In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug fuse in
some way protected the permanent wiring. Which is not its purpose.


It may not be its original purpose, but by the laws of physics it does
protect the upstream single cable (that after the tee off from the ring)
from *overload*.

I believe it is also accepted as valid practise to make that assumption.

Not so. If that were the case, you could have unlimited outlets on a spur
- after that cable would be protected by the 13 amp fuse in each outlet,
by your reckoning.

If the cable that the 20A isolator is controlling *cannot exceed* 13A by
design (because there is a single socket/fused plugtop downstream) then
the 20A isolator can never be subjected to an overload outside of its
design limits.

You are ignoring the possibility of a fault in the socket or spur cable
feeding it.

--
*Always drink upstream from the herd *

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

Dave Plowman (News) wrote:

In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug fuse in
some way protected the permanent wiring. Which is not its purpose.


It may not be its original purpose, but by the laws of physics it does
protect the upstream single cable (that after the tee off from the ring)
from *overload*.

I believe it is also accepted as valid practise to make that assumption.

Not so. If that were the case, you could have unlimited outlets on a spur
- after that cable would be protected by the 13 amp fuse in each outlet,
by your reckoning.

Sorry, logic is faulty - in that scenario the head end of the spur cable
would be subject to the sum of maximum loads downstream,

So: 3 13A sockets on a spur could justifiably result in 39A total load.

This is not what we are talking about - we are talking about a single socket
ona single spur which leads to a design current for the spur of no more
than 13A.




If the cable that the 20A isolator is controlling *cannot exceed* 13A by
design (because there is a single socket/fused plugtop downstream) then
the 20A isolator can never be subjected to an overload outside of its
design limits.

You are ignoring the possibility of a fault in the socket or spur cable
feeding it.

A fault that does not trip the circuit protective device - a fault that
happens to cause L-N currents to flow that are greater than 20A but
insufficient to trip the 32A breaker?

That would be a very specific and unlikely fault. It also invalidates the
whole possibility of using 2.5mm for spur wiring or even rings themselves as
the design criteria for any part of the ring is that the cable shall be
rated for 20A or greater (for the purposes of conductor sizing, derating and
grouping).

Given the IET have decided rings and spurs in 2.5mm2 are OK based on 20A
components being protected by a 32A protective device, I am more than happy
to use a parallel argument for justifying my assertion.

--
Tim Watts

"Dave Plowman (News)" wrote in message
...
In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug fuse in
some way protected the permanent wiring. Which is not its purpose.


It may not be its original purpose, but by the laws of physics it does
protect the upstream single cable (that after the tee off from the ring)
from *overload*.

I believe it is also accepted as valid practise to make that assumption.

Not so. If that were the case, you could have unlimited outlets on a spur
- after that cable would be protected by the 13 amp fuse in each outlet,
by your reckoning.

If the cable that the 20A isolator is controlling *cannot exceed* 13A by
design (because there is a single socket/fused plugtop downstream) then
the 20A isolator can never be subjected to an overload outside of its
design limits.

You are ignoring the possibility of a fault in the socket or spur cable
feeding it.

You are having the same argument I have had several times.
You risk upsetting some of the electricians and/or John if you continue.

You are like me, you think protection should always be at the start of what
you are protecting not at the end.
The regs appear to think its OK to put some of the protection at the end
because nobody will ever get it wrong and if they do its their fault.

BTW the 13A fuse will allow 20A without blowing for a long time
(hours/days) so it is possible to get 40A down a bit of 2.5 mm2 cable
without doing any wiring mods if your house was wired prior to the ban on
double socketed spurs.

dennis@home wrote:



"Dave Plowman (News)" wrote in message
...
In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug fuse in
some way protected the permanent wiring. Which is not its purpose.


It may not be its original purpose, but by the laws of physics it does
protect the upstream single cable (that after the tee off from the ring)
from *overload*.

I believe it is also accepted as valid practise to make that assumption.

Not so. If that were the case, you could have unlimited outlets on a spur
- after that cable would be protected by the 13 amp fuse in each outlet,
by your reckoning.

