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Makes sense.  Our setup would offer redundancy only to the point of the
UPS.  We would have dual power supplies, dual line cords, dual PDUs in the
rack, but both PDUs would plug into the same UPS.  Not an ideal level of
protection, but it would protect from some common things like failed power
supplies, and damaged (or yanked!) cables.

Splitting the 2 supplies between a UPS and a wall plug sounds like trouble
all around!

                                                                       
             Larry Bolhuis                                             
             <lbolhuis@arbsol.                                       
             com>                                                       To
             Sent by:                  Midrange Systems Technical      
             midrange-l-bounce         Discussion                      
             s@xxxxxxxxxxxx            <midrange-l@xxxxxxxxxxxx>   
                                                                        cc
                                                                       
             05/30/2006 12:38                                      Subject
             PM                        Re: Redundant Power             
                                                                       
                                                                       
             Please respond to                                         
             Midrange Systems                                          
                 Technical                                             
                Discussion                                             
             <midrange-l@midra                                         
                 nge.com>                                            
                                                                       
                                                                       




Pretty much the same thing. In order to have two cords you need two
supplies.  In order for it to be effective at all they must be
redundant. For example if you did this with a i270 or an i810 that had
two supplies you would be setting your self up for a failure of the UPS
*OR* the wall plug failing to drop the system because those power
supplies are not redundant.

If the supplies are billed as redundant that Must mean that each can do
all the work if required and without any action by the user. Either of
them can suddenly be the only one working but the system stays up.

In the case described here the supplies each carry roughly 50% of the
load so the outlet and the UPS each get half. If the outlet goes dark
then only the UPS remains to supply both it's current 50% plus the
outlet's 50%. When there isn't that much headroom on the UPS then the
UPS shuts off in self protection.

 - Larry

ChadB@xxxxxxxxxxxxxxxxxxxx wrote:
You're talking about splitting the cords between utility and UPS, and not
about the reduntant power supply, right?



*WARNING* *WARNING* *WARNING*

In this configuration you *MUST* be certain that the UPS is never over
50% load! If it's at even 51% when the power fails and the UPS must
carry all of the load instead of only half it caries now it will drop
like a stone leaving you completely unprotected and of course unpowered
as well!!.

The only way to test this for sure is to unplug all the power supplies
that go into the wall and see if the UPS can stand it!

 - Larry

Chris Bipes wrote:

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