As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running to
below the work surface.

Looking at various old posts in google, people have recommended using
Double Pole Switches or FCUs for this task.

My undertanding is that both of these are double pole switches, the
difference being that the FCU has a fuse protecting the live wire on
the spur. Is this correct?

If so, which should I use?

Finally, I assume that both of these switches have 6 terminals - L,N,E
for the mains and L,N,E for the load. I then wire both ring cables
into the mains part and the cable for the spur into the load part. Is
this correct?

Thanks in advance

Will

My undertanding is that both of these are double pole switches, the
difference being that the FCU has a fuse protecting the live wire on
the spur. Is this correct?

Yes.

If so, which should I use?

You may use either, provided they run to a single accessory. If you run to
multiple accessories, you must use the FCU.

Finally, I assume that both of these switches have 6 terminals - L,N,E
for the mains and L,N,E for the load. I then wire both ring cables
into the mains part and the cable for the spur into the load part. Is
this correct?

Yes, although the earth terminals might be shared, or not marked for load
and supply, in which case you wire to the most convenient earth terminal. I
used 20A DP grid switches, where you can get 1-2 DP switches in a single
box, or 3-4 in a double box. It gave a neater appearance than having 3
adjacent FCUs.

Christian.

"William Joones" wrote in message
om...
As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running to
below the work surface.

Looking at various old posts in google, people have recommended using
Double Pole Switches or FCUs for this task.

My undertanding is that both of these are double pole switches, the
difference being that the FCU has a fuse protecting the live wire on
the spur. Is this correct?

If so, which should I use?

Finally, I assume that both of these switches have 6 terminals - L,N,E
for the mains and L,N,E for the load. I then wire both ring cables
into the mains part and the cable for the spur into the load part. Is
this correct?

Thanks in advance

Will

Yes.

Yes.

And Yes.

The fused switches are not really necessary if your using remote sockets as
the plug on the appliance should be properly fused, but they are used if you
intend to make connections into permanent flex outlets.

"BigWallop" wrote in message ...
"William Joones" wrote in message
om...

As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running to
below the work surface.

Looking at various old posts in google, people have recommended using
Double Pole Switches or FCUs for this task.


Hi. Why would you need to us either a DP switch or a fuse to connect a
socket to a ring? A double socket would need IIRC a 20A switch, and a
single one... presumably 13A one. (Not certain bout those figures, but
think so)


Regards, NT

"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"William Joones" wrote in message
om...

As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running to
below the work surface.

Looking at various old posts in google, people have recommended using
Double Pole Switches or FCUs for this task.


Hi. Why would you need to us either a DP switch or a fuse to connect a
socket to a ring? A double socket would need IIRC a 20A switch, and a
single one... presumably 13A one. (Not certain bout those figures, but
think so)


Regards, NT

A 20 amp DP switch is needed because the socket is unswitched and takes a 13
amp load, but you don't get 13 amp DP switches off the shelf. A double
socket take two 13 amp loads so would need one 30 amp DP Switch to control
it remotely.

Thank you both for your replies.
I'll go the double pole switches I think. Would probably look smarter.
Will

"Christian McArdle" wrote in message ?

You may use either, provided they run to a single accessory. If you run to
multiple accessories, you must use the FCU.


I would add that the above is true so long as the cable size does not
reduce from that of the ring. If you reduce the cable size (eg to
1.5mm sq), then a fused-switch unit is needed.

John

On Mon, 6 Oct 2003 18:49:06 UTC, (N. Thornton) wrote:

Hi. Why would you need to us either a DP switch or a fuse to connect a
socket to a ring? A double socket would need IIRC a 20A switch, and a
single one... presumably 13A one. (Not certain bout those figures, but
think so)

There is no need to have the switch DP instead of SP. But, 13A DP
switches are not readily available. In addition, wiring 'in line' is a
lot easier if you don't have to keep one conductor continuous (and I
wouldn't want to joint it inside the switch box).

--
Bob Eager
rde at tavi.co.uk
PC Server 325*4; PS/2s 9585, 8595, 9595*2, 8580*3,
P70...

