Hi, all.
Happy New Year.

I have a Merlin Gerin board, 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?

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

Is it *all* power rings?
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?

--
Thanks,
Ron

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 |
\================================================= ================/

On 4 Jan,
John Rumm wrote:

[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.

Pedantic point, when does cable cease to be visible? If it is enclosed in
surface run trunking or conduit I'd say it was still visible and didn't need
additional protection. Is this how the 17th edition would view it?




--
B Thumbs
Change lycos to yahoo to reply

wrote:
On 4 Jan,
John Rumm wrote:

[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.

Pedantic point, when does cable cease to be visible? If it is enclosed in
surface run trunking or conduit I'd say it was still visible and didn't need
additional protection. Is this how the 17th edition would view it?

I believe it would... surface wired, or in visible trunking / conduit
ought to be fairly immune to being nailed / screwed through (well at
least by accident anyway!)


--
Cheers,

John.

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

[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.

Pedantic point, when does cable cease to be visible? If it is enclosed
in
surface run trunking or conduit I'd say it was still visible and didn't
need
additional protection. Is this how the 17th edition would view it?

I believe it would... surface wired, or in visible trunking / conduit
ought to be fairly immune to being nailed / screwed through (well at least
by accident anyway!)



How is cable dangling freely in an intenal cavity wall ( say 4x2 or fatter )
considered?




Thanks for your previous answer, it's much as I suspected.

The actual reason I posted was this:

We are having major building work done, with a couple of extensions ( up and
out! )
This adds some new circuits.
Without asking, the electrian ripped out my '16th edition' M-G CU, ( with
many spare slots ) and replaced it with a '17th edition' 'Sector' brand
whole-house RCD unit. We have a big house, with many appliances, including
a *lot* of computer equipment. This is nuisance-tripping up to 5 times a
day. I cannot determine any particular appliance or even circuit that is
causing this. It may not be an actual fault as such, just a cumulation of
normal leakages.

We have just come back from a week's skiing to find a de-frosted freezer and
fridge. And my Humax PVR missed Wallace and Grommit. I'm not best pleased.

There may or may not be an earth fault. It might just be the cumulation of
normal earth leakages. Either way, I can't live with the whole-house
approach. RCBOs would limit the damage to one circuit, and help
fault-finding if a fault is indeed present.

I have a meeting with the artichoke and builder shortly, and I'm going to
insist on changing the configuration away from the
cheapest-way-to-achieve-17th-edition-compliance-whole-house-RCD approach.

To smooth things over, I'm going to offer to supply a new fully-populated CU
myself ( I have access to M-G stuff for less than 1/4 the list price of say
£70 for an RCBO ), and just ask them to shove the 'Sector' whole-house CU
where the sun doesn't shine.


--
Ron

Ron Lowe wrote:

Pedantic point, when does cable cease to be visible? If it is
enclosed in
surface run trunking or conduit I'd say it was still visible and
didn't need
additional protection. Is this how the 17th edition would view it?

I believe it would... surface wired, or in visible trunking / conduit
ought to be fairly immune to being nailed / screwed through (well at
least by accident anyway!)



How is cable dangling freely in an intenal cavity wall ( say 4x2 or
fatter ) considered?

If it was passing through holes in the studs at their centres then you
could argue it is = 50mm from the surface and hence not in need of
further protection.

Thanks for your previous answer, it's much as I suspected.

The actual reason I posted was this:

We are having major building work done, with a couple of extensions ( up
and out! )
This adds some new circuits.
Without asking, the electrian ripped out my '16th edition' M-G CU, (
with many spare slots ) and replaced it with a '17th edition' 'Sector'
brand whole-house RCD unit. We have a big house, with many appliances,
including a *lot* of computer equipment. This is nuisance-tripping up
to 5 times a day. I cannot determine any particular appliance or even
circuit that is causing this. It may not be an actual fault as such,
just a cumulation of normal leakages.

A whole house RCD is not compliant with the 17th edition. In a small
house with relatively few circuits you could get away with two RCDs -
one protecting say downstairs power and upstairs lighting, and the other
doing the inverse. On a larger install I would expect to see more RCDs
or RCBOs used on the non RCD side of a multi split board.

Is it too late to get the sparks back to do the job correctly?

We have just come back from a week's skiing to find a de-frosted freezer
and fridge. And my Humax PVR missed Wallace and Grommit. I'm not best
pleased.

Won't help the fridge, but iPlayer may still have W&G (if not, I have a
copy on Toppy I could stick on DVD for you!)

There may or may not be an earth fault. It might just be the
cumulation of normal earth leakages. Either way, I can't live with the
whole-house approach. RCBOs would limit the damage to one circuit, and
help fault-finding if a fault is indeed present.

Indeed - I can't see how he could have fitted a single RCD and proclaim
it to be compliant. It does not meet the basic requirements for
discrimination.

I have a meeting with the artichoke and builder shortly, and I'm going

(don't you just love spell checkers ;-)

to insist on changing the configuration away from the
cheapest-way-to-achieve-17th-edition-compliance-whole-house-RCD approach.

Yup - what you have is non compliant, and also completely unsuitable for
your circumstances.

To smooth things over, I'm going to offer to supply a new
fully-populated CU myself ( I have access to M-G stuff for less than 1/4
the list price of say £70 for an RCBO ), and just ask them to shove the
'Sector' whole-house CU where the sun doesn't shine.

Not been a great fan of the MG stuff to be honest - ever since meeting
some Proteous MCBs which had a mind of their own. I hope their own label
stuff is better.

Either way, Hager and Contactum both have single module RCBOs available
for under £25 these days.



--
Cheers,

John.

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

Won't help the fridge, but iPlayer may still have W&G (if not, I have a
copy on Toppy I could stick on DVD for you!)

Thanks - but it was in HD, and I've got most of it...
Just waiting for BBC-HD to repeat it.
Should be along in a day or two...

to insist on changing the configuration away from the
cheapest-way-to-achieve-17th-edition-compliance-whole-house-RCD approach.

Yup - what you have is non compliant, and also completely unsuitable for
your circumstances.


I've met the sparks, and I'm not convinced he's the sharpest knife in the
block. I don't want to create a fuss, but I want to provide a way to get
what I want without ****ing him off, so...

To smooth things over, I'm going to offer to supply a new fully-populated
CU myself ( I have access to M-G stuff for less than 1/4 the list price
of say £70 for an RCBO ), and just ask them to shove the 'Sector'
whole-house CU where the sun doesn't shine.

TBH, compared to the cost of the overall project ( = 150K ), this is
peanuts. I just want it to be done right. I get the impression that all
he's done in the past is council flats. This is why I'm in d-i-y. I
would honestly prefer to d-i-y.

Not been a great fan of the MG stuff to be honest - ever since meeting
some Proteous MCBs which had a mind of their own. I hope their own label
stuff is better.

It's just what I have to hand cheaply.
If you look at list prices ( eg RS : £70 +VAT for an MG RCBO ), with a
15-way CU you are up at a grand fairly quickly. I can do the same for a
couple of hundred. And the sparks can shove the twenty quid 'sector' CU
where the sun don't shine.


--
Ron