If the cable that the 20A isolator is controlling *cannot exceed* 13A by
design (because there is a single socket/fused plugtop downstream) then
the 20A isolator can never be subjected to an overload outside of its
design limits.

You are ignoring the possibility of a fault in the socket or spur cable
feeding it.

You are having the same argument I have had several times.
You risk upsetting some of the electricians and/or John if you continue.

You are like me, you think protection should always be at the start of
what you are protecting not at the end.
The regs appear to think its OK to put some of the protection at the end
because nobody will ever get it wrong and if they do its their fault.

BTW the 13A fuse will allow 20A without blowing for a long time
(hours/days)

A usual rule of thumb is 30 minutes for double the current on typical
household fuses/breakers.

But equivalently, 40A through a "20A cable" does not destroy the cable
instantly either. It heats the cable until at some point the cable's max
operating temperature is exceeded (70C for most PVC) and the insulation
starts to suffer degredation.

The fuse/breaker characteristics are designed to match or better the heating
effect so that short term overloads are permitted but long term ones are cut
before the protected components suffer damage.

so it is possible to get 40A down a bit of 2.5 mm2 cable
without doing any wiring mods if your house was wired prior to the ban on
double socketed spurs.

What ban on double socket spurs? Is this in Amendment 1 which I do not have?
Otherwise the 17th Fig 15A clearly allows double socket spurs.

--
Tim Watts

On Tue, 18 Sep 2012 10:33:10 +0100, Tim Watts
wrote:

They're fine if feeding a single socket with fused plug as the plugtop fuse
provides overload protection to the 20A switch.

Thank you. So many great replies; I may not be able to reply to them
all.

At present each "switch" is connected to one single unswitched socket.
I say switch in quotes because now that I have started all this
controversy, I have had another look and not all of them are fused
connection units, some are switches without fuses. Some look newer
than the rest so I don't think a mixture was fitted originally. I
guess it is just a case of what was to hand on the day. When I
redecorate I may possibly change them all to match.

Thanks.

On Tue, 18 Sep 2012 10:03:00 +0100, "David WE Roberts"
wrote:

When I did a kitchen some years ago the advice from this group was that an
unswitched socket under the counter was all you needed - no additional
isolating switch.

Well that would certainly save the hassle of a FCU; these must be a
pain to wire as they have three cables in one box. But as they are
already here, it would be even more hassle to remove them.

That said, like others, I thought that the switch was needed in case
of fire or other emergency but as someone else has said, having the
switch above the appliance probably is not very practical.

Thanks.

On Tue, 18 Sep 2012 03:19:11 -0700 (PDT), sm_jamieson
wrote:

I like others have fitted a socket in the adjacent cabinet, and cut an opening so the socket can be passed through and plugged in.

I suppose, playing devil's advocate, it is quicker to flip a switch
than open a cupboard and reach inside. If I had brand new expensive
cupboards, I don't know I would want to cut holes in them but I don't
think there is a right or wrong answer, just personal choice.

On Tue, 18 Sep 2012 20:27:34 +0100, Andy Champ
wrote:

We've just had the dishwasher catching fire thread.

I must have missed that one; what was it called?

On Tue, 18 Sep 2012 10:34:15 +0100, Roger Mills
wrote:


Are they spurs off the ring main, and are there more than one socket on
each spur? If so, the FCUs are to protect the spur. If there's only one
socket on each spur, I don't see the point of the FCUs.

They are only single sockets, though that said you can spur to a
double. I couldn't see why there needed to be a fuse either. Many
posts seem to suggest whoever did this used whatever they had at the
time. I guess it is a circular thing: FCUs are cheaper because they
are used more and they are used more because they are cheaper!

On Tue, 18 Sep 2012 19:04:03 +0100, "ARW"
wrote:

There is a benefit to using the 20A switch for local authorities and
landlords. If the washer blows a fuse then it is the fuse in the washers
plug top that blows and not the fuse in the fused spur. It saves a calling
out an electrician.

Thanks. I hadn't thought of that.

On Tue, 18 Sep 2012 18:57:55 +0100, "ARW"
wrote:

That is not a requirement. Washing machines and dishwashers do not need
emergency switching.

A push in dishwasher or washing machine can be supplied from an unswitched
socket behind it and requires no other isolation.

