How many 2.5mm T&E into a 13A socket?

[Roger Mills]

I have a dual 13A socket under my kitchen sink - powering the dishwasher
and waste disposal device. I need power for an additional appliance and
would prefer to install an additional socket rather than use a 2-way
adapter.

The current socket has 3 x 2.5mm T&E cables connected to it - which I
assume to be two for the ring main plus a spur. The cables all disappear
behind the cabinets (I didn't install them!) and there's no easy way of
knowing which is the spur - other than separating the 3 and finding out
what doesn't then work, etc.

If there were only two, it would be easy to wire the new socket into the
ring by diverting one of the two to it and then having another short
cable between the two sockets.

If I randomly pick one of the three to divert, I may well achieve the
same thing. But I may instead end up with two daisy-chained spurs. [This
probably wouldn't matter in practice, even though it's not in accordance
with the regs].

However, if I could get FOUR wires into the existing socket, I would
have a ring plus two separate spurs - which would presumably be ok? I
wouldn't then need to worry about which one is the spur.

Is this likely to be possible? Any other relevant comments (ignoring
Part P, of course!)?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

[Tim Watts]

On Monday 01 April 2013 12:56 Roger Mills wrote in uk.d-i-y:

> I have a dual 13A socket under my kitchen sink - powering the dishwasher
> and waste disposal device. I need power for an additional appliance and
> would prefer to install an additional socket rather than use a 2-way
> adapter.
>
> The current socket has 3 x 2.5mm T&E cables connected to it - which I
> assume to be two for the ring main plus a spur. The cables all disappear
> behind the cabinets (I didn't install them!) and there's no easy way of
> knowing which is the spur - other than separating the 3 and finding out
> what doesn't then work, etc.

That might be worth doing - at least when you do the wiring - just to verify
it is sane.

> If there were only two, it would be easy to wire the new socket into the
> ring by diverting one of the two to it and then having another short
> cable between the two sockets.
>
> If I randomly pick one of the three to divert, I may well achieve the
> same thing. But I may instead end up with two daisy-chained spurs. [This
> probably wouldn't matter in practice, even though it's not in accordance
> with the regs].
>
> However, if I could get FOUR wires into the existing socket, I would
> have a ring plus two separate spurs - which would presumably be ok? I
> wouldn't then need to worry about which one is the spur.
>
> Is this likely to be possible? Any other relevant comments (ignoring
> Part P, of course!)?

It would not be compliant - either with the regs or (I believe) with the
terminal capacity of a standard accessory.

The correct way to do this would be to try to cut out a new flush box next
to the existing socket *around* one of the ring cables (not the spur).

Then incorporate into the ring.

If your additional appliance is not power hungry, and given one load is tiny
and the other is heavy but very intermittent (dishwasher - only heavy for
the short time the heater runs) could you use one of the triple faceplates
over the old double backbox?

I would not like to have 2 or 3 heavy power users in those, but for your
scenario it seems reasonable - and better than an adaptor. But not as good
as a new socket.

Cheers,

Tim

--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

[ARW]

Roger Mills wrote:

> The current socket has 3 x 2.5mm T&E cables connected to it - which I
> assume to be two for the ring main plus a spur. The cables all
> disappear behind the cabinets (I didn't install them!) and there's no
> easy way of knowing which is the spur - other than separating the 3
> and finding out what doesn't then work, etc.

No multimeter?

--
Adam

[Bill]

In message <kjbt8i$jq0$1...@dont-email.me>, ARW
<adamwa...@blueyonder.co.uk> writes

I asked a colleague of mine the other day if he had a DVM and he said "A
what?" and he reckons that he is a qualified electrician......

In the OP's case it would be simple to find which pair are the ring,
separate all 3 T&E and then check which 2 were live, the dead one would
be the feed to the spur. At least that is what I would hope to
find......

Unless it was wired by a plumber of course, then a Ouija board maybe of
more help.
>

--
Bill

[Mike Tomlinson]

En el art�culo <artb07...@mid.individual.net>, Roger Mills
<watt....@gmail.com> escribi�:

>The current socket has 3 x 2.5mm T&E cables connected to it - which I
>assume to be two for the ring main plus a spur. The cables all disappear
>behind the cabinets (I didn't install them!) and there's no easy way of
>knowing which is the spur - other than separating the 3 and finding out
>what doesn't then work, etc.

Given that you would have to take the existing socket off to add another
anyway, testing is easy. Power off, take existing socket off, separate
wires, power on, test (carefully!) with a meter to see which two are
live - that'll be the ring. Power off, bit of tape round them to
identify them. The dead wire will be the spur. You can then add the
extra socket into the ring.

>However, if I could get FOUR wires into the existing socket

Bad idea. While you might be able to manage it, the terminals aren't
designed for it, and you'll have fun trying to stuff everything back
into the box, especially as you'll be working under the sink.

--
(\_/)
(='.'=)
(")_(")

[ARW]

Mike Tomlinson wrote:
> En el art�culo <artb07...@mid.individual.net>, Roger Mills
> <watt....@gmail.com> escribi�:
>
> > The current socket has 3 x 2.5mm T&E cables connected to it - which
> > I assume to be two for the ring main plus a spur. The cables all
> > disappear behind the cabinets (I didn't install them!) and there's
> > no easy way of knowing which is the spur - other than separating
> > the 3 and finding out what doesn't then work, etc.
>
> Given that you would have to take the existing socket off to add
> another anyway, testing is easy. Power off, take existing socket
> off, separate wires, power on, test (carefully!) with a meter to see
> which two are live - that'll be the ring. Power off, bit of tape
> round them to identify them. The dead wire will be the spur. You can
> then add the extra socket into the ring.

I was thinking power off and a continuity test!

--
Adam

[Roger Mills]

On 01/04/2013 13:40, Bill wrote:

>
> In the OP's case it would be simple to find which pair are the ring,
> separate all 3 T&E and then check which 2 were live, the dead one would
> be the feed to the spur. At least that is what I would hope to find......
>

Yes, obvious isn't it! I don't why I didn't think of that. My brain must
be addled because of the date, or something. <g>

> Unless it was wired by a plumber of course, then a Ouija board maybe of
> more help.
>>

No, it was was wired by an electrician (and Part P certified) when the
kitchen was re-done a couple of years ago. Although I photographed the
first fix electrical installation prior to plastering, none of photos
show quite what I need to know!

[Roger Mills]

Yes, several! I was thinking in terms of having to disconnect the
circuit at the consumer unit in order to trace it - but it's now obvious
that I don't need to do that.

[Roger Mills]

On 01/04/2013 13:05, Tim Watts wrote:

>
> If your additional appliance is not power hungry, and given one load is tiny
> and the other is heavy but very intermittent (dishwasher - only heavy for
> the short time the heater runs) could you use one of the triple faceplates
> over the old double backbox?
>

The new appliance (boiling water tap) has a 3kW heater but is
intermittent - only coming on to top up the temperature of its
reservoir. The dishwasher is a heavy user - but only when running. The
food waste disposer only runs for a few seconds at a time when we want
to get rid of some solid food waste.

The existing double outlet is surface mounted on the side of the
cabinet, just inside the door - with the wiring coming from the back in
a conduit. So the accessibility isn't too much of a problem. I could
potentially convert it to a triple with (say) a Screwfix 17315 - but
that has a 13A fuse, which would probably blow if the water heater and
dishwasher both operated at the same time. Also, a triple would extend
further into the cabinet (unless mounted vertically) and wouldn't clear
the body of the waste disposer.

So I still think that the best bet is to install an additional single or
double surface mounted socket in close proximity to the existing one.
Each appliance can then draw up to 13A with impunity whenever it wants to.

[Dave Plowman (News)]

In article <artjes...@mid.individual.net>,

Roger Mills <watt....@gmail.com> wrote:
> Yes, several! I was thinking in terms of having to disconnect the
> circuit at the consumer unit in order to trace it - but it's now obvious
> that I don't need to do that.

Easiest way is just to disconnect the earth wires, then find out which one
is connected to the spur socket, by probing a fixing screw on that. If you
can see which TW&E it belongs to, you have your answer. But you do need to
measure a dead short on your DVM, rather than just any old reading.

--
*Real women don't have hot flashes, they have power surges.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[Roger Mills]

On 01/04/2013 15:50, Dave Plowman (News) wrote:
> In article<artjes...@mid.individual.net>,
> Roger Mills<watt....@gmail.com> wrote:
>> Yes, several! I was thinking in terms of having to disconnect the
>> circuit at the consumer unit in order to trace it - but it's now obvious
>> that I don't need to do that.
>
> Easiest way is just to disconnect the earth wires, then find out which one
> is connected to the spur socket, by probing a fixing screw on that. If you
> can see which TW&E it belongs to, you have your answer. But you do need to
> measure a dead short on your DVM, rather than just any old reading.
>

The only problem is that I don't know where the spur goes! I don't know
whether it powers a socket or something like the cooker hood, or heated
drawer.

But, as others have said, if I power down, disconnect all 3, power up
again and check which 2 wires are live, I will know which is the spur -
regardless of what it does.

[Dave Liquorice]

On Mon, 01 Apr 2013 16:10:30 +0100, Roger Mills wrote:

> But, as others have said, if I power down, disconnect all 3, power up
> again and check which 2 wires are live, I will know which is the spur -
> regardless of what it does.

Well you can but I quite like the power down, disconnect all three and
then use a meter to see which lives are still connected to each other. No
second trip back to the CU, no live working. The two still connected to
each other are the ring, the isolated one the spur. The fun starts when
they are still all connected to each other via dead shorts...

--
Cheers
Dave.

[Roger Mills]

On 01/04/2013 17:25, Dave Liquorice wrote:
> On Mon, 01 Apr 2013 16:10:30 +0100, Roger Mills wrote:
>
>> But, as others have said, if I power down, disconnect all 3, power up
>> again and check which 2 wires are live, I will know which is the spur -
>> regardless of what it does.
>
> Well you can but I quite like the power down, disconnect all three and
> then use a meter to see which lives are still connected to each other. No
> second trip back to the CU, no live working. The two still connected to
> each other are the ring, the isolated one the spur.

