With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??

TIA

On Aug 19, 12:46*pm, jim wrote:
With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??


I can't see any point in putting computers on a class C MCB unless you
have a LOT of them and they are all starting up at once...

More likely they are on a separate circuit which is not RCD-protected,
and the red serves to indicate that you shouldn't plug your lawnmower
in. There may also be a UPS somewhere.

On Aug 19, 12:46*pm, jim wrote:
With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??


It might be ring connected to a UPS under the stairs, or it might just
have a big surge suppressor.

On 19/08/2011 12:46, jim wrote:
With a possible move in mind, missus& I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??

Two options he

First one is I would guess that he has wired a circuit with "high
integrity" earthing. This is where you make sure that the earth
connection is in a ring configuration (even on a radial circuit), and
each end connects to independent terminals on each socket or accessory.
This is for use with circuits that may normally experience high earth
leakage currents. (Computer kit switched mode PSUs are often a common
cause of high earth leakages)

The other option is that he has wired in a UPS and provided some
uninterruptable sockets. The colour change would be significant here,
since these sockets are unlikely to be rated for a full 13A load, and
also will not disconnect in the event of an earth fault.



--
Cheers,

John.

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

Are these still commonly (or ever) fitted with non-standard sockets to
admit only plugs with the "Earth" pin rotated through 90 degrees? A
couple of buildings in which I worked had them for IT kit (with "clean"
earths); and it struck me those non-standard sockets if still readily
available wd be a better way to stop someone plugging the hedge trimmer
into a socket which is not RCD-protected.
--
Robin
PM may be sent to rbw0{at}hotmail{dot}com

On 19/08/2011 15:27, Robin wrote:
Are these still commonly (or ever) fitted with non-standard sockets to
admit only plugs with the "Earth" pin rotated through 90 degrees? A

I don't believe there is a requirement to identify or restrict sockets
in this way (although it may be desirable from a users point of view)

couple of buildings in which I worked had them for IT kit (with "clean"
earths); and it struck me those non-standard sockets if still readily
available wd be a better way to stop someone plugging the hedge trimmer
into a socket which is not RCD-protected.

Generally speaking the way to ensure the hedge trimmer is safe is to
make sure all sockets that are likely to be used to feed it are RCD
protected.

If for any reason there is one that is not, then it ought to be at least
labelled as a minimum, but "unusual" sockets for the intended appliance
are also a good solution here.


--
Cheers,

John.

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

Another possibility is that there are two types of mains, "clean" mains and
"dirty" mains.

As I understand it, the clean mains sockets are on their own circuit with
its own MCB at the CU, and only IT related gear and UPS'es are plugged into
this circuit. The dirty mains are your normal appliances with motors which
by themselves chuck out a lot of RFI, EMI , surges, brownouts etc. The
objective here is to stop the other appliances's own noise from affecting
the IT gear.


"John Rumm" wrote in message
...
On 19/08/2011 15:27, Robin wrote:
Are these still commonly (or ever) fitted with non-standard sockets to
admit only plugs with the "Earth" pin rotated through 90 degrees? A

I don't believe there is a requirement to identify or restrict sockets in
this way (although it may be desirable from a users point of view)

couple of buildings in which I worked had them for IT kit (with "clean"
earths); and it struck me those non-standard sockets if still readily
available wd be a better way to stop someone plugging the hedge trimmer
into a socket which is not RCD-protected.

Generally speaking the way to ensure the hedge trimmer is safe is to make
sure all sockets that are likely to be used to feed it are RCD protected.

If for any reason there is one that is not, then it ought to be at least
labelled as a minimum, but "unusual" sockets for the intended appliance
are also a good solution here.


--
Cheers,

John.

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

On Aug 19, 3:45*pm, John Rumm wrote:
On 19/08/2011 15:27, Robin wrote:

Are these still commonly (or ever) fitted with non-standard sockets to
admit only plugs with the "Earth" pin rotated through 90 degrees? *A

I don't believe there is a requirement to identify or restrict sockets
in this way (although it may be desirable from a users point of view)

I vaguely remember a recommendation for labelling. When I installed my
kiln sockets, following the regs as best I could, I did label them as
not having the same RCD protection as the rest of my workshop.

