In article ,
"dennis@home" writes:

"Martin Angove" wrote in message
...

Taking the biggest potential loads there, you'd have to have the kettle,
microwave, WM and tumbler all operating at their maximum capacity
simultaneously even to reach 7.5kW. This is (IMO) unlikely unless you're
in the habit of starting the washing machine while the tumbler is
running then immediately deciding simultaneously to make a cup of tea
and microwave your TV dinner. Just the time taken to read the
instructions and unpack the TV dinner is likely to be enough to allow
the kettle to boil!

Well funny enough...

you take the washing out of the washer and put it in the dryer...
then you put the next load in....

Then you decide on a cuppa having just done the washing.
So you get the iron out and plug it in and then put the kettle on.

And you think it won't happen.....

People just don't blow ring circuit fuses/breakers due to overloading
the ring. I've only come across this in poorly designed industrial
environments where there's been some change of use of the area and
no consideration given to the wiring, but that's going to happen
regardless of the wiring topology in this case.

BTW, forget the kettle and iron -- they don't draw power for long
enough to figure significantly in the diversity.

--
Andrew Gabriel

wrote:

In case you arent aware, fused rings are designed to carry 30A for
short periods. It is only newer mcb'ed rings that are limited to 32A
proper.

In fact even a 32A MCB will supply 40A for an hour or two before
tripping. The wiring will also take it, so again no problem.

trip?? Youre talking about 15th edn RCDs now? Old installs sure didnt
have any trips, other than ELCBs on TT setups which almost never
nuisance trip. Need to distinguish between the 2.

Yup, just got rid of the ELCB on my TT system - never had it trip once
in over a decade (and it did self test ok!).

--
Cheers,

John.

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In message ,
"dennis@home" wrote:


"Martin Angove" wrote in message
...

Taking the biggest potential loads there, you'd have to have the kettle,
microwave, WM and tumbler all operating at their maximum capacity
simultaneously even to reach 7.5kW. This is (IMO) unlikely unless you're
in the habit of starting the washing machine while the tumbler is
running then immediately deciding simultaneously to make a cup of tea
and microwave your TV dinner. Just the time taken to read the
instructions and unpack the TV dinner is likely to be enough to allow
the kettle to boil!

Well funny enough...

you take the washing out of the washer and put it in the dryer...
then you put the next load in....

Then you decide on a cuppa having just done the washing.
So you get the iron out and plug it in and then put the kettle on.

And you think it won't happen.....

Well, given what you have described, it won't. TD+WM+K adds up to 6kW or
so. Most irons are in the 500W to 1kW range and are thermostatically
controlled. At best you have described 7kW of load for maybe as much as
three or four minutes. 500W "in hand" to the nominal spec., and a lot
more to the real limit.

[...]

What is more likely is a bad connection causing overheating, and
this is likely to have worse effects on a radial where all the
circuit current might pass through that connection than on a ring
where there is going to be an alternative (hopefully good) path to
every other point.

Yes but with a radial you are likely to notice the problem with a ring the
appliances work fine and you don't notice the fault.

With a broken connection I'd agree, but I have seen many cases of
"loose" connections on radials which don't exhibit any obvious symptoms
unless you happen to dismantle the problem junction whereupon you spot
the blackened copper and bubbling PVC. Classic example recently was a
45A shower switch to an 8.5kW shower. As far as the people were
concerned, the shower had worked just fine with no problems at all until
a guest decided to use the 45A switch to switch off after having a
shower (the householders usually left it on). The switch jammed in the
off position (though indicating on) and they called me in. I found two
or three loose screws in the switch and obvious signs of sustained
overheating.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Not a computer nerd; merely a techno-weenie.

dennis@home wrote:

No disrespect, but it would seem that you don't understand the concepts of
diversity (both temporal spacing and loading duration) in this case. What
you described does *not* "bust" diversity. In fact your ring will cope
with what you describe without drama.


I understand them..
I just don't agree with them.

OK, so you don't agree. However I don't see why you feel a radial is
better suited to diverse power supply for flexible loads however.

Its just another compromise to save a few quid (very few these days)

I would say it is about better engineering than about cost reduction...

The same fault can affect a radial with a high impedance connection
somewhere before its end point. However with a radial you don't have the
fall-back of an alternate path to mitigate the effects. (Probably a higher
fault loop impedance as well)


So you will find the fault rather than it being hidden by the inadequate
redundant path.

Depends on what you mean by hidden. Given the same fault on both a
radial and a ring (i.e. loose screw on a socket connection), the radial
will melt a cable or overheat the socket, the ring will carry on working
even if the socket will get warm to the touch. How is it better to have
a melted cable?

Standard 2.5mm T&E are not rated to work as redundant paths.. the return is
required for safe operation.

This seems to be a very weak argument: "you need to wire it according to
the design for it to work correctly".

Think about it logically...

You have a rating of about 22A on a 2.5mm T&E cable..

Probably nearer 30A in fact...

Now you are saying its safe to use up to 30-40A...

30% overload for an hour will do it no harm. This is by design. This is
another reason why diversity works well. However we are not talking
about one cable, but two (unless there is a fault)

In many real world cases a radial will actually fair less well with a
wiring fault. It is not safe to assume that all sockets downstream of
the fault will simply stop working.


If the cable can carry that much current safely then why isn't it rated at
30-40A?
Could it be that it isn't safe?

