is third transformer hole an earth?

[Peter Hucker]

On Sun, 09 Nov 2008 22:40:33 -0000, Arfa Daily <arfa.daily@ntlworld.com> wrote:

"Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message
news:4ffba77383dave@davenoise.co.uk...
In article <v6FRk.32439$mr4.6073@newsfe19.ams2>,
Arfa Daily <arfa.daily@ntlworld.com> wrote:
Ringmain circuits in the UK are nominally rated at 30A, but have
*outlets* on them rated to 13A. Bit of a 'picky' point, I know, but
might be a bit misleading to non uk posters, the way you had put it.

Being even more picky they're actually rated at 32 amps.


Well, the cable itself may be rated to 32 amps,

There is no such thing as 32A cable. It depends on where you run it and at what ambient temperature.

and the breaker may be
either 32 amps or 30 amps in an older installation, but never-the-less, this
type of installation has always been known generically as a '30 amp ring
main circuit' and is generally accepted as being safely rated to 30 amps to
include all ages of installation.

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

I'm not so think as you drunk I am...

 

[Peter Hucker]

On Mon, 10 Nov 2008 00:26:24 -0000, Dave Plowman (News) <dave@davenoise.co.uk> wrote:

In article <EFJRk.52823$vm.21202@newsfe08.ams2>,
Arfa Daily <arfa.daily@ntlworld.com> wrote:
Well, the cable itself may be rated to 32 amps, and the breaker may be
either 32 amps or 30 amps in an older installation, but never-the-less,
this type of installation has always been known generically as a '30
amp ring main circuit' and is generally accepted as being safely rated
to 30 amps to include all ages of installation.

Dates from the days of rewirable fuses were it was a nice round figure.
But with those you could comfortably exceed 30 amps if the load was
imposed gently.

Some fuses are really rubbish. I know of someone who ran a kettle for 3 weeks (under normal everyday use) on a 5A fuse before it blew. The kettle element was consuming its rated 10 amps.

MCBs react rather quicker so it's now 32 amps.

It's actually quite tricky to work out the loading in various parts of the
ring since there are so many variables - the lengths and how it is run,
ventilation wise. As well as where the load is actually taken. It's
basically a bit of a bodge - but a very satisfactory one for today's
lifestyle despite being some 60 years old in conception.

60? I thought 60 years ago we had the 5A and 15A star topology?

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

While taxiing at London's Gatwick Airport, the crew of a U.S. Air flight departing for Ft. Lauderdale made a wrong turn and came nose to nose with a United 727.
An irate female ground controller lashed out at the U.S. Air crew, screaming:
"U.S. Air 2771, where the hell are you going? I told you to turn right onto Charlie taxiway! You turned right on Delta!
Stop right there. I know it's difficult for you to tell the difference between C and D, but get it right!"
Continuing her rage to the embarrassed crew, she was now shouting hysterically:
"god! Now you've screwed everything up! It'll take forever to sort this out! You stay right there and don't move till I tell you to!
You can expect progressive taxi instructions in about half an hour and I want you to go exactly where I tell you, when I tell you, and how I tell you! You got that, U.S. Air 2771?"
"Yes, ma'am," the humbled crew responded.
Naturally, the ground control communications frequency fell terribly silent after the verbal bashing of U.S. Air 2771.
Nobody wanted to chance engaging the irate ground controller in her current state of mind. Tension in every cockpit around Gatwick was definitely running high.
Just then an unknown pilot broke the silence and keyed his microphone, asking: "Wasn't I married to you once?"

 

[Meat Plow]

On Sun, 9 Nov 2008 22:40:33 -0000, "Arfa Daily"
<arfa.daily@ntlworld.com>wrote:

"Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message
news:4ffba77383dave@davenoise.co.uk...
In article <v6FRk.32439$mr4.6073@newsfe19.ams2>,
Arfa Daily <arfa.daily@ntlworld.com> wrote:
Ringmain circuits in the UK are nominally rated at 30A, but have
*outlets* on them rated to 13A. Bit of a 'picky' point, I know, but
might be a bit misleading to non uk posters, the way you had put it.

Being even more picky they're actually rated at 32 amps.


Well, the cable itself may be rated to 32 amps, and the breaker may be
either 32 amps or 30 amps in an older installation, but never-the-less, this
type of installation has always been known generically as a '30 amp ring
main circuit' and is generally accepted as being safely rated to 30 amps to
include all ages of installation.

