I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Yet I suspect one could get a very nasty, possible fatal, shock if 240V
had been applied instead of the 15V. from an old AVO Mk 8.

How is the 30mA. trip current arrived at? Is it the current which will
kill only 50% of the population? In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.

Are there any statistics showing deaths which occurred despite the
presence of an RCD?

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

Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Skin is not an ohmic conductor. It looks somewhat capacitive[1], so the
impedance drops as the frequency goes up. It passes less current at DC than
it does at 50Hz.

Likewise flesh - you can get a lot more current to flow at 500KHz...

Theo

[1] It's actually more complicated than that, there are various cell effects
that kick in as the frequency rises, but the general trend can be thought as
behaving a bit like a capacitor.

On 24/07/14 13:54, Theo Markettos wrote:
Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Skin is not an ohmic conductor. It looks somewhat capacitive[1], so the
impedance drops as the frequency goes up. It passes less current at DC than
it does at 50Hz.

********

Likewise flesh - you can get a lot more current to flow at 500KHz...

its not capacitative. Its almost pure resistive.


Theo

[1] It's actually more complicated than that, there are various cell effects
that kick in as the frequency rises, but the general trend can be thought as
behaving a bit like a capacitor.


so you say.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Thursday, 24 July 2014 14:14:47 UTC+1, Tim Watts wrote:
On 24/07/14 13:31, Windmill wrote:



I ask because holding the probes of an ohmmeter one in each hand, and

with wet palms, I couldn't get the reading down to 8 Kohms, the value

which on 240V would pass 30 mA.

20K was the lowest I could manage by gripping tightly.



Yet I suspect one could get a very nasty, possible fatal, shock if 240V

had been applied instead of the 15V. from an old AVO Mk 8.



How is the 30mA. trip current arrived at? Is it the current which will

kill only 50% of the population? In N. America (admittedly a place

where there used to be far more ambulance chasers) the usual limit is

5mA.

http://rjqelectrical.co.uk/2013/11/rcd-trip-current/


"This RCD trip current level is set at 30mA for household RCD's. The reason why the RCD trip current in your house is 30 mA is because this is taken as the compromise between the maximum level the human body can take without risking death and the nuisance "tripping" that would occur if it was set any lower."




I was told 30mA and 40mS were derived from "work" the german WWII

scientists did by torturing and progressively electrocuting prisoners.



It's data that is distasteful in how it was arrived at but that you

would never really be able to arrive at in any legitimate way.



Not sure if that story is true or not, but "mad scientist tortures

people whilst keeping methodical notes" fits many of the WWII era german

scientists to a tee.

On 24/07/14 14:45, Huge wrote:
On 2014-07-24, Tim Watts wrote:
On 24/07/14 13:31, Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Yet I suspect one could get a very nasty, possible fatal, shock if 240V
had been applied instead of the 15V. from an old AVO Mk 8.

How is the 30mA. trip current arrived at? Is it the current which will
kill only 50% of the population? In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.

I was told 30mA and 40mS were derived from "work" the german WWII
scientists did by torturing and progressively electrocuting prisoners.

It's data that is distasteful in how it was arrived at but that you
would never really be able to arrive at in any legitimate way.

Not sure if that story is true or not, but "mad scientist tortures
people whilst keeping methodical notes" fits many of the WWII era german
scientists to a tee.

Wouldn't surprise me. The tables for survival time in cold water are derived
from work done that way.



And other useful gems like "what happens if you pour boiling water in
the ears of a dwarf?" Yes, really...

The Natural Philosopher wrote:
On 24/07/14 13:54, Theo Markettos wrote:
Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Skin is not an ohmic conductor. It looks somewhat capacitive[1], so the
impedance drops as the frequency goes up. It passes less current at DC than
it does at 50Hz.

********

[citation needed]
https://publications.ki.se/xmlui/bit...pdf?sequence=2
is mine.

Likewise flesh - you can get a lot more current to flow at 500KHz...

its not capacitative. Its almost pure resistive.

So why did I build machines to put 25W into patients at 500KHz then if DC
would do?

Theo

In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in
terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.


[1] if only for size
--
Robin
reply to address is (meant to be) valid

On 24/07/2014 13:31, Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

The flaw in this test is that the meter will only be driving a small DC
voltage across the probes. You would find should you repeat the test
with an insulation resistance test meter rather than an ohm meter, you
will get significantly different (and more painful) results.

