a standard yet?

It is a standard - but of the informative type rather than normative.

For the avoidance of doubt:

AMK said:

Is this technical report still being reviewed or revised by the relevant technical committees? If PD IEC/TR 50480:2011 becomes a standard, would it would most likely belong to the IEC 60364 series ?

JPEL/64 have responsibility for this publication in the UK, although it is unlikely to become part of BS 7671 as discussed in a previous post.