I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and
b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Hence the question in my title. Is an RCBO a suitable isolator? And is
the rest of the design sensible? I can't tell from the text, or the
fuzzy picture, but I would assume that the RCBOs per way would be fast
acting, and the 'main fuse' replacement would be slow acting -
otherwise a nuisance trip could take out the whole board, which is
what I though we were trying to move away from.

If the supply is rated at 60A, is that what they would propose for the
'main fuse' equivalent? My understanding is that RCBOs (and MCBs) are
less 'forgiving' of overcurrents than fuses, so I'd actually lose some
peak capacity (not that I use it, but some might).

Of course, I can put the same questions to the firm that put the flyer
through the letterboxes, but I'd prefer some independent opinion
first, if that's possible. Thanks!

Sid

On 11 Nov, 10:10, Sidney Endon-Lee wrote:
I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and
b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' *the
current main fuse.

Hence the question in my title. Is an RCBO a suitable isolator? And is
the rest of the design sensible? I can't tell from the text, or the
fuzzy picture, but I would assume that the RCBOs per way would be fast
acting, and the 'main fuse' replacement would be slow acting -
otherwise a nuisance trip could take out the whole board, which is
what I though we were trying to move away from.

If the supply is rated at 60A, is that what they would propose for the
'main fuse' equivalent? My understanding is that RCBOs (and MCBs) are
less 'forgiving' of overcurrents than fuses, so I'd actually lose some
peak capacity (not that I use it, but some might).

Of course, I can put the same questions to the firm that put the flyer
through the letterboxes, but I'd prefer some independent opinion
first, if that's possible. Thanks!

Sid

Are you sure about the "main fuse" being an RCBO? A double pole RCD
would be more the expected item and to provide discrimination would
need to be time delayed. Otherwise any significant earth fault on any
circuit would trip that cicuits 30mA RCBO "and" the main RCD cutting
power to the whole house.
The use of a 100mA typa S, time delayed RCD as main switch or isolator
is perfectly acceptable. It does beg the question why you think you
need to replace your original consumer unit apart from cosmetic
reasons do you have any genuine concerns about your installation?
I'll bet the firm will also be hoping to pick up on all sorts of extra
works based on things they "find" once they get started.

In article
,
Sidney Endon-Lee wrote:
Of course, I can put the same questions to the firm that put the flyer
through the letterboxes, but I'd prefer some independent opinion
first, if that's possible. Thanks!

17th edition CUs have a conventional 2 pole main isolator switch and two
RCDs feeding a busbar each. On those busbars you have a choice of using
MCBs or RCBOs.

As a general point I'd be wary of using a firm just on the basis of a
flier. Unless neighbours have already used them and can vouch for their
work.

--
*Why don't sheep shrink when it rains?

Dave Plowman London SW
To e-mail, change noise into sound.

Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 10:10

I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and

Which provides the same level of isolation as the MCB that might be there in
a different, but complaint, installation.

b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Your "main fuse" is the one in the elect co's cutout, typically near and
definately before the meter.

A time delayed (type S) RCD may be used in place of the main CU isolator, or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads and it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be essentially
stupid along with RCBOs.

Hence the question in my title. Is an RCBO a suitable isolator?

As much as any equivalent device that might be used is. It will typically
only isolate L and not N (although I have two double pole RCBOs that do
isolate L+N for outside circuits, because it seemed like a good idea,
though beyond basic requirements).

This means that you should not use the RCBO to act as eg as a shower
isolator - you still need the local DP switch. But in every other respect,
the RCBO is a complete replacement for and MCB or fuse.

And is
the rest of the design sensible? I can't tell from the text, or the
fuzzy picture, but I would assume that the RCBOs per way would be fast
acting,

Yes - 30mA earth leakage trip in less than 40mS IIRC - same as any normal
domestic RCD. The current overload curves will be as fast or faster than a
typical domestic fuse and typically the same as an MCB (note there are
different curves, B, C and D: B is typical in domestic and C is
occasionally found,being a bit "slower").

and the 'main fuse' replacement would be slow acting -

Yes - in respect of the RCD trip time. The local per circuit RCBOs should
trip first and not this unit. The only way this should happen is if the
combined earth leakage is high enough but the contributing components are
too low to trip the local RCBO; or if the fault is between the RCD and
RCBOs.

otherwise a nuisance trip could take out the whole board, which is
what I though we were trying to move away from.

Exactly. But do you need the main RCD? Is the place TT earthed - or are they
proposing a split board with the RCD protecting a few random circuits and
the RCBOs bypassing the RCD? In which case the main RCD should also be
30mA/40mS.

If the supply is rated at 60A, is that what they would propose for the
'main fuse' equivalent? My understanding is that RCBOs (and MCBs) are
less 'forgiving' of overcurrents than fuses, so I'd actually lose some
peak capacity (not that I use it, but some might).

Not relevant as the main RCD doesn't do overcurrent protection.

Of course, I can put the same questions to the firm that put the flyer
through the letterboxes, but I'd prefer some independent opinion
first, if that's possible. Thanks!

I'd be wary of responding to a random flyer. If you want the work done, you
might be better getting another quote or two. OTOH, the company *may* be
genuine and you *may* benefit from them doing a bunch of identical work in
the same area (which is obviously of benefit to them too).

HTH

Tim
--
Tim Watts

This space intentionally left blank...

