Re: Split Power on an 825 -- MIDRANGE-L

Walden,

You are very correct. Most properly installed UPSs will have a ground connection to some common point (i.e. 'earth ground'.) This would also normally exist just by being plugged into the wall, even if the input breakers are off. If they don't then the i825 itself is the common ground point between the UPSs, though it has no reference point other than itself. In theory then the 825 itself could become electrically charged. Floating grounds are a hazard and are very problematic. I remember very clearly two different gentlemen being tossed onto their posteriors while disconnecting twinax cables as the cables had significant voltage on them, both due to floating ground. One of them still has red hair!

I do believe though that the construction of the power supplies used in most computers these days take the input voltage which is across the other two connections of the power cord (Neutral and Hot for 110 or X and Y for 208/240,) and feed that into the various electronic bits that comprise the PS in order to create the various DC output voltages (which are *VERY carefully regulated!) The various power supply inputs (other than ground) are completely isolated. I am confident of this last point because we have customers with one supply plugged into 110v and the other into 240v. Were they not isolated, 'unpredictable results would occur.' :-)

 - Larry

Walden H. Leverich wrote:

I've never done this, but I would have a concern stemming from my
college days as an EE. I would think you would need to make sure that
the neutral and ground are common between the two supplies, especially
when the UPS is running on it's own power and is isolated from the
"normal" common.

Since voltage is relative to neutral I can see you getting the "same"
voltage out of each UPS but at wildly different numbers relative to a
common reference. WithOUT thinking about the implications I would think
that you could simply tie both commons and grounds together at a common
reference point (grounding rod).

-Walden

PS. Then again, college was long ago, and I wasn't very good at the high-voltage stuff. <G>

-- Larry Bolhuis IBM eServer Certified Systems Expert: Vice President iSeries Technical Solutions V5R2 Arbor Solutions, Inc. iSeries LPAR Technical Solutions V5R2 1345 Monroe NW Suite 259 iSeries Linux Technical Solutions V5R2 Grand Rapids, MI 49505 iSeries Windows Integration Technical Solutions V5R2 IBM eServer Certified Systems Specialist (616) 451-2500 iSeries System Administrator for OS/400 V5R2 (616) 451-2571 - Fax AS/400 RPG IV Developer (616) 260-4746 - Cell iSeries System Command Operations V5R2

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