Wiring 3 phase transformer

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Steviechia2

Steviechia2

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Massachusetts
I have a transformer- primary is 208 v delta wound and secondary 480 v delta wound.
Question: secondary has X1, X2, X3 which are my 3 hots.It also has (X4) which in the drawing shows between x1 and x2. Is this x4 my xo which I bring my GEC to ? I am feeding a machine which has no nuetral.
 
IMO, you could use X4 as your ground or not use it and treat the secondary as an ungrounded system and install the required detector {250.21(B)}

are you sure X is your 480 volt winding ?
(most the transformers I see have X as the lower voltage)
 
augie47 said:
IMO, you could use X4 as your ground or not use it and treat the secondary as an ungrounded system and install the required detector {250.21(B)}

are you sure X is your 480 volt winding ?
(most the transformers I see have X as the lower voltage)
Click to expand...

You are right x is the lower voltage. So now the question is can i use the secondary as the primary? And now where does the ground go to H1 ?
I have 208 and need to step up to 480
 
Steviechia2 said:
You are right x is the lower voltage. So now the question is can i use the secondary as the primary? And now where does the ground go to H1 ?
I have 208 and need to step up to 480
Click to expand...

Do not connect the 120 volt neutral to the input. Leave that terminal "floating".

Either corner ground the output, any phase will work but only one, or use as ungrounded system. You will need ground fault detection if you go with ungrounded system.
 
kwired said:
Do not connect the 120 volt neutral to the input. Leave that terminal "floating".

Either corner ground the output, any phase will work but only one, or use as ungrounded system. You will need ground fault detection if you go with ungrounded system.
Click to expand...

Ok. corner grounding, would that be bringing the ground to h1, h2, or h3?
 
Steviechia2 said:
Ok. corner grounding, would that be bringing the ground to h1, h2, or h3?
Click to expand...

As kwired noted... ground any one of them... h1, h2, or h3 and have a "grounded" system in which case you also need to address 250.30(A)
OR
Do not ground (h1, h2, or h3) and address 250.21(B) and 250.30(B)
 
Steviechia2 said:
I have a transformer- primary is 208 v delta wound and secondary 480 v delta wound.
Question: secondary has X1, X2, X3 which are my 3 hots.It also has (X4) which in the drawing shows between x1 and x2. Is this x4 my xo which I bring my GEC to ? I am feeding a machine which has no nuetral.
Click to expand...
X4 is typically a mid-winding tap... and definitely not the same as X0...!!!
 
I might add that the fact that you have an X4 may indicate that you don't have a 208 transformer as stated but more likely a 240/120 unit. If you are in fact using a 208 voltage, you may not get your desired 480 output. With taps you may be able to adjust, but it might be worth checking than nameplate.
 
Smart $ said:
X4 is typically a mid-winding tap... and definitely not the same as X0...!!!
Click to expand...

Which gets me to wondering if his "primary" winding isn't 240 volt instead of 208 like he said. If it were 208 then there would be an X0 terminal and it would be the center of a wye. In the OP it is described that it is between X1 and X2.

If he applies 208 input on a 240 rated coil his output on the high side will be around 415 instead of 480.


Augie, I beat you to same answer earlier today on a different thread, now you got me back.
 
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augie47 said:
As kwired noted... ground any one of them... h1, h2, or h3 and have a "grounded" system in which case you also need to address 250.30(A)
OR
Do not ground (h1, h2, or h3) and address 250.21(B) and 250.30(B)
Click to expand...

It turned out that they supplied the wrong transformer and now we have the correct one. So if i connect my building ground to h1, I will not see sparks right ? :jawdrop:
 
infinity said:
What's the difference?
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Mid winding tap on one phase of a delta system is not same as the common at the center of a wye system. I think that is what he is trying to say.

X0 on wye sytem is not a mid winding tap it is the end of three separate windings that happen to be all tied together.
 
infinity said:
What's the difference?
Click to expand...

kwired said:
Mid winding tap on one phase of a delta system is not same as the common at the center of a wye system. I think that is what he is trying to say.

X0 on wye sytem is not a mid winding tap it is the end of three separate windings that happen to be all tied together.
Click to expand...

At first I thought that but Smart is good at hitting me with stuff from left field. :cool:
 
I notice that on the wiring diagrams in the manufacturers catalogs, the midpoint tap on a 240/120 three phase delta transformer is identified as X4 as opposed to XO on a 208Y/120 transformer.
As I recall this is reflected in the field also.
 
augie47 said:
I notice that on the wiring diagrams in the manufacturers catalogs, the midpoint tap on a 240/120 three phase delta transformer is identified as X4 as opposed to XO on a 208Y/120 transformer.
As I recall this is reflected in the field also.
Click to expand...


I'm guessing that somewhere in the annuls of transformer wiring there's a note that says midpoints of three windings are an XO and midpoints of a single winding are X4.
 
augie47 said:
I notice that on the wiring diagrams in the manufacturers catalogs, the midpoint tap on a 240/120 three phase delta transformer is identified as X4 as opposed to XO on a 208Y/120 transformer.
As I recall this is reflected in the field also.
Click to expand...

You were correct it was a 240/120 transformer which we now have the right one. What do you guys think of my #11 post?
 
Steviechia2 said:
You were correct it was a 240/120 transformer which we now have the right one. What do you guys think of my #11 post?
Click to expand...

If you elect to ground H1 on your secondary you should not have a problem.
Remember 250.30, 240.22 and Art 200 all apply.
 
Steviechia2 said:
You were correct it was a 240/120 transformer which we now have the right one. What do you guys think of my #11 post?
Click to expand...

Ground any one phase does not matter which one. Ground more than one point and you have a short circuit between the two points.
 
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