"Tim W" wrote in message
...
Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 10:10

I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and

Which provides the same level of isolation as the MCB that might be there
in
a different, but complaint, installation.

b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Your "main fuse" is the one in the elect co's cutout, typically near and
definately before the meter.

A time delayed (type S) RCD may be used in place of the main CU isolator,
or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads and
it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be essentially
stupid along with RCBOs.

Hence the question in my title. Is an RCBO a suitable isolator?

As much as any equivalent device that might be used is. It will typically
only isolate L and not N (although I have two double pole RCBOs that do
isolate L+N for outside circuits, because it seemed like a good idea,
though beyond basic requirements).

This means that you should not use the RCBO to act as eg as a shower
isolator - you still need the local DP switch. But in every other respect,
the RCBO is a complete replacement for and MCB or fuse.

An RCBO can eliminate equipotential bonding in bathrooms. I believe the
lights and power all have to be off the same RCBO.

"Tim W" wrote in message
...

A time delayed (type S) RCD may be used in place of the main CU isolator,
or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads and
it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be essentially
stupid along with RCBOs.

Why would you want a main RCD if you have double pole RCBOs on all circuits?
I can't see the need for an RCD in this situation.

Than-you for all of the very quick replies. I hope I can clear a
couple of things up

My place is one of a large development of purpose-built flats, built
by the GLC in the 1970s. They all have Wylex rewireable fuses in the
consumer unit, which has a 60A incomer. When I moved in, there was
still an original GLC card of fuse-wire in the cupboard with the
consumer unit. I've not had to use any of it myself, other than for an
electrician to add another 'way' to correct a d-i-y bodge I found in
the kitchen (unfused spur off a socket with three sockets off the
single ring, said spur providing power for the dishwasher, washer/
drier, and sink waste-disposal unit, with a Fridge/freezer plugged
into the ring socket.)

As far as I know, the supply is not TT. Whether it is TN-S, TN-C, or
TN-C-S, I have no idea.

As for why replace it, I like the idea of incorporating RCD
protection, so I'd been thinking off and on about doing it for quite
some time - the flier just crystallised some of my thoughts.

The flier has a fuzzy picture, so I may have mistaken a simple 'main
switch' for an RCBO - the only reason I know they are RCBOs is because
that's what they say in the text, rather than MCBs. My preference
would be to have individual RCBOs if I am replacing what's there, as
I run a fair amount of IT equipment/switch mode power supplies, and
I'd like to have enough headroom for leakage currents.

I've learned something about MCBs (thanks John) and overcurrent. Some
people I've spoken to have preferred fuses because (summarising their
words) "they tolerate a fair degree of overcurrent, and don't weld the
contacts together in fault currents"

Thank-you again all.

Sid

"Sidney Endon-Lee" wrote in message
...
Than-you for all of the very quick replies. I hope I can clear a
couple of things up

My place is one of a large development of purpose-built flats, built
by the GLC in the 1970s. They all have Wylex rewireable fuses in the
consumer unit, which has a 60A incomer. When I moved in, there was
still an original GLC card of fuse-wire in the cupboard with the
consumer unit. I've not had to use any of it myself, other than for an
electrician to add another 'way' to correct a d-i-y bodge I found in
the kitchen (unfused spur off a socket with three sockets off the
single ring, said spur providing power for the dishwasher, washer/
drier, and sink waste-disposal unit, with a Fridge/freezer plugged
into the ring socket.)

As far as I know, the supply is not TT. Whether it is TN-S, TN-C, or
TN-C-S, I have no idea.

As for why replace it, I like the idea of incorporating RCD
protection, so I'd been thinking off and on about doing it for quite
some time - the flier just crystallised some of my thoughts.

The flier has a fuzzy picture, so I may have mistaken a simple 'main
switch' for an RCBO - the only reason I know they are RCBOs is because
that's what they say in the text, rather than MCBs. My preference
would be to have individual RCBOs if I am replacing what's there, as
I run a fair amount of IT equipment/switch mode power supplies, and
I'd like to have enough headroom for leakage currents.

I've learned something about MCBs (thanks John) and overcurrent. Some
people I've spoken to have preferred fuses because (summarising their
words) "they tolerate a fair degree of overcurrent, and don't weld the
contacts together in fault currents"

Thank-you again all.

Sid

I would tend to go for double-pole RCBOs on all circuits. And, I'm this is
right, have the bathroom's light and power off just one and I know it is
easier said than done, that is why some have an RCBO on a surface patress
over the bathroom door in the hall. I think double-pole RCBOs is standard
in new installations in Germany - they use radial rather than ring circuits.
More expensive but worth it.

I'll just make a small observation, which I know is not comparing like
with like, but it seems quite amazing to have gone from fuses with a
replaceable element that (in the case of rewireable) costs a few
pennies, to dual-pole RCBOs which cost 70-80 pounds a piece!

I understand the some of the safety advantages - can't replace the
fuse with a hairgrip, RCD is good. And there's the cost of fitting
things into DIN format. It's still quite a contrast.

Sid

On Nov 11, 2:56*pm, "Doctor Drivel" wrote:
I would tend to go for double-pole RCBOs on all circuits.

Good way of ending with a mile-long CU & higher cost.

I think double-pole RCBOs is standard
in new installations in Germany

Standard in Italy & Germany.
Specifically because polarity is not indicated nor guaranteed.

- they use radial rather than ring circuits.