That's interesting. What do the regs require to have a switch: just
fixed installations like cookers?

Do you generally fit switches, or does it depend what the customer
asks for?

Thanks.

In article ,
Fred wrote:
I suppose, playing devil's advocate, it is quicker to flip a switch
than open a cupboard and reach inside. If I had brand new expensive
cupboards, I don't know I would want to cut holes in them but I don't
think there is a right or wrong answer, just personal choice.

If the appliance is smoking etc, why not just switch it off on the front
panel? That will isolate the problem in the vast majority of the cases.

As regards not cutting holes in new cupboards. how do you plumb in the
sink? ;-)

--
*Born free - taxed to death *

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

In article ,
Fred wrote:
There is a benefit to using the 20A switch for local authorities and
landlords. If the washer blows a fuse then it is the fuse in the
washers plug top that blows and not the fuse in the fused spur. It
saves a calling out an electrician.

Thanks. I hadn't thought of that.

Personally, I can't see the difference between changing a fuse in an FCU
and plug. Both can be done without tools. (on many designs)

--
*We waste time, so you don't have to *

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

On 18/09/2012 16:53, Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
Where do you get the '13 amp max'? The spur circuit must be capable of
tripping the 32 amp protection in the CU in event of a fault.

13A max design current due to a single fused plugtop downstream. The
switch can exceed its design current in normal use irrespective of the
fact it is protected upstream by a 32A device.

The 'design' current is for a reasonable life switching that current.
So I'm not clear how you think a 13 amp fuse downstream of this will stop
it being exceeded? If the appliance shorts, the fuse will blow. A switch
with its contacts made will handle rather more than its rated spec.

Tripping is another issue which will be unaffected by whether the switch
is 20A or 32A. Either way, fault currents can get into 100's of amps
for mS as I'm aware you know - the only debate is whether a 20A switch
would be damaged by the I2t let through, and I would propose that it is
highly unlikely unless it was closed onto a downstream fault - in which
case that could cause damage to 32A switch's contacts too.

The MCB contacts get damaged when it trips?

Not usually on trip, but they can suffer if closed onto a hard fault too
many times.

--
Cheers,

John.

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

On 19/09/2012 13:42, dennis@home wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug fuse in
some way protected the permanent wiring. Which is not its purpose.


It may not be its original purpose, but by the laws of physics it does
protect the upstream single cable (that after the tee off from the ring)
from *overload*.

I believe it is also accepted as valid practise to make that assumption.

Not so. If that were the case, you could have unlimited outlets on a spur
- after that cable would be protected by the 13 amp fuse in each outlet,
by your reckoning.

If the cable that the 20A isolator is controlling *cannot exceed* 13A by
design (because there is a single socket/fused plugtop downstream) then
the 20A isolator can never be subjected to an overload outside of its
design limits.

You are ignoring the possibility of a fault in the socket or spur cable
feeding it.

You are having the same argument I have had several times.

He is not - quite...

Tim's assertion is basically sound - that a single socket fed from a 20A
plate switch is safe. In reality its the design[1] that makes it safe -
that there is also a 13A fuse downstream of it, is a bonus.

[1] i.e. it is to all intents and purposes a traditional unfused spur.

(noting that I don't accept your argument that unfused spurs are unsafe,
so let's not do that again)

You risk upsetting some of the electricians and/or John if you continue.

You are like me,

No need to be nasty ;-)

you think protection should always be at the start of
what you are protecting not at the end.

"Protection" is not one thing. In a circuit you need to consider fault
protection separately from overload protection. They have different
requirements, and effects, plus different causes.

Fault protection must always be at the circuit origin (and possibly
again if there is a point of reduction in cable size). Overload
protection may be at the origin, may be at some other place, or may be
omitted altogether in some circumstances.

The regs appear to think its OK to put some of the protection at the end
because nobody will ever get it wrong and if they do its their fault.

That appears to be your misunderstanding of the regulations and not what
they actually say.

BTW the 13A fuse will allow 20A without blowing for a long time
(hours/days) so it is possible to get 40A down a bit of 2.5 mm2 cable
without doing any wiring mods if your house was wired prior to the ban
on double socketed spurs.


