🚀 go-pugleaf

"Meat Plow" <meat@petitmorte.net> wrote in message 
news:2bcalk.4i2.17.4@news.alt.net...
> On Wed, 12 Nov 2008 21:23:05 -0000, "ian field"
> <gangprobing.alien@ntlworld.com>wrote:
>
>>
>>"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.
>>
>
> Lol yeah that pretty much sums it up. I think he's actually smart
> enough to engage in some useful conversations should he choose to do
> so.

He claims to have a degree in physics, yet according to him he found physics 
too boring so he settled for a tech support job in a computer dept - funny 
how he visits this group yet never seems to contribute in any meaningful 
way.