OK, so what *is* the correct mains voltage in the UK?

I was always taught at school that the mains was exactly 250V. But I 
can't find any documents anywhere which claim that this is the case.

According to Wipikedia (which is never wrong), the original 
specification was

   240V +/- 6%

This was then revised to

   230V +10% / -6%

and then revised again to

   230V +/- 10%

which would therefore allow anything between 207V to 253V.

So does that *really* mean that all UK equipment is supposed to work 
with absolutely any voltage that falls between 207V and 253V?

Post a reply to this message

> OK, so what *is* the correct mains voltage in the UK?

Get a multimeter and a car and you could probably make a nice picture :-)

> I was always taught at school that the mains was exactly 250V. 

I never heard that before.

> and then revised again to
> 
>   230V +/- 10%
> 
> which would therefore allow anything between 207V to 253V.
> 
> So does that *really* mean that all UK equipment is supposed to work 
> with absolutely any voltage that falls between 207V and 253V?

Yes.

Post a reply to this message

"scott" <sco### [at] scottcom> wrote:

> > I was always taught at school that the mains was exactly 250V.
>
> I never heard that before.
>

I have and still say 250 Vac if I don't think about it.

Stephen

Post a reply to this message

Invisible wrote:
> OK, so what *is* the correct mains voltage in the UK?

Don't forget it's AC, so you also have to figure out whether you mean peak, 
RMS, or what. Plus you should check the frequency.

-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

Post a reply to this message

Darren New wrote:
> Invisible wrote:
>> OK, so what *is* the correct mains voltage in the UK?
> 
> Don't forget it's AC, so you also have to figure out whether you mean 
> peak, RMS, or what. Plus you should check the frequency.

230V RMS at 50 Hz. (I don't see any sources stating what the allowable 
variation in frequency is.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

On 4-6-2009 11:41, Invisible wrote:
> OK, so what *is* the correct mains voltage in the UK?
> 
> I was always taught at school that the mains was exactly 250V. But I 
> can't find any documents anywhere which claim that this is the case.
> 
> According to Wipikedia (which is never wrong), the original 
> specification was
> 
>   240V +/- 6%
> 
> This was then revised to
> 
>   230V +10% / -6%
> 
> and then revised again to
> 
>   230V +/- 10%

IIRC it used to be 240 (or perhaps 250) for some islands and 220 for the 
mainland of Europe. The 230 is the result a committee trying to 
standardize the EU.

Post a reply to this message

Orchid XP v8 wrote:
> Darren New wrote:
>> Invisible wrote:
>>> OK, so what *is* the correct mains voltage in the UK?
>>
>> Don't forget it's AC, so you also have to figure out whether you mean 
>> peak, RMS, or what. Plus you should check the frequency.
> 
> 230V RMS at 50 Hz. (I don't see any sources stating what the allowable 
> variation in frequency is.)
> 

Frequency shouldn't vary much. Some alarm clocks are dependent on the 
frequency of the power feed.

-- 
~Mike

Post a reply to this message

Mike Raiford <"m[raiford]!at"@gmail.com> wrote:
> Frequency shouldn't vary much.

  AFAIK, while the voltage can vary quite some (like eg. the stated 10%),
they are extremely careful to have the frequency as accurate as possible.
And we are talking about very tiny fractions of a hertz here.

  If I'm not mistaken, this is so severely imposed that an electric company
feeding the system with even the tiniest discrepance in the frequency or
phase is automatically dropped. I think it has something to do with energy
loss when two sources produce alternate current not exactly in sync. The
only way to avoid energy loss because of desynced AC current is to have
all sources exactly at the same frequency and phase.

  Thus a wall socket is a really accurate and reliable 50 Hz timer.