"BigWallop" wrote in message ...
"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"William Joones" wrote in message
om...

As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running to
below the work surface.

Looking at various old posts in google, people have recommended using
Double Pole Switches or FCUs for this task.


Hi. Why would you need to us either a DP switch or a fuse to connect a
socket to a ring? A double socket would need IIRC a 20A switch, and a
single one... presumably 13A one. (Not certain bout those figures, but
think so)


A 20 amp DP switch is needed because the socket is unswitched and takes a 13
amp load, but you don't get 13 amp DP switches off the shelf. A double
socket take two 13 amp loads so would need one 30 amp DP Switch to control
it remotely.


Hi. ISTR being told a 20A rating was sufficient for feeding one double
socket, since regs take into account a limited amount of diversity.
6kW draw is not expected often IOW. Is that not so?

Why DP?


Regards, NT

John Watson wrote:
"Christian McArdle" wrote in message ?

You may use either, provided they run to a single accessory. If you run to
multiple accessories, you must use the FCU.



I would add that the above is true so long as the cable size does not
reduce from that of the ring. If you reduce the cable size (eg to
1.5mm sq), then a fused-switch unit is needed.

I was under the impression that so long as the cable used could safely
take the full 13A load then it was ok to reduce cable size on the spur.
1.5mm sq ought to be fine I would have thought.

The time you need the FCU is when the potential load from the socket(s)
could potentially overrate the cable conecting back to the ring - e.g.
you have two or more sockets on the spur.

--
Cheers,

John.

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

"John Rumm" wrote in message
...
John Watson wrote:
"Christian McArdle" wrote in message
?

You may use either, provided they run to a single accessory. If you run
to
multiple accessories, you must use the FCU.



I would add that the above is true so long as the cable size does not
reduce from that of the ring. If you reduce the cable size (eg to
1.5mm sq), then a fused-switch unit is needed.

I was under the impression that so long as the cable used could safely
take the full 13A load then it was ok to reduce cable size on the spur.
1.5mm sq ought to be fine I would have thought.

The time you need the FCU is when the potential load from the socket(s)
could potentially overrate the cable conecting back to the ring - e.g.
you have two or more sockets on the spur.

--
Cheers,

John.


Correct.


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"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"William Joones" wrote in message
om...

As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running
to
below the work surface.

Looking at various old posts in google, people have recommended
using
Double Pole Switches or FCUs for this task.


Hi. Why would you need to us either a DP switch or a fuse to connect a
socket to a ring? A double socket would need IIRC a 20A switch, and a
single one... presumably 13A one. (Not certain bout those figures, but
think so)


A 20 amp DP switch is needed because the socket is unswitched and takes
a 13
amp load, but you don't get 13 amp DP switches off the shelf. A double
socket take two 13 amp loads so would need one 30 amp DP Switch to
control
it remotely.


Hi. ISTR being told a 20A rating was sufficient for feeding one double
socket, since regs take into account a limited amount of diversity.
6kW draw is not expected often IOW. Is that not so?

Why DP?


Regards, NT

Would you work on a remote unswitched socket if it still had a neutral
attached ? I wouldn't. That's why we use Double Pole switches to isolate
the socket from both live and neutral supply.

If you want to run a double gang socket, then you have to take into
consideration that both sockets will be used at the same time, so you need
the correct switch gear to control it. Diversity is only considered in the
whole installation, where there is an unlikely event that all appliances and
every socket will be on and used at the one time.


---
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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.524 / Virus Database: 321 - Release Date: 06/10/03

"BigWallop" wrote in message ...
"N. Thornton" wrote in message
om...
"William Joones" wrote in message
om...

As part of renovating my kitchen, I intend to have 2 applicances
(washing machine and dishwasher) plugged in to separate single
unswitched sockets under the work surface, with those sockets
controlled by switches on the wall above the work surface.

The switches will be on a 30amp ring circuit with a spur running
to
below the work surface.
Looking at various old posts in google, people have recommended
using
Double Pole Switches or FCUs for this task.