Good point!

> The fun starts when
> they are still all connected to each other via dead shorts...
>

. . or when nothing is connected to anything, if the ring has a
discontinuity! Hopefully not, since I have reasonable faith in the bloke
who did - and Part P certified - the electrical installation - although
he did do the second fix without noticing that the plasterers had
plastered over a double socket box until I pointed it out!

[harry]

Turn off power, remove socket and separate out the wires.
Turn power on, check out which wires are live, they are the ring the
other (dead one) is the spur.

[harry]

If it's a 3Kw appliance, it would be better on a separate circuit
wired back to the CU rather than on the ring.

[ARW]

So only Dave Liquorice and myself wants to do the job properly and work on a
dead supply:-)?

Easy and safer to do than a live test.


--
Adam

[ARW]

Well that means that any socket that powers my kettle is fucked/not fit for
use/should be on a radial circuit.

--
Adam

[newshound]

On 01/04/2013 16:10, Roger Mills wrote:
> On 01/04/2013 15:50, Dave Plowman (News) wrote:
>> In article<artjes...@mid.individual.net>,
>> Roger Mills<watt....@gmail.com> wrote:
>>> Yes, several! I was thinking in terms of having to disconnect the
>>> circuit at the consumer unit in order to trace it - but it's now obvious
>>> that I don't need to do that.
>>
>> Easiest way is just to disconnect the earth wires, then find out which
>> one
>> is connected to the spur socket, by probing a fixing screw on that. If
>> you
>> can see which TW&E it belongs to, you have your answer. But you do
>> need to
>> measure a dead short on your DVM, rather than just any old reading.
>>
> The only problem is that I don't know where the spur goes! I don't know
> whether it powers a socket or something like the cooker hood, or heated
> drawer.
>
> But, as others have said, if I power down, disconnect all 3, power up
> again and check which 2 wires are live, I will know which is the spur -
> regardless of what it does.

The other "tool" which can be handy is the socket tester thingy which
looks like a 13A plug but has three lights in it. I've butchered one of
these to terminate in three leads with croc clips on. Particularly
useful on lighting roses but also useful here as it will reveal things
like missing live or missing neutral on one half of the ring-main.

If you don't want to butcher one you could temporarily connect each T&E
in turn to a spare single socket for testing.

[newshound]

On 01/04/2013 16:50, ARW wrote:

> harry wrote:

>>
>> Turn off power, remove socket and separate out the wires.
>> Turn power on, check out which wires are live, they are the ring the
>> other (dead one) is the spur.
>
> So only Dave Liquorice and myself wants to do the job properly and work on a
> dead supply:-)?
>
> Easy and safer to do than a live test.
>
>

Don't always agree with Harry; OP may not have a tone generator but
probably has a volt stick, meter, or <horror> neon screwdriver.

If done with a bit of care, the check described above is pretty quick,
safe, and reliable.

[ARW]

So is euthanasia -;)

--
Adam

[Tim Watts]

On Monday 01 April 2013 15:51 Roger Mills wrote in uk.d-i-y:

>
> The new appliance (boiling water tap) has a 3kW heater but is
> intermittent - only coming on to top up the temperature of its
> reservoir. The dishwasher is a heavy user - but only when running. The
> food waste disposer only runs for a few seconds at a time when we want
> to get rid of some solid food waste.
>
> The existing double outlet is surface mounted on the side of the
> cabinet, just inside the door - with the wiring coming from the back in
> a conduit. So the accessibility isn't too much of a problem. I could
> potentially convert it to a triple with (say) a Screwfix 17315 - but
> that has a 13A fuse, which would probably blow if the water heater and
> dishwasher both operated at the same time. Also, a triple would extend
> further into the cabinet (unless mounted vertically) and wouldn't clear
> the body of the waste disposer.
>
> So I still think that the best bet is to install an additional single or
> double surface mounted socket in close proximity to the existing one.
> Each appliance can then draw up to 13A with impunity whenever it wants to.

OK - I'm against the triple. I would not really want those on a double
plate. The disposal unit takes bugger all and runs for seconds - but the
water heater is likely to pull for some minutes and the dishwasher
similarly.

A double socket is rated at 20A max total - and although the loads will be
highly intermittent, I would do the extra work and stick a second seperate
socket in.

An option involving no wall bashing would be to blank off the old socket
box, and use it to hold a joint for the ring and the spur - so two cables
emerge from the box at surface level and you run these around a couple of
surface mounted sockets.

[Dave Plowman (News)]

In article <artmb8...@mid.individual.net>,

Roger Mills <watt....@gmail.com> wrote:
> > Easiest way is just to disconnect the earth wires, then find out which
> > one is connected to the spur socket, by probing a fixing screw on
> > that. If you can see which TW&E it belongs to, you have your answer.
> > But you do need to measure a dead short on your DVM, rather than just
> > any old reading.
> >
> The only problem is that I don't know where the spur goes! I don't know
> whether it powers a socket or something like the cooker hood, or heated
> drawer.

Whatever it is will likely be closest to this socket.

> But, as others have said, if I power down, disconnect all 3, power up
> again and check which 2 wires are live, I will know which is the spur -
> regardless of what it does.

My way is easier. ;-)

--
*Some people are only alive because it is illegal to kill.

[Dave Liquorice]

On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts wrote:

> An option involving no wall bashing would be to blank off the old
> socket box, and use it to hold a joint for the ring and the spur - so
> two cables emerge from the box at surface level and you run these
> around a couple of surface mounted sockets.

Or just cut back the conduit that is feeding the current double socket,
fit another double socket, join those as a ring and take the existing
spur from one of them,

--
Cheers
Dave.

[Dave Liquorice]

On Mon, 01 Apr 2013 18:04:08 +0100, newshound wrote:

>>> Turn off power, remove socket and separate out the wires.
>>> Turn power on, check out which wires are live, they are the ring the
>>> other (dead one) is the spur.
>>
>> So only Dave Liquorice and myself wants to do the job properly and
>> work on a dead supply:-)?
>>
>> Easy and safer to do than a live test.
>>
> Don't always agree with Harry; OP may not have a tone generator but
> probably has a volt stick, meter, or <horror> neon screwdriver.

Why would one want a tone generator? A continuity meter (a normal
facility on any multimeter) is all that is required.

> If done with a bit of care, the check described above is pretty quick,
> safe, and reliable.

FS (low) VO "safe". These wires are in a cupboard under the sink. I'm not
averse to live working but it does make me nervous, very nervous when
there is more than one exposed live conductor. It's easy to keep out of
the way of one, keeping out of the way of two in a confined space is a
different kettle of fish. I really don't like the FLASH BANG and being
splattered with molten copper... Or getting a belt and in both cases
whacking ones head against the cupboard frame or WHY.

--
Cheers
Dave.

[Bill]

In message <nyyfbegfubjuvyypb...@srv1.howhill.co.uk>, Dave
Liquorice <allsortsn...@howhill.com> writes

>On Mon, 01 Apr 2013 18:04:08 +0100, newshound wrote:
>
>>>> Turn off power, remove socket and separate out the wires.
>>>> Turn power on, check out which wires are live, they are the ring the
>>>> other (dead one) is the spur.
>>>
>>> So only Dave Liquorice and myself wants to do the job properly and
>>> work on a dead supply:-)?
>>>
>>> Easy and safer to do than a live test.
>>>
>> Don't always agree with Harry; OP may not have a tone generator but
>> probably has a volt stick, meter, or <horror> neon screwdriver.
>
>Why would one want a tone generator? A continuity meter (a normal
>facility on any multimeter) is all that is required.

I use a tone generator and receiver all the time for tracing data
cables, not often on normal mains cables though.

Dave, is your clock set correctly? You seem to be posting an hour ahead
of the rest of the country.

--
Bill

[Major Scott]

On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Monday 01 April 2013 15:51 Roger Mills wrote in uk.d-i-y:
>
>>
>> The new appliance (boiling water tap) has a 3kW heater but is
>> intermittent - only coming on to top up the temperature of its
>> reservoir. The dishwasher is a heavy user - but only when running. The
>> food waste disposer only runs for a few seconds at a time when we want
>> to get rid of some solid food waste.
>>
>> The existing double outlet is surface mounted on the side of the
>> cabinet, just inside the door - with the wiring coming from the back in
>> a conduit. So the accessibility isn't too much of a problem. I could
>> potentially convert it to a triple with (say) a Screwfix 17315 - but
>> that has a 13A fuse, which would probably blow if the water heater and
>> dishwasher both operated at the same time. Also, a triple would extend
>> further into the cabinet (unless mounted vertically) and wouldn't clear
>> the body of the waste disposer.
>>
>> So I still think that the best bet is to install an additional single or
>> double surface mounted socket in close proximity to the existing one.
>> Each appliance can then draw up to 13A with impunity whenever it wants to.
>
> OK - I'm against the triple. I would not really want those on a double
> plate. The disposal unit takes bugger all and runs for seconds - but the
> water heater is likely to pull for some minutes and the dishwasher
> similarly.
>
> A double socket is rated at 20A max total

Surely there would be thousands of people plugging in two 3kW loads and melting them.....

--
Why do they rate a movie "R" for "adult language?"
The only people I hear using that language are teenagers.

[Tim Watts]

Did I miss this being a surface fitting?

[Tim Watts]

Apparantly not.

[Major Scott]

On Mon, 01 Apr 2013 21:41:16 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>
>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>> wrote:
>>
>
>>> A double socket is rated at 20A max total
>>
>> Surely there would be thousands of people plugging in two 3kW loads and
>> melting them.....
>>
>
> Apparantly not.

Could it be..... they happily take 24 amps?

--
Reality is for people who can't handle alcohol and joints.

