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#99097 - 07/14/06 09:47 PM transformer reconfiguration
miguel Offline
Junior Member

Registered: 07/14/06
Posts: 1
Loc: trinidad
At work while i was troubleshooting a UPS system i noticed that i was not getting an output supply 240 volt i was only getting 120 volts. When i checked the transformer for this system i observed that it needed a 480 volt 3 wire input supply in order to get a 120/240 volt, but the input supply was a single phase 240 volt supply. i am certain that is the main reason why i am not getting 240 volts from this UPS. I WANT TO KNOW IF THERE IS A WAY TO CONFIGURE THE TRANSFORMER TO WORK WITH A SINGLE PHASE 240 VOLTS 3 WIRE INPUT AND STILL BE ABLE TO GET A 120/240 VOLT OUTPUT FROM THIS SYSTEM? i have some spec diagrams i have scanned but i don't know how to post them on this site. IF you're interested in seeing the transformer spec diagrams email me at and i'll email it to you.

2014 / 2011 NEC & Related Books and Study Guides
#99098 - 07/15/06 04:07 AM Re: transformer reconfiguration
Scott35 Offline

Broom Pusher and

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA

Welcome to ECN.

I have a few questions regarding the UPS:


it needed a 480 volt 3 wire input

Is this 3 Wire Input 480 VAC 3 Phase 3 Wire, or 480 VAC 1 Phase 2 Wire + Equipment Grounding Conductor?

3 Phase 3 Wire Input would have 3 individual terminals on the Primary Side of the Transformer, most likely marked "H1", "H2" and "H3".
There would also be a Lug on the Enclosure, where the "EGC" (Equipment Grounding Conductor) would be terminated at.

1 Phase 2 Wire Input would have only 2 terminals on the Primary Side, and may be marked as "H1" and "H2".
The ECG would terminate to a Lug on the Enclosure, or possibly to a Lug on a Terminal Strip inside of a "Cabinet".
The EGC's Lug / Terminal would be Colored Green, or identified with a "Ground" symbol.



First off, _ONLY IF_ the Primary Windings are "Split Coil", and the Primary Side terminations have factory provisions, which allow the Primary Windings to be connected in either Series (480V), or Parallel (240V), the UPS may be used on a 240 VAC System.

If there is no "Input Voltage Changing Provisions" - such as reconfigurable jumpers, etc., then the UPS can only be used with a 480 VAC Input.

Secondly, you mention "A SINGLE PHASE 240 VOLTS 3 WIRE INPUT":

If by this you mean the input Circuitry has 2 Ungrounded Conductors + 1 Grounded "Neutral" Conductor, this may be an incorrect way to feed the UPS - especially if the Primary Windings are Isolated from the Secondary Windings.
If this Circuit is a 240 VAC Single Phase Circuit, the Primary side would only accept 2 Ungrounded Conductors.

If you mean the input is from a 240 VAC 3 Phase 3 Wire Circuit - such as from a 240 VAC 3 Phase 3 Wire Delta System, or a 240/120 VAC 3 Phase 4 Wire Delta System, or even a 208Y/120 VAC 3 Phase 4 Wire System, you have a 3 Phase Power System.
This would be a Circuit with 3 ungrounded Conductors, or a System with 3 "Active Circuit" Conductors having the same Voltage measured across them - as measured between "A-B", "B-C" and "A-C".

Another question regards the Secondary Side's Grounding Electrode System.
If this UPS _IS_ an Isolated Transformer type, the "Output" should be bonded to a Grounding Electrode System - actually the one used with the Utility Supplied Power System on-site.

Way too many questions / scenarios regarding this UPS setup - best if you contact the manufacturer for details.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#99099 - 07/16/06 08:52 AM Re: transformer reconfiguration
JoeTestingEngr Offline

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
The input to your UPS doesn't need to have any specific relationship to the output, other than the power in capability >= the power out plus conversion losses. It is the Alternate Source input that has to be compatable with the UPS output. For instance, I maintain UPS systems with a 120/208 3 phase rectifier input. The output is 120 single phase. The alternate source input is 120 single phase. The inverter phase locks to the alternate source. Two sets of inverse parallel SCRs called the "Static Bypass Switch", provide uninterrupted switching to the alternate source should inverter problems arise. It would be unusual for a UPS to have a center tapped output because the Static Bypass would require 8 SCRs instead of 4. The manufacturer would probably tell you to use a transformer on the output for 120/240.

By the way, I have fixed many types of UPS failures. I have never had one re-configure itself. I don't think that you have either. So the question becomes, "Who changed something external, and how do you put it back?

[This message has been edited by JoeTestingEngr (edited 07-16-2006).]


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