UPS

[Brian Pyle]

I read one time that I shouldn't plug a UPS into a UPS. I am in a situation where this would be an easy solution, because the plugs for my server PDU's don't fit into the receptacles for my building UPS, but my Stand Alone UPS's do, and the PDU plugs fit into these. I am looking for specifics on why not plug a UPS into a UPS?

Thanx

Brian Pyle

[Torsten.]

I can' see any pros, only cons.

The load of the second UPS will be added to the load of the first. Perhaps this will be more than the first can output.

If the first will fail for any reson, the second will fail too.

[A. Clay Stephenson]

It depends upon the design of the UPS but you can easily get into a case of severe resonance effects between the 2 UPS units generating strange harmonics so that rather than the loading seeing a nice sine wave, the load sees a very complex waveform -- possibly with many high-order harmonics which can damage equipment. The proper way to extend run-time is to increase the capacity of the battery packs. The really proper way to increase run-time is to power the UPS via a generator connected through an automatic transfer switch.

[A. Clay Stephenson · Accepted solution]

And here is a reference from APC on the subject:

http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_sid=uz6B5zsh&p_lva=&p_faqid=397

[Brian Pyle]

Thanx for the APC referance. I am not trying to extend my battery duration. I have a building UPS and the plugs on the stand alones fit the recepts but the plugs on the pdu's don't. I am trying to move some load off the diesel generator, to make some power for more AC and was just trying to avoid unesescary work :) I will bite the bullet and change out the recepticles.

Thanx For The Help

Brian Pyle