3 Phase 208 Feeder / Single phase 208 UPS / Three phase IPP panel 1

[gristlehead]

So I only threw up at least twice today. One of the projects I took on recently was getting our plant UPS systems functioning again. We had an old 3 phase 208 to 3 phase 208 UPS system that had been on bypass since 1999. Parts or repair were out of the question as the manufacturer is out of business. We managed to get the old UPS bypassed a second time and get the original bypass power turned off and the unit out. When we went to install the new unit, much to my suprise its a single phase unit. Of course I went back to my notes, yep 3 phase, the qoute says 208/208, but does not say single or three phase. We have not put any power on the unit and the vendor has admitted that yes I asked for 3 phase. So here is the million dollar question. Can I take 2 phases to the new UPS. Come out of the UPS and feed my IPP panel with Two phases. Note that there are only single phase loads on the IPP panel. Then in the IPP panel take the leg I have identified now as the low current leg and split the load on it between the two phases by doubling up and abandoning that phase in the panel? Did I mention I'm sick.

If the ID is larger than the OD then the whole is on the outside Right?

 

[l3city]

gristlehead:

hi there!! have you tried "phase converters"? Check them out, they might be applicable and helpful in your situation. Regards

 

[rbulsara]

You may also be disillusioned.

You loads are probably 120V. The UPS output is 208V line to line. How do you plan to get 120V? Technically you will need a 208:240/120V tranformer with 240V side center-tapped to get 120V.

Practical solution: The load was on bypass for years, so what's the difference? Place the thing back on non-UPS power and have the vendor change the UPS and get the right one. In fact regardless of who made the error, the right way is to bite the bullet and do the right thing.

 

[gristlehead]

Maybe I'm clueless here but, if I'm supplying the UPS with two legs of 208 3 phase that read 208 phase to phase and 120 v phase to N/G. Shouldn't the UPS put out 2 phases that read 208 phase to phase and 120v phase to Neutral/Ground. We have not hooked anything up and the vendor is working on possible replacment.

If the ID is larger than the OD then the whole is on the outside Right?

 

[rbulsara]

Unless I am missing something, a single phase 208V unit will not have a neutral. A 240/120V would.

There must be a wirig diagram in the manual which came with the UPS system, what dose it show?

 

[waross]

No. A single phase 208 volt UPS will put out 208 volts, single phase.
If you connect it to two phases of a three phase panel with no neutral, the panel will not magically develop a neutral complete with the 120 degree phase displacement that is inherent in the 120/208 volt three phase system.
What will happen is that the loads on one line will be in series with the loads on the other line. The voltage from the neutral bar to each line will be in inverse proportion to the load on that line. The voltages will vary as the loads vary, and will sum to 208 volts.
Don't do it. The condition is called an open neutral and will supply over an voltage to the equipment on the lightest loaded line.
respectfully

 

[gristlehead]

Thanks Waross. I've gathered from what your saying is that even if I use the nuetral from the Lighting panel feeding the UPS, when I need the UPS the most(Durring a Power outage) I will loose the nuetral, and create high voltages going to my most critical and expensive equipment.

If the ID is larger than the OD then the whole is on the outside Right?

 

[itsmoked]

So, so, true.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[resqcapt19]

Also, even if you had a single phase UPS with a neutral, if there are any muliwire branch circuits and you change from 3 phase to single phase you will be overloading the neutral conductors from the muliwire branch circuits.
Don

 

[gristlehead]

Just thought I'd give an update. My vendor called at 8:30 am and let me know that it was a manufacturer mistake I was suppose to get a 3 phase unit. Everything we had here in my documents and his said three phase. The unit is being shipped back and we are waiting on the delivery of a new one. I normally don't plug any vendor or manufacture, but it took some balls on someones part at APC to stand up and do the right thing. These kind of things happen from time to time and ussually they don't turn out as well. Again thanks for the replies I learned alot over the last 36 hours.

If the ID is larger than the OD then the whole is on the outside Right?

 

[itsmoked]

Their products seem to be pretty good too. I have 3 of them and they seem to work well.

BTW they often have some excellent referbs for sale that cost a fraction of the new price.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com