Ron Lowe wrote:
Hi, all.
Happy New Year.

And the same to you

I have a Merlin Gerin board,

My commiserations! ;-)

which I need to make some changes to, and
am looking for advice on a couple of points:

1) The M-G range of single-width single-pole RCBOs ( eg RS 467-9723 )
seem to all be type C tripping characteristic. Is it acceptable to use
type C devices in a domestic environment where type B would normally be
used?

Generally speaking yes. The usual implication of using a type C in place
of a type B is that the maximum earth loop impedance of the circuit is
reduced. However since these are RCBOs we are talking about this is a
moot point in this case.

2) Remind me what circuits require RCD protection under 17th edition?

All of em[1].

Is it *all* power rings?

Yes

Or just ones where there's a liklihood of appliances being used outside?
ISTR that lighting circuits in special locations do now. Does that
apply even if all the lighting in the special location ( bathroom ) is 12v?

Given the notes below, there is a fair chance even SELV circuits will
end up needing RCD protection for the mains section of their supply
cable. However to answer your specific question, if you can arrange
things such that the circuit powering the lights never enters the zone,
then it could in theory be unprotected.

[1] In addition to the specific requirements for "additional protection"
in special locations etc, there is also a general requirement for the
protection for buried cables. This basically means if you can't see the
cable (i.e. not surface wired) then it needs to be "protected" in some
way. This can be by encapsulation in a suitably earthed shield (so
cables like earthshield, MICC, SWA cable, or ordinary cable in metal
conduit etc are ok), or by being buried = 50mm from the surface, or by
protection with a RCD with a trip of = 30mA. Hence for most
circumstances it is simpler to provide RCD protection for all circuit
(using several RCDs!) rather than jump through the other hoops unless
there is specific reason to do so.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/