-- 
                                                          - Warp

Post a reply to this message

On 4-6-2009 22:52, Mike Raiford wrote:
> Orchid XP v8 wrote:
>> Darren New wrote:
>>> Invisible wrote:
>>>> OK, so what *is* the correct mains voltage in the UK?
>>>
>>> Don't forget it's AC, so you also have to figure out whether you mean 
>>> peak, RMS, or what. Plus you should check the frequency.
>>
>> 230V RMS at 50 Hz. (I don't see any sources stating what the allowable 
>> variation in frequency is.)
>>
> 
> Frequency shouldn't vary much. Some alarm clocks are dependent on the 
> frequency of the power feed.
> 
Can't find a reference for the tolerance of the frequency even though 
the amplitude tolerance is easy to find. :( Tolerance is at any time a 
few percent. Yet, there should be (almost?) exactly 4320000 cycles in 24 
hours (assuming 50Hz). Under most circumstances the frequency is 
actually very close to 50Hz except at times of (unpredicted) peak 
currents, but that will be compensated later.

Post a reply to this message

Warp wrote:
>   Thus a wall socket is a really accurate and reliable 50 Hz timer.

In the USA, it's a very accurate 60Hz, but if it drifts at all, during the 
last minute of the day, they adjust the frequency to get exactly the right 
number of ticks in. Probably because of the alarm clock thing, if nothing 
else.

It might need to be more regulated on three-phase wiring, and I don't know 
if the frequency is different between the generator and the wall-socket 
(altho I doubt it), so I'm not sure just where the accuracy is enforced.

-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

Post a reply to this message

>> > I was always taught at school that the mains was exactly 250V.
>>
>> I never heard that before.
>
> I have and still say 250 Vac if I don't think about it.

Maybe it was before my time then :-) But the "exactly" part I have never 
heard, and isn't even possible!

Post a reply to this message

>> 230V RMS at 50 Hz. (I don't see any sources stating what the allowable 
>> variation in frequency is.)
>>
>
> Frequency shouldn't vary much. Some alarm clocks are dependent on the 
> frequency of the power feed.

Yeh, the frequency depends on how much power is demanded and what generation 
capacity is online.  In a grid power system like the UK they control the 
frequency by bringing up and shutting down various power generators to cope 
with the demand.  I don't know what the short-term allowed variation is, but 
over the longer-term (eg 1 day) it is controlled very accurately, enough for 
clocks to run off it.

Post a reply to this message

>  If I'm not mistaken, this is so severely imposed that an electric company
> feeding the system with even the tiniest discrepance in the frequency or
> phase is automatically dropped.

It doesn't work like that, you don't get to choose the frequency or phase of 
your generator when it is connected to the system.

An analogy is if you imagine 100 cars all fixed end to end on a track going 
at 100 km/hr.  The steepness of the track can be thought of as the current 
demand, each car as a power station, and the speed as the frequency.  It's 
the job of the controllers of the entire system to predict demand and ask 
more or less cars to join the train, and to tell each driver how much power 
to generate.  As an individual you can't set your own speed and be "out of 
sync" with everyone else, by definition of being connected to the system you 
are generating the same frequency and phase as everyone else.

Post a reply to this message

scott wrote:
>>> > I was always taught at school that the mains was exactly 250V.
>>>
>>> I never heard that before.
>>
>> I have and still say 250 Vac if I don't think about it.
> 
> Maybe it was before my time then :-) But the "exactly" part I have never 
> heard, and isn't even possible!

Well, you don't tell children that, do you? ;-)

Post a reply to this message

scott <sco### [at] scottcom> wrote:
> It doesn't work like that, you don't get to choose the frequency or phase of 
> your generator when it is connected to the system.

> An analogy is if you imagine 100 cars all fixed end to end on a track going 
> at 100 km/hr.  The steepness of the track can be thought of as the current 
> demand, each car as a power station, and the speed as the frequency.  It's 
> the job of the controllers of the entire system to predict demand and ask 
> more or less cars to join the train, and to tell each driver how much power 
> to generate.  As an individual you can't set your own speed and be "out of 
> sync" with everyone else, by definition of being connected to the system you 
> are generating the same frequency and phase as everyone else.

  Of course you can generate an out-of-phase signal. It's just an AC
generator like everything else. What happens is that if you are out of
sync with the other generators, there will be an energy loss because the
out-of-sync signal dampens the others. The worst possible scenario is,
of course, that your generator has a phase shift of 180 degrees compared
to the other generators, which causes maximal energy loss.