See

http://www.diydata.com/planning/ring_main/ring_main.php

http://www.diyfixit.co.uk/diy/electrics/power_circuit/power_circuit_1.html

Arfa

I always thought they were 31.07 amp ringmains.

 

[ian field]

"Peter Hucker" <none@spam.com> wrote in message
newsp.uke2s5z24buhsv@fx62.mshome.net...

On Mon, 10 Nov 2008 00:26:24 -0000, Dave Plowman (News)
dave@davenoise.co.uk> wrote:

In article <EFJRk.52823$vm.21202@newsfe08.ams2>,
Arfa Daily <arfa.daily@ntlworld.com> wrote:
Well, the cable itself may be rated to 32 amps, and the breaker may be
either 32 amps or 30 amps in an older installation, but never-the-less,
this type of installation has always been known generically as a '30
amp ring main circuit' and is generally accepted as being safely rated
to 30 amps to include all ages of installation.

Dates from the days of rewirable fuses were it was a nice round figure.
But with those you could comfortably exceed 30 amps if the load was
imposed gently.

Some fuses are really rubbish. I know of someone who ran a kettle for 3
weeks (under normal everyday use) on a 5A fuse before it blew. The kettle
element was consuming its rated 10 amps.

Some peoples knowledge is really rubbish.

There are defined tables and graphs which accurately describe fusing
capacity of fuses, it is known that a 5A fuse will carry 10A - but not for
very long! If the kettle boils before the fuse wire works up to its melting
temperature then the fuse wire cools again before it blows so you get away
with it another day, but each time the fuse is used above its rated current
it degrades a little and sooner or later will fail within the time it takes
the kettle to boil.

Actually a 5A fuse carrying exactly 5A has a finite fife expectancy - which
actually isn't all that long, unfortunately I can't find the graphs to look
up the exact life expectancy.

 

[Whiskers]

On 2008-11-10, Peter Hucker <none@spam.com> wrote:

On Sat, 08 Nov 2008 22:16:47 -0000, Whiskers <catwheezel@operamail.com> wrote:
On 2008-11-08, catchme <someone@somewhere.net> wrote:
john downie2 wrote:

[...]

Japan's mains apparently runs at 100V, 50 or 60 Hz, and the plugs and
sockets are only superficially similar to those used in the US. They seem
to be rated at 10 12 or 15 Amps. (60 Amps would be pretty nasty if things
went a little awry, even if a 6 KW fire might be useful).

Our UK ring mains are 6kW too, why are you surprised?

[...]

Our power sockets are only 3kW each - but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful with.
60 Amps at a Japanese 100V would be a lot more dangerous than 30 Amps at a
European 230V. (Although either could kill you, so the difference could
be academic as far as the one grasping the wires is concerned).

Notice that fuses and cut-outs are rated in Amps, and that "non-lethal"
stunners for the cops are rated at tens of thousands of volts. In the
right (or wrong!) circumstances, the current that will make a torch bulb
glow can be enough to stop the human heart.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~

 

[Dave Plowman (News)]

In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:

Our power sockets are only 3kW each - but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful
with. 60 Amps at a Japanese 100V would be a lot more dangerous than 30
Amps at a European 230V. (Although either could kill you, so the
difference could be academic as far as the one grasping the wires is
concerned).

Not quite sure what you mean. The current drawn by a given resistance is
proportional to the voltage - and touching a 1000 amp supply is no more
dangerous to a human than touching a 1 amp one.

And since the body resistance would be a constant 230 volts would cause
more current to flow than 100 - so more likely to kill. Indeed in the UK
110 volts is used on building sites for safety reasons. This is obtained
usually via an isolating transformer so there is no potential to ground.

--
*Hang in there, retirement is only thirty years away! *

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

 

[Paul Hovnanian P.E.]

Peter Hucker wrote:

On Sun, 09 Nov 2008 16:51:43 -0000, lars <lars@testbox.tld> wrote:

Peter Hucker:

Power bricks are plastic and don't need to be earthed for safety reasons.
His question, which nobody has answered yet,
is whether the supply NEEDS an earth to operate correctly.

The answer is no.

Then I wonder what it's connected to? The plastic chassis? What good does that do?

Internal surge supression/EMC circuitry.

