Table 4D2A vs Table 4D5

[JohnW2]

In the middle of what now has become a nonsensical mess of a silly thread, I asked (I've just added "(70 degree PVC)" for clarity):

One thing I've never understood is why, although Table 4D2A gives CCC figures for "two core cable (70 degree PVC), with or without a protective conductor" (and says nothing which excludes 'flat cables'), some of the figures for Reference Methods A and C are very slightly different from those given in Table 4D5 ("flat cable {70 degree PVC} with protective conductor").

Can someone help me understand the reason for this?

.. and (probably because most sane people had given up on the thread by then), the only response I reeceived was:

Although I was grateful for that thoughtful response, it didn't fully answer my question, so I wonder if anyone else can help me with their thoughts. Thanks.

Kind Regards, John.

 

[ban-all-sheds]

Once upon a time there was only 4D2A.

You can read about how, and why, 4D5A, with specific ratings for flat twin & earth for installation methods commonplace in domestic dwellings came about here:

http://www.theiet.org/publishing/wi.../pre14-BS7671-amd1-ring-circuits.cfm?type=pdf

Oh...

You already have: //www.diynot.com/forums/viewtopic.php?p=1924664#1924664

(Sorry - couldn't resist - wasn't meant to be sarky)

 

[JohnW2]

Once upon a time there was only 4D2A. You can read about how, and why, 4D5A, with specific ratings for flat twin & earth for installation methods commonplace in domestic dwellings came about here:
http://www.theiet.org/publishing/wi.../pre14-BS7671-amd1-ring-circuits.cfm?type=pdf
Oh...
You already have: //www.diynot.com/forums/viewtopic.php?p=1924664#1924664[/QUOTE]
Thanks. Ah yes, I'd forgotten that. That does indeed, remind me why the CC of 2.5mm² T&E Method A was increased to 20A, so as to 'legalise' 2.5mm² 32A RFCs.

Do I take it, therefore, that the other slight differences between the tables exist simply because the ERA's measurements (which resulted in the above-mentioned increase to 20A) happened to turn up figures slightly different from Table 4D2A - e.g. for 6mm² and 10mm² cables, which obviously are not directly relevant to standard RFCs?

Once(Sorry - couldn't resist - wasn't meant to be sarky)

We're all asllowed some fun

Kind Regards, John.

 

[ban-all-sheds]

Those of a cynical nature might wonder if at least some of the values in Table 4D5A were known before the tests were actually done, so fortuitous were the results, and that other entries were put in to flesh it out for verisimilitude.

But I couldn't possibly comment.

 

[JohnW2]

Those of a cynical nature might wonder if at least some of the values in Table 4D5A were known before the tests were actually done, so fortuitous were the results, and that other entries were put in to flesh it out for verisimilitude.

You read between my lines very well!

Kind Regards, John