-- 
                                                          - Warp

Post a reply to this message

"scott" <sco### [at] scottcom> wrote:
> >  If I'm not mistaken, this is so severely imposed that an electric company
> > feeding the system with even the tiniest discrepance in the frequency or
> > phase is automatically dropped.
>
> It doesn't work like that, you don't get to choose the frequency or phase of
> your generator when it is connected to the system.
>
> An analogy is if you imagine 100 cars all fixed end to end on a track going
> at 100 km/hr.  The steepness of the track can be thought of as the current
> demand, each car as a power station, and the speed as the frequency.  It's
> the job of the controllers of the entire system to predict demand and ask
> more or less cars to join the train, and to tell each driver how much power
> to generate.  As an individual you can't set your own speed and be "out of
> sync" with everyone else, by definition of being connected to the system you
> are generating the same frequency and phase as everyone else.

To expand on what Scott has said. (In a past life I used to work on the
electronic governors of Gas Turbine power generators.)

All the generators in a grid will be at the same frequency and phase. As you
bring a generator online you must wait until the oncoming generator is in phase
with the grid before connecting it. If it is slightly out of phase it creates a
nice bang :) As the load on the grid increases the frequency will try to drop
but the individual governors will increase the throttle valve, supplying the
fuel, to keep it steady. The line voltage will drop instead.
I can’t say much about line transmission as we only had a few hundred meters of
cabling.

Stephen

Post a reply to this message

Warp <war### [at] tagpovrayorg> wrote:
>   Of course you can generate an out-of-phase signal. It's just an AC
> generator like everything else. What happens is that if you are out of
> sync with the other generators, there will be an energy loss because the
> out-of-sync signal dampens the others. The worst possible scenario is,
> of course, that your generator has a phase shift of 180 degrees compared
> to the other generators, which causes maximal energy loss.
>

In RL the other generators will drag the out of phase into phase violently.

Stephen

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Invisible wrote:
> OK, so what *is* the correct mains voltage in the UK?

A related question. why do some countries use 110 and others use 220?

BTW, here in the US I've seen AC voltage expressed as 110, 115 and 120. 
  Generally it's actually somewhere between 105 and 125, devices get 
around this by having voltage regulators. e.g. if the input voltage 
sags, it'll draw more current to keep the output voltage where it wants 
it to be, and vice-versa.. Of course there are limitations, and 
eventually the regulator will output too little voltage, because the 
supply cannot keep up with the current draw, or it'll burn out because 
the input voltage is outside it's operating limits.

This is why battery operated electronics can run until the battery is 
almost flat, even though the battery's voltage continually drops as it's 
drained.

-- 
~Mike

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Mike Raiford wrote:

> This is why battery operated electronics can run until the battery is 
> almost flat, even though the battery's voltage continually drops as it's 
> drained.

Really? That's interesting. I always thought it was the battery outputs 
full voltage until just before it actually dies (which is why battery 
meters are never, ever, under any circumstances, actually accurate).

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> Mike Raiford wrote:
>
> > This is why battery operated electronics can run until the battery is
> > almost flat, even though the battery's voltage continually drops as it's
> > drained.
>
> Really? That's interesting. I always thought it was the battery outputs
> full voltage until just before it actually dies (which is why battery
> meters are never, ever, under any circumstances, actually accurate).

Actually, the battery's resistance increases with depletion, which means the
more current you draw and the lower charge of the battery the lower the voltage
you get. The idle voltage will almost always be the same, regardless of the
charge state of the battery.

Post a reply to this message

>> Really? That's interesting. I always thought it was the battery outputs
>> full voltage until just before it actually dies (which is why battery
>> meters are never, ever, under any circumstances, actually accurate).
> 
> Actually, the battery's resistance increases with depletion, which means the
> more current you draw and the lower charge of the battery the lower the voltage
> you get. The idle voltage will almost always be the same, regardless of the
> charge state of the battery.

I have no idea what internal resistance is. All I know is that a battery 
is a chemical reaction that charges two electrodes until they reach a 
potential high enough to halt the reaction. You draw current and the 
reaction starts up again, replacing the charge just as fast as you can 
remove it - up to a point. I presume as the reactants become more 
dilute, that rate of reaction decreases so the maximum current you can 
draw decreases.