--
Cheers,

John.

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

On 19/09/2012 14:05, Tim Watts wrote:
dennis@home wrote:



"Dave Plowman (News)" wrote in message
...
In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug fuse in
some way protected the permanent wiring. Which is not its purpose.


It may not be its original purpose, but by the laws of physics it does
protect the upstream single cable (that after the tee off from the ring)
from *overload*.

I believe it is also accepted as valid practise to make that assumption.

Not so. If that were the case, you could have unlimited outlets on a spur
- after that cable would be protected by the 13 amp fuse in each outlet,
by your reckoning.

If the cable that the 20A isolator is controlling *cannot exceed* 13A by
design (because there is a single socket/fused plugtop downstream) then
the 20A isolator can never be subjected to an overload outside of its
design limits.

You are ignoring the possibility of a fault in the socket or spur cable
feeding it.

You are having the same argument I have had several times.
You risk upsetting some of the electricians and/or John if you continue.

You are like me, you think protection should always be at the start of
what you are protecting not at the end.
The regs appear to think its OK to put some of the protection at the end
because nobody will ever get it wrong and if they do its their fault.

BTW the 13A fuse will allow 20A without blowing for a long time
(hours/days)

A usual rule of thumb is 30 minutes for double the current on typical
household fuses/breakers.

But equivalently, 40A through a "20A cable" does not destroy the cable
instantly either. It heats the cable until at some point the cable's max
operating temperature is exceeded (70C for most PVC) and the insulation
starts to suffer degredation.

The fuse/breaker characteristics are designed to match or better the heating
effect so that short term overloads are permitted but long term ones are cut
before the protected components suffer damage.

so it is possible to get 40A down a bit of 2.5 mm2 cable
without doing any wiring mods if your house was wired prior to the ban on
double socketed spurs.

What ban on double socket spurs? Is this in Amendment 1 which I do not have?
Otherwise the 17th Fig 15A clearly allows double socket spurs.

There is no ban on double socket spurs in the sense you mean. There may
have been a time in the dim and distant past where two single sockets
were allowed - raising the nominal maximum load from the 20A assumed for
a double socket, to the 26A for a pair of singles.

However given this rule would have existed before the days of well
insulated properties and building materials being in common use, they
would have been a strong likelihood that they were being fed from a
length of 2.5mm^2 T&E, installed using installation method C anyway,
with its normal maximum rating of 27A.


--
Cheers,

John.

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

On 18/09/2012 11:28, Man at B&Q wrote:
On Sep 18, 10:33 am, Tim Watts wrote:
John Walliker wrote:
On Sep 18, 8:12 am, Fred wrote:

In my kitchen I have some unswitched sockets under the counter for the
washing machine and dishwasher. These are switched above the counter
by FCUs. Is there any reason that FCUs are used rather than 20A
switches or is it just whatever they had to hand on the day? Just
curious.

The FCUs are specifically designed to be used as part of a ring final
circuit. It is unclear whether the modular 20A switches are rated in
the same way. Certainly they seem to have much smaller terminals.
This would suggest that 20A switches are suitable
for a radial circuit with a 20A circuit breaker, but maybe not for a
connection to a ring.

John

They're fine if feeding a single socket with fused plug as the plugtop fuse
provides overload protection to the 20A switch.

Only if the overload is downstream of the plug.

How were you planning on introducing an overload upstream of the plug?

(you could introduce a fault upstream of it, but that is a different issue)


--
Cheers,

John.

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

On 19/09/2012 14:38, Fred wrote:
On Tue, 18 Sep 2012 10:33:10 +0100, Tim Watts
wrote:

They're fine if feeding a single socket with fused plug as the plugtop fuse
provides overload protection to the 20A switch.

Thank you. So many great replies; I may not be able to reply to them
all.

At present each "switch" is connected to one single unswitched socket.
I say switch in quotes because now that I have started all this
controversy, I have had another look and not all of them are fused
connection units, some are switches without fuses. Some look newer
than the rest so I don't think a mixture was fitted originally. I
guess it is just a case of what was to hand on the day. When I
redecorate I may possibly change them all to match.

