Wiring 3 phase transformer

[Steviechia2]

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.

 

[augie47]

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)

 

[kwired]

Could also corner ground it and not need ground detection system.

 

[Steviechia2]

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)

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

 

[kwired]

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

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.

 

[Steviechia2]

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.

Ok. corner grounding, would that be bringing the ground to h1, h2, or h3?

 

[augie47]

Ok. corner grounding, would that be bringing the ground to h1, h2, or h3?

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)

 

[Smart $]

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.

X4 is typically a mid-winding tap... and definitely not the same as X0...!!!

 

[augie47]

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.

 

[kwired]

X4 is typically a mid-winding tap... and definitely not the same as X0...!!!

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.

 

[Steviechia2]

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)

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]

X4 is typically a mid-winding tap... and definitely not the same as X0...!!!

What's the difference?

 

[kwired]

What's the difference?

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]

What's the difference?

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.

At first I thought that but Smart is good at hitting me with stuff from left field.

 

[Smart $]

At first I thought that but Smart is good at hitting me with stuff from left field.

Come on now... I'm a centerfielder :lol:

 

[augie47]

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.

 

[infinity]

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.

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.

 

[Steviechia2]

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.

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?

 

[augie47]

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?

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.

 

[kwired]

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?

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