"Johnny Boy" wrote in message
...

I've installed a new kitchen sink and have put supplemental bonding
from the incoming cold water pipe across to the hot water pipe and
also to the sink. The regs don't require this but I can see no harm
in it, and it reinstates the position before the works on the
kitchen. I wonder why this was dropped from the regs?

It wasn't. Supplementary bonding never has been required in kitchens.

I also noted that the main bonding from the water pipe to the block
adjacent the CU is 6mm.sq not the 10mm.sq that the 16th ed.
specifies. I condsider that there's no need to uprate this to
10mm.sq since the regs are not retrospective. Also it would be
almost impossible physically without taking the wire round the
outside of the house! Again, I wonder what was the rationale
for the change?

You're going back to the 14th ed. here. The 15th & 16th editions both
require a minimum main bonding conductor size of at least half that of the
main earthing conductor, with a minimum of 6mm^2, or 10mm^2 for PME. If the
meter tails are 16 or 25mm^2 then the earthing conductor has to be 16mm^2,
hence the minimum main bond size becomes 10mm^2.

The rationale for the change was (a) the 15th ed.'s generally more rigorous
approach to earthing and conductor protection across the whole range of
expected fault current, and (b) the introduction of PME (TN-C-S) supplies to
the UK. 10mm^2 (or larger if the supply authority so required) was written
into leglislation affecting suppliers - originally as the PME Approval, then
in the 1988 Electricity Supply Regulations. I don't think it's in the
current ESQC Regulations (which replaced the ESR this year) but these cite
"British standard requirements" (i.e. BS 7671) instead.

Another change which took place at around the same time was to BS 6004 and
increased the size of the CPC in 2.5mm^2 T&E cable from 1.0 to 1.5mm^2.
Someone realised that - under some conditions with a rewireable fuse - the
CPC was not properly protected by the fuse.

Finally, I know it's been done a while back on previous threads but
what 's the view re 2.5mm.sq unfused spurs from 2.5mm.sq ring mains
(Type B CB at 32A). My personal view is that it's not acceptable on
grounds of cable rating - but it used to be allowed. Anyone know
why this changed?

It didn't. Unfused spurs in 2.5mm^2 are allowed, as they always have been
(provided that the 'as installed' cable rating is 20 A or more). Provided
that the design complies on voltage drop the MCB will give fault and earth
fault protection to the cable. Overload protection is provided downstream
by the fuse in the BS 1363 accessory (plug top or FCU). The load is limited
to 13 or 20 A by the restriction that an unfused spur may only feed one
single or double socket, or one item of fixed equipment. (The assumption
that the load on a double socket will not exceed 20 A is a diversity rule
which has stood the test of time.) The 14th edition was more lax, and
allowed two single sockets on the spur, but that anomaly was removed when
the 15th ed. came into force, which is over 20 years ago now.

--
Andy