No, but it could be that you are exceeding its temperature budget and
hence reducing the expected life.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

If the cable can carry that much current safely then why isn't it rated at
30-40A?

When they rate a cable for 27A, they are also saying that it can really take
twice as much, but they've left a whole load of headroom to allow for short
term (i.e. 10s of minutes) of transient loads (such as
toasters/kettles/washing machines etc).

There's a reason that MCBs are only guaranteed to trip quickly at 5 times
nominal current. It is because the cables are man enough to take 5 times
current for a short period and there's no need to design a system that cuts
out just because with a heavily loaded system you've put the kettle on for 2
minutes, or a motor is winding up.

Christian.

John Rumm wrote:

Yup, just got rid of the ELCB on my TT system - never had it trip once
in over a decade (and it did self test ok!).

Its funny to think one of the oft quoted objections to ELCBs was
nuisance trips. Sure, they might once in a decade or two. The atrocious
record of RCDs has left those objections looking odd.


NT

In message ,
"dennis@home" wrote:

[diversity/ring circuits]
I understand them..
I just don't agree with them.



Without diversity modern living would be impossible. In the
one-radial-per-room scenario we would have at least eight radials in
this small house. Even if they were all 16A that's a non-diversified
8*16A you have to cater for which is 128A which is well over the
capacity of even the largest normally available service fuse (100A).
Without diversity you'd have to assess a cooker at its maximum rating in
the same way as a shower. One 8kW cooker and one 8kW shower makes 66A
while many houses are still on 60A service fuses.

Now I know that this isn't really your argument. You are arguing that a
ring circuit is unsafe because in the event of a break it is 2.5mm2
cable fused at 30/32A and the cable is only rated for 27A at best. I
don't know the figures, but Peter Parry has over the years proved to
have done rigorous research (look for his postings when Part P was
originally proposed) and I am much more prepared to believe him when he
says that the UK system (and by implication the ring final) is amongst
the safest in Europe than I am to believe you who states with no
backround evidence that a many-radials method would be safer.

Its just another compromise to save a few quid (very few these days)


It has probably never saved very much money. The tortures of installing
a ring in certain shapes of houses makes you wonder why people didn't
use radials more often. In the terraces around here they often did.
Where can you buy 20A fuse wire these days? Actually, on that subject,
that's an area where a 3036-protected ring may actually be safer than a
radial: fuse wire of 20A is not commonly available any more, so if a 20A
fuse blows it may be replaced with 30A wire. Wire greater than 30A is
likewise not commonly available so a blown 30A ring fuse is only likely
to be replaced with 30A wire. (Let's ignore the cases where fusewire
isn't used at all and blown fuses are replaced with bits of copper
stripped from T&E)

To be at serious risk of damaging a correctly functioning ring you have
to have a series of improbable coincidences. Either that or the central
heating has broken down, it's the middle of the winter, and you've
managed to find the one homeowner in the town who has more than three or
four portable electric heaters.

Sure, a ring final *is* a compromise (of sorts), but it is a
well-engineered, well-calculated, conservatively-rated and provably safe
compromise.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Noah! Come quick! There's water in the basement!

"John Rumm" wrote in message
...

Depends on what you mean by hidden. Given the same fault on both a radial
and a ring (i.e. loose screw on a socket connection), the radial will melt
a cable or overheat the socket, the ring will carry on working even if the
socket will get warm to the touch. How is it better to have a melted
cable?

You aren't looking at the long term use.
These systems are going to be in use for decades and faults are going to
happen.

With a ring you will get isolated legs which look just like a radial circuit
and will suffer from the same problems as a proper radial circuit.

However a proper radial circuit has been designed that way and will
typically have a ~20A fuse in the circuit and a known distribution of
connection points.

The faulty ring will have a 32A fuse and a random distribution of connection
points..

Now which is safer?


If it were possible for the user to know there was a fault in the ring then
I would say a ring was safer..
but with rings the way they are the user has no hope of knowing there is a
fault.

This makes them unsafe for long term use.
Stick a 20A fuse in and they are safer than radials.


Standard 2.5mm T&E are not rated to work as redundant paths.. the return
is required for safe operation.

This seems to be a very weak argument: "you need to wire it according to
the design for it to work correctly".

Think about it logically...

You have a rating of about 22A on a 2.5mm T&E cable..

Probably nearer 30A in fact...

Now you are saying its safe to use up to 30-40A...

30% overload for an hour will do it no harm. This is by design. This is
another reason why diversity works well. However we are not talking about
one cable, but two (unless there is a fault)

In many real world cases a radial will actually fair less well with a
wiring fault. It is not safe to assume that all sockets downstream of the
fault will simply stop working.


If the cable can carry that much current safely then why isn't it rated
at 30-40A?
Could it be that it isn't safe?

No, but it could be that you are exceeding its temperature budget and
hence reducing the expected life.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Fri, 03 Jun 2005 08:07:56 GMT, "dennis@home"
wrote:

If the cable can carry that much current safely then why isn't it rated at
30-40A?
Could it be that it isn't safe?

You don't seem to understand the cause of most electrical fires.
They don't get started (in domestic settings) by fixed cables being
overloaded. They get caused by poor connections.

The ideal failure case is in fact the cable overheating, melting the
insulation and shorting out to blow the fuse/circuit breaker. The
fire risk in such an unlikely scenario is very low.