Nothing to do with this, although several radial offer better
compliance with 314.1 than a single ring. A ring final circuit however
offers some safety benefit over radial re 2 paths to earth. A radial
final circuit of 20A offers some safety benefit over ring in that a
double 13A socket can actually only supply 19.5A yet has a 32A CPD.
Not a problem except in kitchens with few sockets and lots of heavy
appliances where Things Can Get Toasty.

More expensive but worth it.- Hide quoted text -

Not worth it at all.
Fixed appliances have their own DP isolator, then lockoff the relevant
MCB/RCBO or main switch).

- Have an incomer Main Switch (DP Isolator).
- Have RCBO per circuit or 3x RCD (makes for a long 21-way CU which
requires a tube trip to get from one end to the other).
- Ensure at least 2 spare ways.

Also what brand are they - I ask in case one fails and you can't get
replacements re maintaining type-approval of existing board.
Contactum, Hager, MK, MEM, MG, Square-D are all a "known quantity"
whereas there is some real grotty stuff out there.

Make sure electrical tests (RCD in particular) are done on *your house/
flat* vs done on one and copied for the rest as can happen because it
can save a lot of time and a QA spark is busy looking the other way /
too busy / not checking.

I assume you have a smoke alarm?
Reason I ask is depending on the cost things might be better "spread
around".

I assume your wiring is modern PVC, not Pyro/MICC or TRS rubber?
If the latter you may get involved in a rewire of partial circuits,
one reason they might be suggesting RCBO so they can get "some
circuits back on" and fight any remedials with the remaining. Pyro is
fine, although it has some short comings (if people DIY'd in the past
they might have stuffed something enough to make an RCD trip).

Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 14:32

Than-you for all of the very quick replies. I hope I can clear a
couple of things up

My place is one of a large development of purpose-built flats, built
by the GLC in the 1970s. They all have Wylex rewireable fuses

Whilst a rewireable fuse isn't inherently bad *providing* no-one lashes in
the wrong size wire or a nail (which is the main criticism, along with the
lack of ease of resetting them) - but the lack of RCD protection is well
worth the effort of upgrading the CU. It's also an excellent opportunity to
assess the state of the wiring via the PIR type checks that anyone changing
a CU should be doing. 1970's wiring should be fine, but checks could still
uncover problems or even original errors like broken rings and dodgey
earths.

However, this might be something to watch out for - is the company actually
on the lookout for additional work, with the risk that they might invent
problems that can only be cured with a full rewire. Worth being ready to
challenge them on that, should it happen. Make sure they don't start any
work wihtout an agreed price and scope.

in the
consumer unit, which has a 60A incomer. When I moved in, there was
still an original GLC card of fuse-wire in the cupboard with the
consumer unit. I've not had to use any of it myself, other than for an
electrician to add another 'way' to correct a d-i-y bodge I found in
the kitchen (unfused spur off a socket with three sockets off the
single ring, said spur providing power for the dishwasher, washer/
drier, and sink waste-disposal unit, with a Fridge/freezer plugged
into the ring socket.)

As far as I know, the supply is not TT. Whether it is TN-S, TN-C, or
TN-C-S, I have no idea.

Then there is no perceiveable reason to have a main RCD. They might be
proposing a split board with one main switch, feeding a bunch of RCBOs down
one side for sockets and then an RCD protecting a bunch of MCBs for
lighting or some variation on that scheme.

As for why replace it, I like the idea of incorporating RCD
protection, so I'd been thinking off and on about doing it for quite
some time - the flier just crystallised some of my thoughts.

The flier has a fuzzy picture, so I may have mistaken a simple 'main
switch' for an RCBO - the only reason I know they are RCBOs is because
that's what they say in the text, rather than MCBs. My preference
would be to have individual RCBOs if I am replacing what's there, as
I run a fair amount of IT equipment/switch mode power supplies, and
I'd like to have enough headroom for leakage currents.

I've learned something about MCBs (thanks John) and overcurrent. Some
people I've spoken to have preferred fuses because (summarising their
words) "they tolerate a fair degree of overcurrent, and don't weld the
contacts together in fault currents"

Thank-you again all.

Sid

--
Tim Watts

This space intentionally left blank...

Doctor Drivel
wibbled on Wednesday 11 November 2009 14:56


I would tend to go for double-pole RCBOs on all circuits. And, I'm this is
right, have the bathroom's light and power off just one and I know it is
easier said than done, that is why some have an RCBO on a surface patress
over the bathroom door in the hall. I think double-pole RCBOs is standard
in new installations in Germany - they use radial rather than ring
circuits. More expensive but worth it.

Yes they are considerably more expensive (and harder to source), and usually
take up 2 ways rather than 1 in the CU. If they were cheaper and slimmer,
I'd agree and have done it myself. As it was, I could only justify DP on
external circuits as being a decent compromise.

Cheers

--
Tim Watts

This space intentionally left blank...

js.b1 wrote:
... what brand are they - I ask in case one fails and you can't get
replacements re maintaining type-approval of existing board.
Contactum, Hager, MK, MEM, MG, Square-D are all a "known quantity"
whereas there is some real grotty stuff out there.

Make sure electrical tests (RCD in particular) are done on *your house/
flat* vs done on one and copied for the rest as can happen because it
can save a lot of time and a QA spark is busy looking the other way /
too busy / not checking.

I assume you have a smoke alarm?

Yes, in fact more than one.


Reason I ask is depending on the cost things might be better "spread
around".