[Dave Liquorice]

On Mon, 01 Apr 2013 21:40:49 +0100, Tim Watts wrote:

>> Or just cut back the conduit that is feeding the current double
>> socket, fit another double socket, join those as a ring and take the
>> existing spur from one of them,
>
> Did I miss this being a surface fitting?

Recent comment from the OP mentioned socket near front edge of cupboard
fed by conduit. Well I think it was the OP not thread drift...

--
Cheers
Dave.

[Bill]

In message <5335BC93DD%brian...@lycos.co.uk>, m...@privacy.net writes
>On 1 Apr,

> "Dave Liquorice" <allsortsn...@howhill.com> wrote:
>
>> Well you can but I quite like the power down, disconnect all three and
>> then use a meter to see which lives are still connected to each other. No
>> second trip back to the CU, no live working. The two still connected to
>> each other are the ring, the isolated one the spur. The fun starts when
>> they are still all connected to each other via dead shorts...
>>

>Or none are connected, as I found when testing a friend's wiring. Eventually
>found (several weeks later) a back box which had been plastered over after
>first fix and had never had its socket fitted. 0/10 for the electrician who
>originally tested the system!
>

Not as bad on a safety level, but a friend of mine asked me to check her
new, very expensive flat out, because her TV didn't work. Every point
had the cable neatly coiled in the boxes behind the sockets, just not
connected. In the attic all the cables came to a point on a wall near
to a 13A socket, all ready to be connected to a DA, what DA??

There was an aerial though!! Cable sat next to all the others in the
attic.

Who passed that lot off as complete and tested?

Some dodgy aerial rigger/builder no doubt.

--
Bill
( A different one )

[Dave Liquorice]

On Mon, 1 Apr 2013 20:12:00 +0100, Bill wrote:

>>> Don't always agree with Harry; OP may not have a tone generator but
>>> probably has a volt stick, meter, or <horror> neon screwdriver.
>>
>> Why would one want a tone generator? A continuity meter (a normal
>> facility on any multimeter) is all that is required.
>
> I use a tone generator and receiver all the time for tracing data
> cables,

So do I but that is when the two ends you want to trace are physically
some distance apart not all poking out of a double back box. B-)

> Dave, is your clock set correctly? You seem to be posting an hour
> ahead of the rest of the country.

Vintage (1998) news reader doesn't understand the TZ config.sys setting,
it'll sort itself out next weekend. B-)

--
Cheers
Dave.

[Roger Mills]

On 01/04/2013 18:04, newshound wrote:

>>
> Don't always agree with Harry; OP may not have a tone generator but
> probably has a volt stick, meter, or <horror> neon screwdriver.
>
> If done with a bit of care, the check described above is pretty quick,
> safe, and reliable.
>
>

No, I haven't got a tone generator - but I have got two or three
multi-meters which will measure voltage and resistance (and hence
continuity). So it shouldn't be too difficult to work out which two
wires are connected to each other via the CU - i.e. the ring - with the
power *off*.

[Roger Mills]

On 01/04/2013 18:31, Tim Watts wrote:

>
> An option involving no wall bashing would be to blank off the old socket
> box, and use it to hold a joint for the ring and the spur - so two cables
> emerge from the box at surface level and you run these around a couple of
> surface mounted sockets.
>

There won't be any wall-bashing anyway. the existing socket is in a
surface box screwed to the *side* of the cabinet, only just inside the
door, so I can easily fix another one just below it and connect that
into the ring once I've determined which two of the three wires *are*
the ring.

[Roger Mills]

Precisely - except that I don't need to cut back the conduit since
there's plenty of cable which I can pull through.

[Roger Mills]

On 01/04/2013 20:50, Dave Liquorice wrote:

>
> FS (low) VO "safe". These wires are in a cupboard under the sink. I'm not
> averse to live working but it does make me nervous, very nervous when
> there is more than one exposed live conductor. It's easy to keep out of
> the way of one, keeping out of the way of two in a confined space is a
> different kettle of fish. I really don't like the FLASH BANG and being
> splattered with molten copper... Or getting a belt and in both cases
> whacking ones head against the cupboard frame or WHY.
>

They're actually quite accessible, and I can reach them without any part
of me - except my hands - being in the cupboard. Nevertheless, since I
now realise that it's perfectly simple to work out which wire is which
with the power off, there's no point in having it on!

[Alexander Lamaison]

Oh come on. We'll be running new circuits for kettles next.

Alex

--
Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

[Alexander Lamaison]

Tim Watts <tw+u...@dionic.net> writes:

> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>
>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>> wrote:
>>
>
>>> A double socket is rated at 20A max total
>>
>> Surely there would be thousands of people plugging in two 3kW loads and
>> melting them.....
>>
>
> Apparantly not.

I'm sure Tim's right simply because I've seen the 20A quoted so many
times. But I'd love to know where it comes from. Is this figure in BS
1363?

[Major Scott]

On Mon, 01 Apr 2013 23:53:34 +0100, Alexander Lamaison <aw...@doc.ic.ac.uk> wrote:

> Tim Watts <tw+u...@dionic.net> writes:
>
>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>
>>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>>> wrote:
>>>
>>
>>>> A double socket is rated at 20A max total
>>>
>>> Surely there would be thousands of people plugging in two 3kW loads and
>>> melting them.....
>>>
>>
>> Apparantly not.
>
> I'm sure Tim's right simply because I've seen the 20A quoted so many
> times. But I'd love to know where it comes from. Is this figure in BS
> 1363?

How many (non-electrician) people will know not to stick two high powered devices in a double socket? Take a kitchen for example, where lots of things have heaters. Dishwasher, washing machine, tumble dryer, .....

So, they've made something which is unprotected by a fuse which can take only two thirds of the protection of the ring main fuse/breaker. How stupid is that?

--
The scientific theory I Iike best is that the rings of Saturn are composed entirely of lost airline Luggage. -- Mark Russell

[Alexander Lamaison]

"Major Scott" <n...@spam.com> writes:

> On Mon, 01 Apr 2013 23:53:34 +0100, Alexander Lamaison
> <aw...@doc.ic.ac.uk> wrote:
>
>> Tim Watts <tw+u...@dionic.net> writes:
>>
>>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>>
>>>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>>>> wrote:
>>>>
>>>
>>>>> A double socket is rated at 20A max total
>>>>
>>>> Surely there would be thousands of people plugging in two 3kW loads and
>>>> melting them.....
>>>>
>>>
>>> Apparantly not.
>>
>> I'm sure Tim's right simply because I've seen the 20A quoted so many
>> times. But I'd love to know where it comes from. Is this figure in BS
>> 1363?
>
> How many (non-electrician) people will know not to stick two high
> powered devices in a double socket? Take a kitchen for example, where
> lots of things have heaters. Dishwasher, washing machine, tumble
> dryer, .....
>
> So, they've made something which is unprotected by a fuse which can
> take only two thirds of the protection of the ring main fuse/breaker.
> How stupid is that?

I think (the electricians will correct me if I'm wrong) the problem with
your statement is that 'take' is too imprecise. They're not
firecrackers. They don't get to 20A and pop. The >20A load would have
to be pulled continuosly for hours and hours before it mattered.

Instinctively, it seems dangerous, but if you have a think how you would
arrange for a 20A load that never turned off you'll see that it's pretty
difficult.

[Major Scott]

Normally when you see a maximum rating, you're lucky if you can maintain that for long! If the room's a bit warmer than they tested it at....

> Instinctively, it seems dangerous, but if you have a think how you would
> arrange for a 20A load that never turned off you'll see that it's pretty
> difficult.

Someone decides they want to keep warm in winter when their central heating breaks. Two 3kW fanheaters....

--
Religion is excellent stuff for keeping common people quiet -- Napoleon Bonaparte

[Alexander Lamaison]

They cycle on and off. Stick two of them in close proximity and they'll
spend even more time off. Even though time off may not be nearly as
long as time on (midwinter, 6ft snowdrift) I bet it's plenty enough to
prevent overload.

The reason I'm interested in the 20A rating is not for overload but when
deciding what the design current of a circuit is. Do you use 20A for
each double socket before you apply diversity?

[Major Scott]

Perhaps. But diversity applied to a 30A ring main still has the correct fuse or breaker should diversity not take place as you thought. If the double socket only takes 20A and there's only a 30A fuse protecting it in the CU, it should have it's own 20A fuse.

> The reason I'm interested in the 20A rating is not for overload but when
> deciding what the design current of a circuit is. Do you use 20A for
> each double socket before you apply diversity?

--
History teaches us that no other cause has brought more death than the word of god. -- Giulian Buzila

[Alexander Lamaison]

It's the same situation. A 30A fuse doesn't blow at 30A, so the ring
circuit can be made to carry more current than its 'rated' current,
simply by plugging too much in.

Neither 30A circuit nor 20A socket have protection that kicks in the
moment you exceed that rating. Both rely on making overloads hard, but
not impossible, to achieve.

[John Rumm]

On 01/04/2013 23:53, Alexander Lamaison wrote:
> Tim Watts <tw+u...@dionic.net> writes:
>
>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>
>>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>>> wrote:
>>>
>>
>>>> A double socket is rated at 20A max total
>>>
>>> Surely there would be thousands of people plugging in two 3kW loads and
>>> melting them.....
>>>
>>
>> Apparantly not.
>
> I'm sure Tim's right simply because I've seen the 20A quoted so many
> times. But I'd love to know where it comes from. Is this figure in BS
> 1363?

1363 part 2 1995. Its from the temperature rise test section, where you
are supposed to load a socket with 14A on one side, and a further 6A on
the other when testing a double. The load is then maintained for a
minimum of 4h, and up to a maximum of 8h or when a stable temperature is
reached (whichever comes first). To pass, the temperature rise must be
limited to 52 deg C over ambient.


--
Cheers,

John.

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

[John Rumm]

On 02/04/2013 00:40, Alexander Lamaison wrote:
> "Major Scott" <n...@spam.com> writes:

>>> I think (the electricians will correct me if I'm wrong) the problem with
>>> your statement is that 'take' is too imprecise. They're not
>>> firecrackers. They don't get to 20A and pop. The >20A load would have
>>> to be pulled continuosly for hours and hours before it mattered.
>>
>> Normally when you see a maximum rating, you're lucky if you can
>> maintain that for long! If the room's a bit warmer than they tested
>> it at....