I normally use a 20A plate switch with neon for this application. Say
something like:

http://www.tlc-direct.co.uk/Products/GU2011.html



--
Cheers,

John.

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

Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
They're fine if feeding a single socket with fused plug as the
plugtop fuse provides overload protection to the 20A switch.

The only function of the plug fuse is to protect the appliance cable.

I have read both yours and Tim's post on this one. Here is my view on it.

In conjunction with the rules that a 20A switch must only supply one single
or one double socket when used as as part of an unfused spur then the 13A
fuses in the plug are providing the overload protection.

The rule that states the 20A switch must only supply one single or one
double socket for an unfused spur lays down the "law" and the 13A fuse(s)
enforce the "law".

eg the 13A fuse stops you from using an electric cooker plugged into the
socket controlled by the 20A switch. If you try then the 13A fuse in the
plug will blow before the unfused spur cable is damaged due to overload.

Therefore I do believe that function of a 13A fuse is actually twofold
1. To protect the appliance
2. To ensure overload protection on a correctly installed unfused.

Cheers

--
Adam

Dave Plowman (News) wrote:
In article ,
Fred wrote:
There is a benefit to using the 20A switch for local authorities
and landlords. If the washer blows a fuse then it is the fuse in
the washers plug top that blows and not the fuse in the fused
spur. It saves a calling out an electrician.

Thanks. I hadn't thought of that.

Personally, I can't see the difference between changing a fuse in an
FCU and plug. Both can be done without tools. (on many designs)

But you are not a brain dead tenant demanding your landlords sends round an
electrician.


--
Adam

On Wed, 19 Sep 2012 16:37:46 +0100, "Dave Plowman (News)"
wrote:

Personally, I can't see the difference between changing a fuse in an FCU
and plug. Both can be done without tools. (on many designs)

But you're a member of uk.diy. Adam was talking about landlords and
local authorities with tenants who are not diy minded.

Fred wrote:
On Tue, 18 Sep 2012 18:57:55 +0100, "ARW"
wrote:

That is not a requirement. Washing machines and dishwashers do not
need emergency switching.

A push in dishwasher or washing machine can be supplied from an
unswitched socket behind it and requires no other isolation.

That's interesting. What do the regs require to have a switch: just
fixed installations like cookers?

Do you generally fit switches, or does it depend what the customer
asks for?

I only fit switches above the worktop if the customer asks me to. I discuss
what they want/options available when I quote for the job.

Of course on many jobs I am following a spec sheet and just follow that.
Usually drawn up by some sort of a knobhead known as an architect (scum of
the earth).

--
Adam

dennis@home wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
Tim Watts wrote:
I was discussing your incorrect statement that a 13 amp plug
fuse in some way protected the permanent wiring. Which is not
its purpose.

It may not be its original purpose, but by the laws of physics it
does protect the upstream single cable (that after the tee off
from the ring) from *overload*.

I believe it is also accepted as valid practise to make that
assumption.

Not so. If that were the case, you could have unlimited outlets on
a spur - after that cable would be protected by the 13 amp fuse in
each outlet, by your reckoning.

If the cable that the 20A isolator is controlling *cannot exceed*
13A by design (because there is a single socket/fused plugtop
downstream) then the 20A isolator can never be subjected to an
overload outside of its design limits.

You are ignoring the possibility of a fault in the socket or spur
cable feeding it.

You are having the same argument I have had several times.
You risk upsetting some of the electricians and/or John if you
continue.
You are like me, you think protection should always be at the start
of what you are protecting not at the end.

Ever heard of a condom?

That provides protection at the load end.

--
Adam

On Wed, 19 Sep 2012 17:40:33 +0100, John Rumm
wrote:

I normally use a 20A plate switch with neon for this application

Is there a reason you use one with a neon? I ask because I've never
seen the benefit of neon indicators and I wonder if I am missing
something?

Neons are useful if you cannot tell whether the load has power, so if
you are switching something remotely, I can see neons could be useful;
with the caveat that the neon shows power is going to the switch and
not necessarily to the load. But if switching a dishwasher or washing
machine, can't you tell from the machine whether it is powered or not?

Thanks.