I assume your wiring is modern PVC, not Pyro/MICC or TRS rubber?

All the wiring I have seen is PVC. A previous house had unshuttered BS
546 sockets with exposed conductors, rubber covered-wiring, and also
lead-sheathed paper-wrap. The fuseboxes under the stairs were a wonder
to behold. The landlord didn't care.

If the latter you may get involved in a rewire of partial circuits,
one reason they might be suggesting RCBO so they can get "some
circuits back on" and fight any remedials with the remaining. Pyro is
fine, although it has some short comings (if people DIY'd in the past
they might have stuffed something enough to make an RCD trip).

The electrician who rectified the kitchen bodge ripped out and made
safe the other bodges we could find, including the classic use of
bellwire to carry power to a cupboard light.

Regards,

Sid

"js.b1" wrote in message
...
On Nov 11, 2:56 pm, "Doctor Drivel" wrote:
I would tend to go for double-pole RCBOs on all circuits.

Good way of ending with a mile-long CU & higher cost.


And greater protection and the lot not tripping out only that circuit.

"js.b1" wrote in message
...

Nothing to do with this, although several radial offer better
compliance with 314.1 than a single ring. A ring final circuit however
offers some safety benefit over radial re 2 paths to earth. A radial
final circuit of 20A offers some safety benefit over ring in that a
double 13A socket can actually only supply 19.5A yet has a 32A CPD.
Not a problem except in kitchens with few sockets and lots of heavy
appliances where Things Can Get Toasty.


When using a radial circuit with an RCBO, having a 13A fuse in the plug,
rather than say a 6A using a ring, does not compromise safety, as in Germany
they do not have fuses in plugs at all with the RCBO giving all the
protection and an appliance fuse (pretty sure they have appliance fuses).

"Doctor Drivel" wrote in message
...

"Tim W" wrote in message
...
Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 10:10

I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and

Which provides the same level of isolation as the MCB that might be there
in
a different, but complaint, installation.

b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Your "main fuse" is the one in the elect co's cutout, typically near and
definately before the meter.

A time delayed (type S) RCD may be used in place of the main CU isolator,
or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads and
it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be
essentially
stupid along with RCBOs.

Hence the question in my title. Is an RCBO a suitable isolator?

As much as any equivalent device that might be used is. It will typically
only isolate L and not N (although I have two double pole RCBOs that do
isolate L+N for outside circuits, because it seemed like a good idea,
though beyond basic requirements).

This means that you should not use the RCBO to act as eg as a shower
isolator - you still need the local DP switch. But in every other
respect,
the RCBO is a complete replacement for and MCB or fuse.



An RCBO can eliminate equipotential bonding in bathrooms. I believe the
lights and power all have to be off the same RCBO.

As long as all electrical circuits that enter a bathroom are RCD protected
then the supplementary bonding in the bathroom may be ommited. There is no
need for all the circuits to be supplied by the same RCD or RCBO though.

Adam

"js.b1" wrote in message
...
On Nov 11, 2:56 pm, "Doctor Drivel" wrote:
I would tend to go for double-pole RCBOs on all circuits.

Good way of ending with a mile-long CU & higher cost.

I think double-pole RCBOs is standard
in new installations in Germany

Standard in Italy & Germany.
Specifically because polarity is not indicated nor guaranteed.

- they use radial rather than ring circuits.

Nothing to do with this, although several radial offer better
compliance with 314.1 than a single ring. A ring final circuit however
offers some safety benefit over radial re 2 paths to earth. A radial
final circuit of 20A offers some safety benefit over ring in that a
double 13A socket can actually only supply 19.5A yet has a 32A CPD.
Not a problem except in kitchens with few sockets and lots of heavy
appliances where Things Can Get Toasty.

More expensive but worth it.- Hide quoted text -

Not worth it at all.
Fixed appliances have their own DP isolator, then lockoff the relevant
MCB/RCBO or main switch).


An RCBO can be on a ring or a radial. Rings are still silly and cheap; one
of the reasons they were adopted.....and to have higher currents for
electric heaters post war as the nuclear policy was all electric, using
unmetered nuclear power. Although radials may have high currents at the
sockets too.

I recall a German looking at a British system; the RCD protecting all of the
house and the fused spurs above the worktops with a fuesd plug hidden behind
the appliance. He thought the system was mad and said it was clearly cheap
at the CU but expensive (and ugly) in fused spurs. With a socket under the
kitchen worktop with an inaccessible fuse in the plug behind a heavy
appliance that might blow. Duh!! The fused spurs looks hideous, and
expensive, as well.

Ours system is cheap and sort of nasty. In Germany to isolate a dishwasher
you go to the CU and throw the dual-pole RCBO - L & N off.

About time we went the same way as the rest of the world. On the Continent
each appliance has an RCBO at the CU. So much easier to isolate. The only
advantage of the UK system is that 3kW kettles are common, whereas in Europe
they only go to around 2kW max. But they fill their kettles with hot water
from the combi to make the heat up cheaper and faster.

Look at Continental CUs. Professional setup and on the whole quality
products. Look at the cheapo crap in Screwfix about the size of a paperback
book. On the Continent they have vertical rows of RCBOs.

AIUI in Holland proportionately to population, the number of people killed
by electrical accidents is "half" that of the UK, and they don't have rings.

"ARWadsworth" wrote in message
. ..

"Doctor Drivel" wrote in message
...