--
Paul Hovnanian mailtoaul@Hovnanian.com
------------------------------------------------------------------
Just say 'No' to Windows.
-- Department of Defenestration.

 

[Whiskers]

On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:

In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:
Our power sockets are only 3kW each - but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful
with. 60 Amps at a Japanese 100V would be a lot more dangerous than 30
Amps at a European 230V. (Although either could kill you, so the
difference could be academic as far as the one grasping the wires is
concerned).

Not quite sure what you mean. The current drawn by a given resistance is
proportional to the voltage - and touching a 1000 amp supply is no more
dangerous to a human than touching a 1 amp one.

Well you go right ahead and play with the 1000 Amp wires if you want to,
but wait for me to get out of sight and earshot first - I'm a bit
squeamish.

And since the body resistance would be a constant

It isn't. There's a threshold at around 50V at which the body's internal
resistance drops considerably; after that, the resistance will depend on
the path taken through and/or over the body and the amount of tissue
damage caused - those things being dependent on the energy (ie Amps)
available rather than on the voltage. AC and DC current also have
different effects.

230 volts would cause
more current to flow than 100 - so more likely to kill.

Think of water pipes. A narrow pipe can be likened to a low current cable
(few Amps) and a wide pipe is like a cable carrying a large current (many
Amps). Both can be at the same pressure (Voltage) but one will cause a lot
more damage when it bursts than the other. Even if the wide pipe is at a
lower pressure, it can still deliver a lot more water than the narrow
pipe; likewise, even at a lower voltage a cable carrying a lot of current
will deliver a lot more energy than one with less capacity but at a higer
voltage.

Indeed in the UK
110 volts is used on building sites for safety reasons. This is obtained
usually via an isolating transformer so there is no potential to ground.

I don't know what the regulations are for temporary electrical
installations on construction sites in the UK, but I suspect they aren't
much different from those relating to permanent installations. The use of
110V equipment may have more to do with avoiding such stringent inspection
and installation standards as apply to higher voltages - but the safety
measures in use will be related to the current available, not the voltage.

If there is "no potential to ground" then the system will only be safe
with "double-insulated" appliances.

To deliver a given amount of power, a low voltage supply has to carry more
current (more Amps) than a higher voltage supply, so in that respect it
can be more dangerous.

Once the current is flowing, what matters is the amount of energy (Amps)
not the 'pressure' (Volts) - and where the energy flows. A few milliamps
will stop the heart, if that current flows along a path that disrupts the
tiny nerve signals involved.

Walking across a synthetic carpet can generate a charge of thousands of
Volts - enough to create a spark when you get near another person or a
metal fixture or piece of furniture. But there is very little energy
involved.

See <http://www.pa.msu.edu/sciencet/ask_st/010892.html>.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~

 

[Arfa Daily]

"Whiskers" <catwheezel@operamail.com> wrote in message
news:slrnghja8j.e5j.catwheezel@ID-107770.user.individual.net...

On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:
In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:
Our power sockets are only 3kW each - but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful
with. 60 Amps at a Japanese 100V would be a lot more dangerous than 30
Amps at a European 230V. (Although either could kill you, so the
difference could be academic as far as the one grasping the wires is
concerned).

Not quite sure what you mean. The current drawn by a given resistance is
proportional to the voltage - and touching a 1000 amp supply is no more
dangerous to a human than touching a 1 amp one.

Well you go right ahead and play with the 1000 Amp wires if you want to,
but wait for me to get out of sight and earshot first - I'm a bit
squeamish.

And since the body resistance would be a constant

It isn't. There's a threshold at around 50V at which the body's internal
resistance drops considerably; after that, the resistance will depend on
the path taken through and/or over the body and the amount of tissue
damage caused - those things being dependent on the energy (ie Amps)
available rather than on the voltage. AC and DC current also have
different effects.

230 volts would cause
more current to flow than 100 - so more likely to kill.

Think of water pipes. A narrow pipe can be likened to a low current cable
(few Amps) and a wide pipe is like a cable carrying a large current (many
Amps). Both can be at the same pressure (Voltage) but one will cause a
lot
more damage when it bursts than the other. Even if the wide pipe is at a
lower pressure, it can still deliver a lot more water than the narrow
pipe; likewise, even at a lower voltage a cable carrying a lot of current
will deliver a lot more energy than one with less capacity but at a higer
voltage.