Hi. Why would you need to us either a DP switch or a fuse to
connect a
socket to a ring? A double socket would need IIRC a 20A switch,
and a
single one... presumably 13A one. (Not certain bout those
figures, but
think so)


A 20 amp DP switch is needed because the socket is unswitched and
takes a 13
amp load, but you don't get 13 amp DP switches off the shelf. A
double
socket take two 13 amp loads so would need one 30 amp DP Switch to
control
it remotely.


Hi. ISTR being told a 20A rating was sufficient for feeding one double
socket, since regs take into account a limited amount of diversity.
6kW draw is not expected often IOW. Is that not so?

Why DP?


Would you work on a remote unswitched socket if it still had a neutral
attached ? I wouldn't. That's why we use Double Pole switches to isolate
the socket from both live and neutral supply.

The normal practice would be to switch off power at the CU, surely.

If you want to run a double gang socket, then you have to take into
consideration that both sockets will be used at the same time, so you need
the correct switch gear to control it. Diversity is only considered in the
whole installation, where there is an unlikely event that all appliances and
every socket will be on and used at the one time.

Sounds like good sense to me, yet I've been told that cable feeding
one double socket only needs to be rated at 20A, not 30, so a single
piece of 2.5T&E clipped direct will do. Is that not so?

Regards, NT

In article ,
John Rumm writes:
John Watson wrote:
"Christian McArdle" wrote in message ?

You may use either, provided they run to a single accessory. If you run to
multiple accessories, you must use the FCU.



I would add that the above is true so long as the cable size does not
reduce from that of the ring. If you reduce the cable size (eg to
1.5mm sq), then a fused-switch unit is needed.

I was under the impression that so long as the cable used could safely
take the full 13A load then it was ok to reduce cable size on the spur.
1.5mm sq ought to be fine I would have thought.

The cable also has to be able to take the fault current (short circuit
to neutral or earth) for the time it takes the 30A fuse/MCB to trip
without overheating -- that's where a 1.5mm² cable is likely to come
unstuck (maybe literally;-) Also, it must still pass enough current to
blow the fuse within 400ms (IIRC).

Unless you are prepared to sit down and do the calculations to prove
that it's OK, stick with 2.5mm². And what are you saving anyway? peanuts.

--
Andrew Gabriel

In article ,
"BigWallop" writes:
A 20 amp DP switch is needed because the socket is unswitched and takes a 13
amp load, but you don't get 13 amp DP switches off the shelf. A double
socket take two 13 amp loads so would need one 30 amp DP Switch to control
it remotely.

Actually, double sockets are still only rated 13A (you'll find that
written on the back of them all). However, the British Standard does
require them to be tested at higher than 13A -- can't remember what
it is, but it's less than 2x13A.

--
Andrew Gabriel

In article ,
"Bob Eager" writes:
On Mon, 6 Oct 2003 18:49:06 UTC, (N. Thornton) wrote:

Hi. Why would you need to us either a DP switch or a fuse to connect a
socket to a ring? A double socket would need IIRC a 20A switch, and a
single one... presumably 13A one. (Not certain bout those figures, but
think so)

There is no need to have the switch DP instead of SP. But, 13A DP
switches are not readily available. In addition, wiring 'in line' is a
lot easier if you don't have to keep one conductor continuous (and I
wouldn't want to joint it inside the switch box).

I suggest you use a DP switch if the ring is RCD protected.
Let's say your washing machine develops a neutral-earth short
and trips the RCD. If you switch off your accessible SP switch
you will still be unable to reset the RCD, because the washing
machine is still shorting neutral and earth. Now you have to
heave the washing machine out so you can get the the plug and
unplug it. However, you will likely have first gone off on a
wild goose chase to find the cause, having discounted the
washing machine because the RCD still trips after you switched
it off.

--
Andrew Gabriel

"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"N. Thornton" wrote in message
om...
"William Joones" wrote in message
om...

snipped

The normal practice would be to switch off power at the CU, surely.