"Tim W" wrote in message
...
Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 10:10

I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and

Which provides the same level of isolation as the MCB that might be
there in
a different, but complaint, installation.

b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Your "main fuse" is the one in the elect co's cutout, typically near and
definately before the meter.

A time delayed (type S) RCD may be used in place of the main CU
isolator, or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads and
it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be
essentially
stupid along with RCBOs.

Hence the question in my title. Is an RCBO a suitable isolator?

As much as any equivalent device that might be used is. It will
typically
only isolate L and not N (although I have two double pole RCBOs that do
isolate L+N for outside circuits, because it seemed like a good idea,
though beyond basic requirements).

This means that you should not use the RCBO to act as eg as a shower
isolator - you still need the local DP switch. But in every other
respect,
the RCBO is a complete replacement for and MCB or fuse.



An RCBO can eliminate equipotential bonding in bathrooms. I believe the
lights and power all have to be off the same RCBO.

As long as all electrical circuits that enter a bathroom are RCD protected
then the supplementary bonding in the bathroom may be ommited. There is no
need for all the circuits to be supplied by the same RCD or RCBO though.

That's even better. So all this bonding cable can be thrown out by buying
two RCBOs, one for the shower fan circuit, whatever one that is, and light
circuit the bathroom is off, and 15 minutes fitting at the CU. Much better.

"Tim W" wrote in message
...
Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 14:32

Than-you for all of the very quick replies. I hope I can clear a
couple of things up

My place is one of a large development of purpose-built flats, built
by the GLC in the 1970s. They all have Wylex rewireable fuses

Whilst a rewireable fuse isn't inherently bad *providing* no-one lashes in
the wrong size wire or a nail (which is the main criticism, along with the
lack of ease of resetting them) - but the lack of RCD protection is well
worth the effort of upgrading the CU. It's also an excellent opportunity
to
assess the state of the wiring via the PIR type checks that anyone
changing
a CU should be doing. 1970's wiring should be fine, but checks could still
uncover problems or even original errors like broken rings and dodgey
earths.

In my experience the most common problems found in 1970s installations are

There is no main or supplementary bonding, the landing lightswitch is fed
off the downstairs lighting circuit and takes it's neutral from the upstairs
circuit, high readings on the ring continuity (as you pointed out) and
unfortunately bad DIY.

Minor faults are usually no earth sleeving or red sleeving on the lighting
circuits and the odd brocken switch or socket.

The main reasons I get asked to change CUs are (in no particular order)

1. Just bought a house
2. Rewires
3. Selling a house
4. Wants to rent a house
5. The fuse box has melted etc
6. Addition works such as electric showers or extensions


However, this might be something to watch out for - is the company
actually
on the lookout for additional work, with the risk that they might invent
problems that can only be cured with a full rewire. Worth being ready to
challenge them on that, should it happen. Make sure they don't start any
work wihtout an agreed price and scope.

An excellent suggestion. Although there is more money in changing a CU than
there is in fixing any additional work.

Maybe an alterative quote from someone else would tell you if their standard
rate is a fair price.

Adam

"Doctor Drivel" wrote in message
...

"ARWadsworth" wrote in message
. ..

"Doctor Drivel" wrote in message
...

"Tim W" wrote in message
...
Sidney Endon-Lee
wibbled on Wednesday 11 November 2009 10:10

I'm looking at replacing a somewhat old consumer unit. I'll freely
admit that my electrical skills are not up to it, and I probably don't
have all the necessary test kit, both of which are a shame.

Anyway, a local firm has scented an opportunity (all the places on the
same development have the same, old, consumer unit) and have sent
round a fuzzy before and after picture of what replacing with a new
RCBO based unit would look like, and estimated a standard price, with
an addition if you need more 'ways'.

Anyway, it looks, from the picture, as though they'd remove isolating
switches and seem to have a design that has:

a) an RCBO per way; and

Which provides the same level of isolation as the MCB that might be
there in
a different, but complaint, installation.

b) an RCBO acting as a 'main fuse', sized to be 'equivalent to' the
current main fuse.

Your "main fuse" is the one in the elect co's cutout, typically near
and
definately before the meter.

A time delayed (type S) RCD may be used in place of the main CU
isolator, or
before it in a separate box, if you have a TT (earth rod) installation
earth. This is not and RCBO - it doesn't deal with current overloads
and it
doesn't need to, any more than the main 100A switch in a CU would. The
supplier's fuse does that.

You could also have a non delatey 100A RCD - but this would be
essentially
stupid along with RCBOs.

Hence the question in my title. Is an RCBO a suitable isolator?

As much as any equivalent device that might be used is. It will
typically
only isolate L and not N (although I have two double pole RCBOs that do
isolate L+N for outside circuits, because it seemed like a good idea,
though beyond basic requirements).

This means that you should not use the RCBO to act as eg as a shower
isolator - you still need the local DP switch. But in every other
respect,
the RCBO is a complete replacement for and MCB or fuse.



An RCBO can eliminate equipotential bonding in bathrooms. I believe the
lights and power all have to be off the same RCBO.

As long as all electrical circuits that enter a bathroom are RCD
protected then the supplementary bonding in the bathroom may be ommited.
There is no need for all the circuits to be supplied by the same RCD or
RCBO though.

That's even better. So all this bonding cable can be thrown out by buying
two RCBOs, one for the shower fan circuit, whatever one that is, and light
circuit the bathroom is off, and 15 minutes fitting at the CU. Much
better.