Indeed in the UK
110 volts is used on building sites for safety reasons. This is obtained
usually via an isolating transformer so there is no potential to ground.

I don't know what the regulations are for temporary electrical
installations on construction sites in the UK, but I suspect they aren't
much different from those relating to permanent installations. The use of
110V equipment may have more to do with avoiding such stringent inspection
and installation standards as apply to higher voltages - but the safety
measures in use will be related to the current available, not the voltage.

If there is "no potential to ground" then the system will only be safe
with "double-insulated" appliances.

To deliver a given amount of power, a low voltage supply has to carry more
current (more Amps) than a higher voltage supply, so in that respect it
can be more dangerous.

Once the current is flowing, what matters is the amount of energy (Amps)
not the 'pressure' (Volts) - and where the energy flows. A few milliamps
will stop the heart, if that current flows along a path that disrupts the
tiny nerve signals involved.

Walking across a synthetic carpet can generate a charge of thousands of
Volts - enough to create a spark when you get near another person or a
metal fixture or piece of furniture. But there is very little energy
involved.

See <http://www.pa.msu.edu/sciencet/ask_st/010892.html>.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~

I've got to agree with Dave on this one. Much of what you say appears to be
based on an incorrect understanding of Ohms Law, and how it applies to the
potential for causing electrocution of the human body. The water and pipes
analogy is good for some simple college explanations involving DC systems
with fixed parameters, but its validity for explaining complex dynamic
systems, is tenuous at best.

A system carrying a lot of amps to the load that's drawing it, is no more or
less dangerous than one that's only carrying a small current, except in as
much as there is a greater potential for heat failure at connection points
within that system. A high voltage system, irrespective of how many amps it
is capable of carrying above a few milliamps, is far more dangerous to a
human, than a low voltage system good for a few hundred amps. Given the
(reasonably) constant resistance of any described path through the human
body, a voltage of a hundred volts with a current availability of as little
as 50mA, may be enough to kill under the right (wrong!) circumstances. On
the other hand, a low voltage welding supply, will not have enough voltage
behind it to push enough current through that same path to kill you, even
though that supply is good for 200 amps or more.

As far as your contention that a transformer isolated supply is only safe
with double insulated equipment, that simply isn't true. The only way that
you can drive current through the body from such an isolation transformer,
is to hang yourself across both output terminals. Either terminal to ground
will present no electric shock hazard at all.

Arfa

 

[Peter Hucker]

On Mon, 10 Nov 2008 21:48:40 -0000, Whiskers <catwheezel@operamail.com> wrote:

On 2008-11-10, Peter Hucker <none@spam.com> wrote:
On Sat, 08 Nov 2008 22:16:47 -0000, Whiskers <catwheezel@operamail.com> wrote:
On 2008-11-08, catchme <someone@somewhere.net> wrote:
john downie2 wrote:

[...]

Japan's mains apparently runs at 100V, 50 or 60 Hz, and the plugs and
sockets are only superficially similar to those used in the US. They seem
to be rated at 10 12 or 15 Amps. (60 Amps would be pretty nasty if things
went a little awry, even if a 6 KW fire might be useful).

Our UK ring mains are 6kW too, why are you surprised?

[...]

Our power sockets are only 3kW each

I know, but the reference was to Japanese RINGS.

- but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful with.

It's both. 1 billion amps at 0.5 volts definitely won't do you any harm - mainly because you have too much resistance to conduct 1 billion amps without a much bigger voltage. I'd actually go for the watts being the best measure of danger (but you have to take into account how many watts you will dissipate, not how many are available). I can draw 5kW off a decent car battery into an invertor to power mains appliances, but if I touch the two terminals, I feel nothing, and I certainly don't dissiapte 5kW!

60 Amps at a Japanese 100V would be a lot more dangerous than 30 Amps at a
European 230V. (Although either could kill you, so the difference could
be academic as far as the one grasping the wires is concerned).

Notice that fuses and cut-outs are rated in Amps,

They are mainly to stop a fire from a short. The safety circuit breaker is the earth leakage one.

and that "non-lethal"
stunners for the cops are rated at tens of thousands of volts. In the
right (or wrong!) circumstances, the current that will make a torch bulb
glow can be enough to stop the human heart.

