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Transformer hookup?

Posted By: barbwire

Transformer hookup? - 11/14/07 02:38 AM

Hey All, I have a delta to wye transformer, Secondary side feeding 480v 3 phase elevator controller, Primary 208 volts 3 phase, What do I do with the XO on the secondary side, I was thinking of taking my primary ground to the casing then to xo , secondary ground to xo , biulding steel to casing, does it not matter? should I leave it out of the loop all together?Thanks.
Posted By: JValdes

Re: Transformer hookup? - 11/14/07 05:45 PM

The wye secondary XO is the neutral/ground.

H1,H2 or H3 to XO = 120 volts. It should be on the transformer connections plate.
If you are feeding it to a panel you can bond XO to the panel grounding device.
No need to bond XO to the frame of the XFMR if it feeds a panel. You can bond them in the panel. If it feeds a disco, then bond XO to the frame and grounding electrode or other earth ground. You have a four wire secondary.

Posted By: electure

Re: Transformer hookup? - 11/14/07 11:58 PM

Is this transformer 120/208V 4 wire Wye secondary, 480V 3 wire Delta primary, being used as a step up transformer by backfeeding it?

Posted By: barbwire

Re: Transformer hookup? - 11/15/07 12:24 AM

I dont believe its being back fed, the nameplate on the transformer specifies : 208v Primary, 480V secondary.
Posted By: electure

Re: Transformer hookup? - 11/15/07 12:37 AM

OK smile
Posted By: Scott35

Re: Transformer hookup? - 11/15/07 06:44 AM

Sounds like a Typ-o (Typed Error) on the nameplate... being that there is an X0 terminal on the "OUTPUT" Windings' side


  1. The "X" Terminals are "X0", "X1" and "X2" - with a total of Three (3) "X" side Terminals,
  2. "X0" is physically bonded to one of the "X" Terminals - as in X0 is bonded to X1,
  3. "X0" is bonded to the common starpoint of the Secondary Windings, and all three Windings are connected in a Star (Wye) fashion,
  4. "X0" is derived from a center tap to one Secondary Winding,
  5. "X0" is un used for this setup, and only exists because the Transformer manufacturer builds their equipment with an X0 Terminal by default,
  6. It really is a 480V Closed Delta Primary x 208Y/120V 3Ø 4 Wire Wye Secondary - just with a modified nameplate, indicating reverse connection scheme,
  7. The Transformer is intended to be 208V Delta Primary x 480Y/277 3Ø 4 Wire Wye Secondary,
  8. The Transformer is 25 KVA or less, and is not a "Real" Closed Delta Primary x "Real" Wye Secondary - it is in fact an Open Delta "Tee" on both sides,
  9. You have entered the 'Twilight Zone"...

First off, what schematics are shown on the nameplate?

Does the nameplate's schematic show a Delta x Delta arrangement, or a Delta x Wye arrangement?

Can you visually trace where the "X0" terminal's lead goes to on the Windings?
If this is a Wye Secondary, the X0 lead will terminate to a bus (or bar) which connects to the ends of all three windings - usually at the bottom of the coils.

If the X0 lead terminates to a single coil, then you may have a center tapped Delta.

If the X0 lead terminates to one of the other "X" leads, then you may have provisions for a corner grounded Delta.

If X0 is a lead from what is indicated on the nameplate's schematic as the 'Lower Voltage Windings" - the 208 Volt side, chances are this is a Delta / Wye Isolated Transformer, with the wye side voltage = 208; and therefore the X0 terminal is not used...

If the Transformer is small - like 25KVA or less, then you likely have an Open Delta "Tee" arrangemet, which will come - by default - with an "X0" lead on the "Lower Voltage Side".
That lead is the "86% Tap" of the "Kicker Winding".

We really need to get some more information from you, in order to get a solid answer on your Transformer.

Please record as much data from the Transformer - information on nameplate, plus what is visually inside; and if available, any documentation - then post this information to this thread.

One last question: where did you get this Transformer? Can you get some information from the place of purchase?

Posted By: barbwire

Re: Transformer hookup? - 11/15/07 09:56 PM

O.K. I gave wrong info , nameplate states primary 208V secondary 480V/266V . Nameplate shows Delta- H1 H2 H3 and Wye - X1 X2 X3 ,XO . Yes there are three leads from each winding leading to XO via a commom Bar/Lug. The KVA on this Transformer is 20KVA. Thanks for the Help.
Posted By: Scott35

Re: Transformer hookup? - 11/17/07 06:41 AM


nameplate states primary 208V secondary 480V/266V . Nameplate shows Delta- H1 H2 H3 and Wye - X1 X2 X3 ,XO

Allright-ee then, you have a Delta x Wye Transformer, with that X0 Terminal being the "Common" lead.

Bond that Termination (X0) to the following:
* Grounding Electrode System,
* Equipment Grounding Conductor(s) for the SDS side,
* Transformer Enclosure.

Land the Branch Circuit's Equipment Grounding Conductor
(EGC coming in to the Transformer, with the Branch Circuit that feeds it)
to a separate lug, terminated to the Transformer's Enclosure.

The X0 Termination will be the Termination Point for the SDS' system grounded conductor (AKA - "Neutral").

If there is no need to include the common grounded conductor with the SDS' Secondary Feeders, then you could contemplate not installing it out of the Transformer.
This would apply if the designed loads were only L-L / L-L-L.

If it is cost efficient, go ahead and install that Grounded Conductor between the Transformer and the first Panelboard.

Let us know if you have more Qs.

Posted By: barbwire

Re: Transformer hookup? - 11/18/07 03:51 PM

O.K. so I will terminate my EGC on the primary side to a twin lug in the enclosure, jumped to XO,
Biulding steel is my grounding electrode, that will terminate on the twin lug as well.
All that is left is my secondary EGC (there is no nuetral needed so it will not be provided) it seems I have a choice to terminate this on XO or the enclosure frame as well. Does this sound correct? Thanks for all your help.
Posted By: Scott35

Re: Transformer hookup? - 11/22/07 03:55 AM

Man, I really need to make a drawing with SDS Grounding + Bonding details - maybe I will do it this week...

Anyhow, do this:

1: Bond the EGC from the Branch Circuit feeding the Transformer, to a single barrel lug.
Land that lug on the Transformer's Enclosure someplace convenient.

2: Install a Two Terminal lug on termination "X0".

3: Install an additional Two Terminal lug on the Transformer's Enclosure.

4: Bond the Grounding Electrode Conductor to one of the terminals of the lug at "X0".

5: Install a Bonding Jumper (of appropriate size) between the other terminal of the lug at "X0", and one of the terminals of the lug bonded (mounted) to the Transformer's Enclosure.

6: Terminate the Equipment Grounding Conductor for the "Output" (Secondary Circuit), to the other terminal of the lug bonded to the Enclosure.

Good luck.

Posted By: Scott35

Re: Transformer hookup? - 11/22/07 03:57 AM

Forgot to include the following:

Be sure to "Effectively Bond" the ends of raceways, containing Grounding Electrode Conductors.

There are a few ways to do this, so be sure it is done!!!

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