I would expect this ring in the house is simply a separate ring and
MCB, maybe a split-load CU, to avoid nuisance trips from other rings.

On Fri, 19 Aug 2011 04:46:47 -0700 (PDT), jim
wrote:


In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Most probably high integrity earthing. See

http://www.copperinfo.co.uk/resident...tallations.pdf

On Aug 19, 12:46*pm, jim wrote:
With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??

TIA

In hospitals there are often two suppies. (Essential and non-
essential) One is covered by the emegency generator if the power
fails the other is not. This is/was the reason for specially
identified sockets. (The generator often was not big enough to meet
the entire load.)

In days of yore, when RCCDs were first brought out, there was lots of
"niusance tripping", they were susceptable to "glitches" or voltage
spikes running about the system,so it became common practice to have
sockets not protected by RCCDs for critical loads.
RCCDs especially didn't like portable X ray machines I remember.

RCCDs have improved vastly these days. It's far less of a problem.

harry writes:

RCCDs have improved vastly these days. It's far less of a problem.

I'm still wondering why in the UK (EU?) RCDs trip at around 30 milliamps,
but in Canada and the U.S. their GFIs trip at 5 milliamps.

It's the current level that kills; even 30,000 volts of static won't
hurt you, though it may make you jump, so saying that N. America uses
half the voltage we do for domestic supplies is beside the point.

--
Windmill, Use t m i l l
@ O n e t e l
J.R.R. Tolkien: . c o m
All that is gold does not glister / Not all who wander are lost

harry wrote:
On Aug 19, 12:46 pm, jim wrote:
With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??

TIA

In hospitals there are often two suppies. (Essential and non-
essential) One is covered by the emegency generator if the power
fails the other is not. This is/was the reason for specially
identified sockets. (The generator often was not big enough to meet
the entire load.)

In days of yore, when RCCDs were first brought out, there was lots of
"niusance tripping", they were susceptable to "glitches" or voltage
spikes running about the system,so it became common practice to have
sockets not protected by RCCDs for critical loads.
RCCDs especially didn't like portable X ray machines I remember.

RCCDs have improved vastly these days. It's far less of a problem.

I have not seen a RCD in a hospital (for ward use) on any work I have done.
The nice outside water feature had one.

--
Adam

On 19/08/2011 15:27, Robin wrote:
Are these still commonly (or ever) fitted with non-standard sockets to
admit only plugs with the "Earth" pin rotated through 90 degrees?

'Walsall gauge', as it was known, had all 3 pins rotated by 90 deg. MK
have their own non-standard version of the BS 1363 plug & socket, which
uses a T-shaped (in cross-section) earth pin, like this
http://www.sparksdirect.co.uk/images/lights/647WHIa.jpg

--
Andy

In article ,
"ARWadsworth" writes:

I have not seen a RCD in a hospital (for ward use) on any work I have done.
The nice outside water feature had one.

Medical equipment usually has really expensive ultra low leakage
isolated power supplies.

I had one once, and the mains side was even all waterproofed,
presumably so if a drip bag springs a leak and pours salt water
all over the ECG machine, there's still no way it can become
live.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

'Walsall gauge', as it was known, had all 3 pins rotated by 90 deg. MK
have their own non-standard version of the BS 1363 plug & socket,
which uses a T-shaped (in cross-section) earth pin, like this
http://www.sparksdirect.co.uk/images/lights/647WHIa.jpg

Thanks. I've also met plugs with a round earth pin as shown by #6 in
http://fam-oud.nl/~plugsocket/British2.html But I can't find a picture
of the ones I recall with just the earth pin rotated so my memory may
have been at fault; apologies for that.

--
Robin
PM may be sent to rbw0{at}hotmail{dot}com

I can not see why anyone would do this in a domestic house unless they
had a very large number of computers. A couple of laptops or a couple
of PCs do not necessitate high integrity earthing. An UPS supplying
outlets is interesting, but generally someone uses a local UPS re USB/
Serial control of shutdown.

Computers leak a small amount to earth by design.
A circuit should be designed so this leakage does not pre-sensitise
any RCD protection, that is to say limit the number of computers per
circuit by separate RCD or individual RCBO. A 30mA trip generally
trips at 22-23-25mA so you do not want to go even half that with the
PCs (think most are 1.5mA, limit being 3.5mA).

