[Gllug] OT: Merging UPS outputs

[Chris Hunter]

Chris Bell wrote:

>    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.

A quick application of basic electrical theory will demonstrate that 
this is the very safest way of providing power - the rest of the world 
would do well to learn from us!

>    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.

That's one possibility, another is that the neutrals are 
under-specified.  I sometimes see this in older traffic signal 
installations - the three lives to a signal head are all (for the sake 
of argument) 1mm, and the common neutral return is just another 1mm 
core.  In this instance, it's usually the neutrals that fail!  Also, I 
really prefer PME installations, so the neutral is REALLY at earth 
potential!

Chris



-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug