In article ,
John wrote:

OK, I'll rephrase the question: why can all gens not be synced by
a common time standard instead of by the neighbouring mains
waveform?

I think because there is the unavoidable problem
of phase shift along the transmission cables. The
wavelength of 50Hz is about 6000Km, at which the
phase would have shifted a full 360 degrees.
Sounds no problem, but that represents a 10 degree
sync difference only every 167Km or 104 miles.
That might cause a problem on the UK's grid.

--
Tony Williams.

In message ,
Tony Williams wrote:

In article ,
John wrote:

OK, I'll rephrase the question: why can all gens not be synced by
a common time standard instead of by the neighbouring mains
waveform?

I think because there is the unavoidable problem
of phase shift along the transmission cables. The
wavelength of 50Hz is about 6000Km, at which the
phase would have shifted a full 360 degrees.
Sounds no problem, but that represents a 10 degree
sync difference only every 167Km or 104 miles.
That might cause a problem on the UK's grid.


You mean that if generator "A" and generator "C" are each 100 miles away
from generator "B", are all synchronised together in *absolute* time by
an external reference and all supply the same line, the waveform
supplied by "A" and "C" will be 10 degrees out of phase with that
supplied by "B" as measured from "B".

A=====B=====C

Sounds nasty.

So am I right in thinking that the way it is actually done is
(effectively) to have one generator start first, and for each of the
others to synchronise with the received waveform at their own locations?
In other words the generators are, in absolute terms, out of phase with
each other but due to wavelength / propagation delay / whatever are
for all practical purposes synchronised.

I can see how this would work for a "bus" topology, but not for anything
involving either rings or a mesh as the length of two or more paths
from generator to generator will be different and hence received
waveforms from each one will be different. How is the grid/supergrid
actually organised in this country? How do they do it in the US where
distances are vastly greater?

Learn something new every day on this ng :-)

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Scotty, I've fallen and I can't beam up!

"Martin Angove" wrote in message
...

How do they do it in the US where distances are vastly greater?

I expect there is no true electricity supply sync across the US. It's
simply too big as you say.

Even for the phone network there are occasional clock slips where a bit is
lost or gained.

In article ,
Martin Angove wrote:

You mean that if generator "A" and generator "C" are each 100
miles away from generator "B", are all synchronised together in
*absolute* time by an external reference and all supply the same
line, the waveform supplied by "A" and "C" will be 10 degrees out
of phase with that supplied by "B" as measured from "B".

A=====B=====C

Sounds nasty.

I probably have the numbers widely out, but all transmission
lines have a line wavelength, which is the line length over
which the phase lags by 360 degrees. It means that if a
sinewave is started at point A, then there is a delay before
before it starts at point B, etc. An effective phase shift.

So am I right in thinking that the way it is actually done is
(effectively) to have one generator start first, and for each of
the others to synchronise with the received waveform at their own
locations? In other words the generators are, in absolute terms,
out of phase with each other but due to wavelength / propagation
delay / whatever are for all practical purposes synchronised.

Apparently the re-start after New York's great Blackout
(some years ago now) was very difficult.

I can see how this would work for a "bus" topology, but not for
anything involving either rings or a mesh as the length of two or
more paths from generator to generator will be different and
hence received waveforms from each one will be different. How is
the grid/supergrid actually organised in this country? How do
they do it in the US where distances are vastly greater?

Not my field Martin, so I have no idea how the UK grid
works, nor if there are difficulties with interconnections.

Be interesting to know though.............

--
Tony Williams.

Martin Angove wrote:
In message ,
Tony Williams wrote:

In article ,
John wrote:

OK, I'll rephrase the question: why can all gens not be synced by
a common time standard instead of by the neighbouring mains
waveform?

I think because there is the unavoidable problem
of phase shift along the transmission cables. The
wavelength of 50Hz is about 6000Km, at which the
phase would have shifted a full 360 degrees.
Sounds no problem, but that represents a 10 degree
sync difference only every 167Km or 104 miles.
That might cause a problem on the UK's grid.


You mean that if generator "A" and generator "C" are each 100 miles away
from generator "B", are all synchronised together in *absolute* time by
an external reference and all supply the same line, the waveform
supplied by "A" and "C" will be 10 degrees out of phase with that
supplied by "B" as measured from "B".

A=====B=====C

Sounds nasty.

So am I right in thinking that the way it is actually done is
(effectively) to have one generator start first, and for each of the
others to synchronise with the received waveform at their own locations?
In other words the generators are, in absolute terms, out of phase with
each other but due to wavelength / propagation delay / whatever are
for all practical purposes synchronised.

I can see how this would work for a "bus" topology, but not for anything
involving either rings or a mesh as the length of two or more paths
from generator to generator will be different and hence received
waveforms from each one will be different. How is the grid/supergrid
actually organised in this country? How do they do it in the US where
distances are vastly greater?

Learn something new every day on this ng :-)

Hwyl!

M.

With a mesh, the UK is fairly narrow, so the phase shifts east-west
would be small compared to north-south, I guess.

In principle I imagine one could have no end of phase shift if, and
only if, something... ha, I cant explain it. But I guess its apparent
theres no limit to how much phase shift could be accomodated within a
network, but it would depend very much on its layout and current flows.
You'd have to be careful what you connected to what via what, but in
principle one could presumably operate a grid with a ripple shaped
phase shift, like a ripple in water, with the phase shift adding upto
several whole cycles.

Someone can now explain why this is total twaddle.


NT

On Sun, 03 Jul 2005 19:24:03 -0500, Jim Michaels
wrote:

On Sat, 18 Jun 2005 22:43:26 GMT, Chip
wrote:

On Sat, 18 Jun 2005 22:58:54 +0100,it is alleged that "Mike"
spake thusly in uk.d-i-y:

[snip]

I don't know what frequency (or voltage) he used but Tesla's company
distributed AC mains in the US before it reached Europe.

From http://en.wikipedia.org/wiki/Alternating_current , so it may be
inaccurate but sounds reasonable:

"It is generally accepted that Nikola Tesla chose 60 hertz as the
lowest frequency that would not cause street lighting to flicker
visibly. The origin of the 50 hertz frequency used in other parts of
the world is open to debate but seems likely to be a rounding off of
60hz to the 1 2 5 10 structure popular with metric standards."