If you want to run a double gang socket, then you have to take into
consideration that both sockets will be used at the same time, so you
need
the correct switch gear to control it. Diversity is only considered in
the
whole installation, where there is an unlikely event that all appliances
and
every socket will be on and used at the one time.

Sounds like good sense to me, yet I've been told that cable feeding
one double socket only needs to be rated at 20A, not 30, so a single
piece of 2.5T&E clipped direct will do. Is that not so?

Regards, NT

If you have two appliances connecting to a two gang socket, and both are
known to contain heating elements, then would you trust a single piece of
2.5 mm T&E PVC ?


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Andrew Gabriel wrote:

I would add that the above is true so long as the cable size does not
reduce from that of the ring. If you reduce the cable size (eg to
1.5mm sq), then a fused-switch unit is needed.

I was under the impression that so long as the cable used could safely
take the full 13A load then it was ok to reduce cable size on the spur.
1.5mm sq ought to be fine I would have thought.


The cable also has to be able to take the fault current (short circuit
to neutral or earth) for the time it takes the 30A fuse/MCB to trip
without overheating -- that's where a 1.5mm² cable is likely to come
unstuck (maybe literally;-) Also, it must still pass enough current to
blow the fuse within 400ms (IIRC).

Unless you are prepared to sit down and do the calculations to prove
that it's OK, stick with 2.5mm². And what are you saving anyway? peanuts.

Yup - quiet agree! I was only commenting that there is not actually a
requirement that you must not reduce cable sizes on the spur. Must admit
I tend to find very little use for 1.5mm sq cable!

--
Cheers,

John.

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

In message ,
John Rumm wrote:

Andrew Gabriel wrote:

I would add that the above is true so long as the cable size does not
reduce from that of the ring. If you reduce the cable size (eg to
1.5mm sq), then a fused-switch unit is needed.

I was under the impression that so long as the cable used could safely
take the full 13A load then it was ok to reduce cable size on the spur.
1.5mm sq ought to be fine I would have thought.


The cable also has to be able to take the fault current (short circuit
to neutral or earth) for the time it takes the 30A fuse/MCB to trip
without overheating -- that's where a 1.5mm² cable is likely to come
unstuck (maybe literally;-) Also, it must still pass enough current to
blow the fuse within 400ms (IIRC).

Unless you are prepared to sit down and do the calculations to prove
that it's OK, stick with 2.5mm². And what are you saving anyway? peanuts.

Yup - quiet agree! I was only commenting that there is not actually a
requirement that you must not reduce cable sizes on the spur. Must admit
I tend to find very little use for 1.5mm sq cable!


For a couple of meters or less, as you say, there's not much point
skimping... but just to be pedantic, surely the fuse you have to worry
about on a (single) socket is the 13A in the plug, not the 30/32 in the
board? Now, a double...

Hmmm...

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
.... We laughed, we sang, we danced far into the night.

In message ,
"BigWallop" wrote:


"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"N. Thornton" wrote in message
om...
"William Joones" wrote in message
om...

snipped

The normal practice would be to switch off power at the CU, surely.

If you want to run a double gang socket, then you have to take into
consideration that both sockets will be used at the same time, so you
need
the correct switch gear to control it. Diversity is only considered in
the
whole installation, where there is an unlikely event that all appliances
and
every socket will be on and used at the one time.

Sounds like good sense to me, yet I've been told that cable feeding
one double socket only needs to be rated at 20A, not 30, so a single
piece of 2.5T&E clipped direct will do. Is that not so?

Regards, NT

If you have two appliances connecting to a two gang socket, and both are
known to contain heating elements, then would you trust a single piece of
2.5 mm T&E PVC ?



So do you wire all your spurs in 4mm, just to be safe? If you have this
kind of (expected) loading then you need to think again about the design
of your circuits. On the other hand, IIRC 2.5mmT&E clipped direct is
rated at 27A...

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Don't fight technology, live with it: http://www.livtech.co.uk/
.... James Dean taught Marc Bolan to drive.

"Martin Angove" wrote in message
...
In message ,
"BigWallop" wrote:


"N. Thornton" wrote in message
om...
"BigWallop" wrote in message
...
"N. Thornton" wrote in message
om...
"William Joones" wrote in
message
om...

snipped

The normal practice would be to switch off power at the CU, surely.

If you want to run a double gang socket, then you have to take into
consideration that both sockets will be used at the same time, so
you
need
the correct switch gear to control it. Diversity is only considered
in
the
whole installation, where there is an unlikely event that all
appliances
and
every socket will be on and used at the one time.

Sounds like good sense to me, yet I've been told that cable feeding
one double socket only needs to be rated at 20A, not 30, so a single
piece of 2.5T&E clipped direct will do. Is that not so?

Regards, NT

If you have two appliances connecting to a two gang socket, and both are
known to contain heating elements, then would you trust a single piece
of
2.5 mm T&E PVC ?



So do you wire all your spurs in 4mm, just to be safe? If you have this
kind of (expected) loading then you need to think again about the design
of your circuits. On the other hand, IIRC 2.5mmT&E clipped direct is
rated at 27A...

Hwyl!

M.


Only to a radial two gang socket, Yes. That way, at least I know that it is
going to take the same sort of load as the rest of the ring, which is
literally wired with 5mm cable. I don't pull teeth on the extra 1mm strand.
For a single gang radial socket, then I'd use 2.5.

In article ,
"BigWallop" writes:

Only to a radial two gang socket, Yes. That way, at least I know that it is
going to take the same sort of load as the rest of the ring, which is
literally wired with 5mm cable.

Thinking of a ring that way will give you a very misleading
impression of how it works.

--
Andrew Gabriel

In article ,
Martin Angove writes:
In message ,
John Rumm wrote:
Andrew Gabriel wrote:
The cable also has to be able to take the fault current (short circuit
to neutral or earth) for the time it takes the 30A fuse/MCB to trip
without overheating -- that's where a 1.5mm² cable is likely to come
unstuck (maybe literally;-) Also, it must still pass enough current to
blow the fuse within 400ms (IIRC).

Unless you are prepared to sit down and do the calculations to prove
that it's OK, stick with 2.5mm². And what are you saving anyway? peanuts.

Yup - quiet agree! I was only commenting that there is not actually a
requirement that you must not reduce cable sizes on the spur. Must admit
I tend to find very little use for 1.5mm sq cable!


For a couple of meters or less, as you say, there's not much point
skimping...

And for longer lengths, you're likely to find the impedance is too
high to meet the trip times.

but just to be pedantic, surely the fuse you have to worry
about on a (single) socket is the 13A in the plug, not the 30/32 in the
board? Now, a double...

If the short happens in the connections to the back of the socket... ?

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"BigWallop" writes:

Only to a radial two gang socket, Yes. That way, at least I know that
it is
going to take the same sort of load as the rest of the ring, which is
literally wired with 5mm cable.

Thinking of a ring that way will give you a very misleading
impression of how it works.

--
Andrew Gabriel

This is in the context of the two gang socket being unswitched and being
remotely isolated by DP switch from the ring itself.


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Martin Angove wrote:

For a couple of meters or less, as you say, there's not much point
skimping... but just to be pedantic, surely the fuse you have to worry
about on a (single) socket is the 13A in the plug, not the 30/32 in the
board? Now, a double...

I think the difficult thing with a reduced size cable on the spur is
coping with a wiring fault (or damage) to the spur itself.

The fuse in the plug will protect the flex to the appliance, and in the
case of a fault in the appliance it will also protect the spur wiring.
However a short in the socket itself for example, would necessitate the
spur wire being able to take enough fault current to blow the main fuse
on the ring circuit.

So basically if you are confident the reduced size cable will perform
well enough under fault conditions then you can use it. I suppose the
argument for "skimping" is strongest when you have a contract to wire
five hundred flats all to the same wiring design - the saving in cable
costs may then be noticeable. From a DIY point of view its a wast of
time IMHO.


--
Cheers,

John.

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