J
jonny1982
Guest
No xo (neutral) connection in transformer. How is neutral done?
- Status
- Location
- Massachusetts
It is not.
That would be a straight 3 phase delta secondary. You cannot get a neutral from it. If there was an XO on that unit you would have about 138 volts from any phase conductor to XO.
J
jonny1982
Guest
Does the neutral get pulled straight through from the panel feeding it? The scenario is 480 panel feeding transformer on primary and then out of transformer to new 120/240 panel on secondary
- Location
- Connecticut
- Occupation
- Engineer
Are you trying to get 240/120 on the new panel (3 hots and 1 neutral) or 120/240 on the new panel (2 hots and 1 neutral)?
- Location
- Massachusetts
tidalwave
New User
- Location
- los angeles ca
J
jonny1982
Guest
120/240 on new panel 3 hots 1 neutral
- Location
- Connecticut
- Occupation
- Engineer
You need a transformer that has a delta secondary with a center tap. As Bob pointed out, you can't get what you want from a standard delta secondary.
J
jonny1982
Guest
That's what I thought, thank-you
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
3 hots and a neutral would be 208Y120, not 120/240.
If you have a 120/240V 3 phase 4 wire load center, and you want a transformer for it, you need a special transformer with a center tap (X0) on one winding, typically the A-C winding, the common name is a 240V "high leg" transformer. That gives you 240V 3 phase on any 3 pole breaker, 240V single phase from any 2 pole breaker, and 120V ONLY on single pole breakers that plug into phase A or C and connect to the neutral. If you accidentally connect to B phase (the "High Leg") and neutral, you get 208V and blow up your 120V device. That's why it's often called a "stinger leg", because you get stung with the cost of replacing things if you make that mistake.
There are limitations to how you can load that transformer as well, because the 120V loads will inherently cause a current imbalance.
Greg Wrenn
Member
I have run into this problem except that I am running off of a 480 volt Wye bus bar system. I told the manufacturer that I needed a 240 Wye system so that I could have a neutral. They sent me, I believe, a 240 delta because their is no "xo" to hook up a neutral. So I am assuming their is no way to hook up a 120 receptacle to this because their is no neutral. First, is this accurate? and second what transformer to I need to ask for to get this accomplished I have some 240 volt drills that run 120 volt pumps. We are transferring these machines from a plant that had a 240 delta bus bar system to a plant that has a 480 wye bus bar system.
ptonsparky
Tom
- Occupation
- EC - retired
Is your old equipment single phase or three?
Explain “240 volt drills that run 120 volt pumps”.
ptonsparky
Tom
- Occupation
- EC - retired
Mods, are all old threads open for added content until you close them again?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Mr. Wrenn please feel free to start a new thread. However, you need a 240/120V delta with a center tap, which I believe will be labeled as X5.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
This thread is being closed due to its age.
- Status