[ On Tuesday, April 3, 2001 at 15:20:41 (-0600), Alex Barclay wrote: ]
> Subject: Re: IBM SP2 9056 (two thin nodes, POWER arch)
>
> On Tue, 3 Apr 2001, Lyndon Griffin wrote:
> 
> > to) get 3-phase 208 in my house, my first effort is hacking together a power 
> 
> Is it really a 3 phase system? We use 208 in our lab and it is a biphase
> system derived from 2 120v phases. What is the connector type?

Hmmm... that's possible (though a bit backwards), but doubtful.  I
suspect you're falling for a common mis-perception about what a
multi-phase power system is.

In North America most (all?) household and office 240vac power is only
single phase.  In all of these cases the 120vac power is derived from a
centre-tapped 240vac, single phase transformer.

There are some two-phase systems around, but most places you'll only see
three-phase systems (eg. the big high-tension lines with three heavy
cables on big insulators, and sometimes one smaller cable on a smaller
insulator for a separate ground line).  In both cases though in any
given "last mile" of the grid the 240vac transformers will be fed from
one of the three phases on the local grid.  (Sometimes the second last
leg of the grid will be two of the three phases.)

If the power supply on Lyndon's beast really requires three-phase input
directly then he'll probably have to replace it.  However some IBM gear
I've seen expects single-phase 208vac (eg. AS-400 servers and such),
which is the voltage you'd get if you fed it a single phase of the
output of a three-phase step down transformer.  Some such gear will work
just fine with 240vac too, though one would want to understand the
specifications and requirements of the power supply very well before
just plugging it into a 240vac wall socket.  :-)

-- 
							Greg A. Woods

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