From my own knowledge I am fairly certain that a German company was
responsible for the usage of 50 Hz in Europe, it may have been
Siemens, but my memory is fallible :-)

In any case, in a region like Europe, having a well established AC
system of one frequency in the area would tend to encourage the usage
of that frequency elsewhere to facilitate crossover of equipment and
appliances, thus leading to savings in various things I slept through
in economics class;-)

I always assumed that 50hertz came about as a doubling of 25 hertz to
reduce flicker and improve transformer efficiency.

Also, 60 Cycles Per Second is the logical extension of 60 seconds in a
minute, 60 minutes in a hour.

Sort of like 12 inches to a foot, three feet to a yard, 22 yards to a
chain, 8 chains to a furlong, Bush installing democracy in the Arab
world in an afternoon (whether they wanted it or not).... that type of
thing.

A logical progression......


--

..andy

To email, substitute .nospam with .gl

The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
http://www.diybanter.com

On Sun, 03 Jul 2005 19:24:05 -0500, Jim Michaels
wrote:

On Tue, 28 Jun 2005 23:54:51 +0100, Martin Angove
wrote:

In message ,
Tony Williams wrote:

snip

I can see how this would work for a "bus" topology, but not for anything
involving either rings or a mesh as the length of two or more paths
from generator to generator will be different and hence received
waveforms from each one will be different. How is the grid/supergrid
actually organised in this country? How do they do it in the US where
distances are vastly greater?

The North American power grid consists of four major synchronous
interconnect regions - Western, Eastern, Texas, and Quebec.

...... and New York. On good days at least.



--

..andy

To email, substitute .nospam with .gl

The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
http://www.diybanter.com

In article ,
Jim Michaels wrote:
In US IIUC it would be called 240v, but in fact be 120-0-120, so the
voltage from earth is 120 ac, not 240. In which case the fault
clearance benefit of genuinely 240v would sometimes apply and sometimes
not. Some faults that smoulder at 120 can arc over and trip at 240.

And some that would not cause a fire at 120V will burst into flames at
240V.

Not so - it's the current that causes a fire. If low voltage was safer
from the fire point of view, cars would never suffer electrical fires.

--
*Many people quit looking for work when they find a job *

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

In article ,
Jim Michaels writes:
On 18 Jun 2005 03:30:22 -0700, wrote:

Jim Michaels wrote:
Hi,

I will assume that your post is not bait and is serious

You make some good points, but there are a few I'll pick up on:


On Wed, 1 Jun 2005 10:31:18 +0100, "Christian McArdle"
wrote:

The US electrical system is simply unsafe compared to the rest of the world.

true, at least compared to UK. Maybe not the world, US seems the model
of good practice compared to African practices, and that of many other
countries.


Current, of course). Edison's first great central station, supplying
power for three thousand lamps, was erected at Holborn Viaduct,
London, in 1882. Does anyone know the voltage that was used? In any
case the U.S. Voltage is due to historical factors. I am sure the
British voltage was not selected much more recently.

but this doesnt change the fact that 110 is inherently more dangerous
than 240. With 240v we treat it with respect, with 110v people relax
since it wont electrocute them, and hurts waaay less if they get bit.
They worry less about cord grips etc. The result is fires, which are
the prime killer, not electrocution.


The basic issue is that
very few people die of electrocution, whilst loads of people die from
electrical fires. The electrical fires largely stem from high currents. If
you halve the voltage, you double the current.
NOT TRUE.
You are making multiple invalid assumptions.
1. That U.S. wiring has the same number of circuits for the same load.

still cant figure out what you mean there. For a given load you do have
higher i with lower v, and each load is on 1 circuit as far as i can
see.

UK Ten 100watt lamps at 240V equal 4.166 amps on circuit rated at 6
amps with 1mm wire.

Although lighting circuits are normally protected at 6A, the 1mm²
wiring is actually rated at 12A. The lower value protection is
required because of the choice of lampholders on the circuits.

US Five 100 watt lamps at 120V equals 4.166 amps on 15amp rated
circuit with 14gauge (2.08mm) wire.

In this example the US system has a massively greater safety margin.

Fires tend to start at wiring accessories, cable joins, etc,
and not so much in the middle of a length of wire.


2. That U.S. circuits are not designed for their load.

I dont think that was the assumption:

The proof is that you keep saying "for a given load" and the loads are
NOT the same, we have many more circuits in typical dwelling.

the problem is simply theyre
designed to have a higher incidence of faults.

Simply a system with more smaller circuits each with an equal or
greater degree of safety margin.

As an example a modest 3 bedroom suburban home normally has a 200amp
40 way main panel (CU). That is 200amps in each leg of the incoming
feed using three 85mm cables. this provides 48kW of power. This is a
home with gas space heating, gas water heating, gas clothes drying,,
and often gas cooking.
Even with our maniacal excess it would be hard to overload such a
system to the point of combustion.

Normal UK home has a 100A (24kW) supply.
If you want any more than this, you have to have a 3-phase supply,
but that's quite unusual in a home unless it was very big.

--
Andrew Gabriel

Jim Michaels wrote:
On 18 Jun 2005 03:30:22 -0700, wrote:

The basic issue is that
very few people die of electrocution, whilst loads of people die from
electrical fires. The electrical fires largely stem from high currents. If
you halve the voltage, you double the current.
NOT TRUE.
You are making multiple invalid assumptions.
1. That U.S. wiring has the same number of circuits for the same load.

still cant figure out what you mean there. For a given load you do have
higher i with lower v, and each load is on 1 circuit as far as i can
see.

UK Ten 100watt lamps at 240V equal 4.166 amps on circuit rated at 6
amps with 1mm wire.

US Five 100 watt lamps at 120V equals 4.166 amps on 15amp rated
circuit with 14gauge (2.08mm) wire.

In this example the US system has a massively greater safety margin.

Your analysis is too simplistic. The load current / cable rating is not
something that causes any significant number of fires in either case,
it is a nonissue in reality.

Also I assume you realise 1mm2 is capable of much more than 6A, it is
merely fused at 5A or MCBed at 6A.

Safety margin is determined by looking at what in the system causes
safety failures, and how often. Cable rating doesnt come into it. Your
heavy US cables are merely a waste of resources, achieving nothing
afaics.

