Date   : Fri, 18 Sep 2009 18:22:31 +0100
From   : rs423@... (Mick Champion)
Subject: Leccy @ Acorn World '09

> Phil Blundell wrote:
>
>   
>> It's not such a bad system: the highest potential to ground at any point
>> is 120V, and in most of the inhabited parts of a building the highest
>> potential between any two accessible points would be 120V as well.  (The
>> NEMA-14 outlets tend to be fitted in utility rooms and those kinds of
>> places.)  So, compared to the European 230V system I guess they enjoy a
>> slightly reduced shock risk.
>>     
>
>   
Yet more I didn't know. Just Wiki'd the NEMA-14. I see the US sometimes 
have 3 phase supplies too giving 208 volts instead of 240 apparently.


> Pete Turnbull wrote:
> Logical, on the face of it, but apparently debatable.  There's research 
> to suggest that 120V is about the worst possible voltage. 
> Unsurprisingly, lower voltages, below about 90V, induce such low current 
> via skin resistance as to be unlikely to cause death, and yet, 
> counter-intuitively perhaps, higher voltages are believed more likely to 
> make you jerk away from the live conductor thereby breaking the contact. 
>   
I have had a jolt from 110 volts and I moved quick enough. It wasn't so 
painful as 240/230 though.



>   That's why building site supplies in this country are 55-0-55V and 
> never 0-110V.
>
>   
Is the centre tap connected to mains earth (where possible), or are 
building supplies completely isolated? I presume they have to be earthed 
somehow in case a worker slices through a live cable somewhere.



Mick