Anyone with Roger's Lite accounts?

[Lennart Sorensen]

On Tue, Apr 18, 2006 at 08:41:16PM +0100, Paul Sutton wrote:
> When I was at college we were told that it's the current (Amps) that 
> actually kills you,  in the Uk the mains is 13 Amps, not sure what it is 
> in the USA / Canada, also the Root Mean Squared on the 50 hz frequency 
> means that you multiply this 240 volts by 1.414 (I think).
> 
> We were also told that 50 Hertz (hurts) 60 Kills either as a way of 
> remembering the differnt frequencies or perhps that 60hz is more 
> dangerous, so perhaps the RMS on 60hz is higher,  We also covered 3 
> phase in the UK which is 415 volts and a higher current, certainly ovens 
> here are at 30 AMPS.
> 
> Regarding fire if you short a 9v battery with a screwdriver and say left 
> this in a pile of paper, (stupid I know), it could catch fire, which is 
> why you have to be careful with such equipment this can be done 
> accidently i.e drop battery, and it lands somewhere and shorts, 
> 
> Any comments, can anoyne clarify this.
> 
> 
> what does GFI mean? I will try and find out if we use it or not,

I believe it is Ground Fault Interupter
(http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html)

I believe the idea is that it trips (disconnects) if the power flow
through the live and neutral isn't the same (so some current must be
going through ground instead of the neatral instead, which means
something is shorting somewhere).  So if somehow you touch the live
wire, and get zapped, it should instantly notice that some of the power
isn't returning through the neatral or another phase, and shuts off the
power.  After all the power that goes through you isn't going back the
way it should.  A GFI will trip is the current is off by a few milli
amps, while it would take a short to ground drawing the full 15A or
whatever your breaker is for a longer period for your breaker/fuse to
blow.

I mostly see GFIs installed as part of the outlet in bathrooms and
outdoors, while in europe I have often seen a single GFI installed on
the main incoming 3 phase line to a house, so everything is covered at
once.  Of course given I lived in Denmark, which until very recently
didn't believe in grounded outlets at all, having the GFI protect
everything was probably a good idea.  It seems the theory in north
america has been that if the hot wire shorts to the case of something,
the case is grounded, so it will overload the breaker/fuse and turn of
the power, before any person gets a chance to touch it, and anything
that isn't grounded is supposed to have a fully insulated case so it
can't possibly conduct power to the user.

Len Sorensen
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