Check the test spec in BS1363, the minimum test duration is 4h @ 20A
100% duty cycle.

>>> Instinctively, it seems dangerous, but if you have a think how you would
>>> arrange for a 20A load that never turned off you'll see that it's pretty
>>> difficult.
>>
>> Someone decides they want to keep warm in winter when their central
>> heating breaks. Two 3kW fanheaters....
>
> They cycle on and off. Stick two of them in close proximity and they'll
> spend even more time off. Even though time off may not be nearly as
> long as time on (midwinter, 6ft snowdrift) I bet it's plenty enough to
> prevent overload.

Indeed. However many would still be alarmed by the temperature rise on
the socket and that would probably serve to have them connect things
differently. ;-)

> The reason I'm interested in the 20A rating is not for overload but when
> deciding what the design current of a circuit is. Do you use 20A for
> each double socket before you apply diversity?

You can have an unlimited number of sockets on a circuit, so it does not
really factor. The guideline is to limit the floor area served by the
circuit.

[Tim Watts]

On Monday 01 April 2013 23:53 Alexander Lamaison wrote in uk.d-i-y:

> Tim Watts <tw+u...@dionic.net> writes:
>
>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>
>>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>>> wrote:
>>>
>>
>>>> A double socket is rated at 20A max total
>>>
>>> Surely there would be thousands of people plugging in two 3kW loads and
>>> melting them.....
>>>
>>
>> Apparantly not.
>
> I'm sure Tim's right simply because I've seen the 20A quoted so many
> times. But I'd love to know where it comes from. Is this figure in BS
> 1363?
>
> Alex
>

It's printed on the back of one of mine.

Also, as regs allow a double on a spur and for nominal purposes the cabling
in a ring main is defined to be good for 20A min under all conditions, it
makes sense to limit an oversized accessory at the same.

[Tim Watts]

Oh - in that case, you are right - it would be silly not to just insert a
new socket :)

[Major Scott]

Yes, but you've now got a 20A socket with a 30A fuse, which is even worse. A 20A fuse would allow short term overloads already. Upping that to 30A is too much. Ir surprises me how many petty safety rules there are yet it's so easy to set fire to your wall simply by using two 13A sockets at 13A. How difficult would it have been to make them take 6A more?

--
As the coffin was being lowered into the ground at a Traffic Wardens funeral, a voice from inside screams:
"I'm not dead, I'm not dead. Let me out!"
The Vicar smiles, leans forward sucking air through his teeth and mutters:
"Too late pal, I've already done the paperwork"

[Major Scott]

On Tue, 02 Apr 2013 04:39:29 +0100, John Rumm <see.my.s...@nowhere.null> wrote:

> On 01/04/2013 23:53, Alexander Lamaison wrote:
>> Tim Watts <tw+u...@dionic.net> writes:
>>
>>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>>
>>>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>>>> wrote:
>>>>
>>>
>>>>> A double socket is rated at 20A max total
>>>>
>>>> Surely there would be thousands of people plugging in two 3kW loads and
>>>> melting them.....
>>>>
>>>
>>> Apparantly not.
>>
>> I'm sure Tim's right simply because I've seen the 20A quoted so many
>> times. But I'd love to know where it comes from. Is this figure in BS
>> 1363?
>
> 1363 part 2 1995. Its from the temperature rise test section, where you
> are supposed to load a socket with 14A on one side, and a further 6A on
> the other when testing a double. The load is then maintained for a
> minimum of 4h, and up to a maximum of 8h or when a stable temperature is
> reached (whichever comes first). To pass, the temperature rise must be
> limited to 52 deg C over ambient.

That's pretty hot. Lets say you have a warm room of 23C. That's 75C. I wouldn't want 75C sat in my wall. And that's only at the 20A rating.

--
"His idea of safe sex is an `X' spray-painted on the rump of animals that are known to kick."

[Major Scott]

On Tue, 02 Apr 2013 10:36:34 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Monday 01 April 2013 23:53 Alexander Lamaison wrote in uk.d-i-y:
>
>> Tim Watts <tw+u...@dionic.net> writes:
>>
>>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>>
>>>> On Mon, 01 Apr 2013 18:31:04 +0100, Tim Watts <tw+u...@dionic.net>
>>>> wrote:
>>>>
>>>
>>>>> A double socket is rated at 20A max total
>>>>
>>>> Surely there would be thousands of people plugging in two 3kW loads and
>>>> melting them.....
>>>>
>>>
>>> Apparantly not.
>>
>> I'm sure Tim's right simply because I've seen the 20A quoted so many
>> times. But I'd love to know where it comes from. Is this figure in BS
>> 1363?
>>
>> Alex
>>
>
> It's printed on the back of one of mine.
>
> Also, as regs allow a double on a spur and for nominal purposes the cabling
> in a ring main is defined to be good for 20A min under all conditions, it
> makes sense to limit an oversized accessory at the same.

Depends what cable you use. If I was wiring a spur I'd use something rated at at least 30A.

I don't know who wired this house (it's a Bett home built in 1979), but the ring main looks to have been done with 4mm^2 cable, not the 2.5mm^2 you're referring to. The shower is wired with 6mm^2, and the lights with 2.5mm^2. It's bloody difficult fitting those big wires in I can tell you.

--
How do you play Iraqi bingo?
B-52...F-16...B-2

[Tim Watts]

Your house was wired by a looney - or you've measured wrong...

[Major Scott]

On Tue, 02 Apr 2013 12:31:24 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Tuesday 02 April 2013 12:19 Major Scott wrote in uk.d-i-y:
>
>> On Tue, 02 Apr 2013 10:36:34 +0100, Tim Watts <tw+u...@dionic.net>
>> wrote:
>>
>>> On Monday 01 April 2013 23:53 Alexander Lamaison wrote in uk.d-i-y:
>>>
>>>> Tim Watts <tw+u...@dionic.net> writes:
>>>>
>>>>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>>>>>

>>>>>

>>>>>
>>>>> Apparantly not.
>>>>
>>>> I'm sure Tim's right simply because I've seen the 20A quoted so many
>>>> times. But I'd love to know where it comes from. Is this figure in BS
>>>> 1363?
>>>>
>>>> Alex
>>>>
>>>
>>> It's printed on the back of one of mine.
>>>
>>> Also, as regs allow a double on a spur and for nominal purposes the
>>> cabling in a ring main is defined to be good for 20A min under all
>>> conditions, it makes sense to limit an oversized accessory at the same.
>>
>> Depends what cable you use. If I was wiring a spur I'd use something
>> rated at at least 30A.
>>
>> I don't know who wired this house (it's a Bett home built in 1979), but
>> the ring main looks to have been done with 4mm^2 cable, not the 2.5mm^2
>> you're referring to. The shower is wired with 6mm^2, and the lights with
>> 2.5mm^2. It's bloody difficult fitting those big wires in I can tell you.
>
> Your house was wired by a looney - or you've measured wrong...

I can understand the shower - perhaps he just happened to have that cable available.

And a spur should have thicker cable than a ring, as it's only ONE cable.

The lighting seems over the top, but if it gets embedded in fibreglass.....

--
"First things first, but not necessarily in that order." - Doctor Who

[Tim Watts]

That's the only bit that is likely correct.

> And a spur should have thicker cable than a ring, as it's only ONE cable.
>

No it should not. There are likely to be issues with terminal packing with
mixed cable leading to unreliable joints.

> The lighting seems over the top, but if it gets embedded in
> fibreglass.....

That would be over the top! 1.5mm is heavy enough - 1.0 is often used.

Even if someone had a job lot of cable, to be so cheap as not to get the
right cable would make me very suspicous of everything...

It least they bodged it in the right direction I suppose and didn;t use bell
wire...

[Major Scott]

I don't want 30A going through a 20A cable and making it hot.

If you make sure it's in the grub screw firmly, there is no problem. Why would you think there's a difference between several thin wires and one thick one?

>> The lighting seems over the top, but if it gets embedded in
>> fibreglass.....
>
> That would be over the top! 1.5mm is heavy enough - 1.0 is often used.

I typed the wrong number, it's actually 1.5mm^2, which is rated at 14A, a bit excessive for lighting.

> Even if someone had a job lot of cable, to be so cheap as not to get the
> right cable would make me very suspicous of everything...

I would agree if he had used too thin a cable. If you're doing a few jobs and need 2 different sizes of cable, why buy two reels when the big one will do both?

> It least they bodged it in the right direction I suppose and didn;t use bell
> wire...

Well it's guaranteed the cable will never overheat!

--
Helpdesk: Click on the 'my computer' icon on the left of the screen.
Customer: Your left or my left?

[Tim Watts]

Because several thin wires and one thick one do not pack in the same way as
several identical wires.

There is no accessory that can legitimately take 30A.

A 30A point load on a ring is bad design.

>>> The lighting seems over the top, but if it gets embedded in
>>> fibreglass.....
>>
>> That would be over the top! 1.5mm is heavy enough - 1.0 is often used.
>
> I typed the wrong number, it's actually 1.5mm^2, which is rated at 14A, a
> bit excessive for lighting.

That's sane then and quite correct. I'm using 1.5mm - mostly to given a
little more leeway on the L-E loop impedance.

>
>> Even if someone had a job lot of cable, to be so cheap as not to get the
>> right cable would make me very suspicous of everything...
>
> I would agree if he had used too thin a cable. If you're doing a few jobs
> and need 2 different sizes of cable, why buy two reels when the big one
> will do both?

Because it's a bloody bodge. Next question...

>> It least they bodged it in the right direction I suppose and didn;t use
>> bell wire...
>
> Well it's guaranteed the cable will never overheat!
>

However the same cannot be said of the terminations.

