John Rumm wrote:

What did you plug the socket tester into though? A socket on the cooker
point? If so then it would be correct for the oven to be on a RCD
protected supply anyway, simply because of this socket being there.

Except in the case where there's little or no chance of the socket being
used to supply portable equipment outdoors. In that situation no RCD is
required - unless of course it's a TT-earthed installation (in which
case RCD protection is required, but need not necessarily be 30 mA).

Take your example of the oven: the RCD would reduce the electrocution
risk in the circumstance you described, however how probable is that
particular combination of faults?

The probability of an open circuit CPC should be very low indeed, if the
installation has been done in accordance with BS 7671 [see all of
543-03-xx]. With T&E cable the chance of the CPC being severed in some
way, but not the phase & neutral conductors seems extremely unlikely -
so where was the open circuit? A bad (loose) connection, or one never
made, perhaps. Why was this not picked up in the initial testing of the
installation? Continuity of protective conductors is the very first test...

The downside of placing almost everything on a 30mA RCD when the
installation and equipment are in good condition is absolutely
minimal,

Much depends on what "everything" is, and how much of it there is. One
could argue that the best possible protection would be offered by having
a dedicated RCBO on every circuit. However this is not something you see
often, because cost must also come into the equation.

It's quite true that if everything is (and remains) in good condition
you can go for years and years with a single whole-house 30 mA RCD and
have no trips. The arrangement still doesn't comply with 314-01-01
though because "inconvenience in the event of a fault" hasn't been
minimised. Nobody would put all their circuits on to a single fuse or
MCB (using suitably rated cable throughout) and then use the argument
that it's OK because the risk of such a fuse blowing "when the
installation and equipment are in good condition is absolutely
minimal!"

[Lampholders]
Placing "out of reach" is acceptable in many circumstances.

That isn't the measure (as defined in BS 7671) being used here though,
to avoid shock by direct contact. The measure is still "protection by
barriers or enclosures" [412-03-xx] with an assumption that the
barrier/enclosure is completed by the lamp itself. Reg. 412-03-04 in
general requires that enclosures can't be opened without the use of a
tool, or some interlocking mechanism to disconnect the power first, but
this reg. goes on to make specific (historical) exemptions for ceiling
roses, pull cord switches and lampholders.

As well as the points you made, another is that the area of skin contact
with the live terminal in a lampholder is too small to give rise to a
shock current likely to be high enough to prove fatal.

The idea promulgated that 100mA RCD's are suitable as backup
protection for inadvertent contact is laughable in the extreme. Yes
you might prevent someone else getting zapped but one body on the
kitchen floor is one too many.

Not sure I follow this.

Again it seems that he is not understanding the difference between the
use of an RCD to provide supplementary protection against shock by
direct contact (30 mA RCD, as required for outdoor equipment sockets by
471-16-01, 412-06-02(ii) and in certain other situations, e.g.
bathrooms, in Part 6) and the use of an RCD to provide protection
against shock by indirect contact. This is a very fundamental
misunderstanding, despite the denial.

The only time a 100mA trip RCD would be mandated for protection from
direct or indirect contact is when EEBADS alone cannot be relied on
to do this

Careful... This is still EEBADS, it's just that the RCD (of whatever
trip current) is providing the Automatic Disconnection of Supply, rather
than an OPD [see all of 413-02-xx]. Also it's not actually mandated in
BS 7671 that such an RCD be 100 mA, merely that one may be used. The
advice that an RCD provided /only/ for this purpose should be at least
100 mA appears in the OSG [sect. 3.6.2]

--
Andy