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

PNEUMONOULTRAMICROSCOPICSILICOVOLCANOCONIOSIS (45 letters, a lung disease caused by breathing in particles of siliceous volcanic dust) is the longest word in the English language, beating TETRAMETHYLDIAMINOBENZHYDRYLPHOSPHINOUS ACID, HEPATICOCHOLANGIOCHOLECYSTENTEROSTOMIES, FORMALDEHYDETETRAMETHYLAMIDOFLUORIMUM, and DIMETHYLAMIDOPHENYLDIMETHYLPYRAZOLONE.

 

[Peter Hucker]

On Tue, 11 Nov 2008 02:46:18 -0000, Paul Hovnanian P.E. <paul@hovnanian.com> wrote:

Peter Hucker wrote:

On Sun, 09 Nov 2008 16:51:43 -0000, lars <lars@testbox.tld> wrote:

Peter Hucker:

Power bricks are plastic and don't need to be earthed for safety reasons.
His question, which nobody has answered yet,
is whether the supply NEEDS an earth to operate correctly.

The answer is no.

Then I wonder what it's connected to? The plastic chassis? What good does that do?

Internal surge supression/EMC circuitry.

Ah, required to pass the tests to be able to sell it, but of no concern to the end user.

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

A woman goes into a sporting goods store to buy a shotgun.
"It's for my husband," she tells the clerk.
"Did he tell you what gauge to get?" asked the clerk.
"Are you kidding?" she says. "He doesn't even know that I'm going to shoot him!"

 

[Whiskers]

On 2008-11-11, Arfa Daily <arfa.daily@ntlworld.com> wrote:

"Whiskers" <catwheezel@operamail.com> wrote in message
news:slrnghja8j.e5j.catwheezel@ID-107770.user.individual.net...
On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:
In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:

[...]

A system carrying a lot of amps to the load that's drawing it, is no more or
less dangerous than one that's only carrying a small current, except in as
much as there is a greater potential for heat failure at connection points
within that system. A high voltage system, irrespective of how many amps it
is capable of carrying above a few milliamps, is far more dangerous to a
human, than a low voltage system good for a few hundred amps. Given the
(reasonably) constant resistance of any described path through the human
body, a voltage of a hundred volts with a current availability of as little
as 50mA, may be enough to kill under the right (wrong!) circumstances.

So a charge of 10kV from walking across a carpet (DC) , or a "non-lethal"
50kV "Tazer" (AC), are more dangerous than a 1kV power line? The danger
from 'High Voltage' power lines comes from the vast amount of current they
can deliver.

On
the other hand, a low voltage welding supply, will not have enough voltage
behind it to push enough current through that same path to kill you, even
though that supply is good for 200 amps or more.

What voltage does a 'low voltage' welder operate at? Don't they use
capacitors to raise the supply voltage to at least 40kV? Or can welding
really happen at 12V?

As far as your contention that a transformer isolated supply is only safe
with double insulated equipment, that simply isn't true. The only way that
you can drive current through the body from such an isolation transformer,
is to hang yourself across both output terminals. Either terminal to ground
will present no electric shock hazard at all.

Arfa

Sounds too good to be true.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~

 

[Dave Plowman (News)]

In article <slrnghja8j.e5j.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:

On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:
In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:
Our power sockets are only 3kW each - but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful
with. 60 Amps at a Japanese 100V would be a lot more dangerous than 30
Amps at a European 230V. (Although either could kill you, so the
difference could be academic as far as the one grasping the wires is
concerned).

Not quite sure what you mean. The current drawn by a given resistance
is proportional to the voltage - and touching a 1000 amp supply is no
more dangerous to a human than touching a 1 amp one.

Well you go right ahead and play with the 1000 Amp wires if you want to,
but wait for me to get out of sight and earshot first - I'm a bit
squeamish.

Err, your car has one totally uninsulated conductor carrying many hundreds
of amps when you start it. Perhaps you need to avoid driving...

And since the body resistance would be a constant

It isn't. There's a threshold at around 50V at which the body's
internal resistance drops considerably;

Can you give a reference for this?

after that, the resistance will
depend on the path taken through and/or over the body and the amount of
tissue damage caused - those things being dependent on the energy (ie
Amps) available rather than on the voltage.

It only takes milliamps to kill you under the right conditions. That's why
RCDs are set as they are.

AC and DC current also have different effects.

Not many homes have high voltage DC supplies.

