🚀 go-pugleaf

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?

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