I am thinking the same way as Redsy about the Grounded Conductor mismatch.
Seeing that the stepdown transformer is rated for 120/240 volts (unless this is a typo or just over simplified) would make it either a 1 phase 3 wire secondary, or a 3 phase 4 wire delta secondary.
Either case, the center tap point "X0" should be the Grounded Conductor's termination point - along with all the secondary grounding.
This will limit the voltage to ground to +/- 120 VAC (if the coil with the center tapped point is wound for 240 volts).
If instead, an end of the coil is grounded - such as either "X1" or "X2", this would result in voltage readings as follows:
L1-L2: 240 VAC,
L1-N: 120 VAC,
L2-N: 120 VAC,
N-G: 120 VAC,
L1-G: 240 VAC,
L2-G: 0 VAC
"L1" = Line 1, connected to "X1",
"L2" = line 2, connected to "X2",
"N" = Common "Neutral" conductor, connected to "X0",
"G" = Equipment Grounding Conductor / Grounded Equipment.
In the example above, it would describe how a system would have voltage readings if the "X2" termination and conductor was the grounded conductor.
Your situation may be as simple as this, or something completely different. Best if you can verify all the data relating the effected system, then post results here.
Find out what the connections at the transformer are, type of transformer, if any fuses are blown or faulty breakers, any running motors during voltage tests, and what the voltages read using a DVM.
Scott. s.e.t.