Where risk exists it is in poor contacts which generate heat
sufficient to ignite local materials. You don't need much energy to
do this (typically 100W will be more than adequate)and in many fires
of electrical origin the fuse or MCB involved never trips or does so
far to late to be of use.

Electrical fires are common in the USA. These are caused by a
combination of extensive use of flammable construction materials,
high currents, poor standards of installation and, most
significantly, aluminium cable. Because of poor connections caused
by aluminium corroding so quickly aluminium cable carries a fire risk
approximately 100 times greater than equivalent rated copper cable.

This is why any domestic radial system is intrinsically far less safe
than a ring. Firstly it involves more connections, and connections
are the primary fixed wiring risk, secondly adding sockets to a
radial installation is costly and time consuming, continental
practice is to have far fewer sockets than are installed in UK
houses. As a result the use of extension cords and multiadapters is
far more common and these pose a far greater threat than fixed wiring
of any type ever will.


--
Peter Parry.
http://www.wpp.ltd.uk/

dennis@home wrote:

You aren't looking at the long term use.
These systems are going to be in use for decades and faults are going to
happen.

Are they? If so what would you say is the most likely failure mode:

Complete break in a conductor, or, a terminal screw working loose
leading to a higher resistance connection?

I would suggest the latter is the more likely. If that is the case then
the ring circuit handles the fault better.

However a proper radial circuit has been designed that way and will
typically have a ~20A fuse in the circuit and a known distribution of
connection points.

(not that relevant to the discussion, but a radial will often have a 32A
breaker and 4mm^2 cable...)

The faulty ring will have a 32A fuse and a random distribution of connection
points..
Now which is safer?

There are some fault conditions where a radial will fail outright and a
ring will "limp on", so you can argue the outright failure of the radial
is more desirable, but in many cases you won't get clear black and white
failures like this. So on the balance of probabilities, I would still
say the ring.

If it were possible for the user to know there was a fault in the ring then
I would say a ring was safer..
but with rings the way they are the user has no hope of knowing there is a
fault.

Same applies to a radial unless the fault is completely open circuit
conductor.

With no faults on the circuit, then the ring has clear advantages.


--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Martin Angove" wrote in message
...
In message ,
"dennis@home" wrote:

[diversity/ring circuits]
I understand them..
I just don't agree with them.



Without diversity modern living would be impossible. In the
one-radial-per-room scenario we would have at least eight radials in
this small house. Even if they were all 16A that's a non-diversified
8*16A you have to cater for which is 128A which is well over the
capacity of even the largest normally available service fuse (100A).
Without diversity you'd have to assess a cooker at its maximum rating in
the same way as a shower. One 8kW cooker and one 8kW shower makes 66A
while many houses are still on 60A service fuses.

Modern radials are multiple connection affairs not the old ones with round
fuses in the plugs. 8-)

Now I know that this isn't really your argument. You are arguing that a
ring circuit is unsafe because in the event of a break it is 2.5mm2
cable fused at 30/32A and the cable is only rated for 27A at best. I
don't know the figures, but Peter Parry has over the years proved to
have done rigorous research (look for his postings when Part P was
originally proposed) and I am much more prepared to believe him when he
says that the UK system (and by implication the ring final) is amongst
the safest in Europe than I am to believe you who states with no
backround evidence that a many-radials method would be safer.

Its just another compromise to save a few quid (very few these days)


It has probably never saved very much money. The tortures of installing
a ring in certain shapes of houses makes you wonder why people didn't
use radials more often. In the terraces around here they often did.
Where can you buy 20A fuse wire these days? Actually, on that subject,
that's an area where a 3036-protected ring may actually be safer than a
radial: fuse wire of 20A is not commonly available any more, so if a 20A
fuse blows it may be replaced with 30A wire. Wire greater than 30A is
likewise not commonly available so a blown 30A ring fuse is only likely
to be replaced with 30A wire. (Let's ignore the cases where fusewire
isn't used at all and blown fuses are replaced with bits of copper
stripped from T&E)

I think you will find you have to use a MCB in a modern radial circuit
(probably for the reason you state).

To be at serious risk of damaging a correctly functioning ring you have
to have a series of improbable coincidences. Either that or the central
heating has broken down, it's the middle of the winter, and you've
managed to find the one homeowner in the town who has more than three or
four portable electric heaters.

Why is it so difficult to explain that designing a system which can
(apparantly) function normally with a hidden fault present is bad
engineering.
It is worse if that fault drops the margins of that circuit below what is
safe.
This is the case for a ring main.
It cannot be considered to be good practice these days when there are
alternatives (like fitting a 20A MCB to the ring).

Sure, a ring final *is* a compromise (of sorts), but it is a
well-engineered, well-calculated, conservatively-rated and provably safe
compromise.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
... Noah! Come quick! There's water in the basement!

"John Rumm" wrote in message
...

With no faults on the circuit, then the ring has clear advantages.

Assuming the ring and the radial are both working correctly what are the
advantages of the ring?

"Peter Parry" wrote in message
...

This is why any domestic radial system is intrinsically far less safe
than a ring. Firstly it involves more connections, and connections
are the primary fixed wiring risk,

I think you will find that it requires less connections on a radial than on
the equivilent ring.
There is one less length of cable so less connections.

secondly adding sockets to a
radial installation is costly and time consuming,

This is also untrue, you only need to run a single T&E for the extra socket
not two like on a ring.

continental
practice is to have far fewer sockets than are installed in UK
houses. As a result the use of extension cords and multiadapters is
far more common and these pose a far greater threat than fixed wiring
of any type ever will.

