[Gllug] Electric Shocks

[Alain Williams]

On Fri, May 16, 2003 at 12:04:48PM +0100, t.clarke wrote:
> Since some of you gentlemen are cleary very knowledgable on the subject of
> electicity, maybe someone has the definitive answer to a a couple of questions
> that have fascinated me:
> 
> a) is it true that if you stand on a perfect or near-refect insulator (eg big
> fat rubber mat) and touch an HV source (say several KV relative to earth) you
> won't get a shock ?   - not the sort of thing I wish to test practically !

At first sight yes, but if the voltage is really high and is an alternating one
(eg stepped up mains), you might get corona currents. Go to a big electricity
pylon on a quiet dark night. You will hear a buzzing and may see a slight glow near
the wires.

Have you noticed that birds don't sit on these things ? I don't know if it is
dangerous for them, or just uncomfortable.

> b) we operate a 240V UPS here which 'floats'  - ie one leg is NOT tied down
> to earth.  The suggestion is similarly that touching either wire will not
> produce a shock since there is supposedly nowhere for the current to flow.
> True or false ?

Again: an alternating current may flow, the 'other end' being the capacity of
whatever is connected to the UPS with respect to it's ground.

-- 
Alain Williams

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