[Major Scott]

On Tue, 02 Apr 2013 14:45:51 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Tuesday 02 April 2013 13:27 Major Scott wrote in uk.d-i-y:
>
>> On Tue, 02 Apr 2013 13:21:14 +0100, Tim Watts <tw+u...@dionic.net>
>> wrote:
>>
>>> On Tuesday 02 April 2013 12:48 Major Scott wrote in uk.d-i-y:
>>>
>>>> On Tue, 02 Apr 2013 12:31:24 +0100, Tim Watts <tw+u...@dionic.net>
>>>> wrote:
>>>>
>>>>> On Tuesday 02 April 2013 12:19 Major Scott wrote in uk.d-i-y:
>>>>>

>>
>>>>
>>
>>>>
>>

>>>>>
>>>>> Your house was wired by a looney - or you've measured wrong...
>>>>
>>>> I can understand the shower - perhaps he just happened to have that
>>>> cable available.
>>>
>>> That's the only bit that is likely correct.
>>>
>>>> And a spur should have thicker cable than a ring, as it's only ONE
>>>> cable.
>>>
>>> No it should not. There are likely to be issues with terminal packing
>>> with mixed cable leading to unreliable joints.
>>
>> I don't want 30A going through a 20A cable and making it hot.
>>
>> If you make sure it's in the grub screw firmly, there is no problem. Why
>> would you think there's a difference between several thin wires and one
>> thick one?
>
> Because several thin wires and one thick one do not pack in the same way as
> several identical wires.

You're obviously no good with a screwdriver.

> There is no accessory that can legitimately take 30A.
>
> A 30A point load on a ring is bad design.

Irrelevant. The fuse is 30A, so nothing should melt first.

>>>> The lighting seems over the top, but if it gets embedded in
>>>> fibreglass.....
>>>
>>> That would be over the top! 1.5mm is heavy enough - 1.0 is often used.
>>
>> I typed the wrong number, it's actually 1.5mm^2, which is rated at 14A, a
>> bit excessive for lighting.
>
> That's sane then and quite correct. I'm using 1.5mm - mostly to given a
> little more leeway on the L-E loop impedance.

Why would you need 14A for a 5A circuit? Think how much easier it would be to fit multiway lightswitches with 5A cable.

>>> Even if someone had a job lot of cable, to be so cheap as not to get the
>>> right cable would make me very suspicous of everything...
>>
>> I would agree if he had used too thin a cable. If you're doing a few jobs
>> and need 2 different sizes of cable, why buy two reels when the big one
>> will do both?
>
> Because it's a bloody bodge. Next question...

Overengineering won't do any harm.

>>> It least they bodged it in the right direction I suppose and didn;t use
>>> bell wire...
>>
>> Well it's guaranteed the cable will never overheat!
>
> However the same cannot be said of the terminations.

If you can't fit the wire into the terminal block, then obviously it's no good, but it fits. And the fuller that block is, the less likely it will fall out.

--
TEACHER: Clyde, your composition on "My Dog" is exactly the same as your brother's. Did you copy his?
CLYDE : No, sir. It's the same dog.

[Tim Watts]

Because mine are 10A circuits, type C breakers to boot to reduce liklihood
of spurious tripping. This suits the layout of my house and it not common,
though it is a standard circuit.

In fact you can have a 16A lighting circuit as a standard circuit, though it
is almost unheard of in domestic scenarios.

And you clearly did not understand the concept of loop impedance which is
*as important* (in terms of ensuring that disconnection times are met under
full fault conditions) as not overloading the cable.

I will explain further with numbers if you wish.

>>>> Even if someone had a job lot of cable, to be so cheap as not to get
>>>> the right cable would make me very suspicous of everything...
>>>
>>> I would agree if he had used too thin a cable. If you're doing a few
>>> jobs and need 2 different sizes of cable, why buy two reels when the big
>>> one will do both?
>>
>> Because it's a bloody bodge. Next question...
>
> Overengineering won't do any harm.
>

For the umpteenth time - it will do harm if it exceeds the terminal capacity
or in any way makes the terminations unreliable. Not debating this anymore -
it's your house, I don't care.

>>>> It least they bodged it in the right direction I suppose and didn;t use
>>>> bell wire...
>>>
>>> Well it's guaranteed the cable will never overheat!
>>
>> However the same cannot be said of the terminations.
>
> If you can't fit the wire into the terminal block, then obviously it's no
> good, but it fits. And the fuller that block is, the less likely it will
> fall out.
>

Are the grub screws beefy enough to hold the wire down. Stiff wire flexing
when you push the accessory into the wall will cause a *lot* of strain on
the terminal. Will one of the thin wires find a void between the terminal
and the tick wire that it falls into, losing grip?

[Major Scott]

On Tue, 02 Apr 2013 15:24:55 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Tuesday 02 April 2013 14:58 Major Scott wrote in uk.d-i-y:
>
>> On Tue, 02 Apr 2013 14:45:51 +0100, Tim Watts <tw+u...@dionic.net>
>> wrote:
>>
>>> On Tuesday 02 April 2013 13:27 Major Scott wrote in uk.d-i-y:
>>>
>>>> On Tue, 02 Apr 2013 13:21:14 +0100, Tim Watts <tw+u...@dionic.net>
>>>> wrote:
>>>>
>>>>> On Tuesday 02 April 2013 12:48 Major Scott wrote in uk.d-i-y:
>>>>>

>>
>>>>

>>>>

>>>>
>>

>>>>>

>>>>> That's the only bit that is likely correct.
>>>>>

>>>>>

>>>>> No it should not. There are likely to be issues with terminal packing
>>>>> with mixed cable leading to unreliable joints.
>>>>
>>>> I don't want 30A going through a 20A cable and making it hot.
>>>>
>>>> If you make sure it's in the grub screw firmly, there is no problem.
>>>> Why would you think there's a difference between several thin wires and
>>>> one thick one?
>>>
>>> Because several thin wires and one thick one do not pack in the same way
>>> as several identical wires.
>>
>> You're obviously no good with a screwdriver.
>>
>>> There is no accessory that can legitimately take 30A.
>>>
>>> A 30A point load on a ring is bad design.
>>
>> Irrelevant. The fuse is 30A, so nothing should melt first.
>>

>>>>> That would be over the top! 1.5mm is heavy enough - 1.0 is often used.
>>>>
>>>> I typed the wrong number, it's actually 1.5mm^2, which is rated at 14A,
>>>> a bit excessive for lighting.
>>>
>>> That's sane then and quite correct. I'm using 1.5mm - mostly to given a
>>> little more leeway on the L-E loop impedance.
>>
>> Why would you need 14A for a 5A circuit? Think how much easier it would
>> be to fit multiway lightswitches with 5A cable.
>
> Because mine are 10A circuits, type C breakers to boot to reduce liklihood
> of spurious tripping. This suits the layout of my house and it not common,
> though it is a standard circuit.

Big house? I've got two 5A circuits. So if you turn one off (or there's a fault) you can still see what you're doing with the other.

> In fact you can have a 16A lighting circuit as a standard circuit, though it
> is almost unheard of in domestic scenarios.
>
> And you clearly did not understand the concept of loop impedance which is
> *as important* (in terms of ensuring that disconnection times are met under
> full fault conditions) as not overloading the cable.
>
> I will explain further with numbers if you wish.

I'm not fussy on disconnection times - I've got fuses!

Anyway, if the current limit is less, you don't need as low an impedance surely? Say it was a 0.5 amp circuit....

Also my house was built before we had circuit breakers.

>>>>> Even if someone had a job lot of cable, to be so cheap as not to get
>>>>> the right cable would make me very suspicous of everything...
>>>>
>>>> I would agree if he had used too thin a cable. If you're doing a few
>>>> jobs and need 2 different sizes of cable, why buy two reels when the big
>>>> one will do both?
>>>
>>> Because it's a bloody bodge. Next question...
>>
>> Overengineering won't do any harm.
>
> For the umpteenth time - it will do harm if it exceeds the terminal capacity
> or in any way makes the terminations unreliable. Not debating this anymore -
> it's your house, I don't care.

If it exceeded the terminal capacity, the wire wouldn't fit.

>>>>> It least they bodged it in the right direction I suppose and didn;t use
>>>>> bell wire...
>>>>
>>>> Well it's guaranteed the cable will never overheat!
>>>
>>> However the same cannot be said of the terminations.
>>
>> If you can't fit the wire into the terminal block, then obviously it's no
>> good, but it fits. And the fuller that block is, the less likely it will
>> fall out.
>
> Are the grub screws beefy enough to hold the wire down. Stiff wire flexing
> when you push the accessory into the wall will cause a *lot* of strain on
> the terminal. Will one of the thin wires find a void between the terminal
> and the tick wire that it falls into, losing grip?

Well everything works, so obviously not.

--
I thought the wife would be the ideal candidate for a new TV show.
Turns out I got it all wrong and the program's called Fact Hunt.

[Bill]

In message <oa6r2a-...@squidward.local.dionic.net>, Tim Watts
<tw+u...@dionic.net> writes

> Not debating this anymore -
>it's your house, I don't care.
>

< http://peakwatch.typepad.com/.a/6a00d83452403c69e20168eb9c5fdd970c-pi>
--
Bill

[John Rumm]

The temperature is decided by the typical temperature budget of the
cable feeding the socket, which if PVC insulated, would normally be 70
deg C.

Needless to say the cable does not immediately fail if that temperature
is reached, however the lifetime of its insulation will start to reduce
with overheating.

[Major Scott]

So you'd be happy with things inside your wall being at 70C?

--
One workman asks another, "How long have you been working here?"
The other one replies, "Since they threatened to fire me."

[ARW]

More info here

http://electrical.theiet.org/wiring-regulations/updates/commentary-02-update-2.cfm?type=pdf

--
Adam

[John Rumm]

You are falling into a common trap of conflating overload protection and
fault protection, and also assuming that it falls to the circuit
protective device to proved both for "everything".

In the case of a general purpose socket circuit, the protective device
at the origin of the circuit needs to provide both fault and overload
protection for the circuit as a whole, but not provide overload
protection for each individual accessory, since that can be provided by
other means.