High Integrity Earthing is just that.
For a ring the CPC are connected to separate earth terminals in each
socket and back at the CU. For a radial another CPC is run from the
last socket back to the CU, which is tedious, typically 4mm 6491X Gr/
Ye would be used as CPC re sized sufficiently to not need protection.
Having twice as many screws to come loose on a 1.5mm conductor is
interesting, but hey ho :-)

There was a myth locally, but it soon died out when the actual leakage
current was considered and more importantly measured with a clamp
meter. You would need to have a lot of PCs, if it were an issue on a
radial circuit it would be cheaper to fit an RCBO to that circuit or
circuits.

Hospitals use 10mA RCBO in many places, there are separate "zones" re
electrical design as you go from ward to operating theatre... oxygen
is never a nice gas to have around.

On Aug 20, 9:42*am, "ARWadsworth"
wrote:
harry wrote:
On Aug 19, 12:46 pm, jim wrote:
With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his son
is an electrician and that these were sockets providing high supply
security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make an
informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??

TIA

In hospitals there are often two suppies. (Essential and non-
essential) One is covered by the emegency generator *if the power
fails the other is not. *This is/was the reason for specially
identified sockets. *(The generator often was not big enough to meet
the entire load.)

In days of yore, when RCCDs were first brought out, there was lots of
"niusance tripping", they were susceptable to *"glitches" *or voltage
spikes running about the system,so it became common practice to have
sockets not protected by RCCDs for critical loads.
RCCDs *especially didn't like *portable X ray machines I remember.

RCCDs have improved vastly these days. It's far less of a problem.

I have not seen a RCD in a hospital (for ward use) on any work I have done.
The nice outside water feature had one.

--
Adam- Hide quoted text -

- Show quoted text -

Well I worked in them for thirty yers.

Andy Dingley wrote:
I vaguely remember a recommendation for labelling. When I installed my
kiln sockets, following the regs as best I could, I did label them as
not having the same RCD protection as the rest of my workshop.

Ooo, any advice on that? My workshop tenant is a potter and
as part of the rewire I'm planning on putting in a new seperate
circuit for a kiln. He's currently got a little one plugged into
a 13A socket (I think of it as a mini top-loader). My initial
draft design notes have been to treat the new kiln as a type
of high-power electric cooker. I'm slightly stymied in not
knowing the typical power draw of an electric kiln, and
suppliers' websites aren't much help.

JGH

harry wrote:
On Aug 20, 9:42 am, "ARWadsworth"
wrote:
harry wrote:
On Aug 19, 12:46 pm, jim wrote:
With a possible move in mind, missus & I went viewing.

In one house I noted several red double 13A sockets in red.
Previously I've only seen those in hospitals. Owner said that his
son is an electrician and that these were sockets providing high
supply security for computer use.

Presumably the purpose is to prevent or reduce nuisance tripping.

Unfortunately I didn't get a squint at the CU, but can anyone make
an informed guess as to how the circuits are arranged please?

Just guessing - might he have installed class C MCBs to reduce the
chance of tripping??

TIA

In hospitals there are often two suppies. (Essential and non-
essential) One is covered by the emegency generator if the power
fails the other is not. This is/was the reason for specially
identified sockets. (The generator often was not big enough to meet
the entire load.)

In days of yore, when RCCDs were first brought out, there was lots
of "niusance tripping", they were susceptable to "glitches" or
voltage spikes running about the system,so it became common
practice to have sockets not protected by RCCDs for critical loads.
RCCDs especially didn't like portable X ray machines I remember.

RCCDs have improved vastly these days. It's far less of a problem.

I have not seen a RCD in a hospital (for ward use) on any work I
have done. The nice outside water feature had one.

--
Adam- Hide quoted text -

- Show quoted text -

Well I worked in them for thirty yers.

Well so did the cleaner that retired last year.

Now when I rewired St Catherines (Doncaster) Hospital x-ray department 2
years ago there were no RCDs.

Nor were there any RCDs on any of the wards that I worked on where I added
extra sockets.


