On Sun, 2 May 1999, Rick Copeland wrote:

> At 10:42 PM 5/4/99 -0400, jim@dmv.net wrote:
> >
> >
> >On Tue, 4 May 1999, Jonathan R. Hinds wrote:
> >
> >> Is it triple phase or single phase?
> >> I am going to guess triple eh?
> >> Thanks.
> >
> >
> >There is nothing in a 11/785 that is specifically
> >3 phase.    
> >
> >You can run this machine on 220 single phase. You
> >simply have one less hot leg to balance the loads
> >on. 
> > 
> Well that's not the case on my 11/785.  The fans in my 11/785 are three
> phase 208vac.  Every thing else is single phase.  However, if someone uses
> other than 3 phases to spread the load out to they may well find them
> selves in a situation where enough current is not available to run the
> entire system.


hmm...   you must have an oddball system...  I've never seen anything
other than 120VAC single phase blowers in those machines.   Actually,
the blower motors can be configured to run on 120 or 220, but in the 
dozen or so of these machines I've worked on, I've never seen anything
other than 120VAC used.
 
I said you can run an 11/785 on other than 3 phase, but I suppose I 
should have qualified it as an exercise that isn't for the faint of
heart, or weak of electrical skills.    Modifications are required
to the power controller (or it won't work at all), careful balancing
of the loads is required, and most important the circuits used must
have enough available current and be properly protected.

That said, I have had one of these running in a production shop that
did not have three phase (and couldn't easily get it), but sucessfully
ran a heavily optioned 11/785 for quite some time.   We are talking
11/785 CPU with FPU and two FULL memory cages, completely filling the
cabinet and using all of the power supply slots.  In an adjacent 
expansion cab were two unibus adapters, two RH780's and a CI780.  These
ran on just two 220VAC circuits.   Also in the room were a HSC90, 
12 RA81's and a TU78.   All without the benefit of three phase service
in the building.   Ran great for years.   DEC obviously would not
support such an installation, but that was not an issue.  


Again not for the faint of heart.   You can cause yourself a lot of
problems, some of them affecting your health, if you don't know what you
are doing.


> Rick C.
> 

Jim