Yet I suspect one could get a very nasty, possible fatal, shock if 240V
had been applied instead of the 15V. from an old AVO Mk 8.

Indeed.

How is the 30mA. trip current arrived at? Is it the current which will
kill only 50% of the population? In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.

Have a look at:

http://wiki.diyfaq.org.uk/index.php?...azardCurve.png

Are there any statistics showing deaths which occurred despite the
presence of an RCD?

I have not seen any - and would not expect to see any for this country
in cases where the presence of the RCD is relevant. The reasoning being
that deaths are very rare in the first place, so looking for a much
smaller sub set of the originally very small set is going to be difficult.

Getting stats for those suffering no or reduced injury is also likely to
be hard to isolate, but more doable. You may be able to extract
something from the projected reduction in injuries if there were a
greater uptake of properties fitted with RCDs at the CU.


--
Cheers,

John.

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

On 24/07/2014 13:59, The Natural Philosopher wrote:
On 24/07/14 13:54, Theo Markettos wrote:
Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Skin is not an ohmic conductor. It looks somewhat capacitive[1], so the
impedance drops as the frequency goes up. It passes less current at
DC than
it does at 50Hz.

********

Likewise flesh - you can get a lot more current to flow at 500KHz...

its not capacitative. Its almost pure resistive.

Funny how all those capacitance sensing touch screens still work ok
though...


--
Cheers,

John.

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

On 24/07/14 17:43, Robin wrote:
In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in
terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.


[1] if only for size


5mA vs 30mA is not going to make any difference most of the time. If you
get between L and E you are likely to pull 30mA or more before either
device trips (and get a full on belt while waiting). What's more
important is the device breaks the circuit in 40mS or so to limit the
damage.

In article ,
Robin wrote:
In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in
terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.


[1] if only for size

You can get a single socket with RCD which fits a standard two gang (deep)
box.

--
*Do paediatricians play miniature golf on Wednesdays?

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

On Thursday, July 24, 2014 6:31:54 PM UTC+1, Dave Plowman (News) wrote:
I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.
You can get a single socket with RCD which fits a standard two gang (deep)
box.

Twin socket in a twin gang box
http://www.tlc-direct.co.uk/Products/KBRCD9000.html

Single socket in a single gang box
http://www.tlc-direct.co.uk/Products/SMTFP02WL.html

Of course quite a lot of American 'receptacles' aren't earthed anyway, even if they're 3-pin.

Owain

"Windmill" wrote in message
...

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Yet I suspect one could get a very nasty, possible fatal, shock if 240V
had been applied instead of the 15V. from an old AVO Mk 8.

How is the 30mA. trip current arrived at? Is it the current which will
kill only 50% of the population? In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.

Are there any statistics showing deaths which occurred despite the
presence of an RCD?

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

Most of the resistance of the human body is in the skin because it is oily.
If you wash your hands in detergent, you will see a difference.
10ma through the average heart is considered sufficient to cause fibulation
(stopping the heart)
However if you get an electric shock, the assumption is that only part of
the current goes through the heart (if any)
The current follows the blood vessels. Blood is a good conductor.
220V is only the RMS voltage, (a sort of average) the peak is 320V.

The RCD works by measuring the difference between incoming and outgoing
currents with a current transformer.
In virtually all circumstances, power is cut off before a lethal current can
flow to earth (or through you).
Getting a shock while immersed in water is one exception.

Few people are killed by electric shock these days, usually they get the
shock and fall off a ladder or something.

"whisky-dave" wrote in message
...
On Thursday, 24 July 2014 13:55:20 UTC+1, bert wrote:
In message , Windmill

writes



I ask because holding the probes of an ohmmeter one in each hand, and

with wet palms, I couldn't get the reading down to 8 Kohms, the value

which on 240V would pass 30 mA.

20K was the lowest I could manage by gripping tightly.



Yet I suspect one could get a very nasty, possible fatal, shock if 240V

had been applied instead of the 15V. from an old AVO Mk 8.



How is the 30mA. trip current arrived at? Is it the current which will

kill only 50% of the population? In N. America (admittedly a place

where there used to be far more ambulance chasers) the usual limit is

5mA.