Fred wrote:

I can see neons could be useful;
with the caveat that the neon shows power is going to the switch and
not necessarily to the load. But if switching a dishwasher or washing
machine, can't you tell from the machine whether it is powered or not?

If they're integrated ones, you'd have to open the cupboard door to tell.

dennis@home wrote:

BTW the 13A fuse will allow 20A without blowing for a long time
(hours/days) so it is possible to get 40A down a bit of 2.5 mm2 cable
without doing any wiring mods if your house was wired prior to the
ban on double socketed spurs.

WTF are you talking about?

--
Adam

On 2012-09-19, ARW wrote:

I have read both yours and Tim's post on this one. Here is my view on it.

In conjunction with the rules that a 20A switch must only supply one single
or one double socket when used as as part of an unfused spur then the 13A
fuses in the plug are providing the overload protection.

The rule that states the 20A switch must only supply one single or one
double socket for an unfused spur lays down the "law" and the 13A fuse(s)
enforce the "law".

eg the 13A fuse stops you from using an electric cooker plugged into the
socket controlled by the 20A switch. If you try then the 13A fuse in the
plug will blow before the unfused spur cable is damaged due to overload.

Therefore I do believe that function of a 13A fuse is actually twofold
1. To protect the appliance
2. To ensure overload protection on a correctly installed unfused.


I guess if someone plugs in two 13Â*A kettles on the spurred double,
that isn't enough of an overload to cause damage?

ARW wrote:
Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
They're fine if feeding a single socket with fused plug as the
plugtop fuse provides overload protection to the 20A switch.

The only function of the plug fuse is to protect the appliance
cable.

I have read both yours and Tim's post on this one. Here is my view on
it.
In conjunction with the rules that a 20A switch must only supply one
single or one double socket when used as as part of an unfused spur
then the 13A fuses in the plug are providing the overload protection.

The rule that states the 20A switch must only supply one single or one
double socket for an unfused spur lays down the "law" and the 13A
fuse(s) enforce the "law".

eg the 13A fuse stops you from using an electric cooker plugged into
the socket controlled by the 20A switch. If you try then the 13A fuse
in the plug will blow before the unfused spur cable is damaged due to
overload.
Therefore I do believe that function of a 13A fuse is actually twofold
1. To protect the appliance
2. To ensure overload protection on a correctly installed unfused.

^^spur^^
--
Adam

Adam Funk wrote:
On 2012-09-19, ARW wrote:

I have read both yours and Tim's post on this one. Here is my view
on it.

In conjunction with the rules that a 20A switch must only supply
one single or one double socket when used as as part of an unfused
spur then the 13A fuses in the plug are providing the overload
protection.

The rule that states the 20A switch must only supply one single or
one double socket for an unfused spur lays down the "law" and the
13A fuse(s) enforce the "law".

eg the 13A fuse stops you from using an electric cooker plugged
into the socket controlled by the 20A switch. If you try then the
13A fuse in the plug will blow before the unfused spur cable is
damaged due to overload.

Therefore I do believe that function of a 13A fuse is actually
twofold
1. To protect the appliance
2. To ensure overload protection on a correctly installed unfused.


I guess if someone plugs in two 13 A kettles on the spurred double,
that isn't enough of an overload to cause damage?

A short term overload. That is not problem, unless you watch the kettles
boil in which case it will be a sustained overload:-)

--
Adam

S Viemeister wrote:
On 9/18/2012 3:27 PM, Andy Champ wrote:
On 18/09/2012 10:03, David WE Roberts wrote:
When I did a kitchen some years ago the advice from this group
was that an unswitched socket under the counter was all you
needed - no additional isolating switch.
If the aim is to be able to isolate the unit for servicing,
exchange, or in the event of a fault, then pulling out the plug
should suffice. I assume this advice still stands.

We've just had the dishwasher catching fire thread. Personally I
like the idea of pulling the power without having to move a smoking
machine...
An acquaintance had to redo much of her kitchen earlier this year,
after her dishwasher caught fire.
I made sure to have an over-the-counter switch for mine...

So you sit and watch the dishwasher running with your finger on the
isolation switch just in case it catches fire?

Do you sit and watch the TV with a finger poised above an isolation switch
just in case the TV catches fire?

