🚀 go-pugleaf

"Meat Plow" <meat@petitmorte.net> wrote in message 
news:2bc3rq.btk.19.1@news.alt.net...
> On Wed, 12 Nov 2008 14:50:28 -0000, "Arfa Daily"
> <arfa.daily@ntlworld.com>wrote:
>
>>
>>"Whiskers" <catwheezel@operamail.com> wrote in message
>>news:slrnghlo20.bmt.catwheezel@ID-107770.user.individual.net...
>>> On 2008-11-12, Arfa Daily <arfa.daily@ntlworld.com> wrote:
>>>>
>>>> "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.
>>>>
>>>> You see, there you go getting your apples and oranges mixed up again. A
>>>> static charge from a carpet is not lethal to you because it is an
>>>> extremely
>>>> high resistance source. That is the nature of a static charge. No 
>>>> matter
>>>> whether it is 1kV, 10kV or 40kV, the source resistance will ensure that
>>>> only
>>>> uA will flow for decimals of a uS. Enough to give you a nasty little
>>>> crack,
>>>> yes, but not enough to come within several orders of magnitude of being
>>>> lethal. The same applies to the taser. It is designed to not be able to
>>>> supply enough current (theoretically) to be lethal. However, its aim is
>>>> to
>>>> incapacitate by disrupting nerve activity and causing extreme pain. To 
>>>> do
>>>> this, the charge is applied to the receiving body in multiple
>>>> short-duration
>>>> pulses. In some cases, this has proven to be fatal, I believe, due to 
>>>> the
>>>> length of time that the pulses are delivered for. On the other hand, a
>>>> high
>>>> voltage power line, or even a fairly low voltage household supply, *is*
>>>> potentially lethal not because it can deliver huge amounts of amps, but
>>>> because the voltage that is present, is sufficient to drive *enough*
>>>> (mili)
>>>> amps from that low resistance source through the conduction path within
>>>> the
>>>> body.
>>>
>>> Precisely; it isn't the voltage that's lethal, it's the current.  If the
>>> current isn't available, the voltage is pretty harmless.  High-voltage
>>> mains power lines carry a /lot/ of current, whereas high-voltage 
>>> 'Tazers'
>>> don't.
>>>
>>>>>> 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?
>>>>
>>>> Yes, arc welding can occur at 12v and, in fact, at lower voltages than
>>>> this,
>>>> although there are many different methods these days of generating and
>>>> controlling the welding arc, though none that operate by charging caps 
>>>> to
>>>> the sorts of voltages that you are talking about, as far as I am aware.
>>>> In
>>>> general, arc welding is a high current rather than high voltage system.
>>>> Spot
>>>> welders sometimes work by charging very large capacitors to low 
>>>> voltages.
>>>> The reason that the low voltage arc welder is not capable of killing 
>>>> you,
>>>> any more than a car battery can, is because although both are extremely
>>>> low
>>>> internal resistance sources, and hence capable of supplying large 
>>>> amounts
>>>> of
>>>> current to a low resistance load, the human body is a much higher
>>>> resistance
>>>> load, so the 12v is not capable of pushing enough miliamps through that
>>>> path, to cause electrocution - or even electric shock.
>>>
>>> OK, I'm not familiar with arc welding, and I'm surprised that 12V is
>>> enough to strike an arc.  But your comment that it is the high current
>>> that matters for creating a weld, rather supports my contention that
>>> current is more dangerous than voltage.
>>>
>>> Electron beam welding (which you probaby won't find happening in a 
>>> garden
>>> shed or on a building site) requires many thousand volts, but only a 
>>> small
>>> current (less than 1A).
>>>
>>> The only welding I've ever done myself, involved a coke-burning forge 
>>> and
>>> a heavy hammer.
>>>
>>>>>> 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.
>>>>
>>>> Well, if you understood the principles of isolation transformers, which
>>>> as
>>>> well as being used on building sites for obvious reasons, are also to 
>>>> be
>>>> found in every professional electronics workshop, to render safe, the
>>>> need
>>>> to work on live equipment employing such potentially lethal nasties, as
>>>> switch mode power supplies, then you would know that it isn't too good 
>>>> to
>>>> be
>>>> true - it simply *is* true. Sketch it down on a piece of paper then 
>>>> have
>>>> a
>>>> good think about it.
>>>>
>>>> Arfa
>>>
>>> The only 'isolation transformers' I've come across, are earthed - and
>>> either have an output restricted to 50V or less (that threshold at which
>>> the human body's resistance drops substantially) or provide a good earth
>>> connection for the appliance.  An isolation transformer /does/ 
>>> disconnect
>>> the connection that exists between the power station and the ground and 
>>> is
>>> carried by the 'live' or 'hot' cable, but that is /not/ the same as the
>>> safety 'earth' connection which is meant to provide a relatively safe
>>> return path in case exposed metal parts of the appliance accidentally
>>> become connected to the power supply.
>>
>>
>>Neutral and ground are bonded together at the substation
>>
>>
>>>
>>> The 'earth' connection provided by an 'isolation transformer' to the
>>> appliances running off it, may be arranged to effectively create a
>>> 'short-circuit' on the output windings of the transformer if any current
>>> flows through it, and that should trigger the safety cut-off (probably a
>>> 'residual current device').  Or the 'earth' connection will pass 
>>> straight
>>> through to the same 'earth' as the mains supply provides.
>>>
>>> A double-insulated appliance has no exposed metal parts that can become
>>> connected to the power supply, and that's why they are permitted to be
>>> used with no 'earth'.
>>>
>>> -- 
>>> -- ^^^^^^^^^^
>>> --  Whiskers
>>> -- ~~~~~~~~~~
>>
>>Hmmmm. Your understanding of the principles of ground isolation by use of 
>>a
>>transformer seem very flawed I'm afraid, as also is your knowledge of
>>electricity distribution schemes, and earth / neutral commonality.
>>
>>Arfa
>>
>
> Whiskers is an idiot from the 24hoursupport.helpdesk newsgroup.
> Probably got trolled here by the Hucker idiot.

PHucker usually hangs out on alt.binaries.chatter , I can't recall seeing 
whiskers there. PHucker sometimes trolls on the sci.electronics groups - 
usually asking stupid questions then criticizing the answers he's given.