But yes, as I understand it, the potential difference of an unloaded 
battery is almost constant until it's completely dead. This (I presume) 
is why my phone tells me it's on maximum charge for months on end, until 
the exact moment when I try to make a phonecall...

Post a reply to this message

Mike Raiford wrote:
> A related question. why do some countries use 110 and others use 220?

History, most likely. :-) Whoever does something widespread first tends to 
be at odds with everyone else later, when the flaws in the methods are 
discovered but not worth fixing in an already-widespread system.

> BTW, here in the US I've seen AC voltage expressed as 110, 115 and 120. 

117v RMS, I think is the actual standard. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

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Darren New wrote:
> Mike Raiford wrote:
>> A related question. why do some countries use 110 and others use 220?
> 
> History, most likely. :-) Whoever does something widespread first tends 
> to be at odds with everyone else later, when the flaws in the methods 
> are discovered but not worth fixing in an already-widespread system.
> 

Heh. switching our voltage overnight from 110 to 220 would have 
disastrous consequences.

And why 50hz v.s. 60hz?

Interestingly, PAL's refresh rate is 50hz, vs NTSC's 60hz refresh simply 
because of the difference in AC frequency..

>> BTW, here in the US I've seen AC voltage expressed as 110, 115 and 120. 
> 
> 117v RMS, I think is the actual standard. :-)
> 


-- 
~Mike

Post a reply to this message

Mike Raiford wrote:
>
> Heh. switching our voltage overnight from 110 to 220 would have
> disastrous consequences.

Dunno why US uses 110V, but 220V means less current, which means less
powerloss in cables etc.

> And why 50hz v.s. 60hz?

Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
more current to distract your heart) than 60Hz. This has something to do
with 60Hz almost syncing to some multiply of normal, health heartbeat.
Don't remember the details (I was told this at school something like 12
years ago).

-Aero

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Eero Ahonen wrote:
> Again, dunno why US uses 60Hz,

Damn metric weenies.


-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

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> Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
> more current to distract your heart) than 60Hz. This has something to do
> with 60Hz almost syncing to some multiply of normal, health heartbeat.
> Don't remember the details (I was told this at school something like 12
> years ago).

Well, given that a normal heartbeat ranges from 50 to 150 BPM depending 
on how much exercise you're doing...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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On 6-6-2009 19:44, Orchid XP v8 wrote:
>> Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
>> more current to distract your heart) than 60Hz. This has something to do
>> with 60Hz almost syncing to some multiply of normal, health heartbeat.
>> Don't remember the details (I was told this at school something like 12
>> years ago).
> 
> Well, given that a normal heartbeat ranges from 50 to 150 BPM depending 
> on how much exercise you're doing...
> 
It is not about the rate of the sinus node, which is indeed in that 
range, but about what happens to a muscle if you rapidly stimulate it. 
At 50 and 60 Hz (does not really differ that much, both are lethal) the 
impulses come so rapidly that the tension in the muscle build up to a 
maximum. So all your muscles including your heart are fully contracted.

If you want non lethal AC current you should significantly increase the 
frequency, then by the skin effect the current stay at the surface and 
never reaches the muscles. Standard experiment goes like this: generate 
a very high voltage with a very high frequency so you get arcs of a few 
centimeter. Connect one pole to a volunteer/victim and let the arcs jump 
off his fingers to the other pole. It won't give more tha a prickling 
sensation in the fingers but it looks cool.

It probably would not surprise you that there are good reasons for not 
having high frequency mains power supplies.

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> It might need to be more regulated on three-phase wiring, and I don't know
> if the frequency is different between the generator and the wall-socket
> (altho I doubt it), so I'm not sure just where the accuracy is enforced.

The frequency is all the same, from the high-voltage power grid down to the
light bulb, or the three-phase-driven gadget.

Which is logical given that the voltage is transformed up and down using
straightforward electromagnetic transformators (which is what the AC is for in
the first place).