--
Adam

On Aug 20, 8:01*pm, jgharston wrote:
Andy Dingley wrote:
I vaguely remember a recommendation for labelling. When I installed my
kiln sockets, following the regs as best I could, I did label them as
not having the same RCD protection as the rest of my workshop.

Ooo, any advice on that?

Separate radial, no RCD, round blue sockets, labelled as "No RCD
protection". It also meant I had to go to RCBOs on the rest of the
small shed CU.

My workshop tenant is a potter

This is a glass kiln, possibly a second one later. Ceramics are
usually bigger, slower and more powerful than warm glass. It's 2.4kW,
the bigger one on the future might be up to 5kW (I'd want more bench
space before needing anything bigger).

Glass cycles are more complex than ceramic - they involve a ramp up to
one temperature, short hold, a full power heating to working
temperature, very short hold, crash cool to a lower annealing
temperature and long hold, then a very slow cooling. A working cycle
might take 3-4 hours, but the kiln is running at full power for only a
fraction of this - 15-20 minutes, with about an hour at half-ish power.

On Sat, 20 Aug 2011 10:32:41 -0700 (PDT), harry
wrote:


I have not seen a RCD in a hospital (for ward use) on any work I have done.
The nice outside water feature had one.

--
Adam- Hide quoted text -

- Show quoted text -

Well I worked in them for thirty yers.

Didn't your fingers get all shrivelled up ?

Derek G.

In article ,
lid (Windmill) writes:
harry writes:

RCCDs have improved vastly these days. It's far less of a problem.

I'm still wondering why in the UK (EU?) RCDs trip at around 30 milliamps,
but in Canada and the U.S. their GFIs trip at 5 milliamps.

In the US, GFI's tend to protect just a single (or duplex) outlet,
and sometimes a couple more daisy-chained from it, but typically
just a few appliances max.

In the EU, an RCD tends to protect a whole circuit at a minimum
which is much bigger, and thus many more appliances.

It's the current level that kills; even 30,000 volts of static won't
hurt you, though it may make you jump, so saying that N. America uses
half the voltage we do for domestic supplies is beside the point.

It's a function of the current, and the duration, and the path
through you that kills. 30mA doesn't kill for the length of
time it takes an RCD to trip. Changing to lower value tripping
with multiple appliances generates more nuisance tripping,
without saving any more lives (since no one has died at 30mA
trip as far as I know).

I use a 10mA RCBO for my outside socket circuit, but although
there's more than one socket, there's never been more than
one appliance plugged in in total, either hedge trimmer or
lawn mower. This is probably overkill ;-), but most of the
hedge trimming involves standing on a tall stepladder, so
I'd quite like to go better than not being electrocuted,
and not even fall off the ladder. Having said that, I have
in the past cut through the hedge trimmer flex when it was
on a 30mA RCD (before I had the outside sockets), the current
that tripped the RCD can only have gone through me, but I
didn't feel it.

I have since replaced the hedgetrimmer cord with 3-core flex,
so that if I cut through it again, a connection to earth is
pretty much guaranteed, to ensure the RCD trips quickly. The
earth conductor terminates without connection in the safety
break connector, as the hedge trimmer itself is double
insulated, as are most such outdoor appliances for other
safety reasons.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
Windmill wrote:
I'm still wondering why in the UK (EU?) RCDs trip at around 30 milliamps,
but in Canada and the U.S. their GFIs trip at 5 milliamps.

But how long do these take to trip?

--
*If your feet smell and your nose runs, you're built upside down.

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

On Aug 21, 12:04*pm, "Dave Plowman (News)"
wrote:
In article ,
* *Windmill wrote:
I'm still wondering why in the UK (EU?) RCDs trip at around 30 milliamps,
but in Canada and the U.S. their GFIs trip at 5 milliamps.

But how long do these take to trip?

About 5 minutes given wiring accessory & wiring standards :-))))
Sorry, could not resist.

Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after WWII,
may be a myth but perhaps logical re sweet spot on getting viable
protection and market uptake.

10mA is available, but I think that tends to be used for situations
like swimming pools or hazardous areas etc.

js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after WWII,
may be a myth but perhaps logical re sweet spot on getting viable
protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms was
a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have just
been a load of marketing hype......