Are there any statistics showing deaths which occurred despite the

presence of an RCD?



I think you are assuming that resistance of the human body is passive.

Women on average have a higher resistance than men which is mostly down to
physical size.
Havign an intresting time trying to find real examples of people that have
electocuted themseleves with low voltage batterise i.e 12V such as a PP3
placed on the tongue. Seems that they are just rumours.



Years ago, the lowest voltage anyone was killed by was 40V.
Pretty exceptional though.

On 24/07/2014 14:45, Huge wrote:
On 2014-07-24, Tim Watts wrote:
On 24/07/14 13:31, Windmill wrote:

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Yet I suspect one could get a very nasty, possible fatal, shock if 240V
had been applied instead of the 15V. from an old AVO Mk 8.

How is the 30mA. trip current arrived at? Is it the current which will
kill only 50% of the population? In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.

I was told 30mA and 40mS were derived from "work" the german WWII
scientists did by torturing and progressively electrocuting prisoners.

It's data that is distasteful in how it was arrived at but that you
would never really be able to arrive at in any legitimate way.

Not sure if that story is true or not, but "mad scientist tortures
people whilst keeping methodical notes" fits many of the WWII era german
scientists to a tee.

Wouldn't surprise me. The tables for survival time in cold water are derived
from work done that way.


There was some work done like that by volunteer American servicemen
which I recall being fairly grim reading.

"Windmill" wrote in message
...

I ask because holding the probes of an ohmmeter one in each hand, and
with wet palms, I couldn't get the reading down to 8 Kohms, the value
which on 240V would pass 30 mA.
20K was the lowest I could manage by gripping tightly.

Yet I suspect one could get a very nasty, possible fatal, shock if 240V
had been applied instead of the 15V. from an old AVO Mk 8.

How is the 30mA. trip current arrived at? Is it the current which will
kill only 50% of the population? In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


What were you holding the probes to?

--
Adam

"Tim Watts" wrote in message
news
On 24/07/14 17:43, Robin wrote:
In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in
terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.


[1] if only for size


5mA vs 30mA is not going to make any difference most of the time. If you
get between L and E you are likely to pull 30mA or more before either
device trips (and get a full on belt while waiting). What's more important
is the device breaks the circuit in 40mS or so to limit the damage.


http://www.select.org.uk/downloads/B...ated%20(2).pdf

Does suggest 20mA is the danger point.

--
Adam

In article ,
whisky-dave writes:
Havign an intresting time trying to find real examples of people that have electocuted themseleves with low voltage batterise i.e 12V such as a PP3 placed on the tongue. Seems that they are just rumours.

Lowest I've heard of was a milkman, who routinely moved his milk
float along one house at a time without getting fully into the cab.
One day, he slipped and ended up under the milk float.
He was in contact with the 48V battery terminals, and unable to free
himself. He was slowly electrocuted, although death was not caused
by heart fibulation, but rather more by electroloysis of body tissue.

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

In article ,
"Robin" writes:
In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in

That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea which I haven't seem here, although it
wouldn't work on a ring circuit).

The other issue is that with 120V mains, lower currents appear
to be fatal and it can be difficult to generate 30mA without
having good body contact, so somewhat counter-intuitively, you
need lower trip current to provide same degree of protection
with 120V.

terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

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

On 24/07/2014 20:35, ARW wrote:
"Tim Watts" wrote in message
news
On 24/07/14 17:43, Robin wrote:
In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in
terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.


[1] if only for size


5mA vs 30mA is not going to make any difference most of the time. If
you get between L and E you are likely to pull 30mA or more before
either device trips (and get a full on belt while waiting). What's
more important is the device breaks the circuit in 40mS or so to
limit the damage.


http://www.select.org.uk/downloads/B...ated%20(2).pdf


Does suggest 20mA is the danger point.

Worth keeping in mind that RCDs don't limit the shock current - only the
duration. So the injury from a 50mA shock will be the same from a 10mA
trip RCD as from a 30mA one.


--
Cheers,

John.

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

On 24/07/2014 19:06, harryagain wrote:

10ma through the average heart is considered sufficient to cause fibulation
(stopping the heart)

What, by sticking a leg bone through it? ;-)



--
Cheers,

John.

