My mythical kitchen is slowly creeping towards installation - I bought
the hob last week!

Now planning the wiring and am mindful of the need to be able to isolate
the power to washing machine, dishwasher, hob ignition and extractor
hood. I _really_ do not want to fit fused spur isolators above the
worksurface so I was going to fit all three (running hob and extractor
from the same isolator) in the space under the sink. However, this is
going to make for quite lengthy, parallel, cable runs and I was
wondering if I could incorporate a single isolator for the whole of the
ring on the appliance side of the kitchen.

Is it possible? And could it be done discretely - I don't want
something that looks as though it could have designed for use by the CEGB.

Alternatively (and probably simpler) would a cooker isolator (switch
only), spurred off a socket on the kitchen ring, feeding the four under
surface sockets for the appliances be acceptable? And could I wire
those sockets in series with a suitable weight of T+E? I'm thinking
that the sequence would be:

====SKT====Ring=======
|
Switch ------ W/M --------- D/W----------Hob--------Extractor

TIA

Richard

Richard Savage wrote:
My mythical kitchen is slowly creeping towards installation - I bought
the hob last week!

Now planning the wiring and am mindful of the need to be able to isolate
the power to washing machine, dishwasher, hob ignition and extractor
hood. I _really_ do not want to fit fused spur isolators above the
worksurface so I was going to fit all three (running hob and extractor
from the same isolator) in the space under the sink. However, this is
going to make for quite lengthy, parallel, cable runs and I was
wondering if I could incorporate a single isolator for the whole of the
ring on the appliance side of the kitchen.

Is it possible? And could it be done discretely - I don't want
something that looks as though it could have designed for use by the CEGB.

Alternatively (and probably simpler) would a cooker isolator (switch
only), spurred off a socket on the kitchen ring, feeding the four under
surface sockets for the appliances be acceptable? And could I wire
those sockets in series with a suitable weight of T+E? I'm thinking
that the sequence would be:

====SKT====Ring=======
|
Switch ------ W/M --------- D/W----------Hob--------Extractor


I was in a similar situation, and decided to solve it by placing sockets
(surfacemount metalclad) inside the base units adjacent to appliances. A
hole at the back of the base unit is used for passing the plug through.
Works well, as long as you don't mind sockets in your base units.

--
Grunff

Alternatively (and probably simpler) would a cooker isolator (switch
only), spurred off a socket on the kitchen ring, feeding the four under
surface sockets for the appliances be acceptable? And could I wire
those sockets in series with a suitable weight of T+E? I'm thinking
that the sequence would be:

Put in whatever switches you like. Provided that the appliance is connected
via either an FCU or a plug and socket, then there is no requirement for
switching.

Just ensure that on a 32A ring, the switch must be double pole and rated at:

one single socket = 13A (20A more likely to be found)
one double socket = 20A
more than one socket = 32A (45A more likely to be found)

Alternatively, a 13A FCU may be used to switch for any number of sockets,
provided the expected appliance load is below this, which it isn't.

Personally, I used a 3 x 20A DP grid switch to switch my tumble
dryer/washing machine and dishwasher independently, all fed off a dedicated
32A radial circuit. I used a junction box to drop the 6mm incoming to 3 x
2.5mm that would fit the switch terminals. As each switch only controls one
single socket which will be fused in the plug, this is permissible for both
short circuit and overloading.

Finally, the cable run mustn't be done in 2.5mm cable after the switch if
the third option (more than one socket not limited to 13A) is used. You must
use at least 4mm, probably 6mm cable, which will be a pig to install, as
getting 2 x 6mm into a wiring accessory will not be easy/possible. You may
have to drop to 2.5mm in a large junction box just outside the socket (which
is permissible as you are allowed to assume 20A max from a double socket or
13A max from a single).

Christian.

Thanks to all (i.e. the usual helpful few!)

To try and answer some of your questions:

The units will all be built in and spread around an 'L' shaped area of
worksurface interspersed with drawer units.

I think that the drawer units really make access to sockets behind
unreasonably fiddly and I'm not prepared to have FCUs or appliance
sockets above the worksurface.

There is only one 'cupboard' providing the possible option of locating 3
FCUs and then running radials to sockets close to each appliance. This
under the sink which is approx 2/3 from the top of the upright in the
L. This is why I said something about lengthy cables in the original post.