I will take your word for that.
However Part P will soon up the number of trailing extensions to the
continetal level as they are exempt.
I expect we will see somone electrocuted by a 4 way in the sink soon,
especially if someone has bonded the taps/sink to earth.


--
Peter Parry.
http://www.wpp.ltd.uk/

On Fri, 03 Jun 2005 14:42:37 GMT, "dennis@home"
wrote:


Assuming the ring and the radial are both working correctly what are the
advantages of the ring?

You can put lots and lots of outlets on it without worrying about
where particular loads are going to go. This means you remove the
need for extension leads which are a far greater hazard than the
fixed wiring. They are also often much easier to add to. A spare
bedroom with perhaps 4 outlets can be converted to a home office with
10-20 outlets quite easily and cheaply.


--
Peter Parry.
http://www.wpp.ltd.uk/

On Fri, 03 Jun 2005 14:50:29 GMT, "dennis@home"
wrote:


"Peter Parry" wrote

secondly adding sockets to a
radial installation is costly and time consuming,

This is also untrue, you only need to run a single T&E for the extra socket
not two like on a ring.

The usual addition, nearby existing sockets, involves very little
extra wire, and none of it draped up conduit.

continental
practice is to have far fewer sockets than are installed in UK
houses. As a result the use of extension cords and multiadapters is
far more common and these pose a far greater threat than fixed wiring
of any type ever will.

I will take your word for that.
However Part P will soon up the number of trailing extensions to the
continetal level as they are exempt.

Indeed, something that was pointed out at the time. Part P, on its
own calculations, will kill more than it saves.

--
Peter Parry.
http://www.wpp.ltd.uk/

dennis@home wrote:

With no faults on the circuit, then the ring has clear advantages.


Assuming the ring and the radial are both working correctly what are the
advantages of the ring?

What Peter said, and lower earth fault loop impedance (hence quicker
disconnect times), lower voltage drop, less cable heating (hence power
dissipation). Also the ability to cover larger areas (100m^2) when
required. Easier to install (i.e. getting 2 x 2.5mm^2 cable into a
socket is much easier that 2 x 4mm^2)

--
Cheers,

John.

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

"Peter Parry" wrote in message
...
On Fri, 03 Jun 2005 14:42:37 GMT, "dennis@home"
wrote:


Assuming the ring and the radial are both working correctly what are the
advantages of the ring?

You can put lots and lots of outlets on it without worrying about
where particular loads are going to go. This means you remove the
need for extension leads which are a far greater hazard than the
fixed wiring. They are also often much easier to add to. A spare
bedroom with perhaps 4 outlets can be converted to a home office with
10-20 outlets quite easily and cheaply.

How does that differ from a modern radial circuit?

"John Rumm" wrote in message
...
dennis@home wrote:

With no faults on the circuit, then the ring has clear advantages.


Assuming the ring and the radial are both working correctly what are the
advantages of the ring?

What Peter said, and lower earth fault loop impedance (hence quicker
disconnect times),

Hmm,
An RCD would disconnect an earth fault in 30ms even with a high impedence
earth.
High impedence to earth is probably safer for the individual who completes
the circuit.
I wonder if low impedence earths are a throw back to the days when RCDs
weren't available?

lower voltage drop, less cable heating (hence power dissipation).

I'm sure the extra couple of watts wasted is contributing to global warming
so you may have a point here.

Also the ability to cover larger areas (100m^2) when required.

Thats just rules and they are there to be bent.

Easier to install (i.e. getting 2 x 2.5mm^2 cable into a socket is much
easier that 2 x 4mm^2)

I would use 2.5mm2 for a radial myself and just use more of them.

Owain wrote:
dennis@home wrote:

Electric heaters were usually wired on 15A radials anyway, and that
practice was expected to continue. Also, postwar housing was usually
intended to have some form of fixed heating installation anyway, so the
ring circuit would not have been used for the main heating load.

My parents house, built in 1966, has electrical storage heating on a switched
(what would now be called Economy 7) night time, plus an afternoon boost, supply.

I've never paid it any attention but ISTR that each room with a storage heater
is fed by one 20A fuse. However the kitchen and living room both have two
heaters each, and I think these rooms are each fed by a 30A fuse.

The house is actually across two phases, so there are four fuse boxes,

Ring/Lights phase 1
Heating phase 1
Ring/Lights phase 2
Heating phase 2

The meter/fuse box area is rather large, my father built a cupboard around it
soon after moving in !

I wonder how much of any of that would be reg compliant these days ?

--
Mark
Please replace invalid and invalid with gmx and net to reply.

"Peter Parry" wrote in message
...

Electrical fires are common in the USA.

Totally agree. They have electrics on a par with Eastern Europe


This is why any domestic radial system is intrinsically far less safe
than a ring. Firstly it involves more connections,

Should be about the same so don't agree with this.


continental
practice is to have far fewer sockets than are installed in UK
houses. As a result the use of extension cords and multiadapters is
far more common and these pose a far greater threat than fixed wiring
of any type ever will.

That depends on the country. We all agree French, Spanish, most Low and all
Eastern countries need re-wiring to a safe standard. That's the point of
the whole standardisation process to kick it off.