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

"Andrew Gabriel" wrote in message
...
In article ,
whisky-dave writes:
Havign an intresting time trying to find real examples of people that
have electocuted themseleves with low voltage batterise i.e 12V such as
a PP3 placed on the tongue. Seems that they are just rumours.

Lowest I've heard of was a milkman, who routinely moved his milk
float along one house at a time without getting fully into the cab.
One day, he slipped and ended up under the milk float.
He was in contact with the 48V battery terminals, and unable to free
himself. He was slowly electrocuted, although death was not caused
by heart fibulation, but rather more by electroloysis of body tissue.


Having a milk float parked on his head may not have helped things. Was he
called Jack? I'll get my coat.

--
Adam

On Thu, 24 Jul 2014 17:46:18 +0100, John Rumm wrote:

Are there any statistics showing deaths which occurred despite the
presence of an RCD?

I have not seen any - and would not expect to see any for this country
in cases where the presence of the RCD is relevant. The reasoning being
that deaths are very rare in the first place, so looking for a much
smaller sub set of the originally very small set is going to be difficult.

Getting stats for those suffering no or reduced injury is also likely to
be hard to isolate, but more doable. You may be able to extract
something from the projected reduction in injuries if there were a
greater uptake of properties fitted with RCDs at the CU.

The other set that isn't recorded, I'll bet, is the injuries sustained when
a minor shock - RCD trips - lights go out - panic, drop tool/fall (off)
scenario happens. That's why I like my split CU where the lighting circuits
are on a 100mA RCD.
--
Peter.
The gods will stay away
whilst religions hold sway

You can get a single socket with RCD which fits a standard two gang
(deep) box.

Twin socket in a twin gang box
http://www.tlc-direct.co.uk/Products/KBRCD9000.html

Single socket in a single gang box
http://www.tlc-direct.co.uk/Products/SMTFP02WL.html

Fair cop. I meant to add soemthing like "without ending up with a
product the general public won't buy". I've never seen one with a low
profile. And I see that the instructions for the 1 gang example warns
you may need to "bend back the upper and lower fixing lugs to enable the
RCD to be fitted".

--
Robin
reply to address is (meant to be) valid

That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea ...

Ooo yes.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

Which begs the question why it is so hard to buy a 10mA plug-in RCD in
the UK (other than off eBay from China perhaps).
--
Robin
reply to address is (meant to be) valid

On 25/07/2014 09:14, PeterC wrote:
On Thu, 24 Jul 2014 17:46:18 +0100, John Rumm wrote:

Are there any statistics showing deaths which occurred despite the
presence of an RCD?

I have not seen any - and would not expect to see any for this country
in cases where the presence of the RCD is relevant. The reasoning being
that deaths are very rare in the first place, so looking for a much
smaller sub set of the originally very small set is going to be difficult.

Getting stats for those suffering no or reduced injury is also likely to
be hard to isolate, but more doable. You may be able to extract
something from the projected reduction in injuries if there were a
greater uptake of properties fitted with RCDs at the CU.

The other set that isn't recorded, I'll bet, is the injuries sustained when
a minor shock - RCD trips - lights go out - panic, drop tool/fall (off)
scenario happens. That's why I like my split CU where the lighting circuits
are on a 100mA RCD.

They may well get recorded as a trip or fall, rather than being
associated with the actual cause.

Generally death rate is a poor metric to use in electrical accident
cases since there are (thankfully) too few to be significant. Injury
rates are far higher - but probably get less rigour of classification.



--
Cheers,

John.

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

On Thursday, July 24, 2014 2:12:39 PM UTC+1, whisky-dave wrote:
On Thursday, 24 July 2014 13:55:20 UTC+1, bert wrote:

In message , Windmill



writes







I ask because holding the probes of an ohmmeter one in each hand, and



with wet palms, I couldn't get the reading down to 8 Kohms, the value



which on 240V would pass 30 mA.



20K was the lowest I could manage by gripping tightly.







Yet I suspect one could get a very nasty, possible fatal, shock if 240V



had been applied instead of the 15V. from an old AVO Mk 8.







How is the 30mA. trip current arrived at? Is it the current which will



kill only 50% of the population? In N. America (admittedly a place



where there used to be far more ambulance chasers) the usual limit is



5mA.