If it was my choice I would not provide any isolation, but just put
single, possibly switched, sockets close to each unit and use the MCB in
the CU as an isolator.

It is only the installers who said that each appliance must be supplied
by an FCU/socket pair and cannot simply be plugged into the kitchen ring.

I understand what you say (Christian) about using 6mm cable - I had
feared as much!

The CU is some distance from the kitchen and, needless to say, hidden in
an under-stairs cupboard. In any case is it acceptible to have the MCB
as the only way of isolating the kitchen appliances, especially the
hood? If it is it might be easier to show SWMBO how to test the RCD
which is separate from the CU and thus more accessible!

A big red emergency off button has a certain appeal - is that feasible
(only half joking)? Some sort of remote test switch for the RCD would
have the desired result. Have I heard/read about kitchen over-heat
sensors that can trip the power supply to the kitchen? Presumably they
trip a suitably rated contactor? The ones supplying the last mainframe
room that I worked in used to stick on!!

Cheers guys

Richard

The CU is some distance from the kitchen and, needless to say, hidden in
an under-stairs cupboard. In any case is it acceptible to have the MCB
as the only way of isolating the kitchen appliances, especially the
hood? If it is it might be easier to show SWMBO how to test the RCD
which is separate from the CU and thus more accessible!

No ! it is not and the Hood will need to be fused down via a 3AMP switched
fused spur, now that you have said that the appliances will be built in they
are classed as fixed for the regs and MUST have a means of isolation next to
the appliance that is double pole.

Peter

In article ,
Peter wrote:
No ! it is not and the Hood will need to be fused down via a 3AMP
switched fused spur,

Bollox. It can be on a 3 amp fuse plug. Or run off the lighting circuit
with no additional fusing.

--
*Frankly, scallop, I don't give a clam

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

Peter wrote:


No ! it is not and the Hood will need to be fused down via a 3AMP switched
fused spur, now that you have said that the appliances will be built in they
are classed as fixed for the regs and MUST have a means of isolation next to
the appliance that is double pole.

Peter



My previous reply to your point above seems to have dissapeared into the
ether. Copied he

Sorry, didn't mean to omit that vital element from the equation.. What
exactly is meant by 'next to' the appliance? I suspect that my '3 FCUs
under the sink' solution will be chosen whether or not it qualifies.

Ta

Richard

"Richard Savage" wrote in message
.. .


Peter wrote:


No ! it is not and the Hood will need to be fused down via a 3AMP
switched
fused spur, now that you have said that the appliances will be built in
they
are classed as fixed for the regs and MUST have a means of isolation next
to
the appliance that is double pole.

Peter



My previous reply to your point above seems to have dissapeared into the
ether. Copied he

Sorry, didn't mean to omit that vital element from the equation.. What
exactly is meant by 'next to' the appliance? I suspect that my '3 FCUs
under the sink' solution will be chosen whether or not it qualifies.

Yes that is ok it just means adjacent to and accessible
Peter

So, does your sense of aesthetics rule out using grid-switch FCUs in the
relatively-distant cupboard? That'd take up only one double mounting
box; and with FCUs controlling the spurs to each dedicated socket,
providing closer protection for the cables, the runs from there to each
socket can be in 2.5mmsq.

The "Big Red Switch" does have appeal, but isn't feasible with a ring
(not without bizarre contact arrangements to switch both sides of the
ring *and* preserve continuity of the rest of ring when you bypass the
relevant section). Unless, that is, you have a truly dedicated kitchen
ring, and can replace the twin 2.5mmsqs running back to the CU with a
single 4mmsq or 6mmsq (6mmsq is safe bet, 4mmsq needs calcs on permitted
length), and you put a 45A cooker-style isolator at the point where the
thicker incomer fed out into two arms of the kitchen ring...

Stefek Zaba wrote:

So, does your sense of aesthetics rule out using grid-switch FCUs in
the relatively-distant cupboard? That'd take up only one double
mounting box; and with FCUs controlling the spurs to each dedicated
socket, providing closer protection for the cables, the runs from
there to each socket can be in 2.5mmsq.

The "Big Red Switch" does have appeal, but isn't feasible with a ring
(not without bizarre contact arrangements to switch both sides of the
ring *and* preserve continuity of the rest of ring when you bypass the
relevant section). Unless, that is, you have a truly dedicated kitchen
ring, and can replace the twin 2.5mmsqs running back to the CU with a
single 4mmsq or 6mmsq (6mmsq is safe bet, 4mmsq needs calcs on
permitted length), and you put a 45A cooker-style isolator at the
point where the thicker incomer fed out into two arms of the kitchen
ring...