--
Tciao for Now!

John.

John Williamson wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after WWII,
may be a myth but perhaps logical re sweet spot on getting viable
protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms
was a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have just
been a load of marketing hype......


30/30?

--
Adam

On 21/08/2011 15:41, js.b1 wrote:
On Aug 21, 12:04 pm, "Dave Plowman
wrote:
In ,
wrote:
I'm still wondering why in the UK (EU?) RCDs trip at around 30 milliamps,
but in Canada and the U.S. their GFIs trip at 5 milliamps.

But how long do these take to trip?

About 5 minutes given wiring accessory& wiring standards :-))))
Sorry, could not resist.

Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after WWII,
may be a myth but perhaps logical re sweet spot on getting viable
protection and market uptake.

10mA is available, but I think that tends to be used for situations
like swimming pools or hazardous areas etc.

and livestock protection... horses etc are more susceptible to injury
than us in certain circumstances.

--
Cheers,

John.

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

On 20/08/2011 17:11, js.b1 wrote:
I can not see why anyone would do this in a domestic house unless they
had a very large number of computers. A couple of laptops or a couple
of PCs do not necessitate high integrity earthing. An UPS supplying
outlets is interesting, but generally someone uses a local UPS re USB/
Serial control of shutdown.

Computers leak a small amount to earth by design.
A circuit should be designed so this leakage does not pre-sensitise
any RCD protection, that is to say limit the number of computers per
circuit by separate RCD or individual RCBO. A 30mA trip generally
trips at 22-23-25mA so you do not want to go even half that with the
PCs (think most are 1.5mA, limit being 3.5mA).

We have three PCs, three mains (not separate PSUs) powered printers and
a whole lot of other stuff. Assuming each has a similar mains filter,
that could be as much as 21mA already - we have suffered the occassional
nuisance trip, so I can see why someone might well have a separate cicrcuit!

SteveW

--- Posted via news://freenews.netfront.net/ - Complaints to ---

ARWadsworth wrote:
John Williamson wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after WWII,
may be a myth but perhaps logical re sweet spot on getting viable
protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms
was a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have just
been a load of marketing hype......


30/30?

Disconnecting after 30 milliseconds at 30 milliamps of current imbalance
between live and neutral cables.

--
Tciao for Now!

John.

On 21/08/2011 23:48, John Williamson wrote:
ARWadsworth wrote:
John Williamson wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after WWII,
may be a myth but perhaps logical re sweet spot on getting viable
protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms
was a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have just
been a load of marketing hype......


30/30?

Disconnecting after 30 milliseconds at 30 milliamps of current imbalance
between live and neutral cables.

30 ms is an unlikely trip time on 50Hz - RCDs will normally trip within
two mains cycles - or 40ms. You might manage 30ms in the US on 60Hz
supplies.


--
Cheers,

John.

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

John Rumm wrote:
On 21/08/2011 23:48, John Williamson wrote:
ARWadsworth wrote:
John Williamson wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after
WWII, may be a myth but perhaps logical re sweet spot on getting
viable protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms
was a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have
just been a load of marketing hype......


30/30?

Disconnecting after 30 milliseconds at 30 milliamps of current
imbalance between live and neutral cables.

30 ms is an unlikely trip time on 50Hz - RCDs will normally trip
within two mains cycles - or 40ms.


A 30mA RCD must trip within 200ms at 30mA. The 40ms trip time must be met at
150mA.

--
Adam

On 22/08/2011 08:38, ARWadsworth wrote:
John wrote:
On 21/08/2011 23:48, John Williamson wrote:
ARWadsworth wrote:
John wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after
WWII, may be a myth but perhaps logical re sweet spot on getting
viable protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms
was a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have
just been a load of marketing hype......


30/30?

Disconnecting after 30 milliseconds at 30 milliamps of current
imbalance between live and neutral cables.

30 ms is an unlikely trip time on 50Hz - RCDs will normally trip
within two mains cycles - or 40ms.


A 30mA RCD must trip within 200ms at 30mA. The 40ms trip time must be met at
150mA.