But German extension adaptors are well controlled and so aren't that
dangerous whereas these £2 UK ones appearing really don't look up to it. I
expect there are just as many UK ones as in other countries in fact and so
whilst the rest of Europe is rewired it would be a good idea to do us as
well.

wrote in message
oups.com...

Although very large older houses may have
two lighting rings, smaller (even 4/5 bed) houses of that period as well
as
flats tend to lose all lighting when the trip goes.

And yes I'm British.

trip?? Youre talking about 15th edn RCDs now?

I was referring to anything that breaks the supply.


Old installs sure didnt
have any trips, other than ELCBs on TT setups which almost never
nuisance trip. Need to distinguish between the 2.

We were talking about 70/80s housing or houses rewired in that period. What
period did 15th edition cover ?

"Andrew Gabriel" wrote in message
.. .

We're quite good at exporting our wiring designs around the world
(our 13A plug is used in more countries than any other single plug,

Even if you count small places like Malta or IoM as countries, I think the
US plug comes way ahead.

Plus it's not our 13A plug anyway, it's Swedish.

"Peter Parry" wrote in message
...
Eh? I have 24 sockets in the kitchen - you suggest they should all
be on one radial and this will be "safer"?

I hope not.

I also trust you haven't got all 24 sockets on one ring either as I don't
believe you can monitor usage that accurately.

They are all on one circuit,

So you have the freezer on the RCD ?



then I would have expected them to be wired in physically
separated groups on several rings.

Why?

As a minimum I would expect to see RCD and non-RCD protected (or fast 30mA
and slow 100mA protected) circuits.

"Peter Parry" wrote in message
...
On Thu, 2 Jun 2005 23:44:42 +0100, "Mike" wrote:

"Peter Parry" wrote

And you want to propose ideas from this lot of clowns to the rest of
Europe

Do not confuse technical competence with the ability to convince a
bunch of Euroclown committee functionaries.

Well I do regularly see IEE imcompetance in my area of expertise so I don't
expect it to be different in wiring regulations.


one cannot have
harmonisation on one countries existing standard.

Why not? (Apart from it not being acceptable to the French).

Because all the current systems have problems and to give all existing
manufacturers an equal opportunity in what will be a huge market
(rewiring
half of Western Europe and most of Eastern Europe) they need to have a
new
design with rights to manufacture.

I thought the idea was to produce a better system , not to design a
feeding trough for German industry? Also do you seriously think any
significant _rewiring_ would take place?

There is significant rewiring required - the whole of eastern Europe plus
most of France, low countries and a lot of Spain and Portugal, Greece and so
on. All this is waiting for a harmonised EU standard. I don't see this as
a feeding trough for German industry - our own companies should be able to
compete well if we are part of the initiative. If we aren't then they won't
be able to of course as happens so often with European initiatives.




Standards have nothing to do with quality.

Of course they do - that's the main job of the EN standards after all (or
BSI if you prefer them in that format).

The main aim of standards is to ensure things are standard, not that
they are of good quality.

That is totally incorrect. I have been contributing to standards groups
worldwide (IETF, ETSI, IEEE, ANSI, ATM Forum, ADSL Forum, DAVIC, 3PPP, etc)
for thirty years and I can assure you all had the goal of producing high
quality standards that would stand the test of time.

In message ,
"dennis@home" wrote:


"Martin Angove" wrote in message
...
In message ,
"dennis@home" wrote:

[diversity/ring circuits]
I understand them..
I just don't agree with them.



Without diversity modern living would be impossible. In the
one-radial-per-room scenario we would have at least eight radials in
this small house. Even if they were all 16A that's a non-diversified
8*16A you have to cater for which is 128A which is well over the
capacity of even the largest normally available service fuse (100A).
Without diversity you'd have to assess a cooker at its maximum rating in
the same way as a shower. One 8kW cooker and one 8kW shower makes 66A
while many houses are still on 60A service fuses.

Modern radials are multiple connection affairs not the old ones with round
fuses in the plugs. 8-)

But for the purposes of (non) diversity you have to calculate maximum
demand at the rated capacity of the circuit. If you allow diversity your
maximum demand (sockets circuits) is largest+40% of the rest (IEE
guidelines in the OSG). There can be a big difference between (say) 8
radial socket circuits serving the house and two or three rings.

[...]
Where can you buy 20A fuse wire these days? Actually, on that subject,
that's an area where a 3036-protected ring may actually be safer than a
radial: fuse wire of 20A is not commonly available any more, so if a 20A
fuse blows it may be replaced with 30A wire. Wire greater than 30A is
likewise not commonly available so a blown 30A ring fuse is only likely
to be replaced with 30A wire. (Let's ignore the cases where fusewire
isn't used at all and blown fuses are replaced with bits of copper
stripped from T&E)

I think you will find you have to use a MCB in a modern radial circuit
(probably for the reason you state).


BS3036 rewireable fuses are still allowed in domestic situations for all
standard final circuits. You have to derate the cable to account for the
greater let-through of energy, but MCBs are by no means mandated.

To be at serious risk of damaging a correctly functioning ring you have
to have a series of improbable coincidences. Either that or the central
heating has broken down, it's the middle of the winter, and you've
managed to find the one homeowner in the town who has more than three or
four portable electric heaters.

Why is it so difficult to explain that designing a system which can
(apparantly) function normally with a hidden fault present is bad
engineering.
It is worse if that fault drops the margins of that circuit below what is
safe.
This is the case for a ring main.
It cannot be considered to be good practice these days when there are
alternatives (like fitting a 20A MCB to the ring).


