🚀 go-pugleaf

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.