--
Adam

Adam Funk wrote:

On 2012-09-19, ARW wrote:

I have read both yours and Tim's post on this one. Here is my view on it.

In conjunction with the rules that a 20A switch must only supply one
single or one double socket when used as as part of an unfused spur then
the 13A fuses in the plug are providing the overload protection.

The rule that states the 20A switch must only supply one single or one
double socket for an unfused spur lays down the "law" and the 13A fuse(s)
enforce the "law".

eg the 13A fuse stops you from using an electric cooker plugged into the
socket controlled by the 20A switch. If you try then the 13A fuse in the
plug will blow before the unfused spur cable is damaged due to overload.

Therefore I do believe that function of a 13A fuse is actually twofold
1. To protect the appliance
2. To ensure overload protection on a correctly installed unfused.


I guess if someone plugs in two 13 A kettles on the spurred double,
that isn't enough of an overload to cause damage?

You will actually find that no double 13A socket plate is actually rated to
26A combined total load.

MK did a test of one of their own products a long while back and concluded
that 20A was about as high as it could go.

http://www.theiet.org/forums/forum/m...threadid=33787

ah - 19.5A:

"All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995
and are rated at 13A per unit. Double socket-outlets have been manufactured
and tested to exceed this rating by margin that allows electrical safety and
reduces the risk of heat and mechanical damage to components due to
overloading. It should be noted that BS1363 part 2: 1995 does not allow
double sockets to operate at twice the permissible maximum loading and it
should be remembered that double socket-outlets are not manufactured to be
able to withstand a 26A load for sustained periods of time.

Research by ourselves and third party organisations has shown that all MK
double sockets can safely withstand a continuous load of 19.5A for an
indefinite period. Increasing the load slightly will begin to cause heat and
mechanical stresses on the components in a relatively short period. Testing
showed that a load of 22.3A was sufficient to cause heat stress that would
cause a browning of the faceplates and sufficient heat to cause insulation
damage to cable cores. A load of 24A for 43 hours was sufficient to cause
significant heat damage to the material in which the socket-outlet was
situated and within 75 hours sufficient to cause significant damage that
would lead to the very real potential of fire.

MK recommend that users of their sockets consult professional design
Engineers when designing installations to avoid the possibility of heat and
mechanical stress to components and installations caused by overloading of
MK socket-outlets. "


Of course, your kettle is only drawing power for a short time. If you
plugged 2 3kW room heaters in OTOH, you would be in trouble...
--
Tim Watts

On 19/09/2012 19:28, Fred wrote:
On Wed, 19 Sep 2012 17:40:33 +0100, John Rumm
wrote:

I normally use a 20A plate switch with neon for this application

Is there a reason you use one with a neon? I ask because I've never
seen the benefit of neon indicators and I wonder if I am missing
something?

Just so you can tell at a glance (the ones on the GET range of
accessories are quite small and discrete)

Neons are useful if you cannot tell whether the load has power, so if
you are switching something remotely, I can see neons could be useful;

In some cases appliances are hidden in "kitchen unit door" faced
enclosures...

with the caveat that the neon shows power is going to the switch and
not necessarily to the load. But if switching a dishwasher or washing
machine, can't you tell from the machine whether it is powered or not?

The neon only lights when the switch is on.


--
Cheers,

John.

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In article ,
Tim Watts wrote:
Of course, your kettle is only drawing power for a short time. If you
plugged 2 3kW room heaters in OTOH, you would be in trouble...

Of course this is where the ring circuit works so well in practice. By
judging what won't actually happen. The chances of a room being large
enough to need two 3 kW heaters on for a long period - and it also only
having the one double socket - remote.

Of course those who dislike rings can always invent plenty of 'what ifs'
;-)

--
*No husband has ever been shot while doing the dishes *

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

On 19 Sep,
Tim Watts wrote:

Of course, your kettle is only drawing power for a short time. If you
plugged 2 3kW room heaters in OTOH, you would be in trouble...

I remeber in my youth where I worked we had two electric stills in a lab
(distilling water!) They both had a pair of 3Kw heaters fed by 13a plugs.
Each still was plugged into a double socket, which needed regiular
replacement after a few months. The ring fuse needed frequent replacement as
there also were 3kw ovens on the same circuits.