Unless you can explain how 4A on 32A capable cable tripped at 15A is
safer than 4A on 15A cable tripped at 6A. (figures are examples, not
calculated)


2. That U.S. circuits are not designed for their load.

I dont think that was the assumption:

The proof is that you keep saying "for a given load" and the loads are
NOT the same, we have many more circuits in typical dwelling.

to be honest I dont know what youre referring to, youve snipped the
relevant stuff out.

But I remember just enough to be fairly sure the assumption above didnt
come into it, that IIRC you misunderstood what was being said.


the problem is simply theyre
designed to have a higher incidence of faults.

Simply a system with more smaller circuits each with an equal or
greater degree of safety margin.

Youre not understanding safety margin. Size of cable has nothing to do
with it, once the cables big enough not to overload. Ours are big
enough and much more. Yours are even bigger, but for what? Its just
poor engineering.


As an example a modest 3 bedroom suburban home normally has a 200amp
40 way main panel (CU). That is 200amps in each leg of the incoming
feed using three 85mm cables.

Above ground supply or buried? 85mm2 is awful big, even for 200A. Or is
it aluminium?


this provides 48kW of power. This is a
home with gas space heating, gas water heating, gas clothes drying,,
and often gas cooking.
Even with our maniacal excess it would be hard to overload such a
system to the point of combustion.

Again you miss it. Your systems are overloaded day in day out, not at
the service entrance but at the wall plugs that get too hot, and the
wirenuts that cant reliably maintain their ratings. The result is a
high level of fires.


The practice of push-in
connection on mains sockets is something considered unthinkable here,
for good reason.

They are a homeowner/shoddy contractor item and are frowned upon.

precisely, here theyre illegal and unheard of. There isnt even a black
market in such junk, its just off the scale. Even the occasional 50
year old install isnt that bad.


In US IIUC it would be called 240v, but in fact be 120-0-120, so the
voltage from earth is 120 ac, not 240. In which case the fault
clearance benefit of genuinely 240v would sometimes apply and sometimes
not. Some faults that smoulder at 120 can arc over and trip at 240.

And some that would not cause a fire at 120V will burst into flames at
240V.

yup. the question is which is the greater number. 240 gives much better
clearance rate than 120.


3. Combination of neutral to earth (i.e. effectively TN-C earthing) leading
to electrocution in the event of polarisation swap, or some open circuit
conditions.

snip

Why snip the explanation?

if you could quote all relevant material I might be able to answer.


NT

In article .com,
writes:

Youre not understanding safety margin. Size of cable has nothing to do
with it, once the cables big enough not to overload. Ours are big
enough and much more. Yours are even bigger, but for what? Its just
poor engineering.

Because voltage drop is a serious issue for 120V supplies.
It's not for 240V supplies.

--
Andrew Gabriel

wrote:
Various wrote

The practice of push-in
connection on mains sockets is something considered unthinkable here,
for good reason.

They are a homeowner/shoddy contractor item and are frowned upon.


precisely, here theyre illegal and unheard of. There isnt even a black
market in such junk, its just off the scale. Even the occasional 50
year old install isnt that bad.


Many new lighting fittings on sale in the UK today use push in
connections! Probably other connectors as well.

Regards
Capitol

On 4 Jul 2005 11:11:49 -0700,it is alleged that
spake thusly in uk.d-i-y:

[snip]

Safety margin is determined by looking at what in the system causes
safety failures, and how often. Cable rating doesnt come into it. Your
heavy US cables are merely a waste of resources, achieving nothing
afaics.

Dunno, they seem much sturdier against mechanical damage (stripping
etc).

As an example a modest 3 bedroom suburban home normally has a 200amp
40 way main panel (CU). That is 200amps in each leg of the incoming
feed using three 85mm cables.

Above ground supply or buried? 85mm2 is awful big, even for 200A. Or is
it aluminium?

Generally Alumin(i)um wiring for the service entrance cables upto the
main breaker in the distribution panel.

[snip]

Again you miss it. Your systems are overloaded day in day out, not at
the service entrance but at the wall plugs that get too hot, and the
wirenuts that cant reliably maintain their ratings. The result is a
high level of fires.

Wall outlets and plugs don't get hot when they're new, it tends to be
the older ones that are loose that overheat. I never in 5 years in the
US saw wirenuts that couldn't maintain the ratings *when installed
correctly*.

Most fires are due to overloading extension cords, that is one thing
that really SHOULD be changed, they allow 13 amp rated (16AWG) ext
cords on 20 amp circuits, which is a recipe for disaster, one that all
too often works well:-(

precisely, here theyre illegal and unheard of. There isnt even a black
market in such junk, its just off the scale. Even the occasional 50
year old install isnt that bad.

As someone else has noted, they are appearing on lighting equipment
and scare the bejesus out of me, the ones that are on light fixtures
make the US backstab connections look secure.

[much snippage]

Not trying to further the war:-) Just observations I made.

--
Computers achieved sentience in nineteen seventy five. The reason we're
unaware of this is that they watched TV, saw what we do to sentient
computers, and decided to take it out on us secretly. We call the
result of this descision "Windows"

Chip wrote:
On 4 Jul 2005 11:11:49 -0700,it is alleged that
spake thusly in uk.d-i-y:

Safety margin is determined by looking at what in the system causes
safety failures, and how often. Cable rating doesnt come into it. Your
heavy US cables are merely a waste of resources, achieving nothing
afaics.

Dunno, they seem much sturdier against mechanical damage (stripping
etc).

is that one of the big causes of fires though?


Again you miss it. Your systems are overloaded day in day out, not at
the service entrance but at the wall plugs that get too hot, and the
wirenuts that cant reliably maintain their ratings. The result is a
high level of fires.

Wall outlets and plugs don't get hot when they're new, it tends to be
the older ones that are loose that overheat.

ok, so they are a problem.


I never in 5 years in the
US saw wirenuts that couldn't maintain the ratings *when installed
correctly*.

If users routinely cant install them safely, even after over half a
century of use, theyre a safety problem. Whatever the mechanics of it,
they do cause fires, but are still used. Strips of 12 screw connectors
are very cheap here, even if not as cheap as wirenuts. The cost to save
those lives is trivial. Add in the great cost saved in damaged goods,
and the US's use of wirenuts seems to make no real sense.