230 volts would cause more current to flow than 100 - so more likely
to kill.

Think of water pipes. A narrow pipe can be likened to a low current
cable (few Amps) and a wide pipe is like a cable carrying a large
current (many Amps). Both can be at the same pressure (Voltage) but
one will cause a lot more damage when it bursts than the other.

Electricity doesn't spill out when a cable breaks. ;-)

Even if the wide pipe is at a lower pressure, it can still deliver a lot
more water than the narrow pipe; likewise, even at a lower voltage a
cable carrying a lot of current will deliver a lot more energy than one
with less capacity but at a higer voltage.

All of which is irrelevant when considering potentially lethal current.

Indeed in the UK
110 volts is used on building sites for safety reasons. This is obtained
usually via an isolating transformer so there is no potential to ground.

I don't know what the regulations are for temporary electrical
installations on construction sites in the UK, but I suspect they aren't
much different from those relating to permanent installations.

They are very different.

The use of 110V equipment may have more to do with avoiding such
stringent inspection and installation standards as apply to higher
voltages - but the safety measures in use will be related to the current
available, not the voltage.

You're talking nonsense.

If there is "no potential to ground" then the system will only be safe
with "double-insulated" appliances.

More nonsense.

To deliver a given amount of power, a low voltage supply has to carry
more current (more Amps) than a higher voltage supply, so in that
respect it can be more dangerous.

Only in terms of a fire risk.

Once the current is flowing, what matters is the amount of energy (Amps)
not the 'pressure' (Volts) - and where the energy flows. A few
milliamps will stop the heart, if that current flows along a path that
disrupts the tiny nerve signals involved.

And you can't have that current flow without the voltage.

Walking across a synthetic carpet can generate a charge of thousands of
Volts - enough to create a spark when you get near another person or a
metal fixture or piece of furniture. But there is very little energy
involved.

You seem to be technical terms around without understanding their meaning.

See <http://www.pa.msu.edu/sciencet/ask_st/010892.html>.

Have you actually read it?

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

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

 

[Whiskers]

On 2008-11-11, Peter Hucker <none@spam.com> wrote:

On Mon, 10 Nov 2008 21:48:40 -0000, Whiskers <catwheezel@operamail.com> wrote:

On 2008-11-10, Peter Hucker <none@spam.com> wrote:
On Sat, 08 Nov 2008 22:16:47 -0000, Whiskers <catwheezel@operamail.com> wrote:
On 2008-11-08, catchme <someone@somewhere.net> wrote:
john downie2 wrote:

[...]

- but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful with.

It's both. 1 billion amps at 0.5 volts definitely won't do you any harm
- mainly because you have too much resistance to conduct 1 billion amps
without a much bigger voltage. I'd actually go for the watts being the
best measure of danger (but you have to take into account how many watts
you will dissipate, not how many are available). I can draw 5kW off a
decent car battery into an invertor to power mains appliances, but if I
touch the two terminals, I feel nothing, and I certainly don't dissiapte
5kW!

[...]

You can touch the 12V battery terminals reasonably safely, but don't try
it with the 240V terminals. That voltage is well in excess of the body's
50V limit for being a non-conductor, and the battery can deliver plenty of
Amps to be lethal. It isn't the 240V that kill, it's the 21A.

Turning fresh meat into smoke and ash can dissipate a great many Watts.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~

 

[Peter Hucker]

On Tue, 11 Nov 2008 18:32:56 -0000, Whiskers <catwheezel@operamail.com> wrote:

On 2008-11-11, Peter Hucker <none@spam.com> wrote:
On Mon, 10 Nov 2008 21:48:40 -0000, Whiskers <catwheezel@operamail.com> wrote:

On 2008-11-10, Peter Hucker <none@spam.com> wrote:
On Sat, 08 Nov 2008 22:16:47 -0000, Whiskers <catwheezel@operamail.com> wrote:
On 2008-11-08, catchme <someone@somewhere.net> wrote:
john downie2 wrote:

[...]

- but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful with.

It's both. 1 billion amps at 0.5 volts definitely won't do you any harm
- mainly because you have too much resistance to conduct 1 billion amps
without a much bigger voltage. I'd actually go for the watts being the
best measure of danger (but you have to take into account how many watts
you will dissipate, not how many are available). I can draw 5kW off a
decent car battery into an invertor to power mains appliances, but if I
touch the two terminals, I feel nothing, and I certainly don't dissiapte
5kW!

