TRANSFORMER INSTALL

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My question is that we have to get a new tranformer to feed a 240 volt 3 phase machine, and the voltage available is 480 volt system without high leg that I think is a Wye system. I need someone to help me figure out how to pick out the right transformer, what I know is that if I have a 480 Wye system I need a transformer to be 480 Wye on the primary, and it depends on what voltage that I want on the secondary. Can somebody help me or let me know if I am right or wrong? Thanks for your help.
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
a 480 (primary) to 240 or 208 secondary will work on either a 480 Wye or 480 Delta system.
If it's 480 Wye simply ignore the neutral.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
My question is that we have to get a new tranformer to feed a 240 volt 3 phase machine, and the voltage available is 480 volt system without high leg that I think is a Wye system. I need someone to help me figure out how to pick out the right transformer, what I know is that if I have a 480 Wye system I need a transformer to be 480 Wye on the primary, and it depends on what voltage that I want on the secondary. Can somebody help me or let me know if I am right or wrong? Thanks for your help.

Hopefully your new machine is OK with 208 volt, then you can just use a standard off the shelf 480 delta primary X 120/208 wye secondary transformer of the appropriate size. As Augie said, you don't need orwant a neutral on the primary side. Just keep in mind all the grounding and bonding requirements. If you have to have 240 volt/3 phase that will be another story.
 
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jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
...what I know is that if I have a 480 Wye system I need a transformer to be 480 Wye on the primary,....

No, you do not.
Delta connected transformers are connected to wye sources, in maybe 99.99% of installations.

Get a standard 480V delta to 240/120 delta transformer. With a high-leg 4w output, you will be able to use the X4 terminal as your reference. Make your bond in the transformer and then leave with just your 3 phase conductors + ground.
 

jumper

Senior Member
Do not know what code cycle you are on, but 2011 added this.

450.14 Disconnecting Means. Transformers, other than
Class 2 or Class 3 transformers, shall have a disconnecting
means located either in sight of the transformer or in
a remote location. Where located in a remote location,
the disconnecting means shall be lockable, and the location
shall be field marked on the transformer.
 
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