It also explains why power companies are so eager to get the frequency as
precise as possible: Every phase shift between different power plants feeding
into the grid is a source of power loss. A power plant operating at a full 180°
off-phase would effectively *drain* from the grid whatever power it tried to
feed into it. Which btw wouldn't be healthy for the infrastructure, I guess,
because the annihilated power must go *somewhere*. And that somewhere will heat
up dramatically. Or produce dramatic magnetic fields. Or whatever.

So they rather pop some ultra-heavy-duty breaker at the slightest sign of an
off-phase feed.

Post a reply to this message

Eero Ahonen <aer### [at] removethiszbxtnetinvalid> wrote:
> Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
> more current to distract your heart) than 60Hz. This has something to do
> with 60Hz almost syncing to some multiply of normal, health heartbeat.
> Don't remember the details (I was told this at school something like 12
> years ago).

Doesn't make much sense to me. Normal healthy heartbeat is roughly 1 Hz, with a
wide variation depending on circumstances.

Both 50 and 60 Hz are of course exact multiples of 1.

I guess that if there is a significant difference in lethality, it's probably
because at higher frequencies an AC supply provides a bit more actual power (if
I'm not mistaken, that is).

Post a reply to this message

clipka wrote:
> 
> Doesn't make much sense to me. Normal healthy heartbeat is roughly 1 Hz, with a
> wide variation depending on circumstances.

True. That's what they told us at school (at electric line), but as I
mentioned, it was 12 years ago, so the image in my memory ain't the
clearest one. And, of course, the information might still be false
(wouldn't be the first false information collected from school). Maybe
the bit harder overstimulation might make the effect?

> Both 50 and 60 Hz are of course exact multiples of 1.
> 
> I guess that if there is a significant difference in lethality, it's probably
> because at higher frequencies an AC supply provides a bit more actual power (if
> I'm not mistaken, that is).
> 

The difference was something like 30mA vs. either 25 or 28mA, so it's
not big (and as mentioned, both are lethal even with even low currencies).

Why would there be more actual power with greater frequency? The
phase-angle won't change, the current won't change and RMS voltage won't
change, so U*I*cos(fi) won't change.

-Aero

Post a reply to this message

Eero Ahonen <aer### [at] removethiszbxtnetinvalid> wrote:
> Why would there be more actual power with greater frequency? The
> phase-angle won't change, the current won't change and RMS voltage won't
> change, so U*I*cos(fi) won't change.

You need to invest extra power to get the higher frequency at the same AC
voltage and amps, right?

So where does that extra power end up if you have the otherwise same AC running
through your body?

EM field I'd guess - which may be just the extra "kick" you'd rather do without.

Post a reply to this message

clipka wrote:
> 
> You need to invest extra power to get the higher frequency at the same AC
> voltage and amps, right?

Hmm, possibly.

> So where does that extra power end up if you have the otherwise same AC running
> through your body?

At least part of it goes to heating the generator, which runs faster :).

> EM field I'd guess - which may be just the extra "kick" you'd rather do without.

That actually sounds reasonable. My head is atm too empty to remember
how to calculate energies of EM fields, but it would make sense, while
the field sure is frequency-dependent.

-Aero

Post a reply to this message

Invisible wrote:
> Mike Raiford wrote:
> 
>> This is why battery operated electronics can run until the battery is 
>> almost flat, even though the battery's voltage continually drops as 
>> it's drained.
> 
> Really? That's interesting. I always thought it was the battery outputs 
> full voltage until just before it actually dies (which is why battery 
> meters are never, ever, under any circumstances, actually accurate).

Here's an example of a charge pump voltage regulator:

   http://www.ti.com/lit/gpn/reg711-33

Note the input voltage range; +1.8V to +5.5V vs. the output voltage; +3.3V
for the REG711-3.3.

-- 
Tor Olav
http://subcube.com

Post a reply to this message

Tor Olav Kristensen wrote:
> Invisible wrote:
>> Mike Raiford wrote:
>>
>>> This is why battery operated electronics can run until the battery is 
>>> almost flat, even though the battery's voltage continually drops as 
>>> it's drained.
>>
>> Really? That's interesting. I always thought it was the battery 
>> outputs full voltage until just before it actually dies (which is why 
>> battery meters are never, ever, under any circumstances, actually 
>> accurate).
> 
> Here's an example of a charge pump voltage regulator:
> 
>   http://www.ti.com/lit/gpn/reg711-33
> 
> Note the input voltage range; +1.8V to +5.5V vs. the output voltage; +3.3V
> for the REG711-3.3.