Most fires are due to overloading extension cords, that is one thing
that really SHOULD be changed, they allow 13 amp rated (16AWG) ext
cords on 20 amp circuits, which is a recipe for disaster, one that all
too often works well:-(

why would that cause disaster, given the large cable safety margins?

and why permit 13A rated cable on 20A circuits?

If what youre saying is accurate, the next question is why.


precisely, here theyre illegal and unheard of. There isnt even a black
market in such junk, its just off the scale. Even the occasional 50
year old install isnt that bad.

As someone else has noted, they are appearing on lighting equipment
and scare the bejesus out of me, the ones that are on light fixtures
make the US backstab connections look secure.

We use them only for low current apps in UK, for which they work
satisfactorily. Trying to put over 10A through them is another matter.
They will only maintain a gas tight connection over a very small
contact area.


NT

Chip wrote:
On 4 Jul 2005 11:11:49 -0700,it is alleged that
spake thusly in uk.d-i-y:

Safety margin is determined by looking at what in the system causes
safety failures, and how often. Cable rating doesnt come into it. Your
heavy US cables are merely a waste of resources, achieving nothing
afaics.

Dunno, they seem much sturdier against mechanical damage (stripping
etc).

is that one of the big causes of fires though?


Again you miss it. Your systems are overloaded day in day out, not at
the service entrance but at the wall plugs that get too hot, and the
wirenuts that cant reliably maintain their ratings. The result is a
high level of fires.

Wall outlets and plugs don't get hot when they're new, it tends to be
the older ones that are loose that overheat.

ok, so they are a problem.


I never in 5 years in the
US saw wirenuts that couldn't maintain the ratings *when installed
correctly*.

If users routinely cant install them safely, even after over half a
century of use, theyre a safety problem. Whatever the mechanics of it,
they do cause fires, but are still used. Strips of 12 screw connectors
are very cheap here, even if not as cheap as wirenuts. The cost to save
those lives is trivial. Add in the great cost saved in damaged goods,
and the US's use of wirenuts seems to make no real sense.


Most fires are due to overloading extension cords, that is one thing
that really SHOULD be changed, they allow 13 amp rated (16AWG) ext
cords on 20 amp circuits, which is a recipe for disaster, one that all
too often works well:-(

why would that cause disaster, given the large cable safety margins?

and why permit 13A rated cable on 20A circuits?

If what youre saying is accurate, the next question is why.


precisely, here theyre illegal and unheard of. There isnt even a black
market in such junk, its just off the scale. Even the occasional 50
year old install isnt that bad.

As someone else has noted, they are appearing on lighting equipment
and scare the bejesus out of me, the ones that are on light fixtures
make the US backstab connections look secure.

We use them only for low current apps in UK, for which they work
satisfactorily. Trying to put over 10A through them is another matter.
They will only maintain a gas tight connection over a very small
contact area.


NT

On 5 Jul 2005 04:12:31 -0700,it is alleged that
spake thusly in uk.d-i-y:

[snip]

Dunno, they seem much sturdier against mechanical damage (stripping
etc).

is that one of the big causes of fires though?

Through arcing faults if the cable breaks, it can be.


Again you miss it. Your systems are overloaded day in day out, not at
the service entrance but at the wall plugs that get too hot, and the
wirenuts that cant reliably maintain their ratings. The result is a
high level of fires.

Wall outlets and plugs don't get hot when they're new, it tends to be
the older ones that are loose that overheat.

ok, so they are a problem.

Yes but I've seen the same with the fuse clips on 13 amp UK plugs.
Some makes seem to work loose, this is now mostly fixed. US socket
outlets had the same issues, which are now also mostly fixed.


I never in 5 years in the
US saw wirenuts that couldn't maintain the ratings *when installed
correctly*.

If users routinely cant install them safely, even after over half a
century of use, theyre a safety problem. Whatever the mechanics of it,
they do cause fires, but are still used. Strips of 12 screw connectors
are very cheap here, even if not as cheap as wirenuts. The cost to save
those lives is trivial. Add in the great cost saved in damaged goods,
and the US's use of wirenuts seems to make no real sense.

To be fair, I have seen strip connectors cause burn ups too,
personally I prefer wirenuts as being easier to install.

Many fires with wirenuts were caused by their use on Al cable, in a
few cases with UL approval. This caused and still causes a lot of
anger with US electricians who know from experience it doesn't work,
but nobody listens to them. Pretty much the same as he-(


Most fires are due to overloading extension cords, that is one thing
that really SHOULD be changed, they allow 13 amp rated (16AWG) ext
cords on 20 amp circuits, which is a recipe for disaster, one that all
too often works well:-(

why would that cause disaster, given the large cable safety margins?

Those safety margins are for fixed wiring cables, the fire usually
starts right where someone put the extension cord under a rug.

and why permit 13A rated cable on 20A circuits?

If what youre saying is accurate, the next question is why.


Indeed.

precisely, here theyre illegal and unheard of. There isnt even a black
market in such junk, its just off the scale. Even the occasional 50
year old install isnt that bad.

As someone else has noted, they are appearing on lighting equipment
and scare the bejesus out of me, the ones that are on light fixtures
make the US backstab connections look secure.

We use them only for low current apps in UK, for which they work
satisfactorily. Trying to put over 10A through them is another matter.
They will only maintain a gas tight connection over a very small
contact area.

Germany and Austria use the 'Wago' brand push in connectors, these
seem to have VERY high contact pressure compared to the ones on
ballasts and lampholders, personally I'd trust them at ~16 amps.

I think we should agree to differ over which wiring system is 'best'
overall, my opinion would be 'neither, they were both designed by
committee, but each has strengths and weaknesses, surprisingly often
in the same areas'.

--
Computers achieved sentience in nineteen seventy five. The reason we're
unaware of this is that they watched TV, saw what we do to sentient
computers, and decided to take it out on us secretly. We call the
result of this descision "Windows"

On Sunday, in article

"Jim Michaels" wrote:

On 18 Jun 2005 22:46:09 GMT, (Andrew
Gabriel) wrote:

[Andrew's article pre-dates when I first subscribed to this group, so I'm
piggy-backing on Jim's]

In article ,
Capitol writes:
distribution circuits and products without upgrading. If we were
starting again today the world would probably settle for 230V @ 400 Hz,
giving smaller ( &cheap) transformers without significantly increased
losses.

