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Discussion Starter · #1 · (Edited)
new guy here with an, judging fromt the other posts i have read, easy question.
My electrical history is limited. I worked on the electrical systems of the huey and cobra helicopter in the marines but now i am working as a PLC tech in the modern industry and i am somewhat the quasi electrician here. I am comfortable with household wiring, installing 480V motors and vfd's among other things. The ground i have yet to tread is transformers. I am installing a 3 phase transformer. 480V in and 120/240 out. i will get some more information for you momentarily but where can i start as far as connections go? From what i am told, i need a single leg of 240V out.

Back with the new info. It is an ACME Transformer Cat. No. T-3-53341-1S
I found this diagram as well. Is this correct?

I am thinking it should be wired like this.
Then X1, X2, and X3 are my three phases of 240? Each one will give me 240 to ground?

Super Moderator
Licensed Electrical Contractor
11,796 Posts
You CANNOT get 240v out on only one leg.

What are you trying to do?
What could you possibly have that would require 240v to ground? I can see 208v or 277v, but not 240v.

Do you have anyone there that can guide you a bit better?

Not to sound like a prick, but this site is not intended to give instructions on how to do things to those not qualified.
I am not saying that you are not necessarily qualified, but 480V and 3-phase is not the territory of the unsure.

Give us some more detail and we'll go from there.

76 Posts
Not to sound mean Kurt, but if you can't read that diagram you probably should not wire a 480 volt transformer by yourself. Ask for help from someone in your shop. There is no shame in not knowing.

Bilge Rat
motors and controls.........
8,485 Posts
The secondary of this xfmr is a 120/240 3PH 4W delta. Beware of X3, it's the high leg. 208 to neutral.

31,896 Posts
My question would be what exactly are you unsure of.

Primary/secondary over current protection?


or Connections.

AS stated this is a delta/delta transformer with a center tapped coil

X1 to X2 is 240 VAC
X2 to X3 is 240 VAC
X3 to X1 is 240 VAC

X1 to X4 is 120 VAC
X2 to X4 is 120 VAC
X3 to X4 is 208

In today's distribution this is a bit unusual but still workable, what type of loads are you feeding? Most monern motors are 3 phase 208 requiring a wye connection.

X4 is grounded so
X1 to ground is 120 VAC
X2 to ground is 120 VAC
X3 to ground is 208 VAC

Number one mistake as mentioned is connecting 120 VAC loads to X3 and X4. This is commonly referred to as the smoke test...If it smokes it won't work.
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