'Tis indeed a dedicated kitchen ring. But I don't think that a Big Red
switch will meet the aesthetic requirements of SWMBO. She has already
vetoed red with aluminium edging as the colour scheme for the units ;-)

Richard

In article ,
Richard Savage wrote:
It is only the installers who said that each appliance must be supplied
by an FCU/socket pair and cannot simply be plugged into the kitchen ring.

Who are they? I'd say they're talking ********. I'd certainly want
reasonable access to the sockets, though.

--
*If PROGRESS is for advancement, what does that make CONGRESS mean?

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

"Christian McArdle" wrote in message
. net...
Alternatively (and probably simpler) would a cooker isolator (switch
only), spurred off a socket on the kitchen ring, feeding the four under
surface sockets for the appliances be acceptable? And could I wire
those sockets in series with a suitable weight of T+E? I'm thinking
that the sequence would be:

Put in whatever switches you like. Provided that the appliance is
connected
via either an FCU or a plug and socket, then there is no requirement for
switching.

Just ensure that on a 32A ring, the switch must be double pole and rated
at:

one single socket = 13A (20A more likely to be found)
one double socket = 20A
more than one socket = 32A (45A more likely to be found)

Alternatively, a 13A FCU may be used to switch for any number of sockets,
provided the expected appliance load is below this, which it isn't.

Personally, I used a 3 x 20A DP grid switch to switch my tumble
dryer/washing machine and dishwasher independently, all fed off a
dedicated
32A radial circuit. I used a junction box to drop the 6mm incoming to 3 x
2.5mm that would fit the switch terminals. As each switch only controls
one
single socket which will be fused in the plug, this is permissible for
both
short circuit and overloading.

Finally, the cable run mustn't be done in 2.5mm cable after the switch if
the third option (more than one socket not limited to 13A) is used. You
must
use at least 4mm, probably 6mm cable, which will be a pig to install, as
getting 2 x 6mm into a wiring accessory will not be easy/possible. You may
have to drop to 2.5mm in a large junction box just outside the socket
(which
is permissible as you are allowed to assume 20A max from a double socket
or
13A max from a single).

Christian.

Sorry you cant do this 2.5mm is limited to a 16a mcb !

Wire the appliances on the ring using 20A dp switches above each appliance
with a socket below, the Hood should be on a switched fused spur (3Amp fuse)
and the cooker in 6mm with a 45A DP switch within 2mtrs of Hob

Peter

Peter wrote:

Sorry you cant do this 2.5mm is limited to a 16a mcb !

Wire the appliances on the ring using 20A dp switches above each appliance
with a socket below, the Hood should be on a switched fused spur (3Amp fuse)
and the cooker in 6mm with a 45A DP switch within 2mtrs of Hob

Peter



Similarly sorry. Come what may there will be no switches above the
surface! In one instance (the W/M) that is for aesthetic reasons, in
the other it is because the hob and sink are either above or below the
units (the D/W and hood). Oh, and it is a gas hob (as mentioned in the
initial thread) so we're only worrying about ignition power. The ovens
are on the other side of the room with their own feed.

Please keep the comments coming, being able to argue the toss with bods
who understand the problem is sooo much more satisfying than trying to
discuss it with SWMBO.

Rgds Richard

Peter wrote:


Sorry you cant do this 2.5mm is limited to a 16a mcb !

Sigh. So unfused spurs don't exist, right? Nor is it permissible to
design a circuit where the nature of the load means an overload will not
arise using circuit protection only for short-circuit conditions, but
not for overloads? And I'm hallucinating when I see a 20A MCB 2.5mmsq
entry in the Conventional Cricuits table (7.1) of the OSG?

Hint - those are "rhetorical questions". Meaning, their factual answer
stands in stark contradiction to your simplistic, and plain wrong, claim
that "2.5mm is limited to a 16a mcb"). Yes, to use 2.5mm on circuits
with protective devices rated over 16A needs a bit of thought, sometimes
(gasp) some calculation of earth loop impedance in the cases where there
isn't a precomputed Table in the OSG for us. And your advice at least
errs on the side of caution. But accurate and complete it surely ain't...