400Hz severely reduces the maximum area of a synchronisation zone,
which makes carrying power any distance very much more expensive.
Many of the 50Hz zones are close to their size limit now, so I
don't think anyone would think of distributing at any higher
frequency in Europe. It would be OK on a small isolated island.
400Hz isn't suitable for industrial motors either. Actually, supplies
to large commercial customers at 16 2/3rds Hz and 25Hz used to be
quite common as they much prefer a lower frequency for large motors.
Transformer size is really only an issue on planes and boats, which
often do use 400Hz.

A *lot* of military hardware, neither afloat nor airborne, uses 400Hz for
power distribution, not just to cut down on the mass of transformers, but
also on their bulk.

A radar system with which I spent many years (it was first designed, but
never built, to go with a Predictor and the Vickers 3.7in AA gun,
ca.1946, but not constructed until the early/mid 1950s, and to my certain
knowledge was still being used, in a different role, right through into
the 1990s) had more than five HUNDRED power transformers operating off
"400Hz mains". Each sub-system had its own transformers for valve
heaters, HT supplies to anodes, EHT to klystrons and magnetrons, etc.

(The 400Hz "mains" came from a motor-alternator set, running off 3ph 50Hz
[which came in our instance off the public supply, but "in the field"
could arise from a pair of 27.5kVA Meadows diesel alternators]. The
startup current at switch-on was sufficient to bend the needle on the
electricity board's engineer's tong ammeter, even though it was on the
400A range: he was there to investigate our complaints of insufficient
iron in the substation transformer ;-)

--
Brian {Hamilton Kelly}
"Je n'ai fait celle-ci plus longue que parce que je n'ai pas eu
le loisir de la faire plus courte."
Blaise Pascal, /Lettres Provinciales/, 1657

In article ,
(Brian {Hamilton Kelly}) writes:
On 18 Jun 2005 22:46:09 GMT, (Andrew
Gabriel) wrote:
Transformer size is really only an issue on planes and boats, which
often do use 400Hz.

A *lot* of military hardware, neither afloat nor airborne, uses 400Hz for
power distribution, not just to cut down on the mass of transformers, but
also on their bulk.

Well, perhaps I should have broadened it to say portable/transportable.

I also got some private feedback from someone who used to be in the supply
industry who said transformer size _is_ important to them -- they want
them big and heavy, so they can't be stolen ;-)

--
Andrew Gabriel

Jim Michaels wrote:
On Mon, 04 Jul 2005 11:14:32 +0100, "Dave Plowman (News)"
wrote:

In article ,
Jim Michaels wrote:

Not so - it's the current that causes a fire.
Actually it is the energy current times voltage.

For a given fault twice the voltage equals twice the current!

No again. Faults are not normally ohmic. Higher v creates much higher
i, and of course higher v means lower i breakers... result is a big
difference in fire rates, favouring 240. 240 clears faults much better.

NT

Chip wrote:
:

they do cause fires, but are still used. Strips of 12 screw connectors
are very cheap here, even if not as cheap as wirenuts. The cost to save
those lives is trivial. Add in the great cost saved in damaged goods,
and the US's use of wirenuts seems to make no real sense.

To be fair, I have seen strip connectors cause burn ups too,
personally I prefer wirenuts as being easier to install.

all components have a failure rate, the question is the comparative
rates.


Many fires with wirenuts were caused by their use on Al cable, in a
few cases with UL approval. This caused and still causes a lot of
anger with US electricians who know from experience it doesn't work,
but nobody listens to them. Pretty much the same as he-(

I dont think we allow that here! I cant offhand think of any domestic
wiring sceanrio thats permitted in UK by the 16th but dangerous...
maybe you can. The death rate is remarkably low.


Most fires are due to overloading extension cords, that is one thing
that really SHOULD be changed, they allow 13 amp rated (16AWG) ext
cords on 20 amp circuits, which is a recipe for disaster, one that all
too often works well:-(

why would that cause disaster, given the large cable safety margins?

Those safety margins are for fixed wiring cables, the fire usually
starts right where someone put the extension cord under a rug.

so why are cables with inadequate margins used? Our regs in UK are the
other way, very conservative.

and why permit 13A rated cable on 20A circuits?

If what youre saying is accurate, the next question is why.

Indeed.


I think we should agree to differ over which wiring system is 'best'
overall, my opinion would be 'neither, they were both designed by
committee, but each has strengths and weaknesses, surprisingly often
in the same areas'.

ok. I'll just compare the death rates.


NT

On 6 Jul 2005 13:15:48 -0700,it is alleged that
spake thusly in uk.d-i-y:

[snip]

Many fires with wirenuts were caused by their use on Al cable, in a
few cases with UL approval. This caused and still causes a lot of
anger with US electricians who know from experience it doesn't work,
but nobody listens to them. Pretty much the same as he-(

I dont think we allow that here! I cant offhand think of any domestic
wiring sceanrio thats permitted in UK by the 16th but dangerous...
maybe you can. The death rate is remarkably low.

[snip]
ok. I'll just compare the death rates.

I think both of those come down to 'construction methods' rather than
wiring per se. A fire which in the UK will result in a smell of
hot/burned PVC then a call to an electrician as to why the breaker
keeps tripping now, would likely have burned down many homes in the US
with the all wood construction.

As to dangers, I think the dangers inherent with electricity often
mask other dangers.

As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps. 1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

--
This .signature has been hijacked by the Shellfish Liberation Army.
Please remain clam.

Chip wrote:
On 6 Jul 2005 13:15:48 -0700,it is alleged that :

I dont think we allow that here! I cant offhand think of any domestic
wiring sceanrio thats permitted in UK by the 16th but dangerous...
maybe you can. The death rate is remarkably low.

[snip]
ok. I'll just compare the death rates.

I think both of those come down to 'construction methods' rather than
wiring per se. A fire which in the UK will result in a smell of
hot/burned PVC then a call to an electrician as to why the breaker
keeps tripping now, would likely have burned down many homes in the US
with the all wood construction.

we have a lot of woodframe here as well, though brick is more popular.


As to dangers, I think the dangers inherent with electricity often
mask other dangers.

As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps.

This has been covered in some depth on this ng recently. And the real
life stats bear it out: UK 30A rings are no danger at all.


1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

and increase death rates.


And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

yes, it is a bit. Type C gets recommended here, but Bs are still the
common choice.

So nothing dangerous.


