# Transformer Question



## Blayney86 (Jan 18, 2013)

Hi guys, I have a building with 277/480 3 phase going into a transformer and then going to a 120/240 single phase panel. I haven't ever encountered this before. Did they just skip the high leg? And is that legal. Problem is this S### is old and there are 0 tags or stickers left inside or outside of the transformer to check anything out. 

We are replacing the panels and transformer but not the building wiring. So i need to know if that is probably what they did and if that is legal so i can recreate it again.

Thank you sorry if its a dumb question haha


----------



## dawgs (Dec 1, 2007)

Yes. It's very common. And legal.


----------



## 360max (Jun 10, 2011)




----------



## Blayney86 (Jan 18, 2013)

Is there any other way to get 120/240 single phase from 277/480 3 phase?


----------



## RePhase277 (Feb 5, 2008)

A single phase 480 to 120/240 volt transformer will do it. Just because you have three phase 480 doesn't mean you have to use a three phase transformer. They make double pole 600 volt breakers.


----------



## Blayney86 (Jan 18, 2013)

InPhase277 said:


> A single phase 480 to 120/240 volt transformer will do it. Just because you have three phase 480 doesn't mean you have to use a three phase transformer. They make double pole 600 volt breakers.


I cant seem to find anything that is 277/480 primary single phase they are all 240/480. Do they make a 277/480 primary single phase?


----------



## don_resqcapt19 (Jul 18, 2010)

Blayney86 said:


> I cant seem to find anything that is 277/480 primary single phase they are all 240/480. Do they make a 277/480 primary single phase?


If you have a 3 phase 480Y/277 volt system and you need single phase 120/120, you use a transformer with a 480 volt primary. 
The transformers that are marked 240/480 on the primary can be connected to either a 240 volt or a 480 volt supply.


----------



## RePhase277 (Feb 5, 2008)

Blayney86 said:


> I cant seem to find anything that is 277/480 primary single phase they are all 240/480. Do they make a 277/480 primary single phase?


You don't need a neutral on the primary, so it won't be 480/277. You just need two phases of the 480 system on a double pole breaker or fused switch.


Here's one I found in a quick search: https://www.platt.com/platt-electric-supply/Dry-Type-Transformers-240-X-480-120-240/Eaton/T50E801-T20P11S50AEE/product.aspx?zpid=28349


----------



## Blayney86 (Jan 18, 2013)

thank you very much. hadn't had to do this before.


----------



## frenchelectrican (Mar 15, 2007)

I have done that with small to meduim load and just be aware of sizing the single phase loads for transformer..

You will have do a load caluation for it..


----------