The test regime for double sockets requires a long term loading test
with a 20A load. This is a solid and sensible engineering practice that
reflects a maximum load that will be "higher than reality". While you
may think you can contrive ways to get larger loads onto a single socket
than that, you will find it far harder to achieve in practice. (the fact
that sockets are not melting all around the country every day indicates
that the design has been very well proven in practice).

Some socket makers (MK for example) claim to test their double sockets
with 26A of loading, however many will test only up to the level of that
required by the BS since that is all that is required to put the product
onto the market.

> A 20A fuse would allow short term overloads already. Upping
> that to 30A is too much.

There is nothing stopping you using 20A circuits if you prefer, however
in domestic environments they tent to prove far less flexible in high
load areas like kitchens.

> Ir surprises me how many petty safety rules
> there are yet it's so easy to set fire to your wall simply by using two
> 13A sockets at 13A.

For definitions of "easy" that include really rather difficult. The vast
majority of 13A loads that you can find to plug in, tend to be
relatively short term in real world cases.

> How difficult would it have been to make them take
> 6A more?

What not have a go at costing it and see? Over engineering things for a
one off solution is sometimes acceptable. However for common items that
will be deployed many hundreds of millions of times, a 20% increase in
manufacturing price may well be "too much", especially as the current
design has been proven to work so well and safely.

[ARW]

1.5mm is rated at 20A if clipped direct with no insulation touching it. It
is rated at 10A when surrounded by insulation. Now most people have lighting
cables and insulation in their loft.

Think about it - do you see the reason why it is used?

--
Adam

[Major Scott]

It's not just the cable that gets hot though. I don't want my flammable wall that warm.

--
Dijon vu: the same mustard as before.

[Major Scott]

On Tue, 02 Apr 2013 17:53:00 +0100, ARW <adamwa...@blueyonder.co.uk> wrote:

I've seen a flex (for a fan) melt right through when it was against a radiator. I don't know what the water temperature was (old commercial installation), but it shows that the plastic couldn't handle about 100C or less.

--
Bill Clinton thinks "harass" is two words.

[Major Scott]

It must be pretty common for someone to plug 2 of a dishwasher, washing machine, and tumble dryer into a double socket, and quite likely to run both at once. They've all got pretty powerful heaters in them.

> > A 20A fuse would allow short term overloads already. Upping
> > that to 30A is too much.
>
> There is nothing stopping you using 20A circuits if you prefer, however
> in domestic environments they tent to prove far less flexible in high
> load areas like kitchens.

I'd prefer just to have a double socket than can handle the same as two single ones.

>> Ir surprises me how many petty safety rules
>> there are yet it's so easy to set fire to your wall simply by using two
>> 13A sockets at 13A.
>
> For definitions of "easy" that include really rather difficult. The vast
> majority of 13A loads that you can find to plug in, tend to be
> relatively short term in real world cases.

I can run a tumble dryer for an hour and a half, more if I have a lot of washing to do after coming back from holiday for example. Same applies to the washing machine and dishwasher.

>> How difficult would it have been to make them take
>> 6A more?
>
> What not have a go at costing it and see? Over engineering things for a
> one off solution is sometimes acceptable. However for common items that
> will be deployed many hundreds of millions of times, a 20% increase in
> manufacturing price may well be "too much", especially as the current
> design has been proven to work so well and safely.

But double sockets are pennies. It's not like we're talking about £50 items here. They're nothing compared to the total cost of an installation.

--
In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move.

[Major Scott]

Not on a FIVE amp circuit, no. You've still got double the rating required.

--
You never really learn to swear until you learn to drive.

[John Rumm]

1) An unfused spur is restricted to a single accessory. That limits the
maximum load to 26A.

2) 2.5mm^2 cable has a "clipped direct" rating of 27A - if the
installation conditions are likely to reduce the current capacity of the
cable to below 20A then the designer needs to change the design.

3) Cables are designed to get "hot". So long as they are kept under 70
degrees during normal operation, no harm will come to them.

4) as has been pointed out elsewhere, if you do manage to get an
excessive long term load on the socket, it will typically fail long
before the cable feeding it.

>> That would be over the top! 1.5mm is heavy enough - 1.0 is often used.
>
> I typed the wrong number, it's actually 1.5mm^2, which is rated at 14A,
> a bit excessive for lighting.

10A in its clipped direct rating in fact...

>> Even if someone had a job lot of cable, to be so cheap as not to get the
>> right cable would make me very suspicous of everything...
>
> I would agree if he had used too thin a cable. If you're doing a few
> jobs and need 2 different sizes of cable, why buy two reels when the big
> one will do both?

Well, on the down sides:

1) Material cost - ￜ20 less profit per reel

2) Time / Labour cost - probably another 50% installation time using
heavier than required cable. That could easily be another day on a house
rewire - so another man days lost productivity.

3) Maintainability reduction, circuits are now harder to extend and test
in future (terminations take longer, and terminal space allows for fewer
wires).

The up side:

Can't think of any...

>> It least they bodged it in the right direction I suppose and didn;t
>> use bell
>> wire...
>
> Well it's guaranteed the cable will never overheat!

In some cases it will actually make it more likely. If you have to cram
too many wires in undersized terminals there is a greater possibility
that you will end up with a poor connection that overheats.

[harry]

On Apr 2, 12:48 pm, "Major Scott" <n...@spam.com> wrote:

> On Tue, 02 Apr 2013 12:31:24 +0100, Tim Watts <tw+use...@dionic.net> wrote:
> > On Tuesday 02 April 2013 12:19 Major Scott wrote in uk.d-i-y:
>

> >> On Tue, 02 Apr 2013 10:36:34 +0100, Tim Watts <tw+use...@dionic.net>

> >> wrote:
>
> >>> On Monday 01 April 2013 23:53 Alexander Lamaison wrote in uk.d-i-y:
>

> >>>> Tim Watts <tw+use...@dionic.net> writes:
>
> >>>>> On Monday 01 April 2013 20:14 Major Scott wrote in uk.d-i-y:
>
> >>>>> Apparantly not.
>
> >>>> I'm sure Tim's right simply because I've seen the 20A quoted so many
> >>>> times.  But I'd love to know where it comes from.  Is this figure in BS
> >>>> 1363?
>
> >>>> Alex
>
> >>> It's printed on the back of one of mine.
>
> >>> Also, as regs allow a double on a spur and for nominal purposes the
> >>> cabling in a ring main is defined to be good for 20A min under all
> >>> conditions, it makes sense to limit an oversized accessory at the same.
>
> >> Depends what cable you use.  If I was wiring a spur I'd use something
> >> rated at at least 30A.
>
> >> I don't know who wired this house (it's a Bett home built in 1979), but
> >> the ring main looks to have been done with 4mm^2 cable, not the 2.5mm^2
> >> you're referring to.  The shower is wired with 6mm^2, and the lights with
> >> 2.5mm^2.  It's bloody difficult fitting those big wires in I can tell you.
>
> > Your house was wired by a looney - or you've measured wrong...
>
> I can understand the shower - perhaps he just happened to have that cable available.
>
> And a spur should have thicker cable than a ring, as it's only ONE cable.

Read up about diversity factor.
http://en.wikipedia.org/wiki/Diversity_factor#Diversified_Load

[ARW]

And for the houses with 10A lighting circuits?

--
Adam

[John Rumm]

On 02/04/2013 15:32, Major Scott wrote:
> On Tue, 02 Apr 2013 15:24:55 +0100, Tim Watts <tw+u...@dionic.net> wrote:

>> And you clearly did not understand the concept of loop impedance which is
>> *as important* (in terms of ensuring that disconnection times are met
>> under
>> full fault conditions) as not overloading the cable.
>>
>> I will explain further with numbers if you wish.
>
> I'm not fussy on disconnection times - I've got fuses!

I have read some powerfully dumb stuff in the past, but every now and
then, scotty comes up with a new gem!

[harry]

On Apr 2, 6:21 pm, John Rumm <see.my.signat...@nowhere.null> wrote:
> On 02/04/2013 13:27, Major Scott wrote:
>
>
>
>
>
>
>
>
>
> > On Tue, 02 Apr 2013 13:21:14 +0100, Tim Watts <tw+use...@dionic.net> wrote:
>
> >> On Tuesday 02 April 2013 12:48 Major Scott wrote in uk.d-i-y:
>

> >>> On Tue, 02 Apr 2013 12:31:24 +0100, Tim Watts <tw+use...@dionic.net>

> >>> wrote:
>
> >>>> On Tuesday 02 April 2013 12:19 Major Scott wrote in uk.d-i-y:
>

> >>>>> On Tue, 02 Apr 2013 10:36:34 +0100, Tim Watts <tw+use...@dionic.net>

> 1) Material cost - £20 less profit per reel

>
> 2) Time / Labour cost - probably another 50% installation time using
> heavier than required cable. That could easily be another day on a house
> rewire - so another man days lost productivity.
>
> 3) Maintainability reduction, circuits are now harder to extend and test
> in future (terminations take longer, and terminal space allows for fewer
> wires).
>
> The up side:
>
> Can't think of any...
>
> >> It least they bodged it in the right direction I suppose and didn;t
> >> use bell
> >> wire...
>
> > Well it's guaranteed the cable will never overheat!
>
> In some cases it will actually make it more likely. If you have to cram
> too many wires in undersized terminals there is a greater possibility
> that you will end up with a poor connection that overheats.
>
> --
> Cheers,
>
> John.
>
>

The total lighting load in my house is less than 150W (LEDs and CFLs)
Just over half and amp?
And I never have all the lights turned on.
Why would anyone want 1.5mm2 cable these days?

[ARW]

So fit 1.0mm^2 then. It's the smallest you are allowed to use on a fixed
install.