Stefek

"Stefek Zaba" wrote in message
...
Peter wrote:


Sorry you cant do this 2.5mm is limited to a 16a mcb !

Sigh. So unfused spurs don't exist, right? Nor is it permissible to
design a circuit where the nature of the load means an overload will not
arise using circuit protection only for short-circuit conditions, but
not for overloads? And I'm hallucinating when I see a 20A MCB 2.5mmsq
entry in the Conventional Cricuits table (7.1) of the OSG?

Hint - those are "rhetorical questions". Meaning, their factual answer
stands in stark contradiction to your simplistic, and plain wrong, claim
that "2.5mm is limited to a 16a mcb"). Yes, to use 2.5mm on circuits
with protective devices rated over 16A needs a bit of thought, sometimes
(gasp) some calculation of earth loop impedance in the cases where there
isn't a precomputed Table in the OSG for us. And your advice at least
errs on the side of caution. But accurate and complete it surely ain't...

The context in which the reply was given was reduction of cable size from
6mm to 2.5mm this has to be fused down, there is a limit to the amount of
sockets on an unfused spur you cannot spur all the kitchen appliances onto a
single 2.5mm cable sorry if this was not clear.

Peter

The context in which the reply was given was reduction of cable size from
6mm to 2.5mm this has to be fused down, there is a limit to the amount of
sockets on an unfused spur you cannot spur all the kitchen appliances onto a
single 2.5mm cable sorry if this was not clear.

Agreed - a single 2.5mmsq feeding many sockets, not-fused-down, where
the protective device is (say) a 32A MCB, is indeed a Bad Thing and
should Not Happen. But a 6mmsq "backbone", with short 2.5mmsq feeds
(unfused, connected via junction boxes say) to individual single or even
(though it's sillier) double sockets, would be compliant, though not a
Conventional Final Circuit. Each such single appliance-feeding socket
(a) would be protected against fault current by the upstream 32A MCB -
here the "short" feed is important to keep the earth loop imedance low,
so that operation of the MCB in the required 0.5s can be guaranteed, and
the temperature rise in this faulting cable can be kept within limits;
(b) would be incapable of producing an overload for the rating of the
short length of 2.5mmsq cable, since you can't pull a sustained 27A out
of a single socket (RefMeth1 rating of 2.5mmsq), hard to do so even out
of a double, and the actual connected load - single white-goods
appliance - will in fact pull no more than rating plate says, prolly 2kW
= 8A at peak water-heating time for a "modern" dishwash, possibly the
full 3kW = 12A for an older/fancier/faster water-heating appliance; (c)
closer-rated fault-current protection will be provided by the plug in't
fuse. It's actually a completely direct analogue of the "normal" unfused
spur in 2.5mmsq taken off a 32A 2.5mmsq-both-ways ring: the ring is
fused at higher than the rating of the spur cable, but the combination
of plugfuse and circuit-MCB provide fault protection for the spur cable,
while overload is "designed out" by fitting only one power take-off
point, either single or double socket.

Having said all that, and certain as I am that design calcs would
sanction such a layout in the right circs, I'd still shy away from
installing a circuit like that in an ordinary domestic setup: it's
simply too unintuitive for a subsequent householder or
inspecting/minor-worksing electrician to feel comfortable with. Having
had, in the previous house, a period of enthusiasm for FCUs with
directly-wired-in appliances, and then been inconvenienced when
repairers have needed to reliably disconnect the appliance or wheel in a
spare, I've come to appreciate the wisdom of the standard arrangement
with FCU to act as control switch for easy-to-operate isolation, feeding
a conventional 13A socket (unswitched for preference) at the back of the
appliance.

Stefek

On 11 Oct 2004 "Peter" wrote:

Sorry you cant do this 2.5mm is limited to a 16a mcb !

Wire the appliances on the ring using 20A dp switches above each appliance
with a socket below, the Hood should be on a switched fused spur (3Amp fuse)
and the cooker in 6mm with a 45A DP switch within 2mtrs of Hob

I think if you re-read the OP you'll find it doesn't mention a cooker
at all. It mentions a hob, presumably gas, which has a mains ignition
circuit so a 3amp fused plug or spur is adequate.

--
Richard Porter
Mail to username ricp at domain minijem.plus.com
"You can't have Windows without pains."