NT

On 6 Jul 2005 15:07:55 -0700,it is alleged that
spake thusly in uk.d-i-y:

[snip]


This has been covered in some depth on this ng recently.


I thought it had. (I came in at the tail end I believe).
And the real
life stats bear it out: UK 30A rings are no danger at all.

Indeed not, I just don't like them very much:-)


1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

and increase death rates.

How would that increase death rates?


And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

yes, it is a bit. Type C gets recommended here, but Bs are still the
common choice.

Type C is good yes.

So nothing dangerous.


I keep thinking "halfway down the stairs when the lights go out" or
"carrying a pan of boiling water across the kitchen"

--
You cannot shake hands with a clenched fist.
- Indira Gandhi

In article t,
Chip wrote:
As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps. 1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

So you don't understand the principles of final ring circuits?

And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

Why would lights go out at random on the stairs?

--
*If I worked as much as others, I would do as little as they *

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

On Thu, 07 Jul 2005 00:00:28 +0100,it is alleged that "Dave Plowman
(News)" spake thusly in uk.d-i-y:

In article t,
Chip wrote:
As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps. 1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

So you don't understand the principles of final ring circuits?

Yes I understand the principle. I just don't *LIKE* the principle.


And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

Why would lights go out at random on the stairs?

Because type B 6 amp breakers often trip whenever a lamp blows on the
circuit.

--
The follies which a man regrets most in his life are those
which he didn't commit when he had the opportunity.
- Helen Rowland

In article t,
Chip writes:
On Thu, 07 Jul 2005 00:00:28 +0100,it is alleged that "Dave Plowman
(News)" spake thusly in uk.d-i-y:

In article t,
Chip wrote:
As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps. 1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

So you don't understand the principles of final ring circuits?

Yes I understand the principle. I just don't *LIKE* the principle.

You don't seem to understand why the CPC size can be reduced.

And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

Why would lights go out at random on the stairs?

Because type B 6 amp breakers often trip whenever a lamp blows on the
circuit.

Still using mains filament lamps in 2005? It really is time to move on...

--
Andrew Gabriel

Chip wrote:
And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.
yes, it is a bit. Type C gets recommended here, but Bs are still the
common choice.
Type C is good yes.

I've never had an MCB trip "randomly" or even on a bulb blow.

So nothing dangerous.
I keep thinking "halfway down the stairs when the lights go out" or
"carrying a pan of boiling water across the kitchen"

That is why I have an emergency lighting unit in the
kitchen-dinette-study-lounge.

Owain

On 06 Jul 2005 23:37:41 GMT,it is alleged that andrew@a17 (Andrew
Gabriel) spake thusly in uk.d-i-y:

In article t,
Chip writes:
On Thu, 07 Jul 2005 00:00:28 +0100,it is alleged that "Dave Plowman
(News)" spake thusly in uk.d-i-y:

In article t,
Chip wrote:
As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps. 1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

So you don't understand the principles of final ring circuits?

Yes I understand the principle. I just don't *LIKE* the principle.

You don't seem to understand why the CPC size can be reduced

You are correct, I don't see any circumstances where a reduced earth
conductor could be better than or even equal to a full size one.


And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

Why would lights go out at random on the stairs?

Because type B 6 amp breakers often trip whenever a lamp blows on the
circuit.

Still using mains filament lamps in 2005? It really is time to move on..

So because someone else says they're old fashioned, the public should
be inconvenienced?

--
The follies which a man regrets most in his life are those
which he didn't commit when he had the opportunity.
- Helen Rowland

In article t,
Chip writes:
On 06 Jul 2005 23:37:41 GMT,it is alleged that andrew@a17 (Andrew
Gabriel) spake thusly in uk.d-i-y:

In article t,
Chip writes:
On Thu, 07 Jul 2005 00:00:28 +0100,it is alleged that "Dave Plowman
(News)" spake thusly in uk.d-i-y:

In article t,
Chip wrote:
As to wiring scenarios permitted but dangerous, to name a few we have
ring circuits, which allow the connection of 20A rated cable to a 30
amp circuit protective device. I know in practice they have proved
remarkably resilient, but they still give me the creeps. 1x 16A radial
per room, using 2.5mm cable with a _full size earth_ (none of this
cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the
kitchen (on 4mm cable) would make me happier:-)

So you don't understand the principles of final ring circuits?

Yes I understand the principle. I just don't *LIKE* the principle.

You don't seem to understand why the CPC size can be reduced

You are correct, I don't see any circumstances where a reduced earth
conductor could be better than or even equal to a full size one.

OK then, please think of some likely scenario in which it is undersized.

And 6amp lighting circuits with type B breakers, so that the lights on
the stairs go out at random (quite frequent) intervals is odd too.

Why would lights go out at random on the stairs?

Because type B 6 amp breakers often trip whenever a lamp blows on the
circuit.

Still using mains filament lamps in 2005? It really is time to move on..

So because someone else says they're old fashioned, the public should
be inconvenienced?

Well, when I replace a CU, I don't use a B6 breaker on the lights.
That's largely a question of how competent a designer your electrician
is.

In my own home, I don't have any mains filament lamps indoors that
I can think of at the moment, at least, none on the lighting circuit.
I do have a couple of halogen ones outdoors, but they are on their
own breaker.

--
Andrew Gabriel

In article ,
Jim Michaels writes:
On 04 Jul 2005 18:17:37 GMT, (Andrew
Gabriel) wrote:

In article .com,
writes:

Youre not understanding safety margin. Size of cable has nothing to do
with it, once the cables big enough not to overload. Ours are big
enough and much more. Yours are even bigger, but for what? Its just
poor engineering.

Because voltage drop is a serious issue for 120V supplies.
It's not for 240V supplies.

No, Our supplies are also 240V

Nope -- you require regulation mostly at the 120V level.

--
Andrew Gabriel

"Andrew Gabriel" andrew@a17 wrote in message
.. .
In article t,
Chip writes:
snip

Because type B 6 amp breakers often trip whenever a lamp blows on
the
circuit.

Still using mains filament lamps in 2005? It really is time to move
on...


Why?

In article t,
Chip wrote:
And 6amp lighting circuits with type B breakers, so that the lights
on the stairs go out at random (quite frequent) intervals is odd too.

yes, it is a bit. Type C gets recommended here, but Bs are still the
common choice.