Indeed. Probably also worth pointing out that in reality many RCDs will
exceed the requirement and trip within one cycle, so real world trips in
20ms are quite common IME. Also a 30mA trip RCD can in fact trip on
as little as 66% of that rating - so 20mA (but not less than 50% IIRC)


--
Cheers,

John.

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

In article ,
John Rumm writes:
On 22/08/2011 08:38, ARWadsworth wrote:
John wrote:
On 21/08/2011 23:48, John Williamson wrote:
ARWadsworth wrote:
John wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after
WWII, may be a myth but perhaps logical re sweet spot on getting
viable protection and market uptake.

I was told when they fisrt came out that 50mA for no more than 50ms
was a survivable shock for approaching 100% of the populace.

30/30 gave anacceptable margin for error. Of course, it may have
just been a load of marketing hype......


30/30?

Disconnecting after 30 milliseconds at 30 milliamps of current
imbalance between live and neutral cables.

30 ms is an unlikely trip time on 50Hz - RCDs will normally trip
within two mains cycles - or 40ms.


A 30mA RCD must trip within 200ms at 30mA. The 40ms trip time must be met at
150mA.

Indeed. Probably also worth pointing out that in reality many RCDs will
exceed the requirement and trip within one cycle, so real world trips in
20ms are quite common IME. Also a 30mA trip RCD can in fact trip on
as little as 66% of that rating - so 20mA (but not less than 50% IIRC)

Don't think I've ever found a working one which takes longer than 20ms
to trip, and at 10ms resolution, I sometimes see a trip time of zero.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:
In article ,
John Rumm writes:
On 22/08/2011 08:38, ARWadsworth wrote:
John wrote:
On 21/08/2011 23:48, John Williamson wrote:
ARWadsworth wrote:
John wrote:
js.b1 wrote:
Thought GFCI were 10mA? Elsewhere 30mA was chosen as the lowest
practical for economic mass production outside of Japan after
WWII, may be a myth but perhaps logical re sweet spot on
getting viable protection and market uptake.

I was told when they fisrt came out that 50mA for no more than
50ms was a survivable shock for approaching 100% of the
populace.

30/30 gave anacceptable margin for error. Of course, it may have
just been a load of marketing hype......


30/30?

Disconnecting after 30 milliseconds at 30 milliamps of current
imbalance between live and neutral cables.

30 ms is an unlikely trip time on 50Hz - RCDs will normally trip
within two mains cycles - or 40ms.


A 30mA RCD must trip within 200ms at 30mA. The 40ms trip time must
be met at 150mA.

Indeed. Probably also worth pointing out that in reality many RCDs
will exceed the requirement and trip within one cycle, so real world
trips in 20ms are quite common IME. Also a 30mA trip RCD can in
fact trip on as little as 66% of that rating - so 20mA (but not less
than 50% IIRC)

Don't think I've ever found a working one which takes longer than 20ms
to trip, and at 10ms resolution, I sometimes see a trip time of zero.

Usually between 20 and 28 ms at 30mA in my experience. 20ms or below for 5x
testing.

My new test case says that ALL RCDs trip at zero:-(

To be fair it also claims that the test probes have a resistance 500Mohm.

--
Adam

On Aug 20, 5:11*pm, "js.b1" wrote:
I can not see why anyone would do this in a domestic house unless they
had a very large number of computers. A couple of laptops or a couple
of PCs do not necessitate high integrity earthing. An UPS supplying
outlets is interesting, but generally someone uses a local UPS re USB/
Serial control of shutdown.

Computers leak a small amount to earth by design.
A circuit should be designed so this leakage does not pre-sensitise
any RCD protection, that is to say limit the number of computers per
circuit by separate RCD or individual RCBO. A 30mA trip generally
trips at 22-23-25mA so you do not want to go even half that with the
PCs (think most are 1.5mA, limit being 3.5mA).

High Integrity Earthing is just that.
For a ring the CPC are connected to separate earth terminals in each
socket and back at the CU. For a radial another CPC is run from the
last socket back to the CU, which is tedious, typically 4mm 6491X Gr/
Ye would be used as CPC re sized sufficiently to not need protection.
Having twice as many screws to come loose on a 1.5mm conductor is
interesting, but hey ho :-)

There was a myth locally, but it soon died out when the actual leakage
current was considered and more importantly measured with a clamp
meter. You would need to have a lot of PCs, if it were an issue on a
radial circuit it would be cheaper to fit an RCBO to that circuit or
circuits.