Yep. One RCBO for the electric shower, another for the bathroom lights
extractor fan/ shaver point etc and maybe a third for say an an electrical
heated towel radiator that runs off the sockets.

As long all bathroom circuits are RCD protected and the main equipotential
bonding is done then you can bin the bathroom supplementary bonding.

Adam

In article ,
Doctor Drivel wrote:
When using a radial circuit with an RCBO, having a 13A fuse in the plug,
rather than say a 6A using a ring, does not compromise safety, as in
Germany they do not have fuses in plugs at all with the RCBO giving all
the protection and an appliance fuse (pretty sure they have appliance
fuses).

Then each and every appliance flex must be capable of tripping the RCBO of
that circuit in event of a fault.

--
*The most wasted day of all is one in which we have not laughed.*

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Doctor Drivel wrote:
Ours system is cheap and sort of nasty. In Germany to isolate a
dishwasher you go to the CU and throw the dual-pole RCBO - L & N off.

A safety isolator should be within easy reach of the appliance. The CU
could be several floors away.

--
*Corduroy pillows are making headlines.

Dave Plowman London SW
To e-mail, change noise into sound.

ARWadsworth
wibbled on Wednesday 11 November 2009 17:25


However, this might be something to watch out for - is the company
actually
on the lookout for additional work, with the risk that they might invent
problems that can only be cured with a full rewire. Worth being ready to
challenge them on that, should it happen. Make sure they don't start any
work wihtout an agreed price and scope.

An excellent suggestion. Although there is more money in changing a CU
than there is in fixing any additional work.

Maybe an alterative quote from someone else would tell you if their
standard rate is a fair price.

Adam

Ideally (but slightly unfairly on the contractor as it involves potentially
lots of work for which they might not get paid if the customer backs out):

They assess the installation FOC and produce a checklist of faults on top of
the CU work and don't do anything until the additional work and price has
been agreed, as well as the price for the CU.

What you don't want as a customer is:

CU changed happily. Then they test the final circuits to fill out the EIC,
uncover a multitude of problems (real or invented) and then apply an
exhorbitent charge to fix them otherwise they cannot do the Part P
notification and you end up with a non registered and questionable
installation.

Adam might be kind enough to suggest how this sort of scenario is handled
fairly in the real world?

Cheers

--
Tim Watts

This space intentionally left blank...

"Tim W" wrote in message
...
ARWadsworth
wibbled on Wednesday 11 November 2009 17:25


However, this might be something to watch out for - is the company
actually
on the lookout for additional work, with the risk that they might invent
problems that can only be cured with a full rewire. Worth being ready to
challenge them on that, should it happen. Make sure they don't start any
work wihtout an agreed price and scope.

An excellent suggestion. Although there is more money in changing a CU
than there is in fixing any additional work.

Maybe an alterative quote from someone else would tell you if their
standard rate is a fair price.

Adam

Ideally (but slightly unfairly on the contractor as it involves
potentially
lots of work for which they might not get paid if the customer backs out):

They assess the installation FOC and produce a checklist of faults on top
of
the CU work and don't do anything until the additional work and price has
been agreed, as well as the price for the CU.

What you don't want as a customer is:

CU changed happily. Then they test the final circuits to fill out the EIC,
uncover a multitude of problems (real or invented) and then apply an
exhorbitent charge to fix them otherwise they cannot do the Part P
notification and you end up with a non registered and questionable
installation.

Adam might be kind enough to suggest how this sort of scenario is handled
fairly in the real world?

Cheers

--
Tim Watts

A full electrical PIR on the house electrics at an agreed price before
changing the fuse box to a 17th edition CU is the fairest option. A FOC
assessment on the house electrics is only worth what you pay for it. I do
not do FOC assessments before changing a CU.

Only a madman, conman or cowboy would try to change a fuse box for a 17th
edition CU without testing the circuits before fitting the new CU.


Adam

On Nov 11, 8:22*pm, Tim W wrote:
CU changed happily. Then they test the final circuits to fill out the EIC,
uncover a multitude of problems (real or invented) and then apply an
exhorbitent charge to fix them otherwise they cannot do the Part P
notification and you end up with a non registered and questionable
installation.

Like you agree to pay £1800 cash for a new lighting circuit or I'm not
coming out? :-)

Before installing RCDs for the first time...
1 - Do insulation test first
2 - Check lighting for borrowed neutral/live (often very obvious)

"js.b1" wrote in message
...
On Nov 11, 8:22 pm, Tim W wrote:
CU changed happily. Then they test the final circuits to fill out the EIC,
uncover a multitude of problems (real or invented) and then apply an
exhorbitent charge to fix them otherwise they cannot do the Part P
notification and you end up with a non registered and questionable
installation.

Like you agree to pay £1800 cash for a new lighting circuit or I'm not
coming out? :-)

I'm not "coming out" for any amount of money or any lighting circuit:-)

Before installing RCDs for the first time...
1 - Do insulation test first
2 - Check lighting for borrowed neutral/live (often very obvious)

1.Yes the insulation test is very important. Probably the most important
test.

2 If not easy then a clamp meter shows the borrowed neutrals when you are
suspicious about an existing install.

Adam

In article ,
Doctor Drivel wrote:
Rings are still silly and cheap; one
of the reasons they were adopted.....and to have higher currents for
electric heaters post war as the nuclear policy was all electric, using
unmetered nuclear power.

