Bonding a step up transformer

[jim dungar]

You might want to acquaint the engineers with NEC 450.11(B)

I have seen Schneider Electric transformers whose nameplate now says 'high and low' instead of 'primary and secondary'.

 

[augie47]

I have seen Schneider Electric transformers whose nameplate now says 'high and low' instead of 'primary and secondary'.

That's a good solution
I have little doubt there would be a problem with his install but, putting on my inspectors hat, I'm simply pointing out that the Code says "with manufacturers instructions" so if something goes wrong any other advice might not be sufficient and the E/C ends up suffering.

 

[wwhitney]

Note there is a difference between a (V)/(2V) and a (V)x(2V) transformer, and all I could find are X on the 480 side. I dont really understand why, but the X is only for series or parallel operations and not for 3 wire service.

That makes no sense to me, do you have a reference?

Cheers, Wayne

 

[tortuga]

But as I just mentioned I think I would prefer a skipping the third conductor. Sure having it grounded in the center lowers the system to ground voltage, but does that really matter? What does that gain you?

You mean a neutral? I don't run a neutral, but I do run a EGC.
I think no matter what you have to run a EGC 250.32(B)
Then main reason I center ground in the past is clearances for triplex 225.19, slash rated equipment, 70E etc.

 

[wwhitney]

You mean a neutral? I don't run a neutral, but I do run a EGC.
I think no matter what you have to run a EGC 250.32(B)

See 250.32(B) Exception 2. For long outdoor feeders between outdoor transformers, you can save running an extra wire and use the grounded circuit conductor for fault clearing, omitting an EGC.

Cheers, Wayne

 

[tortuga]

See 250.32(B) Exception 2. For long outdoor feeders between outdoor transformers, you can save running an extra wire and use the grounded circuit conductor for fault clearing, omitting an EGC.

Cheers, Wayne

Ahh right, that could save some $$ with a long undergound pull.
or with my OH triplex system I could call the EGC a neutral and tap off a 240V yard light.
However it wont help me when there is no transformer at the other end just a 480V pump panel.

 

[LarryFine]

That makes no sense to me, do you have a reference?

I think he's saying the secondaries may be connected in series or parallel, but not series using X2-X3 as a center tap. The only difference I can see is the possibility of unequal loading.

 

[wwhitney]

I think he's saying the secondaries may be connected in series or parallel, but not series using X2-X3 as a center tap.

I understand the statement, but I'm not buying it yet.

The only difference I can see is the possibility of unequal loading.

Which I don't see how it could be a problem.

Cheers, Wayne

 

[electrofelon]

That makes no sense to me, do you have a reference?

Cheers, Wayne

See the link in post #7

240 x 480-120/240 V Transformer Ratio

Greetings, Gents - I'm a little confused on '240x480' designation on the high side of the transformer. This is different from ' 480-120/240' designation. Does this mean that I can connect either 240V or 480V supply on the primary and get 240V/120V on the secondary side? What does "X' mean in...

forums.mikeholt.com

As I said, I do not understand either why you can't use an "X" transformer for three-wire service, but that's what it says.

 

[wwhitney]

As I said, I do not understand either why you can't use an "X" transformer for three-wire service, but that's what it says.

Thanks for the link. That document is "IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers," but I guess dry transformers may be similar.

Do we have any examples of transformers that use the X nomenclature on the secondary side? I would think X would only show up on the primary side, as you wouldn't generally want to connect the supply side neutral.

So I guess my hypothesis is that if you have a 240x480 : 120/240 and reverse feed it, it would turn into a 120x240 : 240/480 transformer.

Cheers, Wayne

 

[winnie]

Looking back at the OP's diagram, I don't see secondary OCPD for the step down transformer.

 

[electrofelon]

Thanks for the link. That document is "IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers," but I guess dry transformers may be similar.

Do we have any examples of transformers that use the X nomenclature on the secondary side? I would think X would only show up on the primary side, as you wouldn't generally want to connect the supply side neutral.

So I guess my hypothesis is that if you have a 240x480 : 120/240 and reverse feed it, it would turn into a 120x240 : 240/480 transformer.

Cheers, Wayne

Okay, good catch on the liquid immersed, but yeah I can't imagine the it is different for dry types. It remains unclear to me the difference between the /and the x. Perhaps there is no difference and it is just an assumption on how it will be used, however note it does say "not for three wire service". Another question is whether you could use that just as a system grounding point, with no neutral loading, I assume so but I'm not certain.

 

[tortuga]

I think he's saying the secondaries may be connected in series or parallel, but not series using X2-X3 as a center tap. The only difference I can see is the possibility of unequal loading.

or interlaced vs non-interlaced?
https://books.google.com/books?id=Sn50DwAAQBAJ around page 214

 

[LarryFine]

or interlaced vs non-interlaced?

Is interlaced like bifilar winding?

 

[synchro]

See the link in post #7

240 x 480-120/240 V Transformer Ratio

Greetings, Gents - I'm a little confused on '240x480' designation on the high side of the transformer. This is different from ' 480-120/240' designation. Does this mean that I can connect either 240V or 480V supply on the primary and get 240V/120V on the secondary side? What does "X' mean in...

forums.mikeholt.com

As I said, I do not understand either why you can't use an "X" transformer for three-wire service, but that's what it says.

Perhaps the "X" is placed between the voltages from different and distinct winding arrangements that are configured via jumpers, but all of the voltages within each arrangement may not be available on the output terminals that are provided. And so a 240 x 480 transformer would provide 240V or 480V but not both, because it would not include a bushing or other termination suitable for the output neutral of a 480/240V 3-wire service

In some of the the transformer diagrams from your link, there are terminals that are set back from the outer terminations and they are connected to the windings with shorter line segments than the others. This indicates that they are for jumpers and not for output terminals. The voltages from two different winding arrangements are separated by the "X" in the diagram below that's taken from the document you referenced. For example, for a 14.4kV delta arrangement (the one designated on the right side of the "X" ) the terminals that are jumpered between two 7.2kV windings would not be connected to an output terminal.

 

[wwhitney]

Perhaps the "X" is placed between the voltages from different and distinct winding arrangements that are configured via jumpers, but all of the voltages within each arrangement may not be available on the output terminals that are provided.

So what would be different inside the transformer enclosure between a terminal intended for connecting premises wiring and a terminal intended only for a configuration jumper?

Cheers, Wayne

 

[synchro]

So what would be different inside the transformer enclosure between a terminal intended for connecting premises wiring and a terminal intended only for a configuration jumper?

Cheers, Wayne

For example, a larger dry transformer will typically have connections on the windings themselves at the ends of the individual winding segments, and also often at intermediate tap points. The manufacturer will also provide straps or buses for connecting to external wiring, and these will have wires connected to them that go to individual connection points on the windings themselves. In the 480x240 case they would only need to provide 2 buses, while in the 480/240 case there would be 3 buses.

When I say this I am referring to the IEEE nomenclature that Ethan brought up for either a configurable primary or a secondary. Commonly you see things like 480x240/120V where the "x" is separateing the primary and secondary voltages.

Perhaps Rob (infinity ) might have some relevant pictures of internal transformer connections.