Hospitals use 10mA RCBO in many places, there are separate "zones" re
electrical design as you go from ward to operating theatre... oxygen
is never a nice gas to have around.

I've never understood how using 2 earth terminals per socket was
supposed to improve anything. If an earth terminal comes undone, with
a single earth terminal you've then got 2 CPCs that are twisted
tgoether, which connects, but with 2 terminals you've lost the cpc
entirely.


NT

In article
,
NT wrote:
I've never understood how using 2 earth terminals per socket was
supposed to improve anything. If an earth terminal comes undone, with
a single earth terminal you've then got 2 CPCs that are twisted
tgoether, which connects, but with 2 terminals you've lost the cpc
entirely.

Think twisting conductors is frowned upon. But not here.

--
*The only difference between a rut and a grave is the depth.

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

In article ,
NT writes:
I've never understood how using 2 earth terminals per socket was
supposed to improve anything. If an earth terminal comes undone, with
a single earth terminal you've then got 2 CPCs that are twisted
tgoether, which connects, but with 2 terminals you've lost the cpc
entirely.

Agree - it seemed slightly silly to me, although people don't twist
today's single core conductors.

I try to put in a ring circuit such that the conductors aren't cut
through at any wiring accessory, so that there's no adding up of
resistances of terminal resistances if they start going high, and
the ring is one long continuous length of cable with the ends joined
at the CU, with just the insulation stripped where required.

I always wire ring circuit earths at the CU according to the old
High Integrity Earthing rules in 16th Ed, where each end goes into
a separate terminal. That does seem sensible.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 23/08/2011 11:49, NT wrote:
On Aug 20, 5:11 pm, wrote:
I can not see why anyone would do this in a domestic house unless they
had a very large number of computers. A couple of laptops or a couple
of PCs do not necessitate high integrity earthing. An UPS supplying
outlets is interesting, but generally someone uses a local UPS re USB/
Serial control of shutdown.

Computers leak a small amount to earth by design.
A circuit should be designed so this leakage does not pre-sensitise
any RCD protection, that is to say limit the number of computers per
circuit by separate RCD or individual RCBO. A 30mA trip generally
trips at 22-23-25mA so you do not want to go even half that with the
PCs (think most are 1.5mA, limit being 3.5mA).

High Integrity Earthing is just that.
For a ring the CPC are connected to separate earth terminals in each
socket and back at the CU. For a radial another CPC is run from the
last socket back to the CU, which is tedious, typically 4mm 6491X Gr/
Ye would be used as CPC re sized sufficiently to not need protection.
Having twice as many screws to come loose on a 1.5mm conductor is
interesting, but hey ho :-)

There was a myth locally, but it soon died out when the actual leakage
current was considered and more importantly measured with a clamp
meter. You would need to have a lot of PCs, if it were an issue on a
radial circuit it would be cheaper to fit an RCBO to that circuit or
circuits.

Hospitals use 10mA RCBO in many places, there are separate "zones" re
electrical design as you go from ward to operating theatre... oxygen
is never a nice gas to have around.

I've never understood how using 2 earth terminals per socket was
supposed to improve anything. If an earth terminal comes undone, with
a single earth terminal you've then got 2 CPCs that are twisted
tgoether, which connects, but with 2 terminals you've lost the cpc
entirely.

Remember with high integrity earthing, the CPC is a ring, even on a
radial circuit. Hence there are two paths to earth - and both
connections would have to fail to lose the earth at the socket. A
complete failure at one socket would not affect the earthing of the others.

(As an aside, the wires should not be twisted).

--
Cheers,

John.

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

In article ,
John Rumm wrote:
(As an aside, the wires should not be twisted).

Is the reason simply they may break - at some point in the future if not
at the time?

--
*Remember: First you pillage, then you burn.

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

Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
(As an aside, the wires should not be twisted).

Is the reason simply they may break - at some point in the future if
not at the time?


It makes fault finding difficult.

--
Adam