19 Jan
2009
19 Jan
'09
2:17 p.m.
Ian King (IanK at vulcan.com) wrote:
We *are* running the machine off three separate 110V single-phase
circuits
-
apparently you missed that part.
People need to understand the danger in this - in any multiphase
power
system, the neutral current is the DIFFERENCE of the current in the
individual phases. If the load is perfectly balanced, then the
neutral
current will be zero.
But, if you run the same load from three separate single phase
circuits
and (worst case) the three circuits are all the same phase, then the
neutral
current will be the SUM of all three phase currents. That's 3 times
what it
would be otherwise and runs a serious danger of melting the neutral
and
starting a fire. 
2:59 p.m.
On Monday 19 January 2009, Roger Holmes wrote:
Not if he uses the original pdu and original power cord, which has only
a single 10AWG neutral conductor.
Pat
--
Purdue University Research Computing --- http://www.rcac.purdue.edu/
The Computer Refuge --- http://computer-refuge.org
But, if you
run the same load from three separate single phase
circuits
and (worst case) the three circuits are all the same phase, then
the neutral
current will be the SUM of all three phase currents. That's 3
times what it
would be otherwise and runs a serious danger of melting the neutral
and
starting a fire.
I agree with all but the last bit, because if he's running it from
three separate supplies, surely he will have three neutral
conductors, so no problem. 
3:11 p.m.
New subject: Running 3 phase 780s on single phase power (was RE: hams on classiccmp)
On Monday 19 January 2009 02:59:53 pm Patrick Finnegan wrote:
On Monday 19 January 2009, Roger Holmes wrote:
Not if he uses the original pdu and original power cord, which has only
a single 10AWG neutral conductor.
Ah, THAT was the missing piece...
Now I understand what the concern is with this stuff!
Not being familiar with these systems, is that cord hard-wired in to the
computer end of things? Hooked to a single connector? Something like that?
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
But, if
you run the same load from three separate single phase
circuits and (worst case) the three circuits are all the same phase,
then the neutral current will be the SUM of all three phase currents.
That's 3 times what it would be otherwise and runs a serious danger of
melting the neutral and starting a fire.
I agree with all but the last bit, because if he's running it from
three separate supplies, surely he will have three neutral
conductors, so no problem.
3:34 p.m.
On Monday 19 January 2009, Roy J. Tellason wrote:
On Monday 19 January 2009 02:59:53 pm Patrick Finnegan
wrote:
It terminates on screw terminals (which happen to be part of a 30A,
3phase EMI filter) that are on the switch-side of the PDU, under a
metal cover. So, it's not that hard to remove, but it's not just a
connector. IIRC, from there, it goes through the main breaker and then
multiplexes out to each of the outlets on the back and the internal
transformer that supplies power to run the emergency-off, power-on
relay, etc.
Pat
--
Purdue University Research Computing --- http://www.rcac.purdue.edu/
The Computer Refuge --- http://computer-refuge.org
Not if he uses the original pdu and original
power cord, which has
only a single 10AWG neutral conductor.
Ah, THAT was the missing piece...
Now I understand what the concern is with this stuff!
Not being familiar with these systems, is that cord hard-wired in to
the computer end of things? Hooked to a single connector? Something
like that?
5663
days inactive
5663
days old
4 comments
4 participants
participants (4)
-
cclist＠sydex.com -
pat＠computer-refuge.org -
roger.holmes＠microspot.co.uk -
rtellason＠verizon.net