Type C is good yes.

So nothing dangerous.


I keep thinking "halfway down the stairs when the lights go out" or
"carrying a pan of boiling water across the kitchen"

But given the frequency of power cuts in the US you'd have automatic
emergency lighting anyway?

--
*I have a degree in liberal arts -- do you want fries with that

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

On Thu, 07 Jul 2005 09:48:34 +0100,it is alleged that "Dave Plowman
(News)" spake thusly in uk.d-i-y:

[snip]

I keep thinking "halfway down the stairs when the lights go out" or
"carrying a pan of boiling water across the kitchen"

But given the frequency of power cuts in the US you'd have automatic
emergency lighting anyway?

Seems reasonable yes, the frequency of power cuts *is* much higher in
the US, but emergency lighting's a good idea anywhere.

--
We are just an advanced breed of monkeys on a minor planet of a very
average star. But we can understand the Universe. That makes us something
very special.
- Stephen Hawking

On 07 Jul 2005 00:24:17 GMT,it is alleged that andrew@a17 (Andrew
Gabriel) spake thusly in uk.d-i-y:


You are correct, I don't see any circumstances where a reduced earth
conductor could be better than or even equal to a full size one.

OK then, please think of some likely scenario in which it is undersized.

I just don't like the concept of the protective conductor being a
smaller size than the line conductors potentially feeding fault
current into it.

[snip]

So because someone else says they're old fashioned, the public should
be inconvenienced?

Well, when I replace a CU, I don't use a B6 breaker on the lights.
That's largely a question of how competent a designer your electrician
is.

Sadly most are not 'designers' at all, they install a B6 because
everyone uses 6amp for lighting, and if they just ask for a 6 amp
breaker, a type 'B' is what they get.


In my own home, I don't have any mains filament lamps indoors that
I can think of at the moment, at least, none on the lighting circuit.
I do have a couple of halogen ones outdoors, but they are on their
own breaker.

To be fair we have mostly compact fluorescents. It's just the
chandelier fitting in the living room which looks awful with anything
but 25w candle bulbs, and the GU10 Halogens in the conservatory. I am
intending to switch the GU10's to an FCU off the ring, but it's the
candle bulbs that do the breaker tripping (possibly due to smaller
lead spacing inside the lamps causing the plasma effect suggested
elsewhere).

--
SMS: Abbreviation, multiple meanings-
[1] Short Message Service, cellular telephone messaging method.
[2] SigMonster Sentience, when your sigmonster posts quotes about
sigmonsters.

In article t,
Chip wrote:
I keep thinking "halfway down the stairs when the lights go out" or
"carrying a pan of boiling water across the kitchen"

But given the frequency of power cuts in the US you'd have automatic
emergency lighting anyway?

Seems reasonable yes, the frequency of power cuts *is* much higher in
the US, but emergency lighting's a good idea anywhere.

In my kitchen, the extractor hood lighting is on a separate circuit to
other lighting, and when cooking it's always on. So even if a bulb blowing
*did* trip an MCB, it would not plunge the room into darkness.

Same with stair lighting - it's on two circuits. But I think I'd find my
way downstairs ok in the dark. ;-)

--
*I'll try being nicer if you'll try being smarter

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

Jim Michaels wrote:
On 4 Jul 2005 11:11:49 -0700, wrote:

UK Ten 100watt lamps at 240V equal 4.166 amps on circuit rated at 6
amps with 1mm wire.

US Five 100 watt lamps at 120V equals 4.166 amps on 15amp rated
circuit with 14gauge (2.08mm) wire.

In this example the US system has a massively greater safety margin.

Your analysis is too simplistic. The load current / cable rating is not
something that causes any significant number of fires in either case,
it is a nonissue in reality.

Agreed, There are not many electrical fires due to fixed wiring.

that is not correct.


Also I assume you realise 1mm2 is capable of much more than 6A, it is
merely fused at 5A or MCBed at 6A.

Safety margin is determined by looking at what in the system causes
safety failures, and how often. Cable rating doesnt come into it. Your
heavy US cables are merely a waste of resources, achieving nothing
afaics.

Just a reasonable engineering safety margin.

reasonable safety margin on wire sizes has been addrssed already. I
cant help thinking youre perhaps not keeping up.


the problem is simply theyre
designed to have a higher incidence of faults.

Ridiculous.

hardly, look at the stats, and the practices that are known to cause
fires. Or dont.


We may have more old or poorly maintained installations but safety has
always been a primary concern.

Given what we've read in this thread, that conclusion is simply
impossible to draw.


Simply a system with more smaller circuits each with an equal or
greater degree of safety margin.

Youre not understanding safety margin. Size of cable has nothing to do
with it, once the cables big enough not to overload. Ours are big
enough and much more. Yours are even bigger, but for what? Its just
poor engineering.

Look up safety margin.

That doesnt answer the q at all. Im perfectly familiar with safety
margins, and UK has more than big enough margins in its cable sizes. US
cables are not large for that reason.


this provides 48kW of power. This is a
home with gas space heating, gas water heating, gas clothes drying,,
and often gas cooking.
Even with our maniacal excess it would be hard to overload such a
system to the point of combustion.

Again you miss it. Your systems are overloaded day in day out, not at
the service entrance but at the wall plugs that get too hot,

???????

thats news?

and the
wirenuts that cant reliably maintain their ratings.

???????

The result is a
high level of fires.

???????

thats news too??

I think time to end this discussion. Good luck.


NT

Chip wrote:

I just don't like the concept of the protective conductor being a
smaller size than the line conductors potentially feeding fault
current into it.

There's no logic to that. Protective conductors only have to be sized
to withstand the earth fault current for the time it takes to clear the
fault. Live conductors [1] have be able to withstand continuous
full-load design current as well as (where relevant) occasional
short-term overloads. The principle of using 'undersized' CPCs is very
well established, both in theory and practice, and has been so for a
very long time. The practice doesn't compromise safety; in fact it
avoids over-engineering and saves copper.

For live conductors of up to and including 16mm^2, BS 7671 requires the
designer to check the sizing of any intended under-size CPC using the
adiabatic equation (see Reg. 543-01-03) [2]. However, for twin & earth
cables, detailed calculation can be avoided by using the pre-calculated
final circuits given in Table 7.1 of the On-Site Guide (OSG). Provided
that you don't exceed the circuit lengths given in that table, for the
relevant type of protective device, type of earthing and required
disconnection time, and provided that the earth fault loop impedance
tests out OK (see Appendix 2 of the OSG) then your design and
installation should be safe from this POV.