--
Adam

[ARW]

John Rumm wrote:
> On 02/04/2013 15:32, Major Scott wrote:
> > On Tue, 02 Apr 2013 15:24:55 +0100, Tim Watts
> > <tw+u...@dionic.net> wrote:
>
> > > And you clearly did not understand the concept of loop impedance
> > > which is *as important* (in terms of ensuring that disconnection
> > > times are met under
> > > full fault conditions) as not overloading the cable.
> > >
> > > I will explain further with numbers if you wish.
> >
> > I'm not fussy on disconnection times - I've got fuses!
>
> I have read some powerfully dumb stuff in the past, but every now and
> then, scotty comes up with a new gem!

Stupid is as stupid does.

--
Adam

[Major Scott]

On Tue, 02 Apr 2013 18:21:49 +0100, John Rumm <see.my.s...@nowhere.null> wrote:

> On 02/04/2013 13:27, Major Scott wrote:
>> On Tue, 02 Apr 2013 13:21:14 +0100, Tim Watts <tw+u...@dionic.net> wrote:
>>
>>> On Tuesday 02 April 2013 12:48 Major Scott wrote in uk.d-i-y:
>>>
>>>> On Tue, 02 Apr 2013 12:31:24 +0100, Tim Watts <tw+u...@dionic.net>
>>>> wrote:
>>>>
>>>>> On Tuesday 02 April 2013 12:19 Major Scott wrote in uk.d-i-y:
>>>>>

>>
>>>>
>>
>>>>
>>

>>>>>
>>>>> Your house was wired by a looney - or you've measured wrong...
>>>>
>>>> I can understand the shower - perhaps he just happened to have that
>>>> cable
>>>> available.
>>>
>>> That's the only bit that is likely correct.
>>>
>>>> And a spur should have thicker cable than a ring, as it's only ONE
>>>> cable.
>>>
>>> No it should not. There are likely to be issues with terminal packing
>>> with
>>> mixed cable leading to unreliable joints.
>>
>> I don't want 30A going through a 20A cable and making it hot.
>
> 1) An unfused spur is restricted to a single accessory. That limits the
> maximum load to 26A.

If you fit a decent cable that can handle 30A, it's protected by the CU fuse and you can add more than one item to it.

> 2) 2.5mm^2 cable has a "clipped direct" rating of 27A - if the
> installation conditions are likely to reduce the current capacity of the
> cable to below 20A then the designer needs to change the design.
>
> 3) Cables are designed to get "hot". So long as they are kept under 70
> degrees during normal operation, no harm will come to them.
>
> 4) as has been pointed out elsewhere, if you do manage to get an
> excessive long term load on the socket, it will typically fail long
> before the cable feeding it.
>
>>> That would be over the top! 1.5mm is heavy enough - 1.0 is often used.
>>
>> I typed the wrong number, it's actually 1.5mm^2, which is rated at 14A,
>> a bit excessive for lighting.
>
> 10A in its clipped direct rating in fact...

Still twice the requirement for a 5A lighting circuit. We're overengineering lighting cables and underengineering sockets.....

>>> Even if someone had a job lot of cable, to be so cheap as not to get the
>>> right cable would make me very suspicous of everything...
>>
>> I would agree if he had used too thin a cable. If you're doing a few
>> jobs and need 2 different sizes of cable, why buy two reels when the big
>> one will do both?
>
> Well, on the down sides:
>

> 1) Material cost - £20 less profit per reel

I was thinking of someone just doing two jobs. Not someone doing it for a living where he can use the cable up later on.

> 2) Time / Labour cost - probably another 50% installation time using
> heavier than required cable. That could easily be another day on a house
> rewire - so another man days lost productivity.

I was considering a small job - fitting a shower. As the cable is in the loft, the fitting time of the cable is nothing compared to actually fitting the shower itself.

> 3) Maintainability reduction, circuits are now harder to extend and test
> in future (terminations take longer, and terminal space allows for fewer
> wires).
>
> The up side:
>
> Can't think of any...

It'll last forever as it's never run anywhere near full load. And the cable was handy at the time, no time or fuel wasted going to buy the "correct" type.

>>> It least they bodged it in the right direction I suppose and didn;t
>>> use bell
>>> wire...
>>
>> Well it's guaranteed the cable will never overheat!
>
> In some cases it will actually make it more likely. If you have to cram
> too many wires in undersized terminals there is a greater possibility
> that you will end up with a poor connection that overheats.

Either it fits in or it doesn't.

--
What did the elephant say to the naked man?
How do you pick up anything with that?

[Major Scott]

I'm not into gambling.

--
Chaos will reign over order - it's easier to implement.

[Major Scott]

Then you fit the 1.5mm wire. But this house does not have a 10A circuit.

[Major Scott]

Incase it gets physically broken?

--
The easiest way to find something lost around the house is to buy a replacement.

[Major Scott]

> The total lighting load in my house is less than 150W (LEDs and CFLs)
> Just over half and amp?
> And I never have all the lights turned on.
> Why would anyone want 1.5mm2 cable these days?

I use LEDs (and CFLs until they've all worn out). I've got 60W in this room, which is just LEDs. Ten 6W LEDs (50W halogen equivalent). 8 rooms, that's up to 480W, even when I get everything changed to LED. All the lights are automatic, so it does happen that they are all on at once if I'm moving around the whole house. I like it to be as bright as a sunny day :-)

[Major Scott]

You think fuses are a bad idea? We were using them for decades before these health and safety morons appeared.

--
You have got to remember that women make babies - not a great bit of design work. Messy, noisy and cannot do anything useful.

[Tim Watts]

On Tuesday 02 April 2013 15:32 Major Scott wrote in uk.d-i-y:


> I'm not fussy on disconnection times - I've got fuses!

Then you really do not understand.

Final circuits rated at 32A or less in domestic properties are required to
disconnect from the supply in <=0.4s in the event of a L-E fault.

This disconnection time, for a fuse or a breaker (but not an RCBO) depends,
and only depends on:

1) The current through the breaker/fuse;

2) The trip curve of the breaker or fuse.

1 depends on the sum of supply earth loop impedance and the circuit L-E loop
impedance at the worst point - and of course the supply voltage, which is
deemed to be a nominal 230V.

So, whereas a 1.0mm2 cable may carry the required maximum current of the
circuit, over a given run it will have a higher impedance than a 1.5mm2
cable over the same run.

Therefore, you can see that there will be cases where a 1.0mm2 cable will
not pass enough current under fault conditions to blow your fuse in the
required time. When a TN-S supply starts off with a worse case loop
impedance of 0.8 Ohms, you are already at a significant disadvantage.

None of this is usually a problem with a typical small house, but it can
easily become a problem with larger or oddly shaped properties.

> Anyway, if the current limit is less, you don't need as low an impedance
> surely? Say it was a 0.5 amp circuit....
>

Correct. For a given tripping time and a fixed characteristic (breaker or
fuse type) the required current to give that tripping time is a fixed ratio
over the nominal rated current. But in your case, that assumes that the
breaker is a 0.5A breaker or fuse. Claiming the design current of the
circuit is 0.5A and then protecting it with a 5A fuse does not work.

> Also my house was built before we had circuit breakers.

Irrelevant.

[Tim Watts]

On Tuesday 02 April 2013 18:48 Major Scott wrote in uk.d-i-y:

>> Read up about diversity factor.
>> http://en.wikipedia.org/wiki/Diversity_factor#Diversified_Load
>
> I'm not into gambling.
>

The you should probably ask your electricy company for a 150A supply
depending of whether you have an electric shower and cooker.

And a road with 100 houses should be supplied with 5000A 3 phase cables.

etc etc.

[Major Scott]

Comparing two cable installations, where the cable is on a circuit protected by a fuse rated the same as the cable. One is 10A and one is 5A.

If you double the cable's resistance (10A to 5A cable), you halve the short circuit current through that cable, but you've also halved the fuse rating, so the time to blow the fuse will be the same.

>> Also my house was built before we had circuit breakers.
>
> Irrelevant.

People with fuses aren't so worried about quick trips.

--
Then there was the Eskimo girl who spent the night with her
boyfriend and next morning found she was six months pregnant.

[Major Scott]

On Tue, 02 Apr 2013 19:06:01 +0100, Tim Watts <tw+u...@dionic.net> wrote:

> On Tuesday 02 April 2013 18:48 Major Scott wrote in uk.d-i-y:
>
>>> Read up about diversity factor.
>>> http://en.wikipedia.org/wiki/Diversity_factor#Diversified_Load
>>
>> I'm not into gambling.
>>
>
> The you should probably ask your electricy company for a 150A supply
> depending of whether you have an electric shower and cooker.
>
> And a road with 100 houses should be supplied with 5000A 3 phase cables.
>
> etc etc.

No, it's fine as long as there is adequate protection. The electricity board assumes I will never use more than 100 amps. But if I did, the fuse next to the meter would blow.

But assuming nobody will ever draw 26 amps from a double socket, and having no protection if it did happen, is daft.

--
Eighty percent of married men cheat in America. The rest cheat in Europe.

[Alexander Lamaison]

Unless the circuit was never used it doesn't show that. What it shows
is that the plastic couldn't handle whatever temperature the conductors
became under load with an ambient temperature the same as the radiator.
This could be higher than 100C depending on flex resistance and fan
load.

Alex

--
Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

[Alexander Lamaison]

John Rumm <see.my.s...@nowhere.null> writes:

> On 02/04/2013 00:40, Alexander Lamaison wrote:
>
>> The reason I'm interested in the 20A rating is not for overload but when
>> deciding what the design current of a circuit is. Do you use 20A for
>> each double socket before you apply diversity?
>
> You can have an unlimited number of sockets on a circuit, so it does
> not really factor. The guideline is to limit the floor area served by
> the circuit.

I mean when you're totting up the total load to assess whether the main
cutout is sufficient. OSG says use "100% of current demand of largest
circuit + 40%". So do you just say design current 32A for ring on 32A
MCB so sockets = 32 + (12.8)n?

[Major Scott]

I forgot to mention the fan was switched off. Most people don't use a radiator and a fan on the same day.