Are there any statistics showing deaths which occurred despite the



presence of an RCD?







I think you are assuming that resistance of the human body is passive.



Women on average have a higher resistance than men which is mostly down to physical size.

Havign an intresting time trying to find real examples of people that have electocuted themseleves with low voltage batterise i.e 12V such as a PP3 placed on the tongue. Seems that they are just rumours.

I hope they are rumours, thats how I test PP3s for charge !
I did wonder if it would affect my taste buds, but I don't do it often these days.
Simon.

"Robin" wrote in message
...
That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea ...

Ooo yes.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

Which begs the question why it is so hard to buy a 10mA plug-in RCD in the
UK (other than off eBay from China perhaps).

Because that is where all that cheap stuff comes from now.

In article ,
"Robin" writes:
That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea ...

Ooo yes.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

Which begs the question why it is so hard to buy a 10mA plug-in RCD in
the UK (other than off eBay from China perhaps).

This one is a 10mA RCBO, which was special order and specially expensive!
(MEM/EATON Memshield2 - they only manufactured the 10mA RCBOs to order.)

But I agree on the lack of availability of 10mA RCDs - they used to
exist.

I've been trying to suggest what portable equipment a volunteer repair
organisation should use for mains distribution, and I would love to
suggest 10mA RCDs for use where equipment is being run with covers off,
but the only one I'm aware of is now EOL (as well as being bulky and
power hungry).

(Isolating transformers are out of the question - the kit has to to be
carried by hand across London and wider afield.)

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

On Thu, 24 Jul 2014 06:50:35 -0700 (PDT), whisky-dave
wrote:

On Thursday, 24 July 2014 14:14:47 UTC+1, Tim Watts wrote:
On 24/07/14 13:31, Windmill wrote:



I ask because holding the probes of an ohmmeter one in each hand, and

with wet palms, I couldn't get the reading down to 8 Kohms, the value

which on 240V would pass 30 mA.

20K was the lowest I could manage by gripping tightly.



Yet I suspect one could get a very nasty, possible fatal, shock if 240V

had been applied instead of the 15V. from an old AVO Mk 8.



How is the 30mA. trip current arrived at? Is it the current which will

kill only 50% of the population? In N. America (admittedly a place

where there used to be far more ambulance chasers) the usual limit is

5mA.

http://rjqelectrical.co.uk/2013/11/rcd-trip-current/


"This RCD trip current level is set at 30mA for household RCD's. The reason why the RCD trip current in your house is 30 mA is because this is taken as the compromise between the maximum level the human body can take without risking death and the nuisance "tripping" that would occur if it was set any lower."


Strangely reminiscent of the reasoning behind the "Five A Day"
dietary advice by HMG and the "Ten A Day" advice offered by the French
Government to their citizens. :-)
--
J B Good

On 2014-07-24, Robin wrote:

In N. America (admittedly a place
where there used to be far more ambulance chasers) the usual limit is
5mA.


IIRC the 5mA RCDs in the US are built into the socket and protect
appliances plugged into that, not a whole circuit. Better I suppose in
terms of overall protection but I suspect rather pricey if all sockets
are protected that way; and I'm not sure how the RCD protection would be
fitted into a back box which takes our no doubt world-beating[1] BS1363
sockets.

IIRC, back boxes in the US are usually 2 inches deep --- luxury.

In article ,
Adam Funk wrote:
IIRC, back boxes in the US are usually 2 inches deep --- luxury.

They need to have plenty room for that fire to get a hold. ;-)

--
*No sentence fragments *

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

On Fri, 25 Jul 2014 09:50:06 +0100, Robin wrote:

That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea ...

Ooo yes.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

Which begs the question why it is so hard to buy a 10mA plug-in RCD in
the UK (other than off eBay from China perhaps).

Does seem strange, as I was told (years ago) that hospitals use 10mA RCDs.
--
Peter.
The gods will stay away
whilst religions hold sway

On 25/07/2014 13:56, Johny B Good wrote:
On Thu, 24 Jul 2014 06:50:35 -0700 (PDT), whisky-dave
wrote:

On Thursday, 24 July 2014 14:14:47 UTC+1, Tim Watts wrote:
On 24/07/14 13:31, Windmill wrote:



I ask because holding the probes of an ohmmeter one in each hand, and

with wet palms, I couldn't get the reading down to 8 Kohms, the value

which on 240V would pass 30 mA.