If you scan through Table 7.1 you'll see that most circuits are
voltage-drop-limited, so a larger CPC will confer no advantage in terms
of allowable circuit length. Circuits where the length is limited by Zs
could be stretched by using a full-size CPC, but that rules out using
T&E cable, unless a separate CPC is run.


[1] This term means the current carrying conductors and therefore
includes any neutral.

[2] For 25 and 35mm^2 live conductors a 16mm^2 CPC can be used without
calculation; for larger sizes calculation is only required if the CPC is
less that one half of the live conductor size [BS7671 Table 54G].

--
Andy

If you scan through Table 7.1 you'll see that most circuits are
voltage-drop-limited, so a larger CPC will confer no advantage in terms
of allowable circuit length.

The old style 2.5mm cable certainly used to be earth loop impedence limited
in many circumstances, which is why the CPC was increased to 1.5mm, to
enable longer circuits. As you suggest, there was no need to go larger, as
voltage drop becomes the dominant limit to circuit length.

Christian.

On Thu, 07 Jul 2005 17:25:28 +0100,it is alleged that Andy Wade
spake thusly in uk.d-i-y:

Chip wrote:

I just don't like the concept of the protective conductor being a
smaller size than the line conductors potentially feeding fault
current into it.

There's no logic to that. Protective conductors only have to be sized
to withstand the earth fault current for the time it takes to clear the
fault.

That is where I have issues with the concept, I admit my calculations
verge on the 'worst case scenario' but a 1.5xI(n) fault would not blow
a 30 amp rewireable fuse in under a few minutes, and 45 amps flowing
through 2x1.5mm earth wires seems a generally bad idea to me. I am at
odds with the IEE and the prevailing opinion on this NG for that, and
the worst case is highly unlikely to happen, but I DO overengineer
wiring systems, for example I won't use 1.0mm2 cable, I use 1.5,
always, as the cost difference is minimal. I see no negative safety
implication of oversizing things compared to 'what is allowed'.

One of the things I am looking for is evidence of what is 'unsafe', so
I can avoid doing it :-)

Live conductors [1] have be able to withstand continuous
full-load design current as well as (where relevant) occasional
short-term overloads. The principle of using 'undersized' CPCs is very
well established, both in theory and practice, and has been so for a
very long time. The practice doesn't compromise safety; in fact it
avoids over-engineering and saves copper.

I think the differences are not as major as people at first think, in
the US the neutral on the drop (TN-C-S system before the split) is
often slightly undersized, they just don't extend it to final branch
circuits, we in the UK do, and many other european countries disagree
with this practice.

The saving in copper is minimal, and copper can be (and is) recycled
after the cable reaches the end of its useful life.

A small 'anachronism' is that if wiring in conduit, you use full size
earth conductors AND bond the conduit, which nobody feels is
overengineering, and with MI cable, the sheath is several times the
CSA of the conductors.


For live conductors of up to and including 16mm^2, BS 7671 requires the
designer to check the sizing of any intended under-size CPC using the
adiabatic equation (see Reg. 543-01-03) [2]. However, for twin & earth
cables, detailed calculation can be avoided by using the pre-calculated
final circuits given in Table 7.1 of the On-Site Guide (OSG). Provided
that you don't exceed the circuit lengths given in that table, for the
relevant type of protective device, type of earthing and required
disconnection time, and provided that the earth fault loop impedance
tests out OK (see Appendix 2 of the OSG) then your design and
installation should be safe from this POV.

If you scan through Table 7.1 you'll see that most circuits are
voltage-drop-limited, so a larger CPC will confer no advantage in terms
of allowable circuit length. Circuits where the length is limited by Zs
could be stretched by using a full-size CPC, but that rules out using
T&E cable, unless a separate CPC is run.


[1] This term means the current carrying conductors and therefore
includes any neutral.

[2] For 25 and 35mm^2 live conductors a 16mm^2 CPC can be used without
calculation; for larger sizes calculation is only required if the CPC is
less that one half of the live conductor size [BS7671 Table 54G].

In short, I am not saying the 'UK ring circuits are dangerous' but
more that 'under certain circumstances I can see that different
arrangements could be safer'. It's all a matter of degrees I guess.

--
"The perfect computer has been developed. You just feed in your problems
and they never come out again."
- Al Goodman.

In article t,
Chip writes:
On Thu, 07 Jul 2005 17:25:28 +0100,it is alleged that Andy Wade
spake thusly in uk.d-i-y:

Chip wrote:

I just don't like the concept of the protective conductor being a
smaller size than the line conductors potentially feeding fault
current into it.

There's no logic to that. Protective conductors only have to be sized
to withstand the earth fault current for the time it takes to clear the
fault.

That is where I have issues with the concept, I admit my calculations
verge on the 'worst case scenario' but a 1.5xI(n) fault would not blow
a 30 amp rewireable fuse in under a few minutes, and 45 amps flowing
through 2x1.5mm earth wires seems a generally bad idea to me. I am at

45 amps will be generating some 10kW at the scene of the fault.
It would be pretty impossible to even deliberately engineer such
a fault which lasted more than a few seconds, without it either
shorting completely or blowing itself out into an open circuit.
The generation of 10kW will change the nature of a fault site
very quickly.

There just aren't credible scenarios where large currents flow
for an extended period in the earth conductor.

Live conductors [1] have be able to withstand continuous
full-load design current as well as (where relevant) occasional
short-term overloads. The principle of using 'undersized' CPCs is very
well established, both in theory and practice, and has been so for a
very long time. The practice doesn't compromise safety; in fact it
avoids over-engineering and saves copper.

I think the differences are not as major as people at first think, in
the US the neutral on the drop (TN-C-S system before the split) is
often slightly undersized, they just don't extend it to final branch
circuits, we in the UK do, and many other european countries disagree
with this practice.

On a fully loaded US system, the neutral current is zero.
Same is true of a fully loaded 3-phase system in UK, which
is why 4-wire 3-phase circuits do sometimes have reduced
size neutrals (need to watch out for 3rd-harmonic components
though, which do add in the neutral rather than cancel out).

--
Andrew Gabriel