The biggest problem for me was that the two 'rings' were on seperate (sub)
circuits with seperate origins far away in the basement at least 100 yards
away. (one being a 1950s addition to an originally 1930s installation, the
other really was an original radial with changed outlets).

There were other bits on these two circuits before their origin in the
basement, in rubber covered and lead sheathed cables of great antiquity,
resulting in high loop impedance great earth leakage and no cross bonding.

Until I did an unofficial bond between our fridge and oven (official lekky
due to lack of budget denied there was a problem) there was enough volts
between earths to light a lamp bulb dimly at times and gave a distinct tingle
if you leaned on the oven whilst retreiving one's milk.

Well before current risk assessments but we never killed any of our students.
--
B Thumbs
Change lycos to yahoo to reply

On 2012-09-19, Tim Watts wrote:

Adam Funk wrote:

On 2012-09-19, ARW wrote:

Therefore I do believe that function of a 13A fuse is actually twofold
1. To protect the appliance
2. To ensure overload protection on a correctly installed unfused.


I guess if someone plugs in two 13 A kettles on the spurred double,
that isn't enough of an overload to cause damage?

You will actually find that no double 13A socket plate is actually rated to
26A combined total load.

MK did a test of one of their own products a long while back and concluded
that 20A was about as high as it could go.
....
Of course, your kettle is only drawing power for a short time. If you
plugged 2 3kW room heaters in OTOH, you would be in trouble...

That's another reason I'm glad I have the kettle & toaster in
different corners of the kitchen. :-)

On 2012-09-19, Dave Plowman (News) wrote:

In article ,
Fred wrote:
I suppose, playing devil's advocate, it is quicker to flip a switch
than open a cupboard and reach inside. If I had brand new expensive
cupboards, I don't know I would want to cut holes in them but I don't
think there is a right or wrong answer, just personal choice.

If the appliance is smoking etc, why not just switch it off on the front
panel? That will isolate the problem in the vast majority of the cases.

As regards not cutting holes in new cupboards. how do you plumb in the
sink? ;-)

A Belfast sink propped up?

In article ,
wrote:
I remeber in my youth where I worked we had two electric stills in a lab
(distilling water!) They both had a pair of 3Kw heaters fed by 13a
plugs. Each still was plugged into a double socket, which needed
regiular replacement after a few months. The ring fuse needed frequent
replacement as there also were 3kw ovens on the same circuits.

Well, yes. This is why you don't use rings and domestic regs in such
places. They are for houses, not offices, labs, factories, etc.

--
*When I'm not in my right mind, my left mind gets pretty crowded *

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

On Wed, 19 Sep 2012 22:14:49 +0100, John Rumm
wrote:

In some cases appliances are hidden in "kitchen unit door" faced
enclosures...

I don't have anything that posh All of mine are freestanding.

The neon only lights when the switch is on.

Yes, the point I was trying to make is the neon tells you that the
switch is on, not that the appliance is drawing power. If the
appliance did not work, you would still need to plug something into
the socket to check that it had a voltage across it.

On Wed, 19 Sep 2012 19:05:54 +0100, "ARW"
wrote:

I only fit switches above the worktop if the customer asks me to. I discuss
what they want/options available when I quote for the job.

Of course on many jobs I am following a spec sheet and just follow that.
Usually drawn up by some sort of a knobhead known as an architect (scum of
the earth).

Thanks for the explanation.

On 20/09/2012 11:33, Fred wrote:
On Wed, 19 Sep 2012 22:14:49 +0100, John Rumm
wrote:

In some cases appliances are hidden in "kitchen unit door" faced
enclosures...

I don't have anything that posh All of mine are freestanding.

Well same here (unless you include a fridge), but some folks like to
play the "hunt the appliance" game ;-)

The neon only lights when the switch is on.

Yes, the point I was trying to make is the neon tells you that the
switch is on, not that the appliance is drawing power. If the
appliance did not work, you would still need to plug something into
the socket to check that it had a voltage across it.

I can't think of an obvious reason why the socket would not be working -
if the light is on, since there is no fuse, then the socket must be live.




--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
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