[Gllug] OT: Merging UPS outputs

[Chris Bell]

On Mon 22 Aug, Ken Smith wrote:
> 
> Chris Bell wrote:
> 
> >   So what do you get down the cable, (assumed AC volts)
> >
> >-55, 0, +55, 230
> >
> >-110, 0, +100
> >
> >  
> >
> 
>  From what  I recall from when I lived in Canada many domestic supplies 
> there were effectively 230V center tapped. IE: One phase of the public 3 
> phase supply from a centre tapped winding.  So the supply would be on 
> three wires with a neutral and two 180 degree (not 120 degrees as you 
> might expect) out of phase 115 supplies. The live to live would be 230 V 
> for large capacity appliances like dryers and air conditioners. I'm not 
> sure how the two 115 supplies were are actually normally used for the 
> 115 V outlets. I guess one for one floor of a house and the other for 
> another floor. The 230V 60Hz supply was good for most UK bits that 
> didn't mind 60Hz but couldn't handle the 115V supply. My UK PAL VCR 
> actually worked fine on 115V 60Hz even though it says 240V 50Hz on the 
> back. (Friends sent me tapes so I could get to see home TV.) I also came 
> across 600V 3 phase industrial supplies there - eeek!
> 
> Radial wiring is the norm in North America. Our ring main idea seems to 
> be unique to the UK and other BS1363 places were we have had historical 
> influence - such as S Ireland and Ghana and I think Iraq and probably 
> elsewhere.
> 
> Ken

   That sounds as though they actually generate and distribute a 3-phase
supply, then use a 3 to 6 phase transformer to give a local 6-phase supply
as you cannot earth more than one point at a time.
   Standard practise here is to generate and distribute 3-phase, with the
centre tap tied to earth (via earth spikes, etc) at every transformer and
every main switch. This earthed centre tap is provided as the "neutral" for
single phase operation, with multiple earthing for additional safety.
   I have worked for many years with compact mobile high power equipment
(think in terms of a 25KW total load in a lorry that is driven around the
country from site to site), and although connections are checked for
tightness there are occasional burn-outs. I have seen several damaged
neutral connections, but failed live connections are normally limited to
damage at 13amp sockets caused by a loose fuse connection. I think that
either more neutral connections are made in a smaller space or people just
pay more attention to the tightness of the live connections.

-- 
Chris Bell

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