All right. I need to respond to a few assumptions that
been made and of course ask Matt Sell a question.
At your service... : )
Question first: that shutdown interlock transformer you
is the only thing that really has anything to do with all 3
phases together. Do I have to take any action with this or
will it be fine?
Remove the fuses from F2 and F3 on the power distribution panel. Leave F1
fuse in place.
Comments: the VAX 6000 is really VERY different. It has
COMPLETELY different.... : )
The only concern I had was about something like this
interlock transformer that Matt was talking about. Will
I get all my panels powered, the unswitched and the switched
About this ground alias neutral wire overload, I think
just scare without real substance behind it. Given that I
have a 25 to 50 A 110 V single phase circuit to devote, my
wiring will simply be like this:
If you have that kind of "ampacity", then I don't think you'll need
three extension cords and reel that I have to use....
Just wire it all together. I would be careful about the gauge of wire used
for the neutral - one amp on each phase equals three on the neutral. It may
be too much of a load on the neutral wire.
since the phase, neutral (and ground, not that it
wires are all same gauge, the 30A that go through the phase
line come right out of the neutral line.
On three phase, if you had a 1 amp load on each phase, you would have a
little more than 1 amp through the neutral since they are 120 degrees
apart. With all three phases on one circuit, there is no phase difference
and the neutral bears the same current as all three phases together. It's
been too long since my power distribution classes in college for me to
remember the exact formulas off the top of my head. RF communications and
digital logic were my specialties......
If neutral overloads
phase will too. That's what you have circuit breakers and
the right gauged wireing for.
What size circuit breaker is connected inline with the neutral? That would
determine your total capacity - if connected this way. For example, if you
had a 30 amp breaker on the neutral, then each phase could draw 10 amps
I can see no risk. The only
theoretical risk I could possibly see is that the N line
would be underdimensioned internal to the power distribution
box. But hey, it's DEC, had big DEC ever built anything
The neutrals are separate inside of the distribution box.
Matt had a different problem, which was he didn't
a 30 or 50 A line to begin with.
Tell me about it. I'll need an electrician to make a house call when the
Finally, there is another thought: I might actually
to use a 220 V 2 phase (4 wires) line that can do 60 A.
That was my plan - to move to attempting to "balance" as best as possible
two of the three phases and use 240 V.
It's the same line that goes into my computer room
basement that also runs by my computer room in the
Your house was made for this......
I am thinking of just splicing this wire. It's
certainly not NEC professional, but it will work and the
circuit is overall protected 60 A with big enough wires
everywhere and no problem if power fails (only old
computers who suddenly stop working.)
Careful where you make these modifications. I don't know what your local
building codes are.....
Is there any problem
as far as this interlock transformer is concerned that
suggests I not use the 2x110 V (180 degree) line? I
would do something like this:
That's what I'm hoping to do for mine.
Now, there may be a risk. Remember, when I did this
trick on my 6000 the power would shut down after about
5 minutes run time? It might be a preexisting problem
in the PSU, but it might also be that the interlock stuff
was being fried because of the 180 degree phase difference
i.e. U(P1,P2) being 220 V when it wanted a 120 degree
phase difference with a U(Px,Py) = 110 V * 1.5 = 165 V.
Any idea what it would do, Matt?
I don't think you'll have a problem with the 780. I don't know much about
the 6000's, but the 780 is different as far as the power requirements are.
It seems as if three-phase was used just for the convenience of hooking
this beast up. Once you open that power distribution panel you'll see just
how simple it is. I couldn't believe my luck when I saw the internal wiring.
Hope this helps.....