Single phase transformer no neutral

[tooner_58576]

I have a single phase 277 transformer to 240/120. The transformer in in the middle of a old hydro dam and the 480v feed has no neutral just a ground down the center of the panel above the breakers. Do I ground the H4 and combine the X2 & X3 and take that to the low side neutral on my panel and get my 240/120 on my x1 and x4? Since there is no neutral the secondary voltage is speratic. I don't deal with single phase transformers ever is why I am asking. Thanks

 

[LarryFine]

1. Welcome to the forum.

2. The primary should have two lines, one hot and one neutral. You need to re-purpose one line to become the neutral, in both connection at the source and coloring/identifying.

3. The X2-X3 junction needs a grounding-electrode connection.

 

[winnie]

I agree with @LarryFine you can't use the egc as part of the primary circuit conductors.

This transformerneeds 277V, and that means hot and neutral from a grounded 480/277V system.

IMHO you need a 480:120/240 transformer.

X2, X3, a grounding electrode connection and the EGC all get connected to form the grounded neutral of the 120/240 system

Jonathan

 

[tooner_58576]

Thanks,

Where do i connect the re-purpose wire that's suppose to be the neutral with no neutral buss? Do I make one? How do I do a grounding electrode in the middle of a concrete dam? Lol I appreciate the help.
This wouldn't be a problem if they would have ordered a 3phase 480 transformer.

1. Welcome to the forum.

2. The primary should have two lines, one hot and one neutral. You need to re-purpose one line to become the neutral, in both connection at the source and coloring/identifying.

3. The X2-X3 junction needs a grounding-electrode connection.

 

[hillbilly1]

Thanks,

Where do i connect the re-purpose wire that's suppose to be the neutral with no neutral buss? Do I make one? How do I do a grounding electrode in the middle of a concrete dam? Lol I appreciate the help.
This wouldn't be a problem if they would have ordered a 3phase 480 transformer.

You don’t, you order a 480 volt single phase transformer. Does not need to be a three phase transformer.

 

[don_resqcapt19]

Where do i connect the re-purpose wire that's suppose to be the neutral with no neutral buss?

You would have to pull a neutral from the power source to that panel...assuming that the supply system is 480Y/277. I would not be surprised if the supply system is a 480 delta without a neutral.
As others have said the best choice is a single phase 480-240/120 volt transformer.

 

[winnie]

How do I do a grounding electrode in the middle of a concrete dam? Lol I appreciate the help.
This wouldn't be a problem if they would have ordered a 3phase 480 transformer.

The issue is exactly the same for both single phase and 3 phase transformers. You need a grounding electrode conductor because you are deriving a new grounded service. How do you solve this for the other transformers in this facility?

FWIW we had a discussion about how to use a single conductor as both EGC and GEC, which might be the best approach if you don't have a local point for your grounding electrode connection. I presume that it a dam there is literally tons of rebar but you don't want to be hammering out concrete to expose it https://forums.mikeholt.com/threads/using-egc-as-gec-for-transformers.2573678/

 

[tortuga]

How do I do a grounding electrode in the middle of a concrete dam?

Typically there is a large exposed busbar in the main switching room that is 1/4" X 3" busbar that is the main system ground, you run back to that.


Check the with the plant engineer they should know where the main grounding bus is.