20K was the lowest I could manage by gripping tightly.



Yet I suspect one could get a very nasty, possible fatal, shock if 240V

had been applied instead of the 15V. from an old AVO Mk 8.



How is the 30mA. trip current arrived at? Is it the current which will

kill only 50% of the population? In N. America (admittedly a place

where there used to be far more ambulance chasers) the usual limit is

5mA.

http://rjqelectrical.co.uk/2013/11/rcd-trip-current/


"This RCD trip current level is set at 30mA for household RCD's. The reason why the RCD trip current in your house is 30 mA is because this is taken as the compromise between the maximum level the human body can take without risking death and the nuisance "tripping" that would occur if it was set any lower."


Strangely reminiscent of the reasoning behind the "Five A Day"
dietary advice by HMG and the "Ten A Day" advice offered by the French
Government to their citizens. :-)

Apparently the 5 a day was as much as they thought it was possible to
get Brits to eat...

--
Dave - The Medway Handyman www.medwayhandyman.co.uk

On 25/07/2014 18:38, PeterC wrote:
On Fri, 25 Jul 2014 09:50:06 +0100, Robin wrote:

That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea ...

Ooo yes.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

Which begs the question why it is so hard to buy a 10mA plug-in RCD in
the UK (other than off eBay from China perhaps).

Does seem strange, as I was told (years ago) that hospitals use 10mA RCDs.

Smaller trip thresholds are often specified for use near livestock,
since larger quadrupeds can be more sensitive to electric shock than us
(wide feet spacing etc)


--
Cheers,

John.

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

/Theo Markettos
The Natural Philosopher wrote:
On 24/07/14 13:54, Theo Markettos wrote:

Snip

Likewise flesh - you can get a lot more current to flow at 500KHz...

its not capacitative. Its almost pure resistive.

So why did I build machines to put 25W into patients at 500KHz then if DC
would do?

Theo /q

Bless him it's not been the kindest of weeks gaffe-wise, must be the heat?

Jim K

"PeterC" wrote in message
...
On Fri, 25 Jul 2014 09:50:06 +0100, Robin wrote:

That's partly true, but some US sockets do have a daisy-chaining
terminal for connecting more sockets to the RCD protected side
(a stunningly good idea ...

Ooo yes.

For my outdoor socket circuit, which is only used for the lawn
mower and hedge cutter (at top of tall ladder), I have that on
a 10mA RCD protected TT circuit. With only one appliance in use
at a time, mutiple leakage isn't an issue, and I prefer the idea
of 10mA protection when I'm hanging off the top of a ladder with
the hedge cutter.

Which begs the question why it is so hard to buy a 10mA plug-in RCD in
the UK (other than off eBay from China perhaps).

Does seem strange, as I was told (years ago) that hospitals use 10mA RCDs.


Some of the special equipment might use 10mA. But they pay a fortune for
whatever work they need doing.

--
Adam

On 2014-07-25, Dave Plowman (News) wrote:

In article ,
Adam Funk wrote:
IIRC, back boxes in the US are usually 2 inches deep --- luxury.

They need to have plenty room for that fire to get a hold. ;-)

Ha ha. It does give you a nice amount of room to fit the wire
nuts^W^W^W^W work in, instead of squashing all the wires into a 20 mm
(or whatever, ISTR there was a dispute about the actual depth) here.

On 2014-07-25, The Medway Handyman wrote:

On 25/07/2014 13:56, Johny B Good wrote:

Strangely reminiscent of the reasoning behind the "Five A Day"
dietary advice by HMG and the "Ten A Day" advice offered by the French
Government to their citizens. :-)

Apparently the 5 a day was as much as they thought it was possible to
get Brits to eat...

Does that mean if you eat more fruit & veg, you can drink more
alcohol? ;-)

On Friday, July 25, 2014 9:57:19 PM UTC+1, Adam Funk wrote:
Does that mean if you eat more fruit & veg, you can drink more
alcohol? ;-)

Most alcohol is a fruit or cereal product :-)

Owain