Mind you the local council doesn't seem to realise this, a woman in a council flat gave me her ceiling fan because she was told she mustn't have one in the same room as a gas fire in case it blows it out. She said she'd never use both at once, but he didn't listen. Then she said what about an open window, and he still didn't listen. I would have removed the fan temporarily while he fixed the fire, but she didn't. So I got a free fan.

--
When eating a tongue sandwich, how do you know when you've finished?

[ARW]

So you live in a caravan?

--
Adam

[Alexander Lamaison]

"Major Scott" <n...@spam.com> writes:

> On Tue, 02 Apr 2013 18:21:49 +0100, John Rumm
> <see.my.s...@nowhere.null> wrote:
>
>> On 02/04/2013 13:27, Major Scott wrote:
>>> On Tue, 02 Apr 2013 13:21:14 +0100, Tim Watts <tw+u...@dionic.net> wrote:
>>>
>>>> On Tuesday 02 April 2013 12:48 Major Scott wrote in uk.d-i-y:
>>>>
>>>>> On Tue, 02 Apr 2013 12:31:24 +0100, Tim Watts <tw+u...@dionic.net>
>>>>> wrote:
>>>>>
>>>>>> On Tuesday 02 April 2013 12:19 Major Scott wrote in uk.d-i-y:
>>>>>>
>
>>>
>>>>>
>>>
>>>>>
>>>
>
>>>>>>
>>>>>> Your house was wired by a looney - or you've measured wrong...
>>>>>
>>>>> I can understand the shower - perhaps he just happened to have that
>>>>> cable
>>>>> available.
>>>>
>>>> That's the only bit that is likely correct.
>>>>
>>>>> And a spur should have thicker cable than a ring, as it's only ONE
>>>>> cable.
>>>>
>>>> No it should not. There are likely to be issues with terminal packing
>>>> with
>>>> mixed cable leading to unreliable joints.
>>>
>>> I don't want 30A going through a 20A cable and making it hot.
>>
>> 1) An unfused spur is restricted to a single accessory. That limits the
>> maximum load to 26A.
>
> If you fit a decent cable that can handle 30A, it's protected by the
> CU fuse and you can add more than one item to it.

You seem to be thinking of the items in an electrical installation as
having ratings indicating a magic boundary: a '30A cable' that's
protected by a '30A fuse', in your mind, is good while a '20A cable'
protected by a '30A fuse' is bad.

That's not how it works. Think of the ratings on these things as more
like names than numbers. You can't match circuit components and
protection using the number on the back, like painting-by-numbers.

In case you are still sceptical, consider the difference between a 30A
rewireable fuse and a 30A cartridge fuse which have different protective
'strength' (a 30A rewireable fuse has about the same ability as a 22A
cartridge fuse - if they existed).

[Alexander Lamaison]

"Major Scott" <n...@spam.com> writes:

> On Tue, 02 Apr 2013 19:06:01 +0100, Tim Watts <tw+u...@dionic.net> wrote:
>
>> On Tuesday 02 April 2013 18:48 Major Scott wrote in uk.d-i-y:
>>
>>>> Read up about diversity factor.
>>>> http://en.wikipedia.org/wiki/Diversity_factor#Diversified_Load
>>>
>>> I'm not into gambling.
>>>
>>
>> The you should probably ask your electricy company for a 150A supply
>> depending of whether you have an electric shower and cooker.
>>
>> And a road with 100 houses should be supplied with 5000A 3 phase cables.
>>
>> etc etc.
>
> No, it's fine as long as there is adequate protection. The
> electricity board assumes I will never use more than 100 amps. But if
> I did, the fuse next to the meter would blow.
>

I think this sums up your misunderstanding. A 100A fuse would not blow
just for going over 100A. You have exceed its rating continously for a
period of time. For example, a 100A fuse must not blow when overloaded
at 160A before the overload is carried for _4 hours_!

> But assuming nobody will ever draw 26 amps from a double socket, and
> having no protection if it did happen, is daft.

That's exactly what happens throughout the system, you've just never
realised. There is no protection that kicks in when you exceed either
the rated current of the 20A socket *or* the rated current of any
circuit in your home. The protection in both cases kicks in some time
later if you continue to exceed the rated current and it's safe because
it was specifically engineered that way.

If I could say only one thing it would be not assume you can compare the
ratings of things directly. They're not colour-codes.

[John Rumm]

Buy MK ones then - they claim to test with 2 x 13A loads.

>>> Ir surprises me how many petty safety rules
>>> there are yet it's so easy to set fire to your wall simply by using two
>>> 13A sockets at 13A.
>>
>> For definitions of "easy" that include really rather difficult. The vast
>> majority of 13A loads that you can find to plug in, tend to be
>> relatively short term in real world cases.
>
> I can run a tumble dryer for an hour and a half, more if I have a lot of
> washing to do after coming back from holiday for example. Same applies
> to the washing machine and dishwasher.

Look at the current draw profile and you will find none of them present
continuous 13A loads. Many appliances of that nature are designed with
10A maximum loads, and that will be reduced over time by the action of
the thermostats.

>>> How difficult would it have been to make them take
>>> 6A more?
>>
>> What not have a go at costing it and see? Over engineering things for a
>> one off solution is sometimes acceptable. However for common items that
>> will be deployed many hundreds of millions of times, a 20% increase in
>> manufacturing price may well be "too much", especially as the current
>> design has been proven to work so well and safely.
>

> But double sockets are pennies. It's not like we're talking about ￜ50

> items here. They're nothing compared to the total cost of an installation.

Which re-enforces the point really. If you are buying for your own place
and need a few dozen, then you can splash out a hundred quid extra on
the higher quality ones. If on the other hand you are purchasing for a
new housing estate, the prospect of saving ￜ20K by going for an item
that in all practical purposes will work just as well, is attractive.

Have a look round your house - you will likely have a range of
accessories that don't meet the standards you claim to subscribe to, and
yet here you still are.

[Alexander Lamaison]

Like I said yesterday, sockets aren't firecrackers. They don't burst
into flame in indignation that you exceeded their rating. Are you
running the elements of all three machines on full, simulatanously for
10 hours? No, you couldn't convince the machines to do that even if you
wanted to.

>> > A 20A fuse would allow short term overloads already. Upping
>> > that to 30A is too much.
>>
>> There is nothing stopping you using 20A circuits if you prefer, however
>> in domestic environments they tent to prove far less flexible in high
>> load areas like kitchens.
>
> I'd prefer just to have a double socket than can handle the same as
> two single ones.

Its certainly your right to dream.

>>> Ir surprises me how many petty safety rules
>>> there are yet it's so easy to set fire to your wall simply by using two
>>> 13A sockets at 13A.
>>
>> For definitions of "easy" that include really rather difficult. The vast
>> majority of 13A loads that you can find to plug in, tend to be
>> relatively short term in real world cases.
>
> I can run a tumble dryer for an hour and a half, more if I have a lot
> of washing to do after coming back from holiday for example. Same
> applies to the washing machine and dishwasher.

Let's imagine this socket somehow protected 20A by a 20A fuse (your main
complaint is that it isn't) and that you convinced that lot to run at
26A for an hour and a half contiunously (you couldn't). That would not
even begin to tickle your 20A fuse - it would never blow.

>>> How difficult would it have been to make them take
>>> 6A more?
>>
>> What not have a go at costing it and see? Over engineering things for a
>> one off solution is sometimes acceptable. However for common items that
>> will be deployed many hundreds of millions of times, a 20% increase in
>> manufacturing price may well be "too much", especially as the current
>> design has been proven to work so well and safely.
>

> But double sockets are pennies. It's not like we're talking about �50

> items here. They're nothing compared to the total cost of an
> installation.

Exactly. The ones rated at 20A are pennies. The MK ones, apparently
rated at 26A, are not.

[John Rumm]

If you had two socket circuits, then yes.

Note that the OSG guidance has not changed in many years though, and
modern usage profiles have shifted dramatically in that time.

100% of the kitchen circuit, and then %20 of the next and ignore the
rest might be closer these days.

Some of this is discussed here:

http://wiki.diyfaq.org.uk/index.php?title=Diversity

[John Rumm]

On 02/04/2013 17:36, Major Scott wrote:
> On Tue, 02 Apr 2013 17:30:27 +0100, John Rumm
> <see.my.s...@nowhere.null> wrote:
>
>> On 02/04/2013 11:59, Major Scott wrote:

> So you'd be happy with things inside your wall being at 70C?

Yes of course...

Standard building materials are not combustible at that temperature...

Note also that is the conductor temperature. There will be a temperature
gradient across the insulation, so the touch temperature of the
insulation on the outside will be lower.

[John Rumm]

What is your wall made out of? What temperature will it spontaneously
combust at?

[John Rumm]

On 02/04/2013 18:53, Major Scott wrote:
> On Tue, 02 Apr 2013 18:48:10 +0100, ARW <adamwa...@blueyonder.co.uk>
> wrote:
>
>> John Rumm wrote:
>>> On 02/04/2013 15:32, Major Scott wrote:
>>> > On Tue, 02 Apr 2013 15:24:55 +0100, Tim Watts
>>> > <tw+u...@dionic.net> wrote:
>>>
>>> > > And you clearly did not understand the concept of loop impedance
>>> > > which is *as important* (in terms of ensuring that disconnection
>>> > > times are met under
>>> > > full fault conditions) as not overloading the cable.
>>> > >
>>> > > I will explain further with numbers if you wish.
>>> >
>>> > I'm not fussy on disconnection times - I've got fuses!
>>>
>>> I have read some powerfully dumb stuff in the past, but every now and
>>> then, scotty comes up with a new gem!
>>
>> Stupid is as stupid does.
>
> You think fuses are a bad idea? We were using them for decades before
> these health and safety morons appeared.

No, we think people who put faith in fuses without also ensuring there
is adequate PFC to operate them, are either ignorant or morons.

[John Rumm]

On 02/04/2013 18:21, John Rumm wrote:

> 10A in its clipped direct rating in fact...

Sorry, typo, 20A in clipped direct.