gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
210510-1725 EDT
Look at this paragraph from the first post:
"The panel appears to be a 3 phase panel, it has three lines entering the terminals at the top of breaker. When measuring voltage across each phase to ground (A,B,C) voltage is 125V through each phasehowever when measuring voltage across phases A to C reads 250V, B to C reads 250V, but phase A to B gives a reading of 1V; practically nothing."
Each phase wire (A, B, C) to neutral or EGC is 125V. That alone looks like a center tapped single phase source. Note 2*125 = 250. So it is not a wye source.
If this was a two transformer open delta you could not have two center tapped secondary coils with the center taps connected together. You can have one center tapped secondary connected to a neutral and/or EGC.
Now suppose the secondary BC has an open circuit in its path, then B is unlikely to be close in voltage to A. Putting a reasonable load on B to neutral would cause a major shift in voltage at B.
Next suppose the secondary BC is a conductive path. and that the primary has an open circuit, then a loaded B to neutral would pull down B toward neutral because the impedance of the secondary of a transformer with its primary open will not look like a low impedance.
Next suppose B to C is a short circuit, then the voltage A to B would be 250 V.
Everything points to a three phase panel being used as a single phase panel. Put a scope with channel 1 from neutral to line A, and sync on this signal. Use channel 2 to observe various voltages. Line C to neutral will be 180 degrees from A to neutral. I believe B will be in phase with A.
.l
Look at this paragraph from the first post:
"The panel appears to be a 3 phase panel, it has three lines entering the terminals at the top of breaker. When measuring voltage across each phase to ground (A,B,C) voltage is 125V through each phasehowever when measuring voltage across phases A to C reads 250V, B to C reads 250V, but phase A to B gives a reading of 1V; practically nothing."
Each phase wire (A, B, C) to neutral or EGC is 125V. That alone looks like a center tapped single phase source. Note 2*125 = 250. So it is not a wye source.
If this was a two transformer open delta you could not have two center tapped secondary coils with the center taps connected together. You can have one center tapped secondary connected to a neutral and/or EGC.
Now suppose the secondary BC has an open circuit in its path, then B is unlikely to be close in voltage to A. Putting a reasonable load on B to neutral would cause a major shift in voltage at B.
Next suppose the secondary BC is a conductive path. and that the primary has an open circuit, then a loaded B to neutral would pull down B toward neutral because the impedance of the secondary of a transformer with its primary open will not look like a low impedance.
Next suppose B to C is a short circuit, then the voltage A to B would be 250 V.
Everything points to a three phase panel being used as a single phase panel. Put a scope with channel 1 from neutral to line A, and sync on this signal. Use channel 2 to observe various voltages. Line C to neutral will be 180 degrees from A to neutral. I believe B will be in phase with A.
.l