I also recommend reading this:

   http://www.maxim-ic.com/appnotes.cfm/an_pk/737/

-- 
Tor Olav
http://subcube.com

Post a reply to this message

Invisible wrote:
> This (I presume)
> is why my phone tells me it's on maximum charge for months on end, until
> the exact moment when I try to make a phonecall...

Well, for that you need to consult Murphy's Law, not physics :)

Post a reply to this message

>  Of course you can generate an out-of-phase signal. It's just an AC
> generator like everything else. What happens is that if you are out of
> sync with the other generators, there will be an energy loss because the
> out-of-sync signal dampens the others.

1) That "energy loss" will be enough to annihilate your generator
2) Even if you built your generator to withstand it, the resultant torques 
and currents would pull it into sync with the others
3) It's not even relevant in practise, because there are protection 
mechanisms to avoid exactly the above happening

Post a reply to this message

> I have no idea what internal resistance is.

A pretty accurate model of a battery is a perfect voltage source in series 
with an "internal" resistor.  This then nicely explains how the more current 
you try to draw the lower the apparent voltage will be at the terminals of 
the battery.

Post a reply to this message

scott wrote:
>> I have no idea what internal resistance is.
> 
> A pretty accurate model of a battery is a perfect voltage source in 
> series with an "internal" resistor.  This then nicely explains how the 
> more current you try to draw the lower the apparent voltage will be at 
> the terminals of the battery.

As far as I'm aware, resistors affect only current, not potential. But 
hey, I'm sure you know more about this than me...

Post a reply to this message

Eero Ahonen <aer### [at] removethiszbxtnetinvalid> wrote:
> clipka wrote:
> >
> > You need to invest extra power to get the higher frequency at the same AC
> > voltage and amps, right?
>
> Hmm, possibly.
>
> > So where does that extra power end up if you have the otherwise same AC running
> > through your body?
>
> At least part of it goes to heating the generator, which runs faster :).
>
> > EM field I'd guess - which may be just the extra "kick" you'd rather do without.
>
> That actually sounds reasonable. My head is atm too empty to remember
> how to calculate energies of EM fields, but it would make sense, while
> the field sure is frequency-dependent.
>
> -Aero

It’s not really the power it is the frequency. What happens is that the
electrical impulses to the heart are interrupted and fibrillation occurs. IIRC
there are parts of the heart that receive the electrical impulses from the
brain then transmit secondary impulses to the muscle tissue to contract and
relax in an organised way. The electrical shock interrupts this process and you
get a disorganised high frequency oscillation in different parts of the heart. A
defibrillator is used to stop this effectively stopping the heart and the
natural sinus rhythm can be resumed. Before defibrillators became commonplace
the manual method was to strike the victims chest above the heart with a
controlled blow using the pinkie side of your fist. This was supposed to have
the same effect. I don’t know if it ever worked but that was what I was taught.

Stephen

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Invisible wrote:
> scott wrote:
>>> I have no idea what internal resistance is.
>>
>> A pretty accurate model of a battery is a perfect voltage source in
>> series with an "internal" resistor.  This then nicely explains how the
>> more current you try to draw the lower the apparent voltage will be at
>> the terminals of the battery.
> 
> As far as I'm aware, resistors affect only current, not potential. But
> hey, I'm sure you know more about this than me...

Try putting 2 resistors in series, connect the power (you'll have eg.
+12V on R1+, R1- on R2+ and R2- on ground) and measure voltages between
R1+/R2-, R1+/R1-, R2+/R2-, you might be surprised

+
|
R1
|
R2
|
-

-Aero

Post a reply to this message

On 15-6-2009 14:02, Stephen wrote:
> It’s not really the power it is the frequency. What happens is that the
> electrical impulses to the heart are interrupted and fibrillation occurs. IIRC
> there are parts of the heart that receive the electrical impulses from the
> brain then transmit secondary impulses to the muscle tissue to contract and
> relax in an organised way. 