[...]

You can touch the 12V battery terminals reasonably safely, but don't try
it with the 240V terminals. That voltage is well in excess of the body's
50V limit for being a non-conductor, and the battery can deliver plenty of
Amps to be lethal. It isn't the 240V that kill, it's the 21A.

Turning fresh meat into smoke and ash can dissipate a great many Watts.

But if we compare 110 volts and 240 volts, 240 volts will dissipate far more power in you. Both supplies have enough amps to give your body what it will conduct.

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

Women, you're in good shape as long as you can still touch your toes.
Just remember, using your boobs doesn't count.

 

[Peter Hucker]

On Mon, 10 Nov 2008 23:45:06 -0000, Dave Plowman (News) <dave@davenoise.co.uk> wrote:

In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:
Our power sockets are only 3kW each - but it isn't the Watts that really
hurt, or even the Volts; it's the Amps you really need to be careful
with. 60 Amps at a Japanese 100V would be a lot more dangerous than 30
Amps at a European 230V. (Although either could kill you, so the
difference could be academic as far as the one grasping the wires is
concerned).

Not quite sure what you mean. The current drawn by a given resistance is
proportional to the voltage - and touching a 1000 amp supply is no more
dangerous to a human than touching a 1 amp one.

And since the body resistance would be a constant 230 volts would cause
more current to flow than 100 - so more likely to kill. Indeed in the UK
110 volts is used on building sites for safety reasons. This is obtained
usually via an isolating transformer so there is no potential to ground.

Makes you wonder why they have neutral in households as ground potential..

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

_
/ /\
/ /\ \
/ /||\ \
/ / || \ \
/ / || \ \
/ / || \ \
/ / |_ \ \
/ / /\ \ \ \
/ / / /\ \ \ \
/ / / /||\ \ \ \
/ / / / || \ \ \ \
/ / / / || \ \ \ \
/ / / / _| \ \ \ \
/ / / / / /\ \ \ \ \
/ / / / / /\ \ \ \ \ \
/ / / / / /||\ \ \ \ \ \
/ / / / / / |_ \ \ \ \ \ \
/_/ /_/ /_/ /\_\ \_\ \_\ \_\
\ \ \ \ \ \ \/_/ / / / / / /
\ \ \ \ \ \ || / / / / / /
\ \ \ \ \ \||/ / / / / /
\ \ \ \ \ \/ / / / / /
\ \ \ \ \_\/ / / / /
\ \ \ \ || / / / /
\ \ \ \ || / / / /
\ \ \ \ || / / / /
\ \ \ \||/ / / /
\ \ \ \/ / / /
\ \ \/_/ / /
\ \ || / /
\ \ || / /
\ \ || / /
\ \ || / /
\ \||/ /
\ \/ /
\_\/
||
_..--=='||'==--.._
( '' )
'==--..______..--=='

 

[Peter Hucker]

On Tue, 11 Nov 2008 18:22:40 -0000, Whiskers <catwheezel@operamail.com> wrote:

On 2008-11-11, Arfa Daily <arfa.daily@ntlworld.com> wrote:

"Whiskers" <catwheezel@operamail.com> wrote in message
news:slrnghja8j.e5j.catwheezel@ID-107770.user.individual.net...
On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:
In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:

[...]

A system carrying a lot of amps to the load that's drawing it, is no more or
less dangerous than one that's only carrying a small current, except in as
much as there is a greater potential for heat failure at connection points
within that system. A high voltage system, irrespective of how many amps it
is capable of carrying above a few milliamps, is far more dangerous to a
human, than a low voltage system good for a few hundred amps. Given the
(reasonably) constant resistance of any described path through the human
body, a voltage of a hundred volts with a current availability of as little
as 50mA, may be enough to kill under the right (wrong!) circumstances.

So a charge of 10kV from walking across a carpet (DC) , or a "non-lethal"
50kV "Tazer" (AC), are more dangerous than a 1kV power line? The danger
from 'High Voltage' power lines comes from the vast amount of current they
can deliver.

A tazer limits the current to a lot less than your body could conduct at that voltage. A 110 volt power line and a 1000 volt power line both have more currrent than your body will draw, so the limit is your resistance. And 1000 volts will give you more current for the same resistance.

