"Andy Wade" wrote in message ...
"pickerel" wrote in message

many thanks for lifting some of the fog...

IEE Regs (16th ed/yellow cover) page 197 Table 4B1 gives reduction
factors for cable rating.

You really should be using the blue cover versions. Some significant
changes affecting cable ratings were made in Amendment no. 1 to BS
7671:2001, notably:

yes, I have these amendments by download, but that raises the Q....

- the introduction ........, together with the
definition of a new reference installation mathod (method 6) for
cables in conduit in an insulated wall;

Q What is an 'insulated wall'? Are walls built with light(ish)weight
building blocks considered 'insulating'; or lightweight plasters such
as carlite browing?


- clarification of the requirement for 30/32 A ring circuits, i.e. that
the cable rating _as_installed_ must be 20 A or more (also that you
must consider the likely distribution of load on the cct to ensure
that the cable rating won't be exceeded).

eg 2 x 2.5mm2 FTE cables (on wall under plaster say) touching would
reduce full load rating from 27A to 0.85 x 27A = 23A.

That's correct.

but still over the 20A ring rating - so still OK unless there is some
other adverse factor in the ring?


Please can you clarify what is considered best (or standard) practice
when running ring cable up & down a wall? Separate the cables by the
required gap? Find a completely different routes for the 2 legs? Or
just run them up & down touching, just accepting the grouping
reduction?



IEE On SIte Guide (yellow cover) section 7.2.1 (page 40) & table 6C
(page 116/7) also refer. The heading to Table 6C states the factors
(only) apply to *circuits*.

No, it refers to circuits of single core cables (i.e. 'wires' in conduit,
etc.) and to multicore cables.

streuth, you need to be a lawyer for this. That heading needs reading
very slowly many times: Send for the plain English people...

Many thanks for this clarification & of 7.2.1.

snip

I recommend a thorough reading of the first few pages (headed 'Preface') of
Appendix 4 of BS 7671.


been there, done that, obviously didn't get the t shirt. but will try
again.

HTH

helps a lot, thanks

pickerel