I don't think anyone is disputing the fact that it is possible for a
ring to "break" without any noticeable effects until such time as a
sustained overload occurs. What we are arguing is that the circumstances
you describe are rare; other faults happen first and are coped with
better by a ring. Likewise, even in the case of a break, the chances of
the actual load (rather than the potential load) on any one isolated
part of the ring being sufficient to cause a problem are low: you'd have
to have the break happen near the CU with most appliances connected on
the "long" side of the ex-ring.

And it is only small overloads we are really considering. The cable is
perfectly safe protected by a 30/32A device for short circuits where
hundreds of Amps flow. If it weren't, it wouldn't be allowed for spurs.

You are quibbling the difference between a 27A cable protected at 20A
and a 27A cable protected at 30/32A where the fault causes a sustained
current of up to 45A to be drawn in one leg of the ring. Above that and
the MCB will eventually trip (50A will trip a 32A MCB in around 1,000
seconds). The debate then becomes whether 45A continuously will damage
2.5mm2 cable in such a way as to be the cause of (say) a fire, or
whether it is more likely that this low-level overheating will cause
insulation to flow, eventually causing a live conductor to short on the
CPC causing a dead short, blowing the MCB. I suspect the latter.

It isn't perfect, but it isn't (necessarily) unsafe.

If you're worried, why not wire your rings in 4mm2 cable? At least this
is a more practical solution than downgrading the MCB to 20A. Spurring
is a bit more difficult as getting 3x4mm2 cables into a terminal is
nigh-on impossible...

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... I appreciate your not breathing while I smoke.

Peter Parry wrote:
On Thu, 2 Jun 2005 23:44:42 +0100, "Mike" wrote:
"Peter Parry" wrote

And you want to propose ideas from this lot of clowns to the rest of Europe

Do not confuse technical competence with the ability to convince a
bunch of Euroclown committee functionaries.

testimony versus evidence. Oft confused.


one cannot have
harmonisation on one countries existing standard.

Why not? (Apart from it not being acceptable to the French).

Because all the current systems have problems

no they dont


and to give all existing
manufacturers an equal opportunity in what will be a huge market (rewiring
half of Western Europe and most of Eastern Europe) they need to have a new
design with rights to manufacture.

I thought the idea was to produce a better system , not to design a
feeding trough for German industry?

Ahh, theres your mistake. Who do you think promotes these new
standards? Or did you really think we were spending billions of pounds
to equipotential bond the nations bathrooms in order to save lives?
Hint: lives are not being lost as a result of lack of equi.


Also do you seriously think any
significant _rewiring_ would take place?

er yup, no sht. Commercial premises have to meet the latest standards:
change the standards substantially and you create a multibillion pound
feeding frenzy. With no detectable benefit.


Plus I trust even you recognise the German standard as
superior to ours.

Not until I see some convincing reasons, and there have been none so
far.

And few apart from the UK regard ring mains as safe.

Their evidence being?

I think we've seen enough UK people here decrying ring mains let alone the
Europeans.

A few ill informed posters does not amount to evidence. Where is the
_evidence_ the ring main is unsatisfactory?

there is none. The stats speak for themselves. Interacting with fixed
wiring in the UK is one of the safest things a person can do.


NT

On Fri, 3 Jun 2005 20:18:42 +0100, "Mike" wrote:

"Peter Parry" wrote
Do not confuse technical competence with the ability to convince a
bunch of Euroclown committee functionaries.

Well I do regularly see IEE imcompetance in my area of expertise so I don't
expect it to be different in wiring regulations.

The IEE is usually quite competent. I have no doubt its ability to
influence a committee of politically motivated and well bribed
eurocrats is exactly zero precisely because it will try to rely upon
technical arguments.

I thought the idea was to produce a better system , not to design a
feeding trough for German industry? Also do you seriously think any
significant _rewiring_ would take place?

There is significant rewiring required - the whole of eastern Europe plus
most of France, low countries and a lot of Spain and Portugal, Greece and so
on. All this is waiting for a harmonised EU standard.

Why? They can introduce standards whenever they like if they are
needed. In fact France has many standards, all ignored. You think
they will suddenly take note of a eurostandard and rewire everywhere?
Even CENELEC found this unlikely and required backward compatibility
with Shuko in the initially proposed "standard" (but not for some
reason with UK systems).

I don't see this as
a feeding trough for German industry - our own companies should be able to
compete well if we are part of the initiative.

What initiative? To rewire a house costs several thousands of
pounds. You really think everyone will say "Herr Blurr says we must
so we must"?

The main aim of standards is to ensure things are standard, not that
they are of good quality.

That is totally incorrect. I have been contributing to standards groups
worldwide (IETF, ETSI, IEEE, ANSI, ATM Forum, ADSL Forum, DAVIC, 3PPP, etc)
for thirty years

I thought that was your Scots "friend"?

and I can assure you all had the goal of producing high
quality standards that would stand the test of time.

They failed miserably then didn't they. Standards and quality are
unrelated. There is a standard for a pound weight. It does not make
a pound of potatoes of good quality. There is a eurostandard for
strawberries - which is why they now all taste like pink water.


--
Peter Parry.
http://www.wpp.ltd.uk/

On Fri, 3 Jun 2005 20:11:20 +0100, "Mike" wrote:


"Peter Parry" wrote

They are all on one circuit,

So you have the freezer on the RCD ?

