couzer1023
Member
- Location
- okc, oklahoma
i have a 480v primary delta - 240v secondry delta transformer and i am getting 120v to ground on all phases on secondary side and 240v phase to phase. i thought i should get 208v to ground on b phase.
delta delta transformer
- Thread starter couzer1023
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Do you have a "neutral termiknal" ?
if it's a delta with no X-0 or X-4 terminal, without grounding on phase you have no reference for a "to ground" voltage and could get any reading. In my experience it is a bit unusual to get exactly 120 on all three phases.
Are you sure your secondary is not a wye ?
if it's a delta with no X-0 or X-4 terminal, without grounding on phase you have no reference for a "to ground" voltage and could get any reading. In my experience it is a bit unusual to get exactly 120 on all three phases.
Are you sure your secondary is not a wye ?
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couzer1023
Member
- Location
- okc, oklahoma
there is no neutral, xo, x4. the voltage is not exactly 120v. anyway to measure voltage to find high leg
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
If there is no neutral, then there is no high leg. The high leg is only present if the center is tapped on one of the transformers. The 120 you are getting is probably a "ghost" voltage.
couzer1023
Member
- Location
- okc, oklahoma
so what is the voltage present on each leg individually
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Unless it is a corner grounded system, theoretically, you will get 0 volts to ground, you can touch any one of the phases to ground, and unless there is a fault in the connected equipment, nothing will happen. If it is a corner grounded system, the phase that is grounded will be 240 volts to either of the other two phases, and that phase will be 0 volts to ground. Someone here has a drawing showing how this works and why there is a high leg when the center tap is used.
- Location
- Logan, Utah
Is the secondary grounded?
This sounds like it may be an ungrounded secondary.
Chris
This sounds like it may be an ungrounded secondary.
Chris
couzer1023
Member
- Location
- okc, oklahoma
i am pretty sure the secondary is not grounded.
- Location
- Logan, Utah
Then the system will not have a high leg.
A high leg is created when you ground the center of one of the winding in a delta secondary.
What does this transformer feed?
To be ungrounded the transformer must comply with 250.21.
Chris
couzer1023
Member
- Location
- okc, oklahoma
it feeds all three phase equipment. so with all this info i would assume that i will not need to identify b phase with orange tape
- Location
- Logan, Utah
If this is an ungrounded system then you won't have a high leg.
But if this is an ungrounded system does it comply with 250.21 and 250.30(B)?
Chris
As posted, you have a D x D xfmr without a center tap. Feeding a 3-wire load, you do not have a high leg. The only voltage readings you need to verify are phase to phase. The panel you are feeding must be UL listed as a 3-wire delta. The branch breakers in this panel feeding your 3-phase loads must also be straight 240v listed, not 240/120v. A common misapplication.
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