On
the other hand, a low voltage welding supply, will not have enough voltage
behind it to push enough current through that same path to kill you, even
though that supply is good for 200 amps or more.

What voltage does a 'low voltage' welder operate at? Don't they use
capacitors to raise the supply voltage to at least 40kV? Or can welding
really happen at 12V?

I think it's a pretty low voltage, hence the very thick cables! From memory it's something like 12 volts at 500 amps. And no it's not dangerous to touch, from an electrical point of view - the heating when welding is in progress might be a tad sore though.

As far as your contention that a transformer isolated supply is only safe
with double insulated equipment, that simply isn't true. The only way that
you can drive current through the body from such an isolation transformer,
is to hang yourself across both output terminals. Either terminal to ground
will present no electric shock hazard at all.

Sounds too good to be true.

Why?

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

What's the difference between a church and a cinema?
In a church they say "Pray in the name of Jesus!"
In a cinema they say "Shut up for christ's sake!"

 

[Peter Hucker]

On Tue, 11 Nov 2008 17:57:04 -0000, Dave Plowman (News) <dave@davenoise.co.uk> wrote:

In article <slrnghja8j.e5j.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:
On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:
230 volts would cause more current to flow than 100 - so more likely
to kill.

Think of water pipes. A narrow pipe can be likened to a low current
cable (few Amps) and a wide pipe is like a cable carrying a large
current (many Amps). Both can be at the same pressure (Voltage) but
one will cause a lot more damage when it bursts than the other.

Electricity doesn't spill out when a cable breaks. ;-)

Which is why I suck at plumbing.

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

Do you know what a Jewish dilemma is?
Free ham.

 

[ian field]

"Whiskers" <catwheezel@operamail.com> wrote in message
news:slrnghjjbg.e5j.catwheezel@ID-107770.user.individual.net...

On 2008-11-11, Arfa Daily <arfa.daily@ntlworld.com> wrote:

"Whiskers" <catwheezel@operamail.com> wrote in message
news:slrnghja8j.e5j.catwheezel@ID-107770.user.individual.net...
On 2008-11-10, Dave Plowman (News) <dave@davenoise.co.uk> wrote:
In article <slrnghhb1o.bes.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:

[...]

A system carrying a lot of amps to the load that's drawing it, is no more
or
less dangerous than one that's only carrying a small current, except in
as
much as there is a greater potential for heat failure at connection
points
within that system. A high voltage system, irrespective of how many amps
it
is capable of carrying above a few milliamps, is far more dangerous to a
human, than a low voltage system good for a few hundred amps. Given the
(reasonably) constant resistance of any described path through the human
body, a voltage of a hundred volts with a current availability of as
little
as 50mA, may be enough to kill under the right (wrong!) circumstances.

So a charge of 10kV from walking across a carpet (DC) , or a "non-lethal"
50kV "Tazer" (AC), are more dangerous than a 1kV power line? The danger
from 'High Voltage' power lines comes from the vast amount of current they
can deliver.

See:

http://en.wikipedia.org/wiki/Electric_shock

and scroll down to "Lethality of a shock".

From the table there it is apparent that passing a current anything over
about 0.1A is quite likely to be fatal, so it makes little difference
whether the voltage source is capable of supplying 1A or 1000A.

The lethality of any voltage source that can supply more than about 100mA
will depend on there being sufficient voltage to pass lethal current through
the body according to Ohms law (V/R=I).

Typical estimates for human body resistance:

Unbroken dry skin = about 100,000 - 500,000 Ohms
Unbroken wet skin= About 1000 Ohms
Broken skin= As low as 100 Ohms

The higher the voltage, the greater the likelihood that localised burning
will break the skin resulting in a rapid drop in resistance with consequent
increase in current flow.

 

[Dave Plowman (News)]

In article <slrnghjjbg.e5j.catwheezel@ID-107770.user.individual.net>,
Whiskers <catwheezel@operamail.com> wrote:

So a charge of 10kV from walking across a carpet (DC) , or a
"non-lethal" 50kV "Tazer" (AC), are more dangerous than a 1kV power
line? The danger from 'High Voltage' power lines comes from the vast
amount of current they can deliver.

Sigh. You don't need 'vast amounts of current to kill'. That's why RCDs
are set at 30 mA. Less than that is *generally* safe.

--
*Money isn't everything, but it sure keeps the kids in touch *

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