Who mentioned an RCD? There is no RCD in the Consumer Unit - far to
dangerous.

As a minimum I would expect to see RCD and non-RCD protected (or fast 30mA
and slow 100mA protected) circuits.

Never seen a house fire have you?


--
Peter Parry.
http://www.wpp.ltd.uk/

On Fri, 03 Jun 2005 18:04:40 GMT, "dennis@home"
wrote:

"Peter Parry" wrote

You can put lots and lots of outlets on it without worrying about
where particular loads are going to go. This means you remove the
need for extension leads which are a far greater hazard than the
fixed wiring. They are also often much easier to add to. A spare
bedroom with perhaps 4 outlets can be converted to a home office with
10-20 outlets quite easily and cheaply.

How does that differ from a modern radial circuit?

A Dutch friend has a modern house with a total of 300A of MCB's. On
an 80A supply.

He can't add extra sockets because he is already up to some arbitrary
limit on the number of sockets allowed on a radial. He has just
bought in the local shops several 12 socket extension leads. Ever
seen such a thing on sale in UK?


--
Peter Parry.
http://www.wpp.ltd.uk/

Mike wrote:
"Peter Parry" wrote in message
...
On Thu, 2 Jun 2005 17:44:10 +0100, "Mike" wrote:

Of course it understands it. The IEE were there explaining it.

just as we've explained things to you, but you still dont get them. If
everyone undestood everything explained to them, wow would life be
easy.


Problem is
although it is better than a lot, possibly most of Europe, one cannot
have
harmonisation on one countries existing standard.

Why not? (Apart from it not being acceptable to the French).

Because all the current systems have problems

there are no safety problems with UK system. The stats make that clear,
even if you cant understand ring circuits.


and to give all existing
manufacturers an equal opportunity in what will be a huge market (rewiring
half of Western Europe and most of Eastern Europe) they need to have a new
design with rights to manufacture.

wrong, obviously. Anyone and everyone has rights to manufacture parts
for UK system. And of course many other systems, which are even older,
thus also no longer covered by patents.


Plus I trust even you recognise the German standard as
superior to ours

absence of any evidence or logical explanation noted.


- just it's too expensive.

so it is not the best. Financial efficiency is after all one of the
requirements for a successful system. It is a daftly wasteful system.


And few apart from the UK regard ring mains as safe.

Their evidence being?

I think we've seen enough UK people here decrying ring mains let alone the
Europeans.

We have. It tells us nothing. There are always people that dont
understand the subject, sometimes lots of them.


Works for most things. For example the Internet we are using now wouldn't
work if each country had their own standards.

if you think that argues in favour of your viewpoint you dont
understand logic very well.


Standards have nothing to do with quality.

Of course they do - that's the main job of the EN standards after all (or
BSI if you prefer them in that format).

It ought to be. However in the real world, sometimes they are,
sometimes not.


That is totally incorrect. I have been contributing to standards groups
worldwide (IETF, ETSI, IEEE, ANSI, ATM Forum, ADSL Forum, DAVIC, 3PPP, etc)
for thirty years and I can assure you all had the goal of producing high
quality standards that would stand the test of time.

First a goal does not equal an achievement, but that is fairly obvious.
Life would be so much easier if all goals were achieved, and none
compromised or failed.

Second, this explains a lot. Your grasp of all this is lacking in many
areas, not least assorted basic logical errors, and yes, youre involved
in drawing up standards. No surprise then.

Sorry, but theres only so much bs for one day before someone calls you
on it.


NT

On Fri, 3 Jun 2005 20:00:08 +0100, "Mike" wrote:


"Peter Parry" wrote

continental
practice is to have far fewer sockets than are installed in UK
houses. As a result the use of extension cords and multiadapters is
far more common and these pose a far greater threat than fixed wiring
of any type ever will.

[snip]

But German extension adaptors are well controlled and so aren't that
dangerous

You jest? I've got a box full of the damn things. Some are simply
PVC and will happily burn at any opportunity (Don't forget it was the
Germans who insisted on _lower_ flammability standards for TV's in
the EU than apply anywhere else in the world.) You really think a 12
gang unfused extension I bought in Germany is safe? Have you ever
known a Shuko plug carry 16A without getting so hot it hurt to touch
it?

so whilst the rest of Europe is rewired it would be a good idea to do us as
well.

Apart from the fact that even the well bribed dimwits in Brussels are
not contemplating _rewiring_ anything that is the most facile
argument since lunchtime.

--
Peter Parry.
http://www.wpp.ltd.uk/

"Peter Parry" wrote in message
...

He can't add extra sockets because he is already up to some arbitrary
limit on the number of sockets allowed on a radial. He has just
bought in the local shops several 12 socket extension leads. Ever
seen such a thing on sale in UK?

I have seen 10 way and used 8 way.

"Peter Parry" wrote in message
...
On Fri, 3 Jun 2005 20:18:42 +0100, "Mike" wrote:

There is significant rewiring required - the whole of eastern Europe plus
most of France, low countries and a lot of Spain and Portugal, Greece and
so
on. All this is waiting for a harmonised EU standard.

Why? They can introduce standards whenever they like if they are
needed. In fact France has many standards, all ignored. You think
they will suddenly take note of a eurostandard and rewire everywhere?

Yes - because there will be EU grants to do so.


Even CENELEC found this unlikely and required backward compatibility
with Shuko in the initially proposed "standard" (but not for some
reason with UK systems).

