OK, let me twiddle me greymatters a bit.....

The machine I had ran off 3 phase power on 220
or 440 or something like that.  Obviously, not
my usual house power. Upon looking at individual
power supplies (3 of them, one for each phase),
they were each labelled 110vac!!!!!  Now, the
output of these critters is 48VDC onto the 7000
power bus, which powers the fans and the big
regulator modules that reduce it to usual chip
power and bus power.  Alas, by the time I found
all this out, I had dissassembled my machine for
parts and sent parts to various folks, being
scared away by the 3 phase monster.

Now, since the machine input is 3 x 110vac, or
the bus power is 48vdc, you SHOULD (caveats in
order) be able to power a 7000 class machine by
one of two methods.

1) 48VDC on the main power busses.  You would
   need to build a 48vdc power supply at around
   100 amps and run it off of 220 power like
   from a dryer outlet circuit or somesuch.
   This should be doable, but you would need to
   make sure the control circuitry bits were in
   place.  My thoughts were to build the 100amp
   supply and float it across 4x12v diesel truck
   batteries for regulation.  Simple, and ought
   to work.  I have been doing that kind of thing
   for years powering military 28vdc stuff.  It
   is crude, but works fine.  A VAX is not much
   different, in reality.

2) IFF the 110vac power supplies can be separated
   and IFF they are isolated via isolation type
   transformers (simple 110x110 things at the
   required current load), then you ought to be
   able to separate out each power supply and
   run them on a single phase power with all
   power supplies paralelled in inputs to one
   110v 30 amp circuit (marginal, but ought to
   work and supply enough power).  Separate to
   3 circuits, if needed.  Check the supplies,
   since I don't remember offhand if they did
   or did not have input isolation transformers
   already built into the input circuits.

This all assumes control circuitry for applying
power to the bus is emulated in relays, switches
or however.  I was thinking of using batteries
as floating regulators and just variacing the
power up.

When I first looked at the critter and everyone
was saying 3 phase power, I thought it would be
impossible to power up the beast.  But, when I
saw the power supplies were actually separate
110vac to 48vdc things, I knew DEC did something
right.

I have not actually put it to the test, but,
my expectation is that you can separate out
the power supply on each phase and power them
from a single phase.  

CHECK carefully the labels on the power supplies
and see whether or not they are 110vac single
phase supplies.  Mine were.  If they are, too,
you are mostly there.

Bob