No the heart is autonomous, will even beat outside the body for some 
time (hours) if oxygenated. It's frequency can be modulated by stuff in 
the blood and by nerve tissue that is close to the sinus node when they 
release special molecules.

> The electrical shock interrupts this process and you
> get a disorganised high frequency oscillation in different parts of the heart. 

No, but what happens is much more complicated (i.e. you need a 
complicated model to describe it and even then you see it happening 
without getting much more understanding, but it works).
Standard procedure to induce VF in an open chest heart: hold a 9V 
battery against it. And, no, I don't know how it actually works, but it 
does.

> A defibrillator is used to stop this effectively stopping the heart and the
> natural sinus rhythm can be resumed. Before defibrillators became commonplace
> the manual method was to strike the victims chest above the heart with a
> controlled blow using the pinkie side of your fist. This was supposed to have
> the same effect. I don’t know if it ever worked but that was what I was taught.

I does work sometimes. http://en.wikipedia.org/wiki/Precordial_thump Do 
not apply to people that are not in VF: 
http://en.wikipedia.org/wiki/Commotio_cordis

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andrel wrote:

> No the heart is autonomous, will even beat outside the body for some 
> time (hours) if oxygenated.

Does anybody else find it slightly disturbing that andrel knows such things?

I mean, I know there's a good reason, but even so... kinda grusome.

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andrel <a_l### [at] hotmailcom> wrote:
> On 15-6-2009 14:02, Stephen wrote:
> > It’s not really the power it is the frequency. What happens is that the
> > electrical impulses to the heart are interrupted and fibrillation occurs. IIRC
> > there are parts of the heart that receive the electrical impulses from the
> > brain then transmit secondary impulses to the muscle tissue to contract and
> > relax in an organised way.
>
> No the heart is autonomous, will even beat outside the body for some
> time (hours) if oxygenated. It's frequency can be modulated by stuff in
> the blood and by nerve tissue that is close to the sinus node when they
> release special molecules.
>

I thought that you might respond :)
It was “lies for children” :P


> > The electrical shock interrupts this process and you
> > get a disorganised high frequency oscillation in different parts of the heart.
>
> No, but what happens is much more complicated (i.e. you need a
> complicated model to describe it and even then you see it happening
> without getting much more understanding, but it works).
> Standard procedure to induce VF in an open chest heart: hold a 9V
> battery against it. And, no, I don't know how it actually works, but it
> does.
>

You are the expert I'm only a first aider


> > A defibrillator is used to stop this effectively stopping the heart and the
> > natural sinus rhythm can be resumed. Before defibrillators became commonplace
> > the manual method was to strike the victims chest above the heart with a
> > controlled blow using the pinkie side of your fist. This was supposed to have
> > the same effect. I don’t know if it ever worked but that was what I was taught.
>
> I does work sometimes. http://en.wikipedia.org/wiki/Precordial_thump Do
> not apply to people that are not in VF:

Unless you want to kill them ;)

Stephen

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On 15-6-2009 17:30, Invisible wrote:
> andrel wrote:
> 
>> No the heart is autonomous, will even beat outside the body for some 
>> time (hours) if oxygenated.
> 
> Does anybody else find it slightly disturbing that andrel knows such 
> things?
> 
> I mean, I know there's a good reason, but even so... kinda grusome.

As you may be aware, it is my job. It comes with being in a experimental 
cardiology lab. BTW a beating heart is absolutely not gruesome, I would 
rather say beautiful. I'd be happy to show you if you happen to be in 
Amsterdam some time and an experiment is running. ;)

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Invisible wrote:
> Does anybody else find it slightly disturbing that andrel knows such 
> things?

You don't watch enough TV.

-- 
   Darren New, San Diego CA, USA (PST)
   Insanity is a small city on the western
   border of the State of Mind.

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>>> No the heart is autonomous, will even beat outside the body for some 
>>> time (hours) if oxygenated.
>>
>> Does anybody else find it slightly disturbing that andrel knows such 
>> things?
>>
>> I mean, I know there's a good reason, but even so... kinda grusome.
> 
> As you may be aware, it is my job. It comes with being in a experimental 
> cardiology lab.

Indeed. But still... kinda freaky.

> BTW a beating heart is absolutely not gruesome, I would 
> rather say beautiful. I'd be happy to show you if you happen to be in 
> Amsterdam some time and an experiment is running. ;)

I once saw an operation on TV. They cut open a guy's chest, ripped his 
ripcage apart, and inside was his heart. I swear, it honestly looked 
like it was trying to CLIMB THE HELL OUT OF HIS BODY AND RUN AWAY!! O_O

*shivers*

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>> Does anybody else find it slightly disturbing that andrel knows such 
>> things?
> 
> You don't watch enough TV.

I always thought I watch far too much TV. :-P

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On 15-6-2009 17:33, Stephen wrote:
> andrel <a_l### [at] hotmailcom> wrote:
>> On 15-6-2009 14:02, Stephen wrote:
>>> It’s not really the power it is the frequency. What happens is that the
>>> electrical impulses to the heart are interrupted and fibrillation occurs. IIRC
>>> there are parts of the heart that receive the electrical impulses from the
>>> brain then transmit secondary impulses to the muscle tissue to contract and
>>> relax in an organised way.
>> No the heart is autonomous, will even beat outside the body for some
>> time (hours) if oxygenated. It's frequency can be modulated by stuff in
>> the blood and by nerve tissue that is close to the sinus node when they
>> release special molecules.
>>
> 
> I thought that you might respond :)
> It was “lies for children” :P

Thanks for assuming that there are only kids in this newsgroup. ;)

I disagree, a lie for children is when you explain something highly 
simplified and/or deliberately wrong because the actual facts are to 
difficult. Suggesting that the heart is driven by the nervous system is 
simply wrong and what actually happens is just as easy to understand. 
Involving the brain will in a bright child immediately lead to questions 
what happens when you sleep or are unconscious. The child might even 
fear to go to sleep. It does not explain coma or how a paralysed person 
can live. So, please, if you have children, tell them a simplification 
of the truth, but never that your brain dictates when the heart has to 
beat.

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On 15-6-2009 17:56, Invisible wrote:
>>>> No the heart is autonomous, will even beat outside the body for some 
>>>> time (hours) if oxygenated.
>>>
>>> Does anybody else find it slightly disturbing that andrel knows such 
>>> things?
>>>
>>> I mean, I know there's a good reason, but even so... kinda grusome.
>>
>> As you may be aware, it is my job. It comes with being in a 
>> experimental cardiology lab.
> 
> Indeed. But still... kinda freaky.
> 
>> BTW a beating heart is absolutely not gruesome, I would rather say 
>> beautiful. I'd be happy to show you if you happen to be in Amsterdam 
>> some time and an experiment is running. ;)
> 
> I once saw an operation on TV. They cut open a guy's chest, ripped his 
> ripcage apart, and inside was his heart. I swear, it honestly looked 
> like it was trying to CLIMB THE HELL OUT OF HIS BODY AND RUN AWAY!! O_O
> 
> *shivers*

Was that a dramatazation or an actual procedure?

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>>> BTW a beating heart is absolutely not gruesome, I would rather say 
>>> beautiful. I'd be happy to show you if you happen to be in Amsterdam 
>>> some time and an experiment is running. ;)
>>
>> I once saw an operation on TV. They cut open a guy's chest, ripped his 
>> ripcage apart, and inside was his heart. I swear, it honestly looked 
>> like it was trying to CLIMB THE HELL OUT OF HIS BODY AND RUN AWAY!! O_O
>>
>> *shivers*
> 
> Was that a dramatazation or an actual procedure?

It was meant to be the real thing. Apparently there was something or 
other wrong with this guy's heart, so they were going to rip it out and 
stick a new one in. (I wasn't really paying attention.) The new heart 
looked rather limp and pale. But the still-beating one looked evil! (And 
several sizes too big for the chest cavity, BTW...)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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