There never was 'unmetered' power in the UK - nor was it ever likely. Just
the usual political spouting off. Nuclear power may have lowish running
costs in terms of the fuel needed - but the capital costs have always been
high. And would have to be paid for somehow.

--
*How's my driving? Call 999*

Dave Plowman London SW
To e-mail, change noise into sound.

On Nov 11, 10:20*pm, "ARWadsworth"
wrote:
I'm not "coming out" for any amount of money or any lighting circuit:-)

:-)


Re "unmetered" elec, that always amused me.
1 - Nuclear will just inflate energy company profits & taxation for HM
Treasury
2 - Any incentive for E7 making a substantial comeback must be
eliminated because it would collapse the grid infrastructure, realise
even if just the oil burning people moved to E7 the grid could not
withstand it (never mind the generating plant)
3 - Investment in plant & grid is either non-existent or hopeless,
"The City Does Not Do R&D or Maintenance" - Railways-II
4 - Gov't Investment projects are a blank cheque for the corrupt, paid
by the stupid, monitored by the incompetent, answerable to the next
government which can blame the previous government, providing
employment for innumerable quangos and art journalists too thick to
even spell science without a PR explaining it to them with coloured
bricks and 17 training courses, two marketing consultants, one
advertising consultant and finally their children until
educationalists saw that off.

UK Gov't & Oligarchy long ago decided having Lost The Empire they
would just sponge off the remaining population rather than create the
infrastructure & investment for economic leadership matched to a
portfolio of talents. I always remember one multi-million pound
business owner screaming "it is because of this technology nonsense
that we have to spend money on investment rather than ourselves", then
dumped the clutch with engine screaming in his audi quattro. Summed it
up really, when UK had an empire it appears the idea was no-one
competed - Oligarchy merely assigned it to the appropriate
individuals. Then someone decided to compete, globalisation has little
respect for the hereditary epigeneologists - and likewise the
hereditary can continue until eventually globalisation defeats
nationalism re lost social contract to be replaced of course by
religion (jews want an eye for an eye, koran not far off, christianity
makes you wait until you are dead hence preferred by Bush & Blair).

The bailout for a move to nuclear electric would be smart-meters
teleswitching CO2 heatpumps.

On Wed, 11 Nov 2009 17:12:34 -0800 (PST), js.b1 wrote:

On Nov 11, 10:20*pm, "ARWadsworth"
wrote:
I'm not "coming out" for any amount of money or any lighting circuit:-)

:-)

Re "unmetered" elec, that always amused me.
1 - Nuclear will just inflate energy company profits & taxation for HM
Treasury
2 - Any incentive for E7 making a substantial comeback must be
eliminated because it would collapse the grid infrastructure, realise
even if just the oil burning people moved to E7 the grid could not
withstand it (never mind the generating plant)
3 - Investment in plant & grid is either non-existent or hopeless,
"The City Does Not Do R&D or Maintenance" - Railways-II
4 - Gov't Investment projects are a blank cheque for the corrupt, paid
by the stupid, monitored by the incompetent, answerable to the next
government which can blame the previous government, providing
employment for innumerable quangos and art journalists too thick to
even spell science without a PR explaining it to them with coloured
bricks and 17 training courses, two marketing consultants, one
advertising consultant and finally their children until
educationalists saw that off.

UK Gov't & Oligarchy long ago decided having Lost The Empire they
would just sponge off the remaining population rather than create the
infrastructure & investment for economic leadership matched to a
portfolio of talents. I always remember one multi-million pound
business owner screaming "it is because of this technology nonsense
that we have to spend money on investment rather than ourselves", then
dumped the clutch with engine screaming in his audi quattro. Summed it
up really, when UK had an empire it appears the idea was no-one
competed - Oligarchy merely assigned it to the appropriate
individuals. Then someone decided to compete, globalisation has little
respect for the hereditary epigeneologists - and likewise the
hereditary can continue until eventually globalisation defeats
nationalism re lost social contract to be replaced of course by
religion (jews want an eye for an eye, koran not far off, christianity
makes you wait until you are dead hence preferred by Bush & Blair).


You are Ian Hislop and I claim my £5!

I'd consider you to be cynical, except that the above is true and I agree
with it. Pity that it can't be repeated as widely and frequently as
GordAlmighty regurgitates his own faeces.

The bailout for a move to nuclear electric would be smart-meters
teleswitching CO2 heatpumps.


--
Peter.
The head of a pin will hold more angels if
it's been flattened with an angel-grinder.

"John Rumm" wrote in message
o.uk...
Doctor Drivel wrote:

An RCBO can be on a ring or a radial. Rings are still silly and cheap;

Silly no.

No one else adopted it except the Irish.

I recall a German looking at a British system; the RCD protecting all of
the house and the fused spurs above the worktops with a fuesd plug hidden
behind the appliance. He thought the system was mad and said it was
clearly cheap at the CU but expensive (and ugly) in fused spurs.

Appliances with concealed sockets should have separately accessible
isolation switches.


Appliance fuses in general very rarely blow unless there is a fault in the
appliance, and in that case the chances are you will need to pull it out
from its utility space anyway to fix it.

Sometimes fuses just fail. The Continentals do not have fuses in their
plugs so no problem in removing a heavy appliance.

Ours system is cheap and sort of nasty. In Germany to isolate a

snip drivel

You clearly have a little clue. No one else adopted our ring system.
Amazing eh!