No it didn't. Where do you get this from.



The main aim of standards is to ensure things are standard, not that
they are of good quality.

That is totally incorrect. I have been contributing to standards groups
worldwide (IETF, ETSI, IEEE, ANSI, ATM Forum, ADSL Forum, DAVIC, 3PPP,
etc)
for thirty years

I thought that was your Scots "friend"?

Before he retired he was EU rep on electrical harmonisation. I work on
comms standards and their influence on the semiconductor industry.


and I can assure you all had the goal of producing high
quality standards that would stand the test of time.

They failed miserably then didn't they. Standards and quality are
unrelated. There is a standard for a pound weight. It does not make
a pound of potatoes of good quality. There is a eurostandard for
strawberries - which is why they now all taste like pink water.

Oh don't be so silly. Do you think this discussion could even take place if
a whole host of standards weren't in place to allow our comments to get to
each other.

wrote in message
oups.com...

Sorry, but theres only so much bs for one day before someone calls you
on it.

So I'm calling you on it. You appear to be displaying an anti-Europe streak
which says that everything European is inferior to everything British. Get
real.

Fortunately this time there won't be UK veto on harmonisation when the vote
comes so it should happen.

dennis@home wrote:

What Peter said, and lower earth fault loop impedance (hence quicker
disconnect times),


Hmm,
An RCD would disconnect an earth fault in 30ms even with a high impedence
earth.

If it is a circuit protected by RCD that is.

Not all socket circuits need to be RCD protected. Some you would not
want to be either (like ones with high leakage, such as IT systems for
example)

High impedence to earth is probably safer for the individual who completes
the circuit.

Without an RCD, 1 ohm as opposed to say 0.5 will keep him connected for
a fair bit longer.

I would use 2.5mm2 for a radial myself and just use more of them.

Each to his own, but many find 20A circuits less flexible though.

--
Cheers,

John.

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

Mike wrote:
wrote in message
oups.com...

Sorry, but theres only so much bs for one day before someone calls you
on it.

So I'm calling you on it. You appear to be displaying an anti-Europe streak
which says that everything European is inferior to everything British. Get
real.

silly

"John Rumm" wrote in message
...
dennis@home wrote:

What Peter said, and lower earth fault loop impedance (hence quicker
disconnect times),


Hmm,
An RCD would disconnect an earth fault in 30ms even with a high
impedence earth.

If it is a circuit protected by RCD that is.

Not all socket circuits need to be RCD protected. Some you would not want
to be either (like ones with high leakage, such as IT systems for example)

Why would an IT system have high leakage?
There is no reason for it to have any leakage.

High impedence to earth is probably safer for the individual who
completes the circuit.

Without an RCD, 1 ohm as opposed to say 0.5 will keep him connected for a
fair bit longer.

There would be no difference between such circuits.
The victim would only pass milliamps and there would be no trip without an
RCD.

By high impedance I meant something that would actually limit the current to
safe values.


BTW if you want to design a circuit that is really safer then it would be
possible to add a test box on the end of a radial circuit that measured the
drop from the consumer unit and intentionally applied a trip if there was a
fault. I don't suppose it was practical a few years ago but it is now and
only needs someone to design it and get it approved. It would prevent all
these bad joints from being a problem.

In article ,
"dennis@home" writes:
Why would an IT system have high leakage?

Not sure if everyone is assuming same meaning for IT here.
He means an Information Technology appliance, not an IT earthing
system.

Class I earthed IT appliances are allowed to leak up to 0.75mA
each, which means a design maximum of 5 PC's per 30mA RCD typically.

There is no reason for it to have any leakage.

The required RFI suppressors cause it.

--
Andrew Gabriel

In article ,
dennis@home wrote:
Not all socket circuits need to be RCD protected. Some you would not
want to be either (like ones with high leakage, such as IT systems
for example)

Why would an IT system have high leakage? There is no reason for it to
have any leakage.

SMPS often have RC networks from both line and or neutral to earth for RFI
purposes. Put many on the same circuit...

--
*Don't squat with your spurs on *

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

On Fri, 3 Jun 2005 23:18:26 +0100, "Mike" wrote:


"Peter Parry" wrote

Why? They can introduce standards whenever they like if they are
needed. In fact France has many standards, all ignored. You think
they will suddenly take note of a eurostandard and rewire everywhere?

Yes - because there will be EU grants to do so.

If countries are that exercised by it they can use national grants.
However, I am more than slightly unconvinced that the EU will hand
out thousands of pounds per house for rewiring. Even if they were to
do so the enormity of the task and the shortage of people capable of
doing the work would be such that it would take centuries to
complete.

Even CENELEC found this unlikely and required backward compatibility
with Shuko in the initially proposed "standard" (but not for some
reason with UK systems).

No it didn't. Where do you get this from.

A comment on a 1993 draft document.

Oh don't be so silly. Do you think this discussion could even take place if
a whole host of standards weren't in place to allow our comments to get to
each other.

I did not say standards were not necessary, merely that they are more
often related to what is minimally acceptable rather than good
quality. International standards in particular are often simply
those which a group of people with opposing vested interests can
agree will cause least damage to the interests of each. That does
not make them bad or unnecessary but it does mean they rarely have
anything to do with good quality. The snail like pace of the
standards definition process also means it constantly lag years
behind reality.


--
Peter Parry.
http://www.wpp.ltd.uk/