480v primary to 120/208 -3 phase neutral confusion

R

RPM72

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Location
USA
Occupation
Electrician
Hi all, I’m a bit confused on a transformer I received for installation. Here’s what we have:

112.5 KVA - 480v(D) 3 phase primary step down to 208Y/120 secondary. Commercial application with a mix of light equipment and 120v branch circuits.

My confusion is that the transformer does not have an XO lug for my required neutral even tho the the nameplate shows an XO connection.

Its a tilt up building so I don’t have access to building steel and no plumbing nearby but I do have a 3” compressed air line that runs though out the building.

My questions:

1. Am I able to derive a neutral for my 120v at all off this transformer ?

2. In lieu of nearby steel or plumbing will a couple ground rods help me get the neutral I need?

Thanks in advance
 
RPM72 said:
My questions:

1. Am I able to derive a neutral for my 120v at all off this transformer ?

2. In lieu of nearby steel or plumbing will a couple ground rods help me get the neutral I need?
Click to expand...
#1 If there is no neutral tap it doesn't sound like it without some input from the manufacturer.
#2 Grounding (earthing) doesn't ever help get you neutral. Your neutral gets grounded but it has to be present first.
 
If it shows an X0 connection it pretty much has to have one.

There is no way a transformer that says it has a 208Y/120 secondary does not have an X0 connection short of a factory error of some sort.

The neutral is derived via the transformer. It has nothing to do with whether it is connected to earth or not. The earth connection is a separate issue. The code provides you with a bunch of grounding electrodes you can use. If none of them are present you need to make one. The easiest way is to pound in two ground rods.

Incidentally, building steel is not a legal grounding electrode. Read very carefully what the code actually says about connecting to the metal frame of a building.
 
Can you post a picture of the nameplate or provide the catalog number of the transformer ?
 
RPM72 said:
My confusion is that the transformer does not have an XO lug for my required neutral even tho the the nameplate shows an XO connection.
Click to expand...
Help us out here, are you saying it doesn't have a tap or is simply missing a lug that many times is customer supplied?
 
For a Delta/Wye the transformer should have H1-H2-H3 for the primary and X1-X2-X3-X0 for the secondary. If it does not then it is possibe that it is labeled incorrectly and is actually not a Delta/Wye.
 
infinity said:
For a Delta/Wye the transformer should have H1-H2-H3 for the primary and X1-X2-X3-X0 for the secondary. If it does not then it is possibe that it is labeled incorrectly and is actually not a Delta/Wye.
Click to expand...
I had a buck/boost transformer like that many years ago, the transformer had only numbered leads, and the instructions were printed wrong. It let the magic smoke out, sent it back to the supply house, they claimed it was wired wrong, but manufacturer came back, and said yes, it was their mistake and replaced it.
 
RPM72 said:
Hi all, I’m a bit confused on a transformer I received for installation. Here’s what we have:

112.5 KVA - 480v(D) 3 phase primary step down to 208Y/120 secondary. Commercial application with a mix of light equipment and 120v branch circuits.

My confusion is that the transformer does not have an XO lug for my required neutral even tho the the nameplate shows an XO connection.

Its a tilt up building so I don’t have access to building steel and no plumbing nearby but I do have a 3” compressed air line that runs though out the building.

My questions:

1. Am I able to derive a neutral for my 120v at all off this transformer ?

2. In lieu of nearby steel or plumbing will a couple ground rods help me get the neutral I need?

Thanks in advance
Click to expand...
Kinda sounds like they shipped the wrong transformer. Picture of the terminations would verify.
 
Looks like X0 lead on Delta-WYE xfmr diagram below should be 1 of 4 leads, which measures the same Ohm values across each of the other 3 leads.
1735396484254.png
 
Took them….. I guess I need to find a hosting site…. On a different job for the day so will post later
 
Here’s pics of the label and the taps
 

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petersonra said:
If it shows an X0 connection it pretty much has to have one.

There is no way a transformer that says it has a 208Y/120 secondary does not have an X0 connection short of a factory error of some sort.

The neutral is derived via the transformer. It has nothing to do with whether it is connected to earth or not. The earth connection is a separate issue. The code provides you with a bunch of grounding electrodes you can use. If none of them are present you need to make one. The easiest way is to pound in two ground rods.

Incidentally, building steel is not a legal grounding electrode. Read very carefully what the code actually says about connecting to the metal frame of a building.
Click to expand...
 

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