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:
Rings are still silly and cheap; one
of the reasons they were adopted.....and to have higher currents for
electric heaters post war as the nuclear policy was all electric, using
unmetered nuclear power.

There never was 'unmetered' power in the UK - nor was it ever likely.

They proposed and it was on public info films. See one.

snip drivel by an effing looney

"John Rumm" wrote in message
o.uk...
Doctor Drivel wrote:

"js.b1" wrote in message
...
On Nov 11, 2:56 pm, "Doctor Drivel" wrote:
I would tend to go for double-pole RCBOs on all circuits.

Good way of ending with a mile-long CU & higher cost.


And greater protection and the lot not tripping out only that circuit.

Single pole RCBO devices would offer the same level of fault protection

That is total drivel.

Doctor Drivel
wibbled on Thursday 12 November 2009 17:58

You clearly have a little clue. No one else adopted our ring system.
Amazing eh!

IIRC our ring system was primarily adopted as a way to turn a couple of 15A
radials into a 30A circuit with more 13A sockets on - ie an upgrade path
without the need to throw away a couple of perfectly good bits of whatever
the imperial of 2.5mm2 was. It also saved on copper.

Anyway, a system that allows loads of sockets, and upto 2 and a bit heavy
appliances and umpteen million trivial devices to be plugged in at random
locations without having to use a rediculously massive cable is a pretty
good system.

--
Tim Watts

This space intentionally left blank...

"Tim W" wrote in message
...
Doctor Drivel
wibbled on Thursday 12 November 2009 17:58

You clearly have a little clue. No one else adopted our ring system.
Amazing eh!

IIRC our ring system was primarily adopted as a way to turn a couple of
15A
radials into a 30A circuit with more 13A sockets on - ie an upgrade path
without the need to throw away a couple of perfectly good bits of whatever
the imperial of 2.5mm2 was. It also saved on copper.

Anyway, a system that allows loads of sockets, and upto 2 and a bit heavy
appliances and umpteen million trivial devices to be plugged in at random
locations without having to use a rediculously massive cable is a pretty
good system.

You mean cheap. The drive towards electric heating post WW2 promoted the
ring. The advantage of the ring is that many sockets can be on the ring.
Great for offices with lots of computers. But on the Continent using
radials that is an expensive undertaking. I believe some companies adopted
the UK 3-pin sockets so they could have the fuse in the plug (essential for
a ring). The UK 3-pin plugs are the only plugs that have a fuse in them -
that I know of. They may have some on the Continent specifically for office
purposes. Then they have a cheap way of having many computers around the
office.

"John Rumm" wrote in message
o.uk...

Indeed. Which is why the DP devices are not used that often. The 17th
edition rules for cable protection made RCBOs more desirable (or at least
multiple RCDs[1]). The manufacturers have responded to that need and also
the one of conserving CU space by introducing far more competitively
priced single width SP RCBOs. These are still not exactly cheap, but at
under £20 in many cases are affordable. (still MCB prices are under £2 in
some cases now,

S/fix sells the cheapest RCBO at around £28. Les than £20? Where?

"Doctor Drivel" wrote in message
...

"John Rumm" wrote in message
o.uk...

Indeed. Which is why the DP devices are not used that often. The 17th
edition rules for cable protection made RCBOs more desirable (or at least
multiple RCDs[1]). The manufacturers have responded to that need and also
the one of conserving CU space by introducing far more competitively
priced single width SP RCBOs. These are still not exactly cheap, but at
under £20 in many cases are affordable. (still MCB prices are under £2 in
some cases now,

S/fix sells the cheapest RCBO at around £28. Les than £20? Where?



At an electrical wholesalers. I pay a lot less than £28 for RCBOs

Adam

Doctor Drivel wrote:

They

snip drivel by an effing looney

I followed the instruction.

On Nov 12, 6:11*pm, Owain wrote:
Not quite true - there are unmetered connections, usually for
streetlighting etc, where the cost of metering would be
disproportionate. And that's only the legitimately
unmetered connections, of course!

Indeed :-)

Quite a few street lights round here had their cables running off in
the direction of the nearby house, I presume to their cutout. That
would explain the "dig for electricity" in some areas - until the
metering people checked upstream meters!

I recall there was a "flat fee" system for lighting at one point, with
heating sockets being charged for. You could almost say E7 was
"unmetered" - I recall 2p/minute evening for 300bps telephone
(Micronet) and 1.6p/unit for E7 overnight kWhr.

MK MG MEM 1-module RCBO are typically £14-16-19 on Ebay for boxed new.
TLC do them for about £23 off the top of my head.

Comes down to the brand, quantity & person and which wholesaler.

14 RCBO can be had for £250 which is not that bad - consider how much
14 MCB and 3 100A RCD cost :-)

"John Rumm" wrote in message
...
Doctor Drivel wrote:

"John Rumm" wrote in message
o.uk...
Doctor Drivel wrote:

"js.b1" wrote in message
...
On Nov 11, 2:56 pm, "Doctor Drivel" wrote:
I would tend to go for double-pole RCBOs on all circuits.

Good way of ending with a mile-long CU & higher cost.


And greater protection and the lot not tripping out only that circuit.

Single pole RCBO devices would offer the same level of fault protection

That is total drivel.

I can only assume